Глава 5. MySQL Server Administration

Содержание

5.1. The MySQL Server
5.1.1. Server Option and Variable Reference
5.1.2. Server Command Options
5.1.3. Server System Variables
5.1.4. Using System Variables
5.1.5. Server Status Variables
5.1.6. Server SQL Modes
5.1.7. Server Plugins
5.1.8. Server-Side Help
5.1.9. Server Response to Signals
5.1.10. The Shutdown Process
5.2. MySQL Server Logs
5.2.1. Selecting General Query and Slow Query Log Output Destinations
5.2.2. The Error Log
5.2.3. The General Query Log
5.2.4. The Binary Log
5.2.5. The Slow Query Log
5.2.6. Server Log Maintenance
5.3. General Security Issues
5.3.1. General Security Guidelines
5.3.2. Password Security in MySQL
5.3.3. Making MySQL Secure Against Attackers
5.3.4. Security-Related mysqld Options
5.3.5. Security Issues with LOAD DATA LOCAL
5.3.6. How to Run MySQL as a Normal User
5.4. The MySQL Access Privilege System
5.4.1. Privileges Provided by MySQL
5.4.2. Privilege System Grant Tables
5.4.3. Specifying Account Names
5.4.4. Access Control, Stage 1: Connection Verification
5.4.5. Access Control, Stage 2: Request Verification
5.4.6. When Privilege Changes Take Effect
5.4.7. Causes of Access-Denied Ошибки
5.5. MySQL User Account Management
5.5.1. User Names and Passwords
5.5.2. Adding User Accounts
5.5.3. Removing User Accounts
5.5.4. Setting Account Resource Limits
5.5.5. Assigning Account Passwords
5.5.6. Pluggable Authentication
5.5.7. Proxy Users
5.5.8. Using SSL for Secure Connections
5.5.9. Connecting to MySQL Remotely from Windows with SSH
5.5.10. Auditing MySQL Account Activity
5.6. Running Multiple MySQL Instances on One Machine
5.6.1. Setting Up Multiple Data Directories
5.6.2. Running Multiple MySQL Instances on Windows
5.6.3. Running Multiple MySQL Instances on Unix
5.6.4. Using Client Programs in a Multiple-Server Environment
5.7. Tracing mysqld Using DTrace
5.7.1. mysqld DTrace Probe Reference

MySQL Server (mysqld) is the main program that does most of the work in a MySQL installation. This section provides an overview of MySQL Server and covers topics that deal with administering a MySQL installation:

  • Server configuration

  • The server log files

  • Security issues and user-account management

  • Management of multiple servers on a single machine

5.1. The MySQL Server

mysqld is the MySQL server. The following discussion covers these MySQL server configuration topics:

  • Startup options that the server supports

  • Server system variables

  • Server status variables

  • How to set the server SQL mode

  • The server shutdown process

Замечание

Not all storage engines are supported by all MySQL server binaries and configurations. To find out how to determine which storage engines your MySQL server installation supports, see Section 12.7.5.17, “SHOW ENGINES Синтаксис”.

5.1.1. Server Option and Variable Reference

The following table provides a list of all the command line options, server and status variables applicable within mysqld.

The table lists command-line options (Cmd-line), options valid in configuration files (Option file), server system variables (System Var), and status variables (Status var) in one unified list, with notification of where each option/variable is valid. If a server option set on the command line or in an option file differs from the name of the corresponding server system or status variable, the variable name is noted immediately below the corresponding option. For status variables, the scope of the variable is shown (Scope) as either global, session, or both. Please see the corresponding sections for details on setting and using the options and variables. Where appropriate, a direct link to further information on the item as available.

For a version of this table that is specific to MySQL Cluster, see Section 16.3.4.1, “MySQL Cluster mysqld Option and Variable Reference”.

Table 5.1. Option/Variable Summary

NameCmd-LineOption fileSystem VarStatus VarVar ScopeDynamic
abort-slave-event-countYesYes    
Aborted_clients   YesGlobalNo
Aborted_connects   YesGlobalNo
allow-suspicious-udfsYesYes    
ansiYesYes    
authentication_windows_log_levelYesYes    
authentication_windows_use_principal_nameYesYes    
auto_increment_incrementYesYesYes BothYes
auto_increment_offsetYesYesYes BothYes
autocommitYesYesYes BothYes
automatic_sp_privileges  Yes GlobalYes
back_logYesYesYes GlobalNo
basedirYesYesYes GlobalNo
big-tablesYesYes  BothYes
- Variable: big_tables  Yes BothYes
bind-addressYesYesYes GlobalNo
Binlog_cache_disk_use   YesGlobalNo
binlog_cache_sizeYesYesYes GlobalYes
Binlog_cache_use   YesGlobalNo
binlog_direct_non_transactional_updatesYesYesYes BothYes
binlog-do-dbYesYes    
binlog-formatYesYes  BothYes
- Variable: binlog_format  Yes BothYes
binlog-ignore-dbYesYes    
binlog-row-event-max-sizeYesYes    
Binlog_stmt_cache_disk_use   YesGlobalNo
binlog_stmt_cache_sizeYesYesYes GlobalYes
Binlog_stmt_cache_use   YesGlobalNo
bootstrapYesYes    
bulk_insert_buffer_sizeYesYesYes BothYes
Bytes_received   YesBothNo
Bytes_sent   YesBothNo
character_set_client  Yes BothYes
character-set-client-handshakeYesYes    
character_set_connection  Yes BothYes
character_set_database[a]  Yes BothYes
character-set-filesystemYesYes  BothYes
- Variable: character_set_filesystem  Yes BothYes
character_set_results  Yes BothYes
character-set-serverYesYes  BothYes
- Variable: character_set_server  Yes BothYes
character_set_system  Yes GlobalNo
character-sets-dirYesYes  GlobalNo
- Variable: character_sets_dir  Yes GlobalNo
chrootYesYes    
collation_connection  Yes BothYes
collation_database[b]  Yes BothYes
collation-serverYesYes  BothYes
- Variable: collation_server  Yes BothYes
Com_admin_commands   YesBothNo
Com_alter_db   YesBothNo
Com_alter_db_upgrade   YesBothNo
Com_alter_event   YesBothNo
Com_alter_function   YesBothNo
Com_alter_procedure   YesBothNo
Com_alter_server   YesBothNo
Com_alter_table   YesBothNo
Com_alter_tablespace   YesBothNo
Com_analyze   YesBothNo
Com_assign_to_keycache   YesBothNo
Com_begin   YesBothNo
Com_binlog   YesBothNo
Com_call_procedure   YesBothNo
Com_change_db   YesBothNo
Com_change_master   YesBothNo
Com_check   YesBothNo
Com_checksum   YesBothNo
Com_commit   YesBothNo
Com_create_db   YesBothNo
Com_create_event   YesBothNo
Com_create_function   YesBothNo
Com_create_index   YesBothNo
Com_create_procedure   YesBothNo
Com_create_server   YesBothNo
Com_create_table   YesBothNo
Com_create_trigger   YesBothNo
Com_create_udf   YesBothNo
Com_create_user   YesBothNo
Com_create_view   YesBothNo
Com_dealloc_sql   YesBothNo
Com_delete   YesBothNo
Com_delete_multi   YesBothNo
Com_do   YesBothNo
Com_drop_db   YesBothNo
Com_drop_event   YesBothNo
Com_drop_function   YesBothNo
Com_drop_index   YesBothNo
Com_drop_procedure   YesBothNo
Com_drop_server   YesBothNo
Com_drop_table   YesBothNo
Com_drop_trigger   YesBothNo
Com_drop_user   YesBothNo
Com_drop_view   YesBothNo
Com_empty_query   YesBothNo
Com_execute_sql   YesBothNo
Com_flush   YesBothNo
Com_grant   YesBothNo
Com_ha_close   YesBothNo
Com_ha_open   YesBothNo
Com_ha_read   YesBothNo
Com_help   YesBothNo
Com_insert   YesBothNo
Com_insert_select   YesBothNo
Com_install_plugin   YesBothNo
Com_kill   YesBothNo
Com_load   YesBothNo
Com_lock_tables   YesBothNo
Com_optimize   YesBothNo
Com_preload_keys   YesBothNo
Com_prepare_sql   YesBothNo
Com_purge   YesBothNo
Com_purge_before_date   YesBothNo
Com_release_savepoint   YesBothNo
Com_rename_table   YesBothNo
Com_rename_user   YesBothNo
Com_repair   YesBothNo
Com_replace   YesBothNo
Com_replace_select   YesBothNo
Com_reset   YesBothNo
Com_resignal   YesBothNo
Com_revoke   YesBothNo
Com_revoke_all   YesBothNo
Com_rollback   YesBothNo
Com_rollback_to_savepoint   YesBothNo
Com_savepoint   YesBothNo
Com_select   YesBothNo
Com_set_option   YesBothNo
Com_show_authors   YesBothNo
Com_show_binlog_events   YesBothNo
Com_show_binlogs   YesBothNo
Com_show_charsets   YesBothNo
Com_show_collations   YesBothNo
Com_show_contributors   YesBothNo
Com_show_create_db   YesBothNo
Com_show_create_event   YesBothNo
Com_show_create_func   YesBothNo
Com_show_create_proc   YesBothNo
Com_show_create_table   YesBothNo
Com_show_create_trigger   YesBothNo
Com_show_databases   YesBothNo
Com_show_engine_logs   YesBothNo
Com_show_engine_mutex   YesBothNo
Com_show_engine_status   YesBothNo
Com_show_errors   YesBothNo
Com_show_events   YesBothNo
Com_show_fields   YesBothNo
Com_show_function_code   YesBothNo
Com_show_function_status   YesBothNo
Com_show_grants   YesBothNo
Com_show_keys   YesBothNo
Com_show_logs   YesBothNo
Com_show_master_status   YesBothNo
Com_show_new_master   YesBothNo
Com_show_open_tables   YesBothNo
Com_show_plugins   YesBothNo
Com_show_privileges   YesBothNo
Com_show_procedure_code   YesBothNo
Com_show_procedure_status   YesBothNo
Com_show_processlist   YesBothNo
Com_show_profile   YesBothNo
Com_show_profiles   YesBothNo
Com_show_relaylog_events   YesBothNo
Com_show_slave_hosts   YesBothNo
Com_show_slave_status   YesBothNo
Com_show_status   YesBothNo
Com_show_storage_engines   YesBothNo
Com_show_table_status   YesBothNo
Com_show_tables   YesBothNo
Com_show_triggers   YesBothNo
Com_show_variables   YesBothNo
Com_show_warnings   YesBothNo
Com_signal   YesBothNo
Com_slave_start   YesBothNo
Com_slave_stop   YesBothNo
Com_stmt_close   YesBothNo
Com_stmt_execute   YesBothNo
Com_stmt_fetch   YesBothNo
Com_stmt_prepare   YesBothNo
Com_stmt_reprepare   YesBothNo
Com_stmt_reset   YesBothNo
Com_stmt_send_long_data   YesBothNo
Com_truncate   YesBothNo
Com_uninstall_plugin   YesBothNo
Com_unlock_tables   YesBothNo
Com_update   YesBothNo
Com_update_multi   YesBothNo
Com_xa_commit   YesBothNo
Com_xa_end   YesBothNo
Com_xa_prepare   YesBothNo
Com_xa_recover   YesBothNo
Com_xa_rollback   YesBothNo
Com_xa_start   YesBothNo
completion_typeYesYesYes BothYes
Compression   YesSessionNo
concurrent_insertYesYesYes GlobalYes
connect_timeoutYesYesYes GlobalYes
Connections   YesGlobalNo
consoleYesYes    
core-fileYesYes    
Created_tmp_disk_tables   YesBothNo
Created_tmp_files   YesGlobalNo
Created_tmp_tables   YesBothNo
datadirYesYesYes GlobalNo
date_format  Yes GlobalNo
datetime_format  Yes GlobalNo
debugYesYesYes BothYes
debug_sync  Yes SessionYes
debug-sync-timeoutYesYes    
default-storage-engineYesYes  BothYes
- Variable: default_storage_engine  Yes BothYes
default-time-zoneYesYes    
default_week_formatYesYesYes BothYes
defaults-extra-fileYes     
defaults-fileYes     
defaults-group-suffixYes     
delay-key-writeYesYes  GlobalYes
- Variable: delay_key_write  Yes GlobalYes
Delayed_errors   YesGlobalNo
delayed_insert_limitYesYesYes GlobalYes
Delayed_insert_threads   YesGlobalNo
delayed_insert_timeoutYesYesYes GlobalYes
delayed_queue_sizeYesYesYes GlobalYes
Delayed_writes   YesGlobalNo
des-key-fileYesYes    
disconnect-slave-event-countYesYes    
div_precision_incrementYesYesYes BothYes
enable-lockingYesYes    
enable-named-pipeYesYes    
- Variable: named_pipe      
enable-pstackYesYes    
engine-condition-pushdownYesYes  BothYes
- Variable: engine_condition_pushdown  Yes BothYes
error_count  Yes SessionNo
event-schedulerYesYes  GlobalYes
- Variable: event_scheduler  Yes GlobalYes
exit-infoYesYes    
expire_logs_daysYesYesYes GlobalYes
external-lockingYesYes    
- Variable: skip_external_locking      
external_user  Yes SessionNo
federatedYesYes    
flushYesYesYes GlobalYes
Flush_commands   YesGlobalNo
flush_timeYesYesYes GlobalYes
foreign_key_checks  Yes BothYes
ft_boolean_syntaxYesYesYes GlobalYes
ft_max_word_lenYesYesYes GlobalNo
ft_min_word_lenYesYesYes GlobalNo
ft_query_expansion_limitYesYesYes GlobalNo
ft_stopword_fileYesYesYes GlobalNo
gdbYesYes    
general-logYesYes  GlobalYes
- Variable: general_log  Yes GlobalYes
general_log_fileYesYesYes GlobalYes
group_concat_max_lenYesYesYes BothYes
Handler_commit   YesBothNo
Handler_delete   YesBothNo
Handler_discover   YesBothNo
Handler_prepare   YesBothNo
Handler_read_first   YesBothNo
Handler_read_key   YesBothNo
Handler_read_last   YesBothNo
Handler_read_next   YesBothNo
Handler_read_prev   YesBothNo
Handler_read_rnd   YesBothNo
Handler_read_rnd_next   YesBothNo
Handler_rollback   YesBothNo
Handler_savepoint   YesBothNo
Handler_savepoint_rollback   YesBothNo
Handler_update   YesBothNo
Handler_write   YesBothNo
have_compress  Yes GlobalNo
have_crypt  Yes GlobalNo
have_csv  Yes GlobalNo
have_dynamic_loading  Yes GlobalNo
have_geometry  Yes GlobalNo
have_innodb  Yes GlobalNo
have_ndbcluster  Yes GlobalNo
have_openssl  Yes GlobalNo
have_partitioning  Yes GlobalNo
have_profiling  Yes GlobalNo
have_query_cache  Yes GlobalNo
have_rtree_keys  Yes GlobalNo
have_ssl  Yes GlobalNo
have_symlink  Yes GlobalNo
helpYesYes    
hostname  Yes GlobalNo
identity  Yes SessionYes
ignore-builtin-innodbYesYes  GlobalNo
- Variable: ignore_builtin_innodb  Yes GlobalNo
init_connectYesYesYes GlobalYes
init-fileYesYes  GlobalNo
- Variable: init_file  Yes GlobalNo
init-rpl-roleYesYes    
init_slaveYesYesYes GlobalYes
innodbYesYes    
innodb_adaptive_flushingYesYesYes GlobalYes
innodb_adaptive_hash_indexYesYesYes GlobalYes
innodb_additional_mem_pool_sizeYesYesYes GlobalNo
innodb_autoextend_incrementYesYesYes GlobalYes
innodb_autoinc_lock_modeYesYesYes GlobalNo
innodb_buffer_pool_instancesYesYesYes GlobalNo
Innodb_buffer_pool_pages_data   YesGlobalNo
Innodb_buffer_pool_pages_dirty   YesGlobalNo
Innodb_buffer_pool_pages_flushed   YesGlobalNo
Innodb_buffer_pool_pages_free   YesGlobalNo
Innodb_buffer_pool_pages_latched   YesGlobalNo
Innodb_buffer_pool_pages_misc   YesGlobalNo
Innodb_buffer_pool_pages_total   YesGlobalNo
Innodb_buffer_pool_read_ahead   YesGlobalNo
Innodb_buffer_pool_read_ahead_evicted   YesGlobalNo
Innodb_buffer_pool_read_requests   YesGlobalNo
Innodb_buffer_pool_reads   YesGlobalNo
innodb_buffer_pool_sizeYesYesYes GlobalNo
Innodb_buffer_pool_wait_free   YesGlobalNo
Innodb_buffer_pool_write_requests   YesGlobalNo
innodb_change_bufferingYesYesYes GlobalYes
innodb_checksumsYesYesYes GlobalNo
innodb_commit_concurrencyYesYesYes GlobalYes
innodb_concurrency_ticketsYesYesYes GlobalYes
innodb_data_file_pathYesYesYes GlobalNo
Innodb_data_fsyncs   YesGlobalNo
innodb_data_home_dirYesYesYes GlobalNo
Innodb_data_pending_fsyncs   YesGlobalNo
Innodb_data_pending_reads   YesGlobalNo
Innodb_data_pending_writes   YesGlobalNo
Innodb_data_read   YesGlobalNo
Innodb_data_reads   YesGlobalNo
Innodb_data_writes   YesGlobalNo
Innodb_data_written   YesGlobalNo
Innodb_dblwr_pages_written   YesGlobalNo
Innodb_dblwr_writes   YesGlobalNo
innodb_doublewriteYesYesYes GlobalNo
innodb_fast_shutdownYesYesYes GlobalYes
innodb_file_formatYesYesYes GlobalYes
innodb_file_format_checkYesYesYes GlobalNo
innodb_file_format_maxYesYesYes GlobalYes
innodb_file_per_tableYesYesYes GlobalYes
innodb_flush_log_at_trx_commitYesYesYes GlobalYes
innodb_flush_methodYesYesYes GlobalNo
innodb_force_recoveryYesYesYes GlobalNo
Innodb_have_atomic_builtins   YesGlobalNo
innodb_io_capacityYesYesYes GlobalYes
innodb_large_prefixYesYesYes GlobalYes
innodb_lock_wait_timeoutYesYesYes BothYes
innodb_locks_unsafe_for_binlogYesYesYes GlobalNo
innodb_log_buffer_sizeYesYesYes GlobalNo
innodb_log_file_sizeYesYesYes GlobalNo
innodb_log_files_in_groupYesYesYes GlobalNo
innodb_log_group_home_dirYesYesYes GlobalNo
Innodb_log_waits   YesGlobalNo
Innodb_log_write_requests   YesGlobalNo
Innodb_log_writes   YesGlobalNo
innodb_max_dirty_pages_pctYesYesYes GlobalYes
innodb_max_purge_lagYesYesYes GlobalYes
innodb_mirrored_log_groupsYesYesYes GlobalNo
innodb_old_blocks_pctYesYesYes GlobalYes
innodb_old_blocks_timeYesYesYes GlobalYes
innodb_open_filesYesYesYes GlobalNo
Innodb_os_log_fsyncs   YesGlobalNo
Innodb_os_log_pending_fsyncs   YesGlobalNo
Innodb_os_log_pending_writes   YesGlobalNo
Innodb_os_log_written   YesGlobalNo
Innodb_page_size   YesGlobalNo
Innodb_pages_created   YesGlobalNo
Innodb_pages_read   YesGlobalNo
Innodb_pages_written   YesGlobalNo
innodb_purge_batch_sizeYesYesYes GlobalNo
innodb_purge_threadsYesYesYes GlobalNo
innodb_read_ahead_thresholdYesYesYes GlobalYes
innodb_read_io_threadsYesYesYes GlobalNo
innodb_replication_delayYesYesYes GlobalYes
innodb_rollback_on_timeoutYesYesYes GlobalNo
innodb_rollback_segmentsYesYesYes GlobalYes
Innodb_row_lock_current_waits   YesGlobalNo
Innodb_row_lock_time   YesGlobalNo
Innodb_row_lock_time_avg   YesGlobalNo
Innodb_row_lock_time_max   YesGlobalNo
Innodb_row_lock_waits   YesGlobalNo
Innodb_rows_deleted   YesGlobalNo
Innodb_rows_inserted   YesGlobalNo
Innodb_rows_read   YesGlobalNo
Innodb_rows_updated   YesGlobalNo
innodb_spin_wait_delayYesYesYes GlobalYes
innodb_stats_methodYesYesYes BothYes
innodb_stats_on_metadataYesYesYes GlobalYes
innodb_stats_sample_pagesYesYesYes GlobalYes
innodb-status-fileYesYesYes GlobalNo
innodb_strict_modeYesYesYes BothYes
innodb_support_xaYesYesYes BothYes
innodb_sync_spin_loopsYesYesYes GlobalYes
innodb_table_locksYesYesYes BothYes
innodb_thread_concurrencyYesYesYes GlobalYes
innodb_thread_sleep_delayYesYesYes GlobalYes
Innodb_truncated_status_writes   YesGlobalNo
innodb_use_native_aioYesYesYes GlobalNo
innodb_use_sys_mallocYesYesYes GlobalNo
innodb_version  Yes GlobalNo
innodb_write_io_threadsYesYesYes GlobalNo
insert_id  Yes SessionYes
installYes     
install-manualYes     
interactive_timeoutYesYesYes BothYes
join_buffer_sizeYesYesYes BothYes
keep_files_on_createYesYesYes BothYes
Key_blocks_not_flushed   YesGlobalNo
Key_blocks_unused   YesGlobalNo
Key_blocks_used   YesGlobalNo
key_buffer_sizeYesYesYes GlobalYes
key_cache_age_thresholdYesYesYes GlobalYes
key_cache_block_sizeYesYesYes GlobalYes
key_cache_division_limitYesYesYes GlobalYes
Key_read_requests   YesGlobalNo
Key_reads   YesGlobalNo
Key_write_requests   YesGlobalNo
Key_writes   YesGlobalNo
languageYesYesYes GlobalNo
large_files_support  Yes GlobalNo
large_page_size  Yes GlobalNo
large-pagesYesYes  GlobalNo
- Variable: large_pages  Yes GlobalNo
last_insert_id  Yes SessionYes
Last_query_cost   YesSessionNo
lc-messagesYesYes  BothYes
- Variable: lc_messages  Yes BothYes
lc-messages-dirYesYes  GlobalNo
- Variable: lc_messages_dir  Yes GlobalNo
lc_time_names  Yes BothYes
license  Yes GlobalNo
local_infile  Yes GlobalYes
local-infileYesYes    
- Variable: local_infile      
lock_wait_timeoutYesYesYes BothYes
locked_in_memory  Yes GlobalNo
logYesYesYes GlobalYes
log_bin  Yes GlobalNo
log-binYesYesYes GlobalNo
log-bin-indexYesYes    
log-bin-trust-function-creatorsYesYes  GlobalYes
- Variable: log_bin_trust_function_creators  Yes GlobalYes
log-bin-trust-routine-creatorsYesYes  GlobalYes
- Variable: log_bin_trust_routine_creators  Yes GlobalYes
log_bin_use_v1_row_eventsYesYesYes GlobalNo
log-bin-use-v1-row-eventsYesYes  GlobalNo
- Variable: log_bin_use_v1_row_events  Yes GlobalNo
log-errorYesYes  GlobalNo
- Variable: log_error  Yes GlobalNo
log-isamYesYes    
log-outputYesYes  GlobalYes
- Variable: log_output  Yes GlobalYes
log-queries-not-using-indexesYesYes  GlobalYes
- Variable: log_queries_not_using_indexes  Yes GlobalYes
log-short-formatYesYes    
log-slave-updatesYesYes  GlobalNo
- Variable: log_slave_updates  Yes GlobalNo
log-slow-admin-statementsYesYes    
log-slow-queriesYesYes  GlobalYes
- Variable: log_slow_queries  Yes GlobalYes
log-slow-slave-statementsYesYes    
log-tcYesYes    
log-tc-sizeYesYes    
log-warningsYesYes  BothYes
- Variable: log_warnings  Yes BothYes
long_query_timeYesYesYes BothYes
low-priority-updatesYesYes  BothYes
- Variable: low_priority_updates  Yes BothYes
lower_case_file_systemYesYesYes GlobalNo
lower_case_table_namesYesYesYes GlobalNo
master-connect-retryYesYes    
master-hostYesYes    
master-info-fileYesYes    
master-passwordYesYes    
master-portYesYes    
master-retry-countYesYes    
master-sslYesYes    
master-ssl-caYesYes    
master-ssl-capathYesYes    
master-ssl-certYesYes    
master-ssl-cipherYesYes    
master-ssl-keyYesYes    
master-userYesYes    
max_allowed_packetYesYesYes GlobalYes
max_binlog_cache_sizeYesYesYes GlobalYes
max-binlog-dump-eventsYesYes    
max_binlog_sizeYesYesYes GlobalYes
max_binlog_stmt_cache_sizeYesYesYes GlobalYes
max_connect_errorsYesYesYes GlobalYes
max_connectionsYesYesYes GlobalYes
max_delayed_threadsYesYesYes BothYes
max_error_countYesYesYes BothYes
max_heap_table_sizeYesYesYes BothYes
max_insert_delayed_threads  Yes BothYes
max_join_sizeYesYesYes BothYes
max_length_for_sort_dataYesYesYes BothYes
max_long_data_sizeYesYesYes GlobalNo
max_prepared_stmt_countYesYesYes GlobalYes
max_relay_log_sizeYesYesYes GlobalYes
max_seeks_for_keyYesYesYes BothYes
max_sort_lengthYesYesYes BothYes
max_sp_recursion_depthYesYesYes BothYes
max_tmp_tablesYesYesYes BothYes
Max_used_connections   YesGlobalNo
max_user_connectionsYesYesYes BothYes
max_write_lock_countYesYesYes GlobalYes
memlockYesYesYes GlobalNo
metadata_locks_cache_size  Yes GlobalNo
min-examined-row-limitYesYesYes BothYes
myisam-block-sizeYesYes    
myisam_data_pointer_sizeYesYesYes GlobalYes
myisam_max_sort_file_sizeYesYesYes GlobalYes
myisam_mmap_sizeYesYesYes GlobalNo
myisam-recoverYesYes    
- Variable: myisam_recover_options      
myisam-recover-optionsYesYes    
- Variable: myisam_recover_options      
myisam_recover_options  Yes GlobalNo
myisam_repair_threadsYesYesYes BothYes
myisam_sort_buffer_sizeYesYesYes BothYes
myisam_stats_methodYesYesYes BothYes
myisam_use_mmapYesYesYes GlobalYes
named_pipe  Yes GlobalNo
Ndb_api_bytes_received_count   YesGlobalNo
Ndb_api_bytes_received_count_session   YesSessionNo
Ndb_api_bytes_received_count_slave   YesGlobalNo
Ndb_api_bytes_sent_count   YesGlobalNo
Ndb_api_bytes_sent_count_session   YesSessionNo
Ndb_api_bytes_sent_count_slave   YesGlobalNo
Ndb_api_event_bytes_count   YesGlobalNo
Ndb_api_event_bytes_count_injector   YesGlobalNo
Ndb_api_event_data_count   YesGlobalNo
Ndb_api_event_data_count_injector   YesGlobalNo
Ndb_api_event_nondata_count   YesGlobalNo
Ndb_api_event_nondata_count_injector   YesGlobalNo
Ndb_api_pk_op_count   YesGlobalNo
Ndb_api_pk_op_count_session   YesSessionNo
Ndb_api_pk_op_count_slave   YesGlobalNo
Ndb_api_pruned_scan_count   YesGlobalNo
Ndb_api_pruned_scan_count_session   YesSessionNo
Ndb_api_pruned_scan_count_slave   YesGlobalNo
Ndb_api_range_scan_count   YesGlobalNo
Ndb_api_range_scan_count_session   YesSessionNo
Ndb_api_range_scan_count_slave   YesGlobalNo
Ndb_api_read_row_count   YesGlobalNo
Ndb_api_read_row_count_session   YesSessionNo
Ndb_api_read_row_count_slave   YesGlobalNo
Ndb_api_scan_batch_count   YesGlobalNo
Ndb_api_scan_batch_count_session   YesSessionNo
Ndb_api_scan_batch_count_slave   YesGlobalNo
Ndb_api_table_scan_count   YesGlobalNo
Ndb_api_table_scan_count_session   YesSessionNo
Ndb_api_table_scan_count_slave   YesGlobalNo
Ndb_api_trans_abort_count   YesGlobalNo
Ndb_api_trans_abort_count_session   YesSessionNo
Ndb_api_trans_abort_count_slave   YesGlobalNo
Ndb_api_trans_close_count   YesGlobalNo
Ndb_api_trans_close_count_session   YesSessionNo
Ndb_api_trans_close_count_slave   YesGlobalNo
Ndb_api_trans_commit_count   YesGlobalNo
Ndb_api_trans_commit_count_session   YesSessionNo
Ndb_api_trans_commit_count_slave   YesGlobalNo
Ndb_api_trans_local_read_row_count   YesGlobalNo
Ndb_api_trans_local_read_row_count_session   YesSessionNo
Ndb_api_trans_local_read_row_count_slave   YesGlobalNo
Ndb_api_trans_start_count   YesGlobalNo
Ndb_api_trans_start_count_session   YesSessionNo
Ndb_api_trans_start_count_slave   YesGlobalNo
Ndb_api_uk_op_count   YesGlobalNo
Ndb_api_uk_op_count_session   YesSessionNo
Ndb_api_uk_op_count_slave   YesGlobalNo
Ndb_api_wait_exec_complete_count   YesGlobalNo
Ndb_api_wait_exec_complete_count_session   YesSessionNo
Ndb_api_wait_exec_complete_count_slave   YesGlobalNo
Ndb_api_wait_meta_request_count   YesGlobalNo
Ndb_api_wait_meta_request_count_session   YesSessionNo
Ndb_api_wait_meta_request_count_slave   YesGlobalNo
Ndb_api_wait_nanos_count   YesGlobalNo
Ndb_api_wait_nanos_count_session   YesSessionNo
Ndb_api_wait_nanos_count_slave   YesGlobalNo
Ndb_api_wait_scan_result_count   YesGlobalNo
Ndb_api_wait_scan_result_count_session   YesSessionNo
Ndb_api_wait_scan_result_count_slave   YesGlobalNo
ndb_autoincrement_prefetch_szYesYesYes BothYes
ndb-batch-sizeYesYesYes GlobalNo
ndb-blob-read-batch-bytesYesYesYes BothYes
ndb-blob-write-batch-bytesYesYesYes BothYes
ndb_cache_check_timeYesYesYes GlobalYes
ndb-cluster-connection-poolYesYesYesYesGlobalNo
Ndb_cluster_node_id   YesBothNo
Ndb_config_from_host   YesBothNo
Ndb_conflict_fn_epoch   YesGlobalNo
Ndb_conflict_fn_epoch_trans   YesGlobalNo
Ndb_conflict_fn_max   YesGlobalNo
Ndb_conflict_fn_old   YesGlobalNo
Ndb_conflict_trans_conflict_commit_count   YesGlobalNo
Ndb_conflict_trans_detect_iter_count   YesGlobalNo
Ndb_conflict_trans_reject_count   YesGlobalNo
Ndb_conflict_trans_row_conflict_count   YesGlobalNo
Ndb_conflict_trans_row_reject_count   YesGlobalNo
ndb-connectstringYesYes    
ndb-deferred-constraintsYesYes  BothYes
- Variable: ndb_deferred_constraints  Yes BothYes
ndb_deferred_constraintsYesYesYes BothYes
ndb_distributionYesYesYes BothYes
ndb-distributionYesYes  BothYes
- Variable: ndb_distribution  Yes BothYes
ndb_execute_count   YesGlobalNo
ndb_extra_loggingYesYesYes GlobalYes
ndb_force_sendYesYesYes BothYes
ndb_index_stat_cache_entriesYesYes    
ndb_index_stat_enableYesYes    
ndb_index_stat_update_freqYesYes    
ndb_join_pushdown  Yes GlobalNo
ndb-log-apply-statusYesYes  GlobalNo
- Variable: ndb_log_apply_status  Yes GlobalNo
ndb_log_binYes Yes BothYes
ndb_log_binlog_indexYes Yes GlobalYes
ndb_log_empty_epochsYesYesYes GlobalYes
ndb-log-empty-epochsYesYesYes GlobalYes
ndb_log_orig  Yes GlobalNo
ndb-log-transaction-idYesYes  GlobalNo
- Variable: ndb_log_transaction_id  Yes GlobalNo
ndb_log_transaction_id  Yes GlobalNo
ndb-log-update-as-writeYesYesYes GlobalYes
ndb_log_updated_onlyYesYesYes GlobalYes
ndb-mgmd-hostYesYes    
ndb-nodeidYesYes YesGlobalNo
Ndb_number_of_data_nodes   YesGlobalNo
ndb_optimization_delay  Yes GlobalYes
ndb_optimized_node_selectionYesYes    
ndb_pruned_scan_count   YesGlobalNo
Ndb_pushed_queries_defined   YesGlobalNo
Ndb_pushed_queries_dropped   YesGlobalNo
Ndb_pushed_queries_executed   YesGlobalNo
ndb_pushed_reads   YesGlobalNo
ndb_report_thresh_binlog_epoch_slipYesYes    
ndb_report_thresh_binlog_mem_usageYesYes    
ndb_scan_count   YesGlobalNo
ndb_table_no_logging  Yes SessionYes
ndb_table_temporary  Yes SessionYes
ndb_use_copying_alter_table  Yes BothNo
ndb_use_exact_count  Yes BothYes
ndb_use_transactionsYesYesYes BothYes
ndb-wait-connectedYesYesYes GlobalNo
ndb-wait-setupYesYesYes GlobalNo
ndbclusterYesYes    
- Variable: have_ndbcluster      
ndbinfo_database  Yes GlobalNo
ndbinfo_max_bytesYes Yes BothYes
ndbinfo_max_rowsYes Yes BothYes
ndbinfo_show_hiddenYes Yes BothYes
ndbinfo_table_prefixYes Yes BothYes
ndbinfo_version  Yes GlobalNo
net_buffer_lengthYesYesYes BothYes
net_read_timeoutYesYesYes BothYes
net_retry_countYesYesYes BothYes
net_write_timeoutYesYesYes BothYes
newYesYesYes BothYes
no-defaultsYes     
Not_flushed_delayed_rows   YesGlobalNo
oldYesYesYes GlobalNo
old-alter-tableYesYes  BothYes
- Variable: old_alter_table  Yes BothYes
old-passwordsYesYes  BothYes
- Variable: old_passwords  Yes BothYes
old-style-user-limitsYesYes    
one-threadYesYes    
Open_files   YesGlobalNo
open-files-limitYesYes  GlobalNo
- Variable: open_files_limit  Yes GlobalNo
Open_streams   YesGlobalNo
Open_table_definitions   YesGlobalNo
Open_tables   YesBothNo
Opened_files   YesGlobalNo
Opened_table_definitions   YesBothNo
Opened_tables   YesBothNo
optimizer_prune_levelYesYesYes BothYes
optimizer_search_depthYesYesYes BothYes
optimizer_switchYesYesYes BothYes
partitionYesYes  GlobalNo
- Variable: have_partitioning  Yes GlobalNo
performance_schemaYesYesYes GlobalNo
Performance_schema_cond_classes_lost   YesGlobalNo
Performance_schema_cond_instances_lost   YesGlobalNo
performance_schema_events_waits_history_long_sizeYesYesYes GlobalNo
performance_schema_events_waits_history_sizeYesYesYes GlobalNo
Performance_schema_file_classes_lost   YesGlobalNo
Performance_schema_file_handles_lost   YesGlobalNo
Performance_schema_file_instances_lost   YesGlobalNo
Performance_schema_locker_lost   YesGlobalNo
performance_schema_max_cond_classesYesYesYes GlobalNo
performance_schema_max_cond_instancesYesYesYes GlobalNo
performance_schema_max_file_classesYesYesYes GlobalNo
performance_schema_max_file_handlesYesYesYes GlobalNo
performance_schema_max_file_instancesYesYesYes GlobalNo
performance_schema_max_mutex_classesYesYesYes GlobalNo
performance_schema_max_mutex_instancesYesYesYes GlobalNo
performance_schema_max_rwlock_classesYesYesYes GlobalNo
performance_schema_max_rwlock_instancesYesYesYes GlobalNo
performance_schema_max_table_handlesYesYesYes GlobalNo
performance_schema_max_table_instancesYesYesYes GlobalNo
performance_schema_max_thread_classesYesYesYes GlobalNo
performance_schema_max_thread_instancesYesYesYes GlobalNo
Performance_schema_mutex_classes_lost   YesGlobalNo
Performance_schema_mutex_instances_lost   YesGlobalNo
Performance_schema_rwlock_classes_lost   YesGlobalNo
Performance_schema_rwlock_instances_lost   YesGlobalNo
Performance_schema_table_handles_lost   YesGlobalNo
Performance_schema_table_instances_lost   YesGlobalNo
Performance_schema_thread_classes_lost   YesGlobalNo
Performance_schema_thread_instances_lost   YesGlobalNo
pid-fileYesYes  GlobalNo
- Variable: pid_file  Yes GlobalNo
pluginYesYes    
plugin_dirYesYesYes GlobalNo
plugin-loadYesYes    
portYesYesYes GlobalNo
port-open-timeoutYesYes    
preload_buffer_sizeYesYesYes BothYes
Prepared_stmt_count   YesGlobalNo
print-defaultsYes     
profiling  Yes BothYes
profiling_history_sizeYesYesYes BothYes
protocol_version  Yes GlobalNo
proxy_user  Yes SessionNo
pseudo_thread_id  Yes SessionYes
Qcache_free_blocks   YesGlobalNo
Qcache_free_memory   YesGlobalNo
Qcache_hits   YesGlobalNo
Qcache_inserts   YesGlobalNo
Qcache_lowmem_prunes   YesGlobalNo
Qcache_not_cached   YesGlobalNo
Qcache_queries_in_cache   YesGlobalNo
Qcache_total_blocks   YesGlobalNo
Queries   YesBothNo
query_alloc_block_sizeYesYesYes BothYes
query_cache_limitYesYesYes GlobalYes
query_cache_min_res_unitYesYesYes GlobalYes
query_cache_sizeYesYesYes GlobalYes
query_cache_typeYesYesYes BothYes
query_cache_wlock_invalidateYesYesYes BothYes
query_prealloc_sizeYesYesYes BothYes
Questions   YesBothNo
rand_seed1  Yes SessionYes
rand_seed2  Yes SessionYes
range_alloc_block_sizeYesYesYes BothYes
read_buffer_sizeYesYesYes BothYes
read_onlyYesYesYes GlobalYes
read_rnd_buffer_sizeYesYesYes BothYes
relay-logYesYes    
relay-log-indexYesYes  BothNo
- Variable: relay_log_index  Yes BothNo
relay_log_indexYesYesYes GlobalNo
relay-log-info-fileYesYes    
- Variable: relay_log_info_file      
relay_log_info_fileYesYesYes GlobalNo
relay_log_purgeYesYesYes GlobalYes
relay_log_recoveryYesYesYes GlobalYes
relay_log_space_limitYesYesYes GlobalNo
removeYes     
replicate-do-dbYesYes    
replicate-do-tableYesYes    
replicate-ignore-dbYesYes    
replicate-ignore-tableYesYes    
replicate-rewrite-dbYesYes    
replicate-same-server-idYesYes    
replicate-wild-do-tableYesYes    
replicate-wild-ignore-tableYesYes    
report-hostYesYes  GlobalNo
- Variable: report_host  Yes GlobalNo
report-passwordYesYes  GlobalNo
- Variable: report_password  Yes GlobalNo
report-portYesYes  GlobalNo
- Variable: report_port  Yes GlobalNo
report-userYesYes  GlobalNo
- Variable: report_user  Yes GlobalNo
rpl_recovery_rank  Yes GlobalYes
Rpl_semi_sync_master_clients   YesGlobalNo
rpl_semi_sync_master_enabled  Yes GlobalYes
Rpl_semi_sync_master_net_avg_wait_time   YesGlobalNo
Rpl_semi_sync_master_net_wait_time   YesGlobalNo
Rpl_semi_sync_master_net_waits   YesGlobalNo
Rpl_semi_sync_master_no_times   YesGlobalNo
Rpl_semi_sync_master_no_tx   YesGlobalNo
Rpl_semi_sync_master_status   YesGlobalNo
Rpl_semi_sync_master_timefunc_failures   YesGlobalNo
rpl_semi_sync_master_timeout  Yes GlobalYes
rpl_semi_sync_master_trace_level  Yes GlobalYes
Rpl_semi_sync_master_tx_avg_wait_time   YesGlobalNo
Rpl_semi_sync_master_tx_wait_time   YesGlobalNo
Rpl_semi_sync_master_tx_waits   YesGlobalNo
rpl_semi_sync_master_wait_no_slave  Yes GlobalYes
Rpl_semi_sync_master_wait_pos_backtraverse   YesGlobalNo
Rpl_semi_sync_master_wait_sessions   YesGlobalNo
Rpl_semi_sync_master_yes_tx   YesGlobalNo
rpl_semi_sync_slave_enabled  Yes GlobalYes
Rpl_semi_sync_slave_status   YesGlobalNo
rpl_semi_sync_slave_trace_level  Yes GlobalYes
Rpl_status   YesGlobalNo
safe-modeYesYes    
safe-show-databaseYesYesYes GlobalYes
safe-user-createYesYes    
safemalloc-mem-limitYesYes    
secure-authYesYes  GlobalYes
- Variable: secure_auth  Yes GlobalYes
secure-file-privYesYes  GlobalNo
- Variable: secure_file_priv  Yes GlobalNo
Select_full_join   YesBothNo
Select_full_range_join   YesBothNo
Select_range   YesBothNo
Select_range_check   YesBothNo
Select_scan   YesBothNo
server-idYesYes  GlobalYes
- Variable: server_id  Yes GlobalYes
server-id-bitsYesYes  GlobalNo
- Variable: server_id_bits  Yes GlobalNo
shared_memory  Yes GlobalNo
shared_memory_base_name  Yes GlobalNo
show-slave-auth-infoYesYes    
skip-character-set-client-handshakeYesYes    
skip-concurrent-insertYesYes    
- Variable: concurrent_insert      
skip-event-schedulerYesYes    
skip-external-lockingYesYes  GlobalNo
- Variable: skip_external_locking  Yes GlobalNo
skip-grant-tablesYesYes    
skip-host-cacheYesYes    
skip-lockingYesYes    
skip-log-warningsYes     
skip-name-resolveYesYes  GlobalNo
- Variable: skip_name_resolve  Yes GlobalNo
skip-ndbclusterYesYes    
skip-networkingYesYes  GlobalNo
- Variable: skip_networking  Yes GlobalNo
skip-newYesYes    
skip-partitionYesYes    
skip-safemallocYesYes    
skip-show-databaseYesYes  GlobalNo
- Variable: skip_show_database  Yes GlobalNo
skip-slave-startYesYes    
skip-sslYesYes    
skip-stack-traceYesYes    
skip-symbolic-linksYes     
skip-symlinkYesYes    
skip-thread-priorityYesYes    
slave_allow_batchingYesYesYes GlobalYes
slave_compressed_protocolYesYesYes GlobalYes
slave_exec_mode  Yes GlobalYes
Slave_heartbeat_period   YesGlobalNo
slave-load-tmpdirYesYes  GlobalNo
- Variable: slave_load_tmpdir  Yes GlobalNo
slave-net-timeoutYesYes  GlobalYes
- Variable: slave_net_timeout  Yes GlobalYes
Slave_open_temp_tables   YesGlobalNo
Slave_received_heartbeats   YesGlobalNo
Slave_retried_transactions   YesGlobalNo
Slave_running   YesGlobalNo
slave-skip-errorsYesYes  GlobalNo
- Variable: slave_skip_errors  Yes GlobalNo
slave_transaction_retriesYesYesYes GlobalYes
slave_type_conversionsYesYesYes GlobalNo
Slow_launch_threads   YesBothNo
slow_launch_timeYesYesYes GlobalYes
Slow_queries   YesBothNo
slow-query-logYesYes  GlobalYes
- Variable: slow_query_log  Yes GlobalYes
slow_query_log_fileYesYesYes GlobalYes
slow-start-timeoutYesYes    
socketYesYesYes GlobalNo
sort_buffer_sizeYesYesYes BothYes
Sort_merge_passes   YesBothNo
Sort_range   YesBothNo
Sort_rows   YesBothNo
Sort_scan   YesBothNo
sporadic-binlog-dump-failYesYes    
sql_auto_is_null  Yes BothYes
sql_big_selects  Yes BothYes
sql_big_tables  Yes BothYes
sql_buffer_result  Yes BothYes
sql_log_bin  Yes BothYes
sql_log_off  Yes BothYes
sql_log_update  Yes SessionYes
sql_low_priority_updates  Yes BothYes
sql_max_join_size  Yes BothYes
sql-modeYesYes  BothYes
- Variable: sql_mode  Yes BothYes
sql_notes  Yes BothYes
sql_quote_show_create  Yes BothYes
sql_safe_updates  Yes BothYes
sql_select_limit  Yes BothYes
sql_slave_skip_counter  Yes GlobalYes
sql_warnings  Yes BothYes
sslYesYes    
Ssl_accept_renegotiates   YesGlobalNo
Ssl_accepts   YesGlobalNo
ssl-caYesYes  GlobalNo
- Variable: ssl_ca  Yes GlobalNo
Ssl_callback_cache_hits   YesGlobalNo
ssl-capathYesYes  GlobalNo
- Variable: ssl_capath  Yes GlobalNo
ssl-certYesYes  GlobalNo
- Variable: ssl_cert  Yes GlobalNo
ssl-cipherYesYes  GlobalNo
- Variable: ssl_cipher  Yes GlobalNo
Ssl_cipher   YesBothNo
Ssl_cipher_list   YesBothNo
Ssl_client_connects   YesGlobalNo
Ssl_connect_renegotiates   YesGlobalNo
Ssl_ctx_verify_depth   YesGlobalNo
Ssl_ctx_verify_mode   YesGlobalNo
Ssl_default_timeout   YesBothNo
Ssl_finished_accepts   YesGlobalNo
Ssl_finished_connects   YesGlobalNo
ssl-keyYesYes  GlobalNo
- Variable: ssl_key  Yes GlobalNo
Ssl_session_cache_hits   YesGlobalNo
Ssl_session_cache_misses   YesGlobalNo
Ssl_session_cache_mode   YesGlobalNo
Ssl_session_cache_overflows   YesGlobalNo
Ssl_session_cache_size   YesGlobalNo
Ssl_session_cache_timeouts   YesGlobalNo
Ssl_sessions_reused   YesBothNo
Ssl_used_session_cache_entries   YesGlobalNo
Ssl_verify_depth   YesBothNo
Ssl_verify_mode   YesBothNo
ssl-verify-server-certYesYes    
Ssl_version   YesBothNo
standaloneYesYes    
storage_engine  Yes BothYes
symbolic-linksYesYes    
sync_binlogYesYesYes GlobalYes
sync_frmYesYesYes GlobalYes
sync_master_infoYesYesYes GlobalYes
sync_relay_logYesYesYes GlobalYes
sync_relay_log_infoYesYesYes GlobalYes
sysdate-is-nowYesYes    
system_time_zone  Yes GlobalNo
table_definition_cacheYesYesYes GlobalYes
table_lock_wait_timeoutYesYesYes GlobalYes
Table_locks_immediate   YesGlobalNo
Table_locks_waited   YesGlobalNo
table_open_cacheYesYesYes GlobalYes
table_type  Yes BothYes
tc-heuristic-recoverYesYes    
Tc_log_max_pages_used   YesGlobalNo
Tc_log_page_size   YesGlobalNo
Tc_log_page_waits   YesGlobalNo
temp-poolYesYes    
thread_cache_sizeYesYesYes GlobalYes
thread_concurrencyYesYesYes GlobalNo
thread_handlingYesYesYes GlobalNo
thread_pool_algorithmYesYesYes GlobalNo
thread_pool_high_priority_connectionYesYesYes BothYes
thread_pool_max_unused_threadsYesYesYes GlobalYes
thread_pool_prio_kickup_timerYesYesYes BothYes
thread_pool_sizeYesYesYes GlobalNo
thread_pool_stall_limitYesYesYes GlobalYes
thread_stackYesYesYes GlobalNo
Threads_cached   YesGlobalNo
Threads_connected   YesGlobalNo
Threads_created   YesGlobalNo
Threads_running   YesGlobalNo
time_format  Yes GlobalNo
time_zoneYesYesYes BothYes
timed_mutexesYesYesYes GlobalYes
timestamp  Yes SessionYes
tmp_table_sizeYesYesYes BothYes
tmpdirYesYesYes GlobalNo
transaction_alloc_block_sizeYesYesYes BothYes
transaction-isolationYesYes    
- Variable: tx_isolation      
transaction_prealloc_sizeYesYesYes BothYes
tx_isolation  Yes BothYes
unique_checks  Yes BothYes
updatable_views_with_limitYesYesYes BothYes
Uptime   YesGlobalNo
Uptime_since_flush_status   YesGlobalNo
userYesYes    
verboseYesYes    
version  Yes GlobalNo
version_comment  Yes GlobalNo
version_compile_machine  Yes GlobalNo
version_compile_os  Yes GlobalNo
wait_timeoutYesYesYes BothYes
warning_count  Yes SessionNo

[a] This option is dynamic, but only the server should set this information. You should not set the value of this variable manually.

[b] This option is dynamic, but only the server should set this information. You should not set the value of this variable manually.

5.1.2. Server Command Options

When you start the mysqld server, you can specify program options using any of the methods described in Section 4.2.3, “Specifying Program Options”. The most common methods are to provide options in an option file or on the command line. However, in most cases it is desirable to make sure that the server uses the same options each time it runs. The best way to ensure this is to list them in an option file. See Section 4.2.3.3, “Using Option Files”.

mysqld reads options from the [mysqld] and [server] groups. mysqld_safe reads options from the [mysqld], [server], [mysqld_safe], and [safe_mysqld] groups. mysql.server reads options from the [mysqld] and [mysql.server] groups.

An embedded MySQL server usually reads options from the [server], [embedded], and [xxxxx_SERVER] groups, where xxxxx is the name of the application into which the server is embedded.

mysqld accepts many command options. For a brief summary, execute mysqld --help. To see the full list, use mysqld --verbose --help.

The following list shows some of the most common server options. Additional options are described in other sections:

You can also set the values of server system variables by using variable names as options, as described at the end of this section.

Some options control the size of buffers or caches. For a given buffer, the server might need to allocate internal data structures. These structures typically are allocated from the total memory allocated to the buffer, and the amount of space required might be platform dependent. This means that when you assign a value to an option that controls a buffer size, the amount of space actually available might differ from the value assigned. In some cases, the amount might be less than the value assigned. It is also possible that the server will adjust a value upward. For example, if you assign a value of 0 to an option for which the minimal value is 1024, the server will set the value to 1024.

Values for buffer sizes, lengths, and stack sizes are given in bytes unless otherwise specified.

Some options take file name values. Unless otherwise specified, the default file location is the data directory if the value is a relative path name. To specify the location explicitly, use an absolute path name. Suppose that the data directory is /var/mysql/data. If a file-valued option is given as a relative path name, it will be located under /var/mysql/data. If the value is an absolute path name, its location is as given by the path name.

  • --help, -?

    Command-Line Format-?
    --help
    Option-File Formathelp

    Display a short help message and exit. Use both the --verbose and --help options to see the full message.

  • --allow-suspicious-udfs

    Command-Line Format--allow-suspicious-udfs
    Option-File Formatallow-suspicious-udfs
     Permitted Values
    Typeboolean
    DefaultFALSE

    This option controls whether user-defined functions that have only an xxx symbol for the main function can be loaded. By default, the option is off and only UDFs that have at least one auxiliary symbol can be loaded; this prevents attempts at loading functions from shared object files other than those containing legitimate UDFs. See Section 22.3.2.6, “User-Defined Function Security Precautions”.

  • --ansi

    Command-Line Format--ansi
    -a
    Option-File Formatansi

    Use standard (ANSI) SQL syntax instead of MySQL syntax. For more precise control over the server SQL mode, use the --sql-mode option instead. See Section 1.8.3, “Running MySQL in ANSI Mode”, and Section 5.1.6, “Server SQL Modes”.

  • --basedir=path, -b path

    Command-Line Format--basedir=path
    -b
    Option-File Formatbasedir
    Option Sets VariableYes, basedir
    Variable Namebasedir
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

    The path to the MySQL installation directory. All paths are usually resolved relative to this directory.

  • --big-tables

    Command-Line Format--big-tables
    Option-File Formatbig-tables
    Option Sets VariableYes, big_tables
    Variable Namebig-tables
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean

    Enable large result sets by saving all temporary sets in files. This option prevents most “table full” errors, but also slows down queries for which in-memory tables would suffice. Since MySQL 3.23.2, the server is able to handle large result sets automatically by using memory for small temporary tables and switching to disk tables where necessary.

  • --bind-address=IP

    Command-Line Format--bind-address=name
    Option-File Formatbind-address=name
    Variable Namebind-address
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring
    Default0.0.0.0
    Range0.0.0.0 .. 255.255.255.255

    The IP address to bind to. Only one address can be selected. If this option is specified multiple times, the last address given is used.

    If no address or 0.0.0.0 is specified, the server listens on all interfaces.

  • --binlog-format={ROW|STATEMENT|MIXED}

    Command-Line Format--binlog-format=format
    Option-File Formatbinlog-format=format
    Option Sets VariableYes, binlog_format
    Variable Namebinlog_format
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeenumeration
    DefaultSTATEMENT
    Valid Values

    ROW

    STATEMENT

    MIXED

    Specify whether to use row-based, statement-based, or mixed replication. Statement-based is the default in MySQL 5.5. See Section 15.1.2, “Replication Formats”.

    Previous to MySQL 5.5, setting the binary logging format without enabling binary logging prevented the MySQL server from starting. In MySQL 5.5, the server starts in such cases, the binlog_format global system variable is set, and a warning is logged instead of an error. (Bug #42928)

  • --bootstrap

    Command-Line Format--bootstrap
    Option-File Formatbootstrap

    This option is used by the mysql_install_db script to create the MySQL privilege tables without having to start a full MySQL server.

    This option is unavailable if MySQL was configured with the DISABLE_GRANT_OPTIONS compiler flag. See Section 2.9.4, “MySQL Source-Configuration Options”.

  • --character-sets-dir=path

    Command-Line Format--character-sets-dir=path
    Option-File Formatcharacter-sets-dir=path
    Option Sets VariableYes, character_sets_dir
    Variable Namecharacter-sets-dir
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typedirectory name

    The directory where character sets are installed. See Section 9.5, “Character Set Configuration”.

  • --character-set-client-handshake

    Command-Line Format--character-set-client-handshake
    Option-File Formatcharacter-set-client-handshake
     Permitted Values
    Typeboolean
    DefaultTRUE

    Do not ignore character set information sent by the client. To ignore client information and use the default server character set, use --skip-character-set-client-handshake; this makes MySQL behave like MySQL 4.0.

  • --character-set-filesystem=charset_name

    Command-Line Format--character-set-filesystem=name
    Option-File Formatcharacter-set-filesystem
    Option Sets VariableYes, character_set_filesystem
    Variable Namecharacter_set_filesystem
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring

    The file system character set. This option sets the character_set_filesystem system variable.

  • --character-set-server=charset_name, -C charset_name

    Command-Line Format--character-set-server
    Option-File Formatcharacter-set-server
    Option Sets VariableYes, character_set_server
    Variable Namecharacter_set_server
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring

    Use charset_name as the default server character set. See Section 9.5, “Character Set Configuration”. If you use this option to specify a nondefault character set, you should also use --collation-server to specify the collation.

  • --chroot=path, -r path

    Command-Line Format--chroot=name
    -r name
    Option-File Formatchroot
     Permitted Values
    Typefile name

    Put the mysqld server in a closed environment during startup by using the chroot() system call. This is a recommended security measure. Note that use of this option somewhat limits LOAD DATA INFILE and SELECT ... INTO OUTFILE.

  • --collation-server=collation_name

    Command-Line Format--collation-server
    Option-File Formatcollation-server
    Option Sets VariableYes, collation_server
    Variable Namecollation_server
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring

    Use collation_name as the default server collation. See Section 9.5, “Character Set Configuration”.

  • --console

    Command-Line Format--console
    Option-File Formatconsole
    Platform Specificwindows

    (Windows only.) Write error log messages to stderr and stdout even if --log-error is specified. mysqld does not close the console window if this option is used.

  • --core-file

    Command-Line Format--core-file
    Option-File Formatcore-file
     Permitted Values
    Typeboolean
    DefaultFALSE

    Write a core file if mysqld dies. The name and location of the core file is system dependent. On Linux, a core file named core.pid is written to the current working directory of the process, which for mysqld is the data directory. pid represents the process ID of the server process. On Mac OS X, a core file named core.pid is written to the /cores directory. On Solaris, use the coreadm command to specify where to write the core file and how to name it.

    For some systems, to get a core file you must also specify the --core-file-size option to mysqld_safe. See Section 4.3.2, “mysqld_safe — MySQL Server Startup Script”. On some systems, such as Solaris, you do not get a core file if you are also using the --user option. There might be additional restrictions or limitations. For example, it might be necessary to execute ulimit -c unlimited before starting the server. Consult your system documentation.

  • --datadir=path, -h path

    Command-Line Format--datadir=path
    -h
    Option-File Formatdatadir
    Option Sets VariableYes, datadir
    Variable Namedatadir
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

    The path to the data directory.

  • --debug[=debug_options], -# [debug_options]

    Command-Line Format--debug[=debug_options]
    Option-File Formatdebug
    Variable Namedebug
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring
    Default'd:t:o,/tmp/mysqld.trace'

    If MySQL is configured with -DWITH_DEBUG=1, you can use this option to get a trace file of what mysqld is doing. A typical debug_options string is 'd:t:o,file_name'. The default is 'd:t:i:o,mysqld.trace'. See MySQL Internals: Porting.

    Using -DWITH_DEBUG=1 to configure MySQL with debugging support enables you to use the --debug="d,parser_debug" option when you start the server. This causes the Bison parser that is used to process SQL statements to dump a parser trace to the server's standard error output. Typically, this output is written to the error log.

    This option may be given multiple times. Values that begin with + or - are added to or subtracted from the previous value. For example, --debug=T --debug=+P sets the value to P:T.

  • --debug-sync-timeout[=N]

    Command-Line Format--debug-sync-timeout[=#]
    Option-File Formatdebug-sync-timeout
     Permitted Values
    Typenumeric

    Controls whether the Debug Sync facility for testing and debugging is enabled. Use of Debug Sync requires that MySQL be configured with the -DENABLE_DEBUG_SYNC=1 option (see Section 2.9.4, “MySQL Source-Configuration Options”). If Debug Sync is not compiled in, this option is not available. The option value is a timeout in seconds. The default value is 0, which disables Debug Sync. To enable it, specify a value greater than 0; this value also becomes the default timeout for individual synchronization points. If the option is given without a value, the timeout is set to 300 seconds.

    For a description of the Debug Sync facility and how to use synchronization points, see MySQL Internals: Test Synchronization.

  • --default-character-set=charset_name

    Command-Line Format--default-character-set=name
    -C name
    Option-File Formatdefault-character-set=name
    Deprecated5.0
     Permitted Values
    Typestring

    Use charset_name as the default character set. This option is deprecated in favor of --character-set-server. See Section 9.5, “Character Set Configuration”. --default-character-set was removed in MySQL 5.5.3.

  • --default-collation=collation_name

    Command-Line Format--default-collation=name
    Option-File Formatdefault-collation=name
    Deprecated4.1.3
     Permitted Values
    Typestring

    Use collation_name as the default collation. This option is deprecated in favor of --collation-server. See Section 9.5, “Character Set Configuration”. --default-collation was removed in MySQL 5.5.3.

  • --default-storage-engine=type

    Command-Line Format--default-storage-engine=name
    Option-File Formatdefault-storage-engine
    Option Sets VariableYes, default_storage_engine
    Variable Namedefault_storage_engine
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values (<= 5.5.4)
    Typeenumeration
    DefaultMyISAM
     Permitted Values (>= 5.5.5)
    Typeenumeration
    DefaultInnoDB

    Set the default storage engine (table type) for tables. See Глава 13, Storage Engines.

  • --default-time-zone=timezone

    Command-Line Format--default-time-zone=name
    Option-File Formatdefault-time-zone
     Permitted Values
    Typestring

    Set the default server time zone. This option sets the global time_zone system variable. If this option is not given, the default time zone is the same as the system time zone (given by the value of the system_time_zone system variable.

  • --delay-key-write[={OFF|ON|ALL}]

    Command-Line Format--delay-key-write[=name]
    Option-File Formatdelay-key-write
    Option Sets VariableYes, delay_key_write
    Variable Namedelay-key-write
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeenumeration
    DefaultON
    Valid Values

    ON

    OFF

    ALL

    Specify how to use delayed key writes. Delayed key writing causes key buffers not to be flushed between writes for MyISAM tables. OFF disables delayed key writes. ON enables delayed key writes for those tables that were created with the DELAY_KEY_WRITE option. ALL delays key writes for all MyISAM tables. See Section 7.11.2, “Tuning Server Parameters”, and Section 13.5.1, “MyISAM Startup Options”.

    Замечание

    If you set this variable to ALL, you should not use MyISAM tables from within another program (such as another MySQL server or myisamchk) when the tables are in use. Doing so leads to index corruption.

  • --des-key-file=file_name

    Command-Line Format--des-key-file=file_name
    Option-File Formatdes-key-file=file_name

    Read the default DES keys from this file. These keys are used by the DES_ENCRYPT() and DES_DECRYPT() functions.

  • --enable-named-pipe

    Command-Line Format--enable-named-pipe
    Option-File Formatenable-named-pipe
    Option Sets VariableYes, named_pipe
    Platform Specificwindows

    Enable support for named pipes. This option applies only on Windows.

  • --enable-pstack

    Version Removed5.5.7
    Command-Line Format--enable-pstack
    Option-File Formatenable-pstack
    Deprecated5.1.54
     Permitted Values
    Typeboolean
    DefaultFALSE

    This option is nonfunctional before MySQL 5.5.7 and removed in 5.5.7.

  • --engine-condition-pushdown={ON|OFF}

    Version Deprecated5.5.3
    Command-Line Format--engine-condition-pushdown
    Option-File Formatengine-condition-pushdown
    Option Sets VariableYes, engine_condition_pushdown
    Variable Nameengine_condition_pushdown
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Deprecated5.5.3, by optimizer_switch
     Permitted Values
    Typeboolean
    DefaultON

    Sets the engine_condition_pushdown system variable. For more information, see Section 7.13.3, “Engine Condition Pushdown Optimization”.

  • --event-scheduler[=value]

    Command-Line Format--event-scheduler[=value]
    Option-File Formatevent-scheduler
    Option Sets VariableYes, event_scheduler
    Variable Nameevent_scheduler
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeenumeration
    DefaultOFF
    Valid Values

    ON

    OFF

    DISABLED

    Enable or disable, and start or stop, the event scheduler.

    For detailed information, see The --event-scheduler Option.

  • --exit-info[=flags], -T [flags]

    Command-Line Format--exit-info[=flags]
    -T [flags]
    Option-File Formatexit-info
     Permitted Values
    Typenumeric

    This is a bit mask of different flags that you can use for debugging the mysqld server. Do not use this option unless you know exactly what it does!

  • --external-locking

    Command-Line Format--external-locking
    Option-File Formatexternal-locking
    Option Sets VariableYes, skip_external_locking
    Disabled byskip-external-locking
     Permitted Values
    Typeboolean
    DefaultFALSE

    Enable external locking (system locking), which is disabled by default as of MySQL 4.0. Note that if you use this option on a system on which lockd does not fully work (such as Linux), it is easy for mysqld to deadlock.

    External locking affects only MyISAM table access. For more information, including conditions under which it can and cannot be used, see Section 7.10.5, “External Locking”.

  • --flush

    Command-Line Format--flush
    Option-File Formatflush
    Variable Nameflush
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    Flush (synchronize) all changes to disk after each SQL statement. Normally, MySQL does a write of all changes to disk only after each SQL statement and lets the operating system handle the synchronizing to disk. See Section C.5.4.2, “What to Do If MySQL Keeps Crashing”.

  • --gdb

    Command-Line Format--gdb
    Option-File Formatgdb
     Permitted Values
    Typeboolean
    DefaultFALSE

    Install an interrupt handler for SIGINT (needed to stop mysqld with ^C to set breakpoints) and disable stack tracing and core file handling. See MySQL Internals: Porting.

  • --general-log[={0|1}]

    Command-Line Format--general-log
    Option-File Formatgeneral-log
    Option Sets VariableYes, general_log
    Variable Namegeneral_log
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    Specify the initial general query log state. With no argument or an argument of 1, the --general-log option enables the log. If omitted or given with an argument of 0, the option disables the log.

  • --init-file=file_name

    Command-Line Format--init-file=file_name
    Option-File Formatinit-file=file_name
    Option Sets VariableYes, init_file
    Variable Nameinit_file
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

    Read SQL statements from this file at startup. Each statement must be on a single line and should not include comments.

    This option is unavailable if MySQL was configured with the DISABLE_GRANT_OPTIONS compiler flag. See Section 2.9.4, “MySQL Source-Configuration Options”.

  • --innodb-xxx

    The InnoDB options are listed in Section 13.3.4, “InnoDB Startup Options and System Variables”.

  • --install [service_name]

    Command-Line Format--install [service_name]

    (Windows only) Install the server as a Windows service that starts automatically during Windows startup. The default service name is MySQL if no service_name value is given. For more information, see Section 2.3.6.7, “Starting MySQL as a Windows Service”.

  • --install-manual [service_name]

    Command-Line Format--install-manual [service_name]

    (Windows only) Install the server as a Windows service that must be started manually. It does not start automatically during Windows startup. The default service name is MySQL if no service_name value is given. For more information, see Section 2.3.6.7, “Starting MySQL as a Windows Service”.

  • --language=lang_name, -L lang_name

    Command-Line Format--language=name
    -L
    Option-File Formatlanguage
    Option Sets VariableYes, language
    Variable Namelanguage
    Variable ScopeGlobal
    Dynamic VariableNo
    Deprecated5.6.1
     Permitted Values
    Typedirectory name
    Default/usr/local/mysql/share/mysql/english/

    The language to use for error messages. lang_name can be given as the language name or as the full path name to the directory where the language files are installed. See Section 9.2, “Setting the Error Message Language”.

    As of MySQL 5.5, --lc-messages-dir and --lc-messages should be used rather than --language, which is deprecated and handled as an alias for --lc-messages-dir.

  • --large-pages

    Command-Line Format--large-pages
    Option-File Formatlarge-pages
    Option Sets VariableYes, large_pages
    Variable Namelarge_pages
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform Specificlinux
     Permitted Values
    Type (linux)boolean
    DefaultFALSE

    Some hardware/operating system architectures support memory pages greater than the default (usually 4KB). The actual implementation of this support depends on the underlying hardware and operating system. Applications that perform a lot of memory accesses may obtain performance improvements by using large pages due to reduced Translation Lookaside Buffer (TLB) misses.

    MySQL 5.5 supports the Linux implementation of large page support (which is called HugeTLB in Linux). See Section 7.11.4.2, “Enabling Large Page Support”. For Solaris support of large pages, see the description of the --super-large-pages option.

    --large-pages is disabled by default.

  • --lc-messages=locale_name

    Command-Line Format--lc-messages=name
    Option-File Formatlc-messages
    Option Sets VariableYes, lc_messages
    Variable Namelc-messages
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring

    The locale to use for error messages. The server converts the argument to a language name and combines it with the value of the --lc-messages-dir to produce the location for the error message file. See Section 9.2, “Setting the Error Message Language”.

  • --lc-messages-dir=path

    Command-Line Format--lc-messages-dir=path
    Option-File Formatlc-messages-dir
    Option Sets VariableYes, lc_messages_dir
    Variable Namelc-messages-dir
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typedirectory name

    The directory where error messages are located. The value is used together with the value of --lc-messages to produce the location for the error message file. See Section 9.2, “Setting the Error Message Language”.

  • --log[=file_name], -l [file_name]

    Command-Line Format--log[=name]
    -l
    Option-File Formatlog
    Option Sets VariableYes, log
    Variable Namelog
    Variable ScopeGlobal
    Dynamic VariableYes
    Deprecated5.1.29, by general-log
     Permitted Values
    Typestring
    DefaultOFF

    This option enables logging to the general query log, which contains entries that record client connections and SQL statements received from clients. The log output destination can be selected with the --log-output option. If you omit the file name, MySQL uses host_name.log as the file name. See Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”, and Section 5.2.3, “The General Query Log”.

    The --log option is deprecated and is removed (along with the log system variable) in MySQL 5.6. Instead, use the --general_log option to enable the general query log and the --general_log_file=file_name option to set the general query log file name.

  • --log-error[=file_name]

    Command-Line Format--log-error[=name]
    Option-File Formatlog-error
    Option Sets VariableYes, log_error
    Variable Namelog_error
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

    Log errors and startup messages to this file. See Section 5.2.2, “The Error Log”. If you omit the file name, MySQL uses host_name.err. If the file name has no extension, the server adds an extension of .err.

  • --log-isam[=file_name]

    Command-Line Format--log-isam[=name]
    Option-File Formatlog-isam
     Permitted Values
    Typefile name

    Log all MyISAM changes to this file (used only when debugging MyISAM).

  • --log-long-format

    Command-Line Format--log-long-format
    -0
    Option-File Formatlog-long-format
    Deprecated4.1

    Log extra information to the binary log and slow query log, if they have been activated. For example, the user name and timestamp are logged for all queries. This option is deprecated, as it now represents the default logging behavior. (See the description for --log-short-format.) The --log-queries-not-using-indexes option is available for the purpose of logging queries that do not use indexes to the slow query log. --log-long-format was removed in MySQL 5.5.3.

  • --log-output[=value,...]

    Command-Line Format--log-output[=name]
    Option-File Formatlog-output
    Option Sets VariableYes, log_output
    Variable Namelog_output
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeset
    DefaultFILE
    Valid Values

    TABLE

    FILE

    NONE

    This option determines the destination for general query log and slow query log output. The option value can be given as one or more of the words TABLE, FILE, or NONE. If the option is given without a value, the default is FILE. TABLE select logging to the general_log and slow_log tables in the mysql database as a destination. FILE selects logging to log files as a destination. NONE disables logging. If NONE is present in the option value, it takes precedence over any other words that are present. TABLE and FILE can both be given to select to both log output destinations.

    This option selects log output destinations, but does not enable log output. To do that, use the --general_log and --slow_query_log options. For FILE logging, the --general_log_file and -slow_query_log_file options determine the log file location. For more information, see Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”.

  • --log-queries-not-using-indexes

    Command-Line Format--log-queries-not-using-indexes
    Option-File Formatlog-queries-not-using-indexes
    Option Sets VariableYes, log_queries_not_using_indexes
    Variable Namelog_queries_not_using_indexes
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    If you are using this option with the slow query log enabled, queries that are expected to retrieve all rows are logged. See Section 5.2.5, “The Slow Query Log”. This option does not necessarily mean that no index is used. For example, a query that uses a full index scan uses an index but would be logged because the index would not limit the number of rows.

  • --log-short-format

    Command-Line Format--log-short-format
    Option-File Formatlog-short-format
     Permitted Values
    Typeboolean
    DefaultFALSE

    Log less information to the binary log and slow query log, if they have been activated.

  • --log-slow-admin-statements

    Command-Line Format--log-slow-admin-statements
    Option-File Formatlog-slow-admin-statements
     Permitted Values
    Typeboolean
    DefaultFALSE

    Log slow administrative statements such as OPTIMIZE TABLE, ANALYZE TABLE, and ALTER TABLE to the slow query log.

  • --log-slow-queries[=file_name]

    Command-Line Format--log-slow-queries[=name]
    Option-File Formatlog-slow-queries
    Option Sets VariableYes, log_slow_queries
    Variable Namelog_slow_queries
    Variable ScopeGlobal
    Dynamic VariableYes
    Deprecated5.1.29, by slow-query-log
     Permitted Values
    Typeboolean

    This option enables logging to the slow query log, which contains entries for all queries that have taken more than long_query_time seconds to execute. See the descriptions of the --log-long-format and --log-short-format options for details. The log output destination can be selected with the --log-output option. If you omit the file name, MySQL uses host_name-slow.log as the file name. See Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”, and Section 5.2.5, “The Slow Query Log”.

    The --log-slow-queries option is deprecated and is removed (along with the log_slow_queries system variable) in MySQL 5.6. Instead, use the --slow_query_log option to enable the slow query log and the --slow_query_log_file=file_name option to set the slow query log file name.

  • --log-tc=file_name

    Command-Line Format--log-tc=name
    Option-File Formatlog-tc
     Permitted Values
    Typefile name
    Defaulttc.log

    The name of the memory-mapped transaction coordinator log file (for XA transactions that affect multiple storage engines when the binary log is disabled). The default name is tc.log. The file is created under the data directory if not given as a full path name. Currently, this option is unused.

  • --log-tc-size=size

    Command-Line Format--log-tc-size=#
    Option-File Formatlog-tc-size
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default24576
    Max Value4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default24576
    Max Value18446744073709547520

    The size in bytes of the memory-mapped transaction coordinator log. The default size is 24KB.

  • --log-warnings[=level], -W [level]

    Command-Line Format--log-warnings[=#]
    -W [#]
    Option-File Formatlog-warnings
    Option Sets VariableYes, log_warnings
    Variable Namelog_warnings
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Disabled byskip-log-warnings
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default1
    Range0 .. 18446744073709547520

    Print out warnings such as Aborted connection... to the error log. Enabling this option is recommended, for example, if you use replication (you get more information about what is happening, such as messages about network failures and reconnections). This option is enabled (1) by default, and the default level value if omitted is 1. To disable this option, use --log-warnings=0. If the value is greater than 1, aborted connections are written to the error log, and access-denied errors for new connection attempts are written. See Section C.5.2.11, “Communication Ошибки and Aborted Connections”.

    If a slave server was started with --log-warnings enabled, the slave prints messages to the error log to provide information about its status, such as the binary log and relay log coordinates where it starts its job, when it is switching to another relay log, when it reconnects after a disconnect, and so forth. The server logs messages about statements that are unsafe for statement-based logging only if --log-warnings is enabled.

  • --low-priority-updates

    Command-Line Format--low-priority-updates
    Option-File Formatlow-priority-updates
    Option Sets VariableYes, low_priority_updates
    Variable Namelow_priority_updates
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultFALSE

    Give table-modifying operations (INSERT, REPLACE, DELETE, UPDATE) lower priority than selects. This can also be done using {INSERT | REPLACE | DELETE | UPDATE} LOW_PRIORITY ... to lower the priority of only one query, or by SET LOW_PRIORITY_UPDATES=1 to change the priority in one thread. This affects only storage engines that use only table-level locking (MyISAM, MEMORY, MERGE). See Section 7.10.2, “Table Locking Issues”.

  • --min-examined-row-limit=number

    Command-Line Format--min-examined-row-limit=#
    Option-File Formatmin-examined-row-limit
    Variable Namemin_examined_row_limit
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default0
    Range0 .. 4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default0
    Range0 .. 18446744073709547520

    When this option is set, queries which examine fewer than number rows are not written to the slow query log. The default is 0.

  • --memlock

    Command-Line Format--memlock
    Option-File Formatmemlock
    Variable Namelocked_in_memory
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typeboolean
    DefaultFALSE

    Lock the mysqld process in memory. This option might help if you have a problem where the operating system is causing mysqld to swap to disk.

    --memlock works on systems that support the mlockall() system call; this includes Solaris as well as most Linux distributions that use a 2.4 or newer kernel. On Linux systems, you can tell whether or not mlockall() (and thus this option) is supported by checking to see whether or not it is defined in the system mman.h file, like this:

    shell> grep mlockall /usr/include/sys/mman.h
    

    If mlockall() is supported, you should see in the output of the previous command something like the following:

    extern int mlockall (int __flags) __THROW;
    Important

    Using this option requires that you run the server as root, which, for reasons of security, is normally not a good idea. See Section 5.3.6, “How to Run MySQL as a Normal User”.

    You must not try to use this option on a system that does not support the mlockall() system call; if you do so, mysqld will very likely crash as soon as you try to start it.

  • --myisam-block-size=N

    Command-Line Format--myisam-block-size=#
    Option-File Formatmyisam-block-size
     Permitted Values
    Typenumeric
    Default1024
    Range1024 .. 16384

    The block size to be used for MyISAM index pages.

  • --myisam-recover[=option[,option]...]]

    This option is renamed as of MySQL 5.5.3 to --myisam-recover-options. See the description of that option for more information.

  • --myisam-recover-options[=option[,option]...]]

    Version Introduced5.5.3
    Command-Line Format--myisam-recover-options[=name]
    Option-File Formatmyisam-recover-options
    Option Sets VariableYes, myisam_recover_options
     Permitted Values
    Typeenumeration
    DefaultOFF
    Valid Values

    OFF

    DEFAULT

    BACKUP

    FORCE

    QUICK

    Set the MyISAM storage engine recovery mode. The option value is any combination of the values of DEFAULT, OFF, BACKUP, FORCE, or QUICK. If you specify multiple values, separate them by commas. Specifying the option with no argument is the same as specifying DEFAULT, and specifying with an explicit value of "" disables recovery (same as not giving the option). If recovery is enabled, each time mysqld opens a MyISAM table, it checks whether the table is marked as crashed or was not closed properly. (The last option works only if you are running with external locking disabled.) If this is the case, mysqld runs a check on the table. If the table was corrupted, mysqld attempts to repair it.

    The following options affect how the repair works.

    OptionОписание
    DEFAULTRecovery without backup, forcing, or quick checking.
    OFFRecovery without backup, forcing, or quick checking.
    BACKUPIf the data file was changed during recovery, save a backup of the tbl_name.MYD file as tbl_name-datetime.BAK.
    FORCERun recovery even if we would lose more than one row from the .MYD file.
    QUICKDo not check the rows in the table if there are not any delete blocks.

    Before the server automatically repairs a table, it writes a note about the repair to the error log. If you want to be able to recover from most problems without user intervention, you should use the options BACKUP,FORCE. This forces a repair of a table even if some rows would be deleted, but it keeps the old data file as a backup so that you can later examine what happened.

    This option was named --myisam-recover, before MySQL 5.5.3. The old option name still works because it is recognized as an unambiguous prefix of the new name, --myisam-recover-options. (Option prefix recognition occurs as described in Section 4.2.3, “Specifying Program Options”.)

    The option value OFF is available as of MySQL 5.5.3.

    See Section 13.5.1, “MyISAM Startup Options”.

  • --old-alter-table

    Command-Line Format--old-alter-table
    Option-File Formatold-alter-table
    Option Sets VariableYes, old_alter_table
    Variable Nameold_alter_table
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    When this option is given, the server does not use the optimized method of processing an ALTER TABLE operation. It reverts to using a temporary table, copying over the data, and then renaming the temporary table to the original, as used by MySQL 5.0 and earlier. For more information on the operation of ALTER TABLE, see Section 12.1.7, “ALTER TABLE Синтаксис”.

  • --old-passwords

    Command-Line Format--old_passwords
    Option-File Formatold-passwords
    Option Sets VariableYes, old_passwords
    Variable Nameold_passwords
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultFALSE

    Force the server to generate short (pre-4.1) password hashes for new passwords. This is useful for compatibility when the server must support older client programs. See Section 5.3.2.3, “Password Hashing in MySQL”.

  • --old-style-user-limits

    Command-Line Format--old-style-user-limits
    Option-File Formatold-style-user-limits
     Permitted Values
    Typeboolean
    DefaultFALSE

    Enable old-style user limits. (Before MySQL 5.0.3, account resource limits were counted separately for each host from which a user connected rather than per account row in the user table.) See Section 5.5.4, “Setting Account Resource Limits”.

  • --one-thread

    Command-Line Format--one-thread
    Option-File Formatone-thread

    Only use one thread (for debugging under Linux). This option is available only if the server is built with debugging enabled. See MySQL Internals: Porting.

    This option is deprecated and is removed in MySQL 5.6. Use --thread_handling=no-threads instead.

  • --open-files-limit=count

    Command-Line Format--open-files-limit=#
    Option-File Formatopen-files-limit
    Option Sets VariableYes, open_files_limit
    Variable Nameopen_files_limit
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default0
    Range0 .. 65535

    Changes the number of file descriptors available to mysqld. You should try increasing the value of this option if mysqld gives you the error Too many open files. mysqld uses the option value to reserve descriptors with setrlimit(). If the requested number of file descriptors cannot be allocated, mysqld writes a warning to the error log.

    mysqld may attempt to allocate more than the requested number of descriptors (if they are available), using the values of max_connections and table_open_cache to estimate whether more descriptors will be needed.

  • --partition[=value]

    Command-Line Format--partition
    Option-File Formatpartition
    Option Sets VariableYes, have_partitioning
    Variable Namepartition
    Variable ScopeGlobal
    Dynamic VariableNo
    Disabled byskip-partition
     Permitted Values
    Typeboolean
    DefaultON

    Enables or disables user-defined partitioning support in the MySQL Server.

  • --pid-file=path

    Command-Line Format--pid-file=file_name
    Option-File Formatpid-file=file_name
    Option Sets VariableYes, pid_file
    Variable Namepid_file
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

    The path name of the process ID file. The server creates the file in the data directory unless an absolute path name is given to specify a different directory. This file is used by other programs such as mysqld_safe to determine the server's process ID.

  • --plugin-xxx

    Specifies an option that pertains to a server plugin. For example, many storage engines can be built as plugins, and for such engines, options for them can be specified with a --plugin prefix. Thus, the --innodb_file_per_table option for InnoDB can be specified as --plugin-innodb_file_per_table.

    For boolean options that can be enabled or disabled, the --skip prefix and other alternative formats are supported as well (see Section 4.2.3.2, “Program Option Modifiers”). For example, --skip-plugin-innodb_file_per_table disables innodb_file_per_table.

    The rationale for the --plugin prefix is that it enables plugin options to be specified unambiguously if there is a name conflict with a built-in server option. For example, were a plugin writer to name a plugin “sql” and implement a “mode” option, the option name might be --sql-mode, which would conflict with the built-in option of the same name. In such cases, references to the conflicting name are resolved in favor of the built-in option. To avoid the ambiguity, users can specify the plugin option as --plugin-sql-mode. Use of the --plugin prefix for plugin options is recommended to avoid any question of ambiguity.

  • --plugin-load=plugin_list

    Command-Line Format--plugin-load=plugin_list
    Option-File Formatplugin-load=plugin_list
     Permitted Values
    Typestring

    This option tells the server to load the named plugins at startup. The option value is a semicolon-separated list of name=plugin_library pairs. Each name is the name of the plugin, and plugin_library is the name of the shared library that contains the plugin code. Each library file must be located in the directory named by the plugin_dir system variable. For example, if plugins named myplug1 and myplug2 have library files myplug1.so and myplug2.so, use this option to load them at startup:

    shell> mysqld --plugin-load=myplug1=myplug1.so;myplug2=myplug2.so
    

    All plugins to load must be named in the same --plugin-load option. If multiple --plugin-load options are given, only the last one is used.

    If a plugin library is named without any preceding plugin name, the server loads all plugins in the library.

    Each plugin is loaded for a single invocation of mysqld only. After a restart, the plugin is not loaded unless --plugin-load is used again. This is in contrast to INSTALL PLUGIN, which adds an entry to the mysql.plugins table to cause the plugin to be loaded for every normal server startup.

    Under normal startup, the server determines which plugins to load by reading the mysql.plugins system table. If the server is started with the --skip-grant-tables option, it does not consult the mysql.plugins table and does not load plugins listed there. --plugin-load enables plugins to be loaded even when --skip-grant-tables is given. --plugin-load also enables plugins to be loaded at startup under configurations when plugins cannot be loaded at runtime.

    For additional information about plugin loading, see Section 5.1.7.1, “Installing and Uninstalling Plugins”.

  • --port=port_num, -P port_num

    Command-Line Format--port=#
    -P
    Option-File Formatport
    Option Sets VariableYes, port
    Variable Nameport
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default3306

    The port number to use when listening for TCP/IP connections. The port number must be 1024 or higher unless the server is started by the root system user.

  • --port-open-timeout=num

    Command-Line Format--port-open-timeout=#
    Option-File Formatport-open-timeout
     Permitted Values
    Typenumeric
    Default0

    On some systems, when the server is stopped, the TCP/IP port might not become available immediately. If the server is restarted quickly afterward, its attempt to reopen the port can fail. This option indicates how many seconds the server should wait for the TCP/IP port to become free if it cannot be opened. The default is not to wait.

  • --remove [service_name]

    Command-Line Format--remove [service_name]

    (Windows only) Remove a MySQL Windows service. The default service name is MySQL if no service_name value is given. For more information, see Section 2.3.6.7, “Starting MySQL as a Windows Service”.

  • --safe-mode

    Command-Line Format--safe-mode
    Option-File Formatsafe-mode
    Deprecated5.0

    Skip some optimization stages.

  • --safe-show-database

    Version Removed5.5.3
    Command-Line Format--safe-show-database(until 4.1.1) 
    Option-File Formatsafe-show-database
    Variable Namesafe_show_database
    Variable ScopeGlobal
    Dynamic VariableYes
    Deprecated4.0.2
     Permitted Values
    Typeboolean

    This option is deprecated and does not do anything because there is a SHOW DATABASES privilege that can be used to control access to database names on a per-account basis. See Section 5.4.1, “Privileges Provided by MySQL”. --safe-show-database was removed in MySQL 5.5.3.

  • --safe-user-create

    Command-Line Format--safe-user-create
    Option-File Formatsafe-user-create
     Permitted Values
    Typeboolean
    DefaultFALSE

    If this option is enabled, a user cannot create new MySQL users by using the GRANT statement unless the user has the INSERT privilege for the mysql.user table or any column in the table. If you want a user to have the ability to create new users that have those privileges that the user has the right to grant, you should grant the user the following privilege:

    GRANT INSERT(user) ON mysql.user TO 'user_name'@'host_name';
    

    This ensures that the user cannot change any privilege columns directly, but has to use the GRANT statement to give privileges to other users.

  • --secure-auth

    Command-Line Format--secure-auth
    Option-File Formatsecure-auth
    Option Sets VariableYes, secure_auth
    Variable Namesecure_auth
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultFALSE

    Disallow authentication by clients that attempt to use accounts that have old (pre-4.1) passwords.

  • --secure-file-priv=path

    Command-Line Format--secure-file-priv=path
    Option-File Formatsecure-file-priv=path
    Option Sets VariableYes, secure_file_priv
    Variable Namesecure-file-priv
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring

    This option limits the effect of the LOAD_FILE() function and the LOAD DATA and SELECT ... INTO OUTFILE statements to work only with files in the specified directory.

  • --shared-memory

    Enable shared-memory connections by local clients. This option is available only on Windows.

  • --shared-memory-base-name=name

    The name of shared memory to use for shared-memory connections. This option is available only on Windows. The default name is MYSQL. The name is case sensitive.

  • --skip-concurrent-insert

    Turn off the ability to select and insert at the same time on MyISAM tables. (This is to be used only if you think you have found a bug in this feature.) See Section 7.10.3, “Concurrent Inserts”.

  • --skip-external-locking

    Do not use external locking (system locking). This affects only MyISAM table access. For more information, including conditions under which it can and cannot be used, see Section 7.10.5, “External Locking”.

    External locking has been disabled by default since MySQL 4.0.

  • --skip-event-scheduler

    Command-Line Format--skip-event-scheduler
    --disable-event-scheduler
    Option-File Formatskip-event-scheduler

    Turns the Event Scheduler OFF. This is not the same as disabling the Event Scheduler, which requires setting --event-scheduler=DISABLED; see The --event-scheduler Option, for more information.

  • --skip-grant-tables

    This option causes the server to start without using the privilege system at all, which gives anyone with access to the server unrestricted access to all databases. You can cause a running server to start using the grant tables again by executing mysqladmin flush-privileges or mysqladmin reload command from a system shell, or by issuing a MySQL FLUSH PRIVILEGES statement after connecting to the server. This option also suppresses loading of plugins that were installed with the INSTALL PLUGIN statement, user-defined functions (UDFs), and scheduled events. To cause plugins to be loaded anyway, use the --plugin-load option.

    --skip-grant-tables is unavailable if MySQL was configured with the DISABLE_GRANT_OPTIONS compiler flag. See Section 2.9.4, “MySQL Source-Configuration Options”.

  • --skip-host-cache

    Do not use the internal host name cache for faster name-to-IP resolution. Instead, query the DNS server every time a client connects. See Section 7.11.5.2, “How MySQL Uses DNS”.

  • --skip-innodb

    Disable the InnoDB storage engine. In this case, the server will not start if the default storage engine is set to InnoDB. Use --default-storage-engine to set the default to some other engine if necessary.

  • --skip-name-resolve

    Do not resolve host names when checking client connections. Use only IP addresses. If you use this option, all Host column values in the grant tables must be IP addresses or localhost. See Section 7.11.5.2, “How MySQL Uses DNS”.

  • --skip-networking

    Do not listen for TCP/IP connections at all. All interaction with mysqld must be made using named pipes or shared memory (on Windows) or Unix socket files (on Unix). This option is highly recommended for systems where only local clients are permitted. See Section 7.11.5.2, “How MySQL Uses DNS”.

  • --skip-partition

    Command-Line Format--skip-partition
    --disable-partition
    Option-File Formatskip-partition

    Disables user-defined partitioning. Existing partitioned tables cannot be accessed when the server has been started with this option.

  • --ssl*

    Options that begin with --ssl specify whether to permit clients to connect using SSL and indicate where to find SSL keys and certificates. See Section 5.5.8.3, “SSL Command Options”.

  • --standalone

    Command-Line Format--standalone
    Option-File Formatstandalone
    Platform Specificwindows

    Available on Windows only; instructs the MySQL server not to run as a service.

  • --super-large-pages

    Standard use of large pages in MySQL attempts to use the largest size supported, up to 4MB. Under Solaris, a “super large pages” feature enables uses of pages up to 256MB. This feature is available for recent SPARC platforms. It can be enabled or disabled by using the --super-large-pages or --skip-super-large-pages option.

  • --symbolic-links, --skip-symbolic-links

    Command-Line Format--symbolic-links
    Option-File Formatsymbolic-links

    Enable or disable symbolic link support. This option has different effects on Windows and Unix:

  • --skip-safemalloc

    Version Removed5.5.6
    Command-Line Format--skip-safemalloc
    Option-File Formatskip-safemalloc

    Previously, if MySQL was configured with full debugging support, all MySQL programs check for memory overruns during each memory allocation and memory freeing operation. This checking is very slow, so for the server you can avoid it when you do not need it by using the --skip-safemalloc option.

    safemalloc, along with this option, was removed in MySQL 5.5.6.

  • --skip-show-database

    Command-Line Format--skip-show-database
    Option-File Formatskip-show-database
    Option Sets VariableYes, skip_show_database
    Variable Nameskip_show_database
    Variable ScopeGlobal
    Dynamic VariableNo

    With this option, the SHOW DATABASES statement is permitted only to users who have the SHOW DATABASES privilege, and the statement displays all database names. Without this option, SHOW DATABASES is permitted to all users, but displays each database name only if the user has the SHOW DATABASES privilege or some privilege for the database. Note that any global privilege is considered a privilege for the database.

  • --skip-stack-trace

    Command-Line Format--skip-stack-trace
    Option-File Formatskip-stack-trace

    Do not write stack traces. This option is useful when you are running mysqld under a debugger. On some systems, you also must use this option to get a core file. See MySQL Internals: Porting.

  • --skip-thread-priority

    Command-Line Format--skip-thread-priority
    Option-File Formatskip-thread-priority
    Deprecated5.1.29

    Disable using thread priorities for faster response time. This option is deprecated and is removed in MySQL 5.6.

  • --slow-query-log[={0|1}]

    Command-Line Format--slow-query-log
    Option-File Formatslow-query-log
    Option Sets VariableYes, slow_query_log
    Variable Nameslow_query_log
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    Specify the initial slow query log state. With no argument or an argument of 1, the --slow-query-log option enables the log. If omitted or given with an argument of 0, the option disables the log.

  • --slow-start-timeout=timeout

    Version Introduced5.5.20
    Command-Line Format--slow-start-timeout=#
    Option-File Formatslow-start-timeout=#
     Permitted Values
    Type (windows)numeric
    Default15000

    This option controls the Windows service control manager's service start timeout. The value is the maximum number of milliseconds that the service control manager waits before trying to kill the windows service during startup. The default value is 15000 (15 seconds). If the MySQL service takes too long to start, you may need to increase this value. A value of 0 means there is no timeout.

  • --socket=path

    Command-Line Format--socket=name
    Option-File Formatsocket
    Option Sets VariableYes, socket
    Variable Namesocket
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name
    Default/tmp/mysql.sock

    On Unix, this option specifies the Unix socket file to use when listening for local connections. The default value is /tmp/mysql.sock. If this option is given, the server creates the file in the data directory unless an absolute path name is given to specify a different directory. On Windows, the option specifies the pipe name to use when listening for local connections that use a named pipe. The default value is MySQL (not case sensitive).

  • --sql-mode=value[,value[,value...]]

    Command-Line Format--sql-mode=name
    Option-File Formatsql-mode
    Option Sets VariableYes, sql_mode
    Variable Namesql_mode
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeset
    Default''
    Valid Values

    ALLOW_INVALID_DATES

    ANSI_QUOTES

    ERROR_FOR_DIVISION_BY_ZERO

    HIGH_NOT_PRECEDENCE

    IGNORE_SPACE

    NO_AUTO_CREATE_USER

    NO_AUTO_VALUE_ON_ZERO

    NO_BACKSLASH_ESCAPES

    NO_DIR_IN_CREATE

    NO_ENGINE_SUBSTITUTION

    NO_FIELD_OPTIONS

    NO_KEY_OPTIONS

    NO_TABLE_OPTIONS

    NO_UNSIGNED_SUBTRACTION

    NO_ZERO_DATE

    NO_ZERO_IN_DATE

    ONLY_FULL_GROUP_BY

    PAD_CHAR_TO_FULL_LENGTH

    PIPES_AS_CONCAT

    REAL_AS_FLOAT

    STRICT_ALL_TABLES

    STRICT_TRANS_TABLES

    Set the SQL mode. See Section 5.1.6, “Server SQL Modes”.

  • --sysdate-is-now

    Command-Line Format--sysdate-is-now
    Option-File Formatsysdate-is-now
     Permitted Values
    Typeboolean
    DefaultFALSE

    SYSDATE() by default returns the time at which it executes, not the time at which the statement in which it occurs begins executing. This differs from the behavior of NOW(). This option causes SYSDATE() to be an alias for NOW(). For information about the implications for binary logging and replication, see the description for SYSDATE() in Section 11.7, “Date and Time Functions” and for SET TIMESTAMP in Section 5.1.3, “Server System Variables”.

  • --tc-heuristic-recover={COMMIT|ROLLBACK}

    Command-Line Format--tc-heuristic-recover=name
    Option-File Formattc-heuristic-recover
     Permitted Values
    Typeenumeration
    Valid Values

    COMMIT

    RECOVER

    The type of decision to use in the heuristic recovery process. Currently, this option is unused.

  • --temp-pool

    Command-Line Format--temp-pool
    Option-File Formattemp-pool
     Permitted Values
    Typeboolean
    DefaultTRUE

    This option causes most temporary files created by the server to use a small set of names, rather than a unique name for each new file. This works around a problem in the Linux kernel dealing with creating many new files with different names. With the old behavior, Linux seems to “leak” memory, because it is being allocated to the directory entry cache rather than to the disk cache. This option is ignored except on Linux.

  • --transaction-isolation=level

    Command-Line Format--transaction-isolation=name
    Option-File Formattransaction-isolation
    Option Sets VariableYes, tx_isolation
     Permitted Values
    Typeenumeration
    Valid Values

    READ-UNCOMMITTED

    READ-COMMITTED

    REPEATABLE-READ

    SERIALIZABLE

    Sets the default transaction isolation level. The level value can be READ-UNCOMMITTED, READ-COMMITTED, REPEATABLE-READ, or SERIALIZABLE. See Section 12.3.6, “SET TRANSACTION Синтаксис”.

    The default transaction isolation level can also be set in the running server using SET TRANSACTION or by setting the tx_isolation system variable.

  • --tmpdir=path, -t path

    Command-Line Format--tmpdir=path
    -t
    Option-File Formattmpdir
    Option Sets VariableYes, tmpdir
    Variable Nametmpdir
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

    The path of the directory to use for creating temporary files. It might be useful if your default /tmp directory resides on a partition that is too small to hold temporary tables. This option accepts several paths that are used in round-robin fashion. Paths should be separated by colon characters (“:”) on Unix and semicolon characters (“;”) on Windows. If the MySQL server is acting as a replication slave, you should not set --tmpdir to point to a directory on a memory-based file system or to a directory that is cleared when the server host restarts. For more information about the storage location of temporary files, see Section C.5.4.4, “Where MySQL Stores Temporary Files”. A replication slave needs some of its temporary files to survive a machine restart so that it can replicate temporary tables or LOAD DATA INFILE operations. If files in the temporary file directory are lost when the server restarts, replication fails.

  • --user={user_name|user_id}, -u {user_name|user_id}

    Command-Line Format--user=name
    -u name
    Option-File Formatuser
     Permitted Values
    Typestring

    Run the mysqld server as the user having the name user_name or the numeric user ID user_id. (“User” in this context refers to a system login account, not a MySQL user listed in the grant tables.)

    This option is mandatory when starting mysqld as root. The server changes its user ID during its startup sequence, causing it to run as that particular user rather than as root. See Section 5.3.1, “General Security Guidelines”.

    To avoid a possible security hole where a user adds a --user=root option to a my.cnf file (thus causing the server to run as root), mysqld uses only the first --user option specified and produces a warning if there are multiple --user options. Options in /etc/my.cnf and $MYSQL_HOME/my.cnf are processed before command-line options, so it is recommended that you put a --user option in /etc/my.cnf and specify a value other than root. The option in /etc/my.cnf is found before any other --user options, which ensures that the server runs as a user other than root, and that a warning results if any other --user option is found.

  • --verbose, -v

    Use this option with the --help option for detailed help.

  • --version, -V

    Display version information and exit.

You can assign a value to a server system variable by using an option of the form --var_name=value. For example, --key_buffer_size=32M sets the key_buffer_size variable to a value of 32MB.

Note that when you assign a value to a variable, MySQL might automatically correct the value to stay within a given range, or adjust the value to the closest permissible value if only certain values are permitted.

If you want to restrict the maximum value to which a variable can be set at runtime with SET, you can define this by using the --maximum-var_name=value command-line option.

You can change the values of most system variables for a running server with the SET statement. See Section 12.7.4, “SET Синтаксис”.

Section 5.1.3, “Server System Variables”, provides a full description for all variables, and additional information for setting them at server startup and runtime. Section 7.11.2, “Tuning Server Parameters”, includes information on optimizing the server by tuning system variables.

5.1.3. Server System Variables

The MySQL server maintains many system variables that indicate how it is configured. Each system variable has a default value. System variables can be set at server startup using options on the command line or in an option file. Most of them can be changed dynamically while the server is running by means of the SET statement, which enables you to modify operation of the server without having to stop and restart it. You can refer to system variable values in expressions.

There are several ways to see the names and values of system variables:

  • To see the values that a server will use based on its compiled-in defaults and any option files that it reads, use this command:

    mysqld --verbose --help
  • To see the values that a server will use based on its compiled-in defaults, ignoring the settings in any option files, use this command:

    mysqld --no-defaults --verbose --help
  • To see the current values used by a running server, use the SHOW VARIABLES statement.

This section provides a description of each system variable. Variables with no version indicated are present in all MySQL 5.5 releases. For historical information concerning their implementation, please see http://dev.mysql.com/doc/refman/5.0/en/, and http://dev.mysql.com/doc/refman/4.1/en/.

The following table lists all available system variables:

Table 5.2. System Variable Summary

NameCmd-LineOption fileSystem VarVar ScopeDynamic
auto_increment_incrementYesYesYesBothYes
auto_increment_offsetYesYesYesBothYes
autocommitYesYesYesBothYes
automatic_sp_privileges  YesGlobalYes
back_logYesYesYesGlobalNo
basedirYesYesYesGlobalNo
big-tablesYesYes  Yes
- Variable: big_tables  YesBothYes
bind-addressYesYesYesGlobalNo
binlog_cache_sizeYesYesYesGlobalYes
binlog_direct_non_transactional_updatesYesYesYesBothYes
binlog-formatYesYes  Yes
- Variable: binlog_format  YesBothYes
binlog_stmt_cache_sizeYesYesYesGlobalYes
bulk_insert_buffer_sizeYesYesYesBothYes
character_set_client  YesBothYes
character_set_connection  YesBothYes
character_set_database[a]  YesBothYes
character-set-filesystemYesYes  Yes
- Variable: character_set_filesystem  YesBothYes
character_set_results  YesBothYes
character-set-serverYesYes  Yes
- Variable: character_set_server  YesBothYes
character_set_system  YesGlobalNo
character-sets-dirYesYes  No
- Variable: character_sets_dir  YesGlobalNo
collation_connection  YesBothYes
collation_database[b]  YesBothYes
collation-serverYesYes  Yes
- Variable: collation_server  YesBothYes
completion_typeYesYesYesBothYes
concurrent_insertYesYesYesGlobalYes
connect_timeoutYesYesYesGlobalYes
datadirYesYesYesGlobalNo
date_format  YesGlobalNo
datetime_format  YesGlobalNo
debugYesYesYesBothYes
debug_sync  YesSessionYes
default-storage-engineYesYes  Yes
- Variable: default_storage_engine  YesBothYes
default_week_formatYesYesYesBothYes
delay-key-writeYesYes  Yes
- Variable: delay_key_write  YesGlobalYes
delayed_insert_limitYesYesYesGlobalYes
delayed_insert_timeoutYesYesYesGlobalYes
delayed_queue_sizeYesYesYesGlobalYes
div_precision_incrementYesYesYesBothYes
engine-condition-pushdownYesYes  Yes
- Variable: engine_condition_pushdown  YesBothYes
error_count  YesSessionNo
event-schedulerYesYes  Yes
- Variable: event_scheduler  YesGlobalYes
expire_logs_daysYesYesYesGlobalYes
external_user  YesSessionNo
flushYesYesYesGlobalYes
flush_timeYesYesYesGlobalYes
foreign_key_checks  YesBothYes
ft_boolean_syntaxYesYesYesGlobalYes
ft_max_word_lenYesYesYesGlobalNo
ft_min_word_lenYesYesYesGlobalNo
ft_query_expansion_limitYesYesYesGlobalNo
ft_stopword_fileYesYesYesGlobalNo
general-logYesYes  Yes
- Variable: general_log  YesGlobalYes
general_log_fileYesYesYesGlobalYes
group_concat_max_lenYesYesYesBothYes
have_compress  YesGlobalNo
have_crypt  YesGlobalNo
have_csv  YesGlobalNo
have_dynamic_loading  YesGlobalNo
have_geometry  YesGlobalNo
have_innodb  YesGlobalNo
have_ndbcluster  YesGlobalNo
have_openssl  YesGlobalNo
have_partitioning  YesGlobalNo
have_profiling  YesGlobalNo
have_query_cache  YesGlobalNo
have_rtree_keys  YesGlobalNo
have_ssl  YesGlobalNo
have_symlink  YesGlobalNo
hostname  YesGlobalNo
identity  YesSessionYes
ignore-builtin-innodbYesYes  No
- Variable: ignore_builtin_innodb  YesGlobalNo
init_connectYesYesYesGlobalYes
init-fileYesYes  No
- Variable: init_file  YesGlobalNo
init_slaveYesYesYesGlobalYes
innodb_adaptive_flushingYesYesYesGlobalYes
innodb_adaptive_hash_indexYesYesYesGlobalYes
innodb_additional_mem_pool_sizeYesYesYesGlobalNo
innodb_autoextend_incrementYesYesYesGlobalYes
innodb_autoinc_lock_modeYesYesYesGlobalNo
innodb_buffer_pool_instancesYesYesYesGlobalNo
innodb_buffer_pool_sizeYesYesYesGlobalNo
innodb_change_bufferingYesYesYesGlobalYes
innodb_checksumsYesYesYesGlobalNo
innodb_commit_concurrencyYesYesYesGlobalYes
innodb_concurrency_ticketsYesYesYesGlobalYes
innodb_data_file_pathYesYesYesGlobalNo
innodb_data_home_dirYesYesYesGlobalNo
innodb_doublewriteYesYesYesGlobalNo
innodb_fast_shutdownYesYesYesGlobalYes
innodb_file_formatYesYesYesGlobalYes
innodb_file_format_checkYesYesYesGlobalNo
innodb_file_format_maxYesYesYesGlobalYes
innodb_file_per_tableYesYesYesGlobalYes
innodb_flush_log_at_trx_commitYesYesYesGlobalYes
innodb_flush_methodYesYesYesGlobalNo
innodb_force_recoveryYesYesYesGlobalNo
innodb_io_capacityYesYesYesGlobalYes
innodb_large_prefixYesYesYesGlobalYes
innodb_lock_wait_timeoutYesYesYesBothYes
innodb_locks_unsafe_for_binlogYesYesYesGlobalNo
innodb_log_buffer_sizeYesYesYesGlobalNo
innodb_log_file_sizeYesYesYesGlobalNo
innodb_log_files_in_groupYesYesYesGlobalNo
innodb_log_group_home_dirYesYesYesGlobalNo
innodb_max_dirty_pages_pctYesYesYesGlobalYes
innodb_max_purge_lagYesYesYesGlobalYes
innodb_mirrored_log_groupsYesYesYesGlobalNo
innodb_old_blocks_pctYesYesYesGlobalYes
innodb_old_blocks_timeYesYesYesGlobalYes
innodb_open_filesYesYesYesGlobalNo
innodb_purge_batch_sizeYesYesYesGlobalNo
innodb_purge_threadsYesYesYesGlobalNo
innodb_read_ahead_thresholdYesYesYesGlobalYes
innodb_read_io_threadsYesYesYesGlobalNo
innodb_replication_delayYesYesYesGlobalYes
innodb_rollback_on_timeoutYesYesYesGlobalNo
innodb_rollback_segmentsYesYesYesGlobalYes
innodb_spin_wait_delayYesYesYesGlobalYes
innodb_stats_methodYesYesYesBothYes
innodb_stats_on_metadataYesYesYesGlobalYes
innodb_stats_sample_pagesYesYesYesGlobalYes
innodb-status-fileYesYesYesGlobalNo
innodb_strict_modeYesYesYesBothYes
innodb_support_xaYesYesYesBothYes
innodb_sync_spin_loopsYesYesYesGlobalYes
innodb_table_locksYesYesYesBothYes
innodb_thread_concurrencyYesYesYesGlobalYes
innodb_thread_sleep_delayYesYesYesGlobalYes
innodb_use_native_aioYesYesYesGlobalNo
innodb_use_sys_mallocYesYesYesGlobalNo
innodb_version  YesGlobalNo
innodb_write_io_threadsYesYesYesGlobalNo
insert_id  YesSessionYes
interactive_timeoutYesYesYesBothYes
join_buffer_sizeYesYesYesBothYes
keep_files_on_createYesYesYesBothYes
key_buffer_sizeYesYesYesGlobalYes
key_cache_age_thresholdYesYesYesGlobalYes
key_cache_block_sizeYesYesYesGlobalYes
key_cache_division_limitYesYesYesGlobalYes
languageYesYesYesGlobalNo
large_files_support  YesGlobalNo
large_page_size  YesGlobalNo
large-pagesYesYes  No
- Variable: large_pages  YesGlobalNo
last_insert_id  YesSessionYes
lc-messagesYesYes  Yes
- Variable: lc_messages  YesBothYes
lc-messages-dirYesYes  No
- Variable: lc_messages_dir  YesGlobalNo
lc_time_names  YesBothYes
license  YesGlobalNo
local_infile  YesGlobalYes
lock_wait_timeoutYesYesYesBothYes
locked_in_memory  YesGlobalNo
logYesYesYesGlobalYes
log_bin  YesGlobalNo
log-binYesYesYesGlobalNo
log-bin-trust-function-creatorsYesYes  Yes
- Variable: log_bin_trust_function_creators  YesGlobalYes
log-bin-trust-routine-creatorsYesYes  Yes
- Variable: log_bin_trust_routine_creators  YesGlobalYes
log_bin_use_v1_row_eventsYesYesYesGlobalNo
log-bin-use-v1-row-eventsYesYes  No
- Variable: log_bin_use_v1_row_events  YesGlobalNo
log-errorYesYes  No
- Variable: log_error  YesGlobalNo
log-outputYesYes  Yes
- Variable: log_output  YesGlobalYes
log-queries-not-using-indexesYesYes  Yes
- Variable: log_queries_not_using_indexes  YesGlobalYes
log-slave-updatesYesYes  No
- Variable: log_slave_updates  YesGlobalNo
log-slow-queriesYesYes  Yes
- Variable: log_slow_queries  YesGlobalYes
log-warningsYesYes  Yes
- Variable: log_warnings  YesBothYes
long_query_timeYesYesYesBothYes
low-priority-updatesYesYes  Yes
- Variable: low_priority_updates  YesBothYes
lower_case_file_systemYesYesYesGlobalNo
lower_case_table_namesYesYesYesGlobalNo
max_allowed_packetYesYesYesGlobalYes
max_binlog_cache_sizeYesYesYesGlobalYes
max_binlog_sizeYesYesYesGlobalYes
max_binlog_stmt_cache_sizeYesYesYesGlobalYes
max_connect_errorsYesYesYesGlobalYes
max_connectionsYesYesYesGlobalYes
max_delayed_threadsYesYesYesBothYes
max_error_countYesYesYesBothYes
max_heap_table_sizeYesYesYesBothYes
max_insert_delayed_threads  YesBothYes
max_join_sizeYesYesYesBothYes
max_length_for_sort_dataYesYesYesBothYes
max_long_data_sizeYesYesYesGlobalNo
max_prepared_stmt_countYesYesYesGlobalYes
max_relay_log_sizeYesYesYesGlobalYes
max_seeks_for_keyYesYesYesBothYes
max_sort_lengthYesYesYesBothYes
max_sp_recursion_depthYesYesYesBothYes
max_tmp_tablesYesYesYesBothYes
max_user_connectionsYesYesYesBothYes
max_write_lock_countYesYesYesGlobalYes
memlockYesYesYesGlobalNo
metadata_locks_cache_size  YesGlobalNo
min-examined-row-limitYesYesYesBothYes
myisam_data_pointer_sizeYesYesYesGlobalYes
myisam_max_sort_file_sizeYesYesYesGlobalYes
myisam_mmap_sizeYesYesYesGlobalNo
myisam_recover_options  YesGlobalNo
myisam_repair_threadsYesYesYesBothYes
myisam_sort_buffer_sizeYesYesYesBothYes
myisam_stats_methodYesYesYesBothYes
myisam_use_mmapYesYesYesGlobalYes
named_pipe  YesGlobalNo
ndb_autoincrement_prefetch_szYesYesYesBothYes
ndb-batch-sizeYesYesYesGlobalNo
ndb-blob-read-batch-bytesYesYesYesBothYes
ndb-blob-write-batch-bytesYesYesYesBothYes
ndb_cache_check_timeYesYesYesGlobalYes
ndb-cluster-connection-poolYesYesYesGlobalNo
ndb-deferred-constraintsYesYes  Yes
- Variable: ndb_deferred_constraints  YesBothYes
ndb_deferred_constraintsYesYesYesBothYes
ndb_distributionYesYesYesBothYes
ndb-distributionYesYes  Yes
- Variable: ndb_distribution  YesBothYes
ndb_extra_loggingYesYesYesGlobalYes
ndb_force_sendYesYesYesBothYes
ndb_join_pushdown  YesGlobalNo
ndb-log-apply-statusYesYes  No
- Variable: ndb_log_apply_status  YesGlobalNo
ndb_log_binYes YesBothYes
ndb_log_binlog_indexYes YesGlobalYes
ndb_log_empty_epochsYesYesYesGlobalYes
ndb-log-empty-epochsYesYesYesGlobalYes
ndb_log_orig  YesGlobalNo
ndb-log-transaction-idYesYes  No
- Variable: ndb_log_transaction_id  YesGlobalNo
ndb_log_transaction_id  YesGlobalNo
ndb-log-update-as-writeYesYesYesGlobalYes
ndb_log_updated_onlyYesYesYesGlobalYes
ndb_optimization_delay  YesGlobalYes
ndb_table_no_logging  YesSessionYes
ndb_table_temporary  YesSessionYes
ndb_use_copying_alter_table  YesBothNo
ndb_use_exact_count  YesBothYes
ndb_use_transactionsYesYesYesBothYes
ndb-wait-connectedYesYesYesGlobalNo
ndb-wait-setupYesYesYesGlobalNo
ndbinfo_database  YesGlobalNo
ndbinfo_max_bytesYes YesBothYes
ndbinfo_max_rowsYes YesBothYes
ndbinfo_show_hiddenYes YesBothYes
ndbinfo_table_prefixYes YesBothYes
ndbinfo_version  YesGlobalNo
net_buffer_lengthYesYesYesBothYes
net_read_timeoutYesYesYesBothYes
net_retry_countYesYesYesBothYes
net_write_timeoutYesYesYesBothYes
newYesYesYesBothYes
oldYesYesYesGlobalNo
old-alter-tableYesYes  Yes
- Variable: old_alter_table  YesBothYes
old-passwordsYesYes  Yes
- Variable: old_passwords  YesBothYes
open-files-limitYesYes  No
- Variable: open_files_limit  YesGlobalNo
optimizer_prune_levelYesYesYesBothYes
optimizer_search_depthYesYesYesBothYes
optimizer_switchYesYesYesBothYes
partitionYesYes  No
- Variable: have_partitioning  YesGlobalNo
performance_schemaYesYesYesGlobalNo
performance_schema_events_waits_history_long_sizeYesYesYesGlobalNo
performance_schema_events_waits_history_sizeYesYesYesGlobalNo
performance_schema_max_cond_classesYesYesYesGlobalNo
performance_schema_max_cond_instancesYesYesYesGlobalNo
performance_schema_max_file_classesYesYesYesGlobalNo
performance_schema_max_file_handlesYesYesYesGlobalNo
performance_schema_max_file_instancesYesYesYesGlobalNo
performance_schema_max_mutex_classesYesYesYesGlobalNo
performance_schema_max_mutex_instancesYesYesYesGlobalNo
performance_schema_max_rwlock_classesYesYesYesGlobalNo
performance_schema_max_rwlock_instancesYesYesYesGlobalNo
performance_schema_max_table_handlesYesYesYesGlobalNo
performance_schema_max_table_instancesYesYesYesGlobalNo
performance_schema_max_thread_classesYesYesYesGlobalNo
performance_schema_max_thread_instancesYesYesYesGlobalNo
pid-fileYesYes  No
- Variable: pid_file  YesGlobalNo
plugin_dirYesYesYesGlobalNo
portYesYesYesGlobalNo
preload_buffer_sizeYesYesYesBothYes
profiling  YesBothYes
profiling_history_sizeYesYesYesBothYes
protocol_version  YesGlobalNo
proxy_user  YesSessionNo
pseudo_thread_id  YesSessionYes
query_alloc_block_sizeYesYesYesBothYes
query_cache_limitYesYesYesGlobalYes
query_cache_min_res_unitYesYesYesGlobalYes
query_cache_sizeYesYesYesGlobalYes
query_cache_typeYesYesYesBothYes
query_cache_wlock_invalidateYesYesYesBothYes
query_prealloc_sizeYesYesYesBothYes
rand_seed1  YesSessionYes
rand_seed2  YesSessionYes
range_alloc_block_sizeYesYesYesBothYes
read_buffer_sizeYesYesYesBothYes
read_onlyYesYesYesGlobalYes
read_rnd_buffer_sizeYesYesYesBothYes
relay-log-indexYesYes  No
- Variable: relay_log_index  YesBothNo
relay_log_indexYesYesYesGlobalNo
relay_log_info_fileYesYesYesGlobalNo
relay_log_purgeYesYesYesGlobalYes
relay_log_recoveryYesYesYesGlobalYes
relay_log_space_limitYesYesYesGlobalNo
report-hostYesYes  No
- Variable: report_host  YesGlobalNo
report-passwordYesYes  No
- Variable: report_password  YesGlobalNo
report-portYesYes  No
- Variable: report_port  YesGlobalNo
report-userYesYes  No
- Variable: report_user  YesGlobalNo
rpl_recovery_rank  YesGlobalYes
rpl_semi_sync_master_enabled  YesGlobalYes
rpl_semi_sync_master_timeout  YesGlobalYes
rpl_semi_sync_master_trace_level  YesGlobalYes
rpl_semi_sync_master_wait_no_slave  YesGlobalYes
rpl_semi_sync_slave_enabled  YesGlobalYes
rpl_semi_sync_slave_trace_level  YesGlobalYes
safe-show-databaseYesYesYesGlobalYes
secure-authYesYes  Yes
- Variable: secure_auth  YesGlobalYes
secure-file-privYesYes  No
- Variable: secure_file_priv  YesGlobalNo
server-idYesYes  Yes
- Variable: server_id  YesGlobalYes
server-id-bitsYesYes  No
- Variable: server_id_bits  YesGlobalNo
shared_memory  YesGlobalNo
shared_memory_base_name  YesGlobalNo
skip-external-lockingYesYes  No
- Variable: skip_external_locking  YesGlobalNo
skip-name-resolveYesYes  No
- Variable: skip_name_resolve  YesGlobalNo
skip-networkingYesYes  No
- Variable: skip_networking  YesGlobalNo
skip-show-databaseYesYes  No
- Variable: skip_show_database  YesGlobalNo
slave_allow_batchingYesYesYesGlobalYes
slave_compressed_protocolYesYesYesGlobalYes
slave_exec_mode  YesGlobalYes
slave-load-tmpdirYesYes  No
- Variable: slave_load_tmpdir  YesGlobalNo
slave-net-timeoutYesYes  Yes
- Variable: slave_net_timeout  YesGlobalYes
slave-skip-errorsYesYes  No
- Variable: slave_skip_errors  YesGlobalNo
slave_transaction_retriesYesYesYesGlobalYes
slave_type_conversionsYesYesYesGlobalNo
slow_launch_timeYesYesYesGlobalYes
slow-query-logYesYes  Yes
- Variable: slow_query_log  YesGlobalYes
slow_query_log_fileYesYesYesGlobalYes
socketYesYesYesGlobalNo
sort_buffer_sizeYesYesYesBothYes
sql_auto_is_null  YesBothYes
sql_big_selects  YesBothYes
sql_big_tables  YesBothYes
sql_buffer_result  YesBothYes
sql_log_bin  YesBothYes
sql_log_off  YesBothYes
sql_log_update  YesSessionYes
sql_low_priority_updates  YesBothYes
sql_max_join_size  YesBothYes
sql-modeYesYes  Yes
- Variable: sql_mode  YesBothYes
sql_notes  YesBothYes
sql_quote_show_create  YesBothYes
sql_safe_updates  YesBothYes
sql_select_limit  YesBothYes
sql_slave_skip_counter  YesGlobalYes
sql_warnings  YesBothYes
ssl-caYesYes  No
- Variable: ssl_ca  YesGlobalNo
ssl-capathYesYes  No
- Variable: ssl_capath  YesGlobalNo
ssl-certYesYes  No
- Variable: ssl_cert  YesGlobalNo
ssl-cipherYesYes  No
- Variable: ssl_cipher  YesGlobalNo
ssl-keyYesYes  No
- Variable: ssl_key  YesGlobalNo
storage_engine  YesBothYes
sync_binlogYesYesYesGlobalYes
sync_frmYesYesYesGlobalYes
sync_master_infoYesYesYesGlobalYes
sync_relay_logYesYesYesGlobalYes
sync_relay_log_infoYesYesYesGlobalYes
system_time_zone  YesGlobalNo
table_definition_cacheYesYesYesGlobalYes
table_lock_wait_timeoutYesYesYesGlobalYes
table_open_cacheYesYesYesGlobalYes
table_type  YesBothYes
thread_cache_sizeYesYesYesGlobalYes
thread_concurrencyYesYesYesGlobalNo
thread_handlingYesYesYesGlobalNo
thread_pool_algorithmYesYesYesGlobalNo
thread_pool_high_priority_connectionYesYesYesBothYes
thread_pool_max_unused_threadsYesYesYesGlobalYes
thread_pool_prio_kickup_timerYesYesYesBothYes
thread_pool_sizeYesYesYesGlobalNo
thread_pool_stall_limitYesYesYesGlobalYes
thread_stackYesYesYesGlobalNo
time_format  YesGlobalNo
time_zoneYesYesYesBothYes
timed_mutexesYesYesYesGlobalYes
timestamp  YesSessionYes
tmp_table_sizeYesYesYesBothYes
tmpdirYesYesYesGlobalNo
transaction_alloc_block_sizeYesYesYesBothYes
transaction_prealloc_sizeYesYesYesBothYes
tx_isolation  YesBothYes
unique_checks  YesBothYes
updatable_views_with_limitYesYesYesBothYes
version  YesGlobalNo
version_comment  YesGlobalNo
version_compile_machine  YesGlobalNo
version_compile_os  YesGlobalNo
wait_timeoutYesYesYesBothYes
warning_count  YesSessionNo

[a] This option is dynamic, but only the server should set this information. You should not set the value of this variable manually.

[b] This option is dynamic, but only the server should set this information. You should not set the value of this variable manually.

For additional system variable information, see these sections:

Замечание

Some of the following variable descriptions refer to “enabling” or “disabling” a variable. These variables can be enabled with the SET statement by setting them to ON or 1, or disabled by setting them to OFF or 0. However, before MySQL 5.5.10, to set such a variable on the command line or in an option file, you must set it to 1 or 0; setting it to ON or OFF will not work. For example, on the command line, --delay_key_write=1 works but --delay_key_write=ON does not. As of MySQL 5.5.10, boolean variables can be set at startup to the values ON, TRUE, OFF, and FALSE (not case sensitive). See Section 4.2.3.2, “Program Option Modifiers”.

Some system variables control the size of buffers or caches. For a given buffer, the server might need to allocate internal data structures. These structures typically are allocated from the total memory allocated to the buffer, and the amount of space required might be platform dependent. This means that when you assign a value to a system variable that controls a buffer size, the amount of space actually available might differ from the value assigned. In some cases, the amount might be less than the value assigned. It is also possible that the server will adjust a value upward. For example, if you assign a value of 0 to a variable for which the minimal value is 1024, the server will set the value to 1024.

Values for buffer sizes, lengths, and stack sizes are given in bytes unless otherwise specified.

Some system variables take file name values. Unless otherwise specified, the default file location is the data directory if the value is a relative path name. To specify the location explicitly, use an absolute path name. Suppose that the data directory is /var/mysql/data. If a file-valued variable is given as a relative path name, it will be located under /var/mysql/data. If the value is an absolute path name, its location is as given by the path name.

  • authentication_windows_log_level

    Version Introduced5.5.16
    Command-Line Format--authentication_windows_log_level
    Option-File Formatauthentication_windows_log_level
    Option Sets VariableYes, authentication_windows_log_level
     Permitted Values
    Typenumeric
    Default0
    Range0 .. 4

    This variable is available only if the authentication_windows Windows authentication plugin is enabled and debugging code is enabled. See Section 5.5.6.3, “The Windows Native Authentication Plugin”.

    This variable sets the logging level for the Windows authentication plugin. The following table shows the permitted values.

    ValueОписание
    0No logging
    1Log only error messages
    2Log level 1 messages and warning messages
    3Log level 2 messages and information notes
    4Log level 3 messages and debug messages

    This variable was added in MySQL 5.5.16.

  • authentication_windows_use_principal_name

    Version Introduced5.5.16
    Command-Line Format--authentication_windows_use_principal_name
    Option-File Formatauthentication_windows_use_principal_name
    Option Sets VariableYes, authentication_windows_use_principal_name
     Permitted Values
    Typeboolean
    DefaultON

    This variable is available only if the authentication_windows Windows authentication plugin is enabled. See Section 5.5.6.3, “The Windows Native Authentication Plugin”.

    A client that authenticates using the InitSecurityContext() function should provide a string identifying the service to which it connects (targetName). MySQL uses the principal name (UPN) of the account under which the server is running. The UPN has the form user_id@computer_name and need not be registered anywhere to be used. This UPN is sent by the server at the beginning of authentication handshake.

    This variable controls whether the server sends the UPN in the initial challenge. By default, the variable is enabled. For security reasons, it can be disabled to avoid sending the server's account name to a client in clear text. If the variable is disabled, the server always sends a 0x00 byte in the first challenge, the client does not specify targetName, and as a result, NTLM authentication is used.

    If the server fails to obtain its UPN (which will happen primarily in environments that do not support Kerberos authentication), the UPN is not sent by the server and NTLM authentication is used.

    This variable was added in MySQL 5.5.16.

  • autocommit

    Command-Line Format--autocommit[=#]
    Option-File Formatautocommit
    Option Sets VariableYes, autocommit
    Variable Nameautocommit
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean

    The autocommit mode. If set to 1, all changes to a table take effect immediately. If set to 0, you must use COMMIT to accept a transaction or ROLLBACK to cancel it. If autocommit is 0 and you change it to 1, MySQL performs an automatic COMMIT of any open transaction. Another way to begin a transaction is to use a START TRANSACTION or BEGIN statement. See Section 12.3.1, “START TRANSACTION, COMMIT, and ROLLBACK Синтаксис”.

    By default, client connections begin with autocommit set to 1. To cause clients to begin with a default of 0, set the global autocommit value by starting the server with the --autocommit=0 option. To set the variable using an option file, include these lines:

    [mysqld]
    autocommit=0

    Before MySQL 5.5.8, the global autocommit value cannot be set at startup. As a workaround, set the init_connect system variable:

    SET GLOBAL init_connect='SET autocommit=0';

    The init_connect variable can also be set on the command line or in an option file. To set the variable as just shown using an option file, include these lines:

    [mysqld]
    init_connect='SET autocommit=0'

    The content of init_connect is not executed for users that have the SUPER privilege (unlike the effect of setting the global autocommit value at startup).

  • automatic_sp_privileges

    Variable Nameautomatic_sp_privileges
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultTRUE

    When this variable has a value of 1 (the default), the server automatically grants the EXECUTE and ALTER ROUTINE privileges to the creator of a stored routine, if the user cannot already execute and alter or drop the routine. (The ALTER ROUTINE privilege is required to drop the routine.) The server also automatically drops those privileges from the creator when the routine is dropped. If automatic_sp_privileges is 0, the server does not automatically add or drop these privileges.

    The creator of a routine is the account used to execute the CREATE statement for it. This might not be the same as the account named as the DEFINER in the routine definition.

    See also Section 18.2.2, “Stored Routines and MySQL Privileges”.

  • back_log

    Command-Line Format--back_log=#
    Option-File Formatback_log
    Option Sets VariableYes, back_log
    Variable Nameback_log
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default50
    Range1 .. 65535

    The number of outstanding connection requests MySQL can have. This comes into play when the main MySQL thread gets very many connection requests in a very short time. It then takes some time (although very little) for the main thread to check the connection and start a new thread. The back_log value indicates how many requests can be stacked during this short time before MySQL momentarily stops answering new requests. You need to increase this only if you expect a large number of connections in a short period of time.

    In other words, this value is the size of the listen queue for incoming TCP/IP connections. Your operating system has its own limit on the size of this queue. The manual page for the Unix listen() system call should have more details. Check your OS documentation for the maximum value for this variable. back_log cannot be set higher than your operating system limit.

  • basedir

    Command-Line Format--basedir=path
    -b
    Option-File Formatbasedir
    Option Sets VariableYes, basedir
    Variable Namebasedir
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

    The MySQL installation base directory. This variable can be set with the --basedir option. Relative path names for other variables usually are resolved relative to the base directory.

  • big_tables

    If set to 1, all temporary tables are stored on disk rather than in memory. This is a little slower, but the error The table tbl_name is full does not occur for SELECT operations that require a large temporary table. The default value for a new connection is 0 (use in-memory temporary tables). Normally, you should never need to set this variable, because in-memory tables are automatically converted to disk-based tables as required.

    Замечание

    This variable was formerly named sql_big_tables.

  • bulk_insert_buffer_size

    Command-Line Format--bulk_insert_buffer_size=#
    Option-File Formatbulk_insert_buffer_size
    Option Sets VariableYes, bulk_insert_buffer_size
    Variable Namebulk_insert_buffer_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default8388608
    Range0 .. 4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default8388608
    Range0 .. 18446744073709547520

    MyISAM uses a special tree-like cache to make bulk inserts faster for INSERT ... SELECT, INSERT ... VALUES (...), (...), ..., and LOAD DATA INFILE when adding data to nonempty tables. This variable limits the size of the cache tree in bytes per thread. Setting it to 0 disables this optimization. The default value is 8MB.

  • character_set_client

    Variable Namecharacter_set_client
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring

    The character set for statements that arrive from the client. The session value of this variable is set using the character set requested by the client when the client connects to the server. (Many clients support a --default-character-set option to enable this character set to be specified explicitly. See also Section 9.1.4, “Connection Character Sets and Collations”.) The global value of the variable is used to set the session value in cases when the client-requested value is unknown or not available, or the server is configured to ignore client requests:

    • The client is from a version of MySQL older than MySQL 4.1, and thus does not request a character set.

    • The client requests a character set not known to the server. For example, a Japanese-enabled client requests sjis when connecting to a server not configured with sjis support.

    • mysqld was started with the --skip-character-set-client-handshake option, which causes it to ignore client character set configuration. This reproduces MySQL 4.0 behavior and is useful should you wish to upgrade the server without upgrading all the clients.

    ucs2, utf16, and utf32 cannot be used as a client character set, which means that they also do not work for SET NAMES or SET CHARACTER SET.

  • character_set_connection

    Variable Namecharacter_set_connection
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring

    The character set used for literals that do not have a character set introducer and for number-to-string conversion.

  • character_set_database

    Variable Namecharacter_set_database
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    FootnoteThis option is dynamic, but only the server should set this information. You should not set the value of this variable manually.
     Permitted Values
    Typestring

    The character set used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as character_set_server.

  • character_set_filesystem

    Command-Line Format--character-set-filesystem=name
    Option-File Formatcharacter-set-filesystem
    Option Sets VariableYes, character_set_filesystem
    Variable Namecharacter_set_filesystem
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring

    The file system character set. This variable is used to interpret string literals that refer to file names, such as in the LOAD DATA INFILE and SELECT ... INTO OUTFILE statements and the LOAD_FILE() function. Such file names are converted from character_set_client to character_set_filesystem before the file opening attempt occurs. The default value is binary, which means that no conversion occurs. For systems on which multi-byte file names are permitted, a different value may be more appropriate. For example, if the system represents file names using UTF-8, set character_set_filesystem to 'utf8'.

  • character_set_results

    Variable Namecharacter_set_results
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring

    The character set used for returning query results such as result sets or error messages to the client.

  • character_set_server

    Command-Line Format--character-set-server
    Option-File Formatcharacter-set-server
    Option Sets VariableYes, character_set_server
    Variable Namecharacter_set_server
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring

    The server's default character set.

  • character_set_system

    Variable Namecharacter_set_system
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring

    The character set used by the server for storing identifiers. The value is always utf8.

  • character_sets_dir

    Command-Line Format--character-sets-dir=path
    Option-File Formatcharacter-sets-dir=path
    Option Sets VariableYes, character_sets_dir
    Variable Namecharacter-sets-dir
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typedirectory name

    The directory where character sets are installed.

  • collation_connection

    Variable Namecollation_connection
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring

    The collation of the connection character set.

  • collation_database

    Variable Namecollation_database
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    FootnoteThis option is dynamic, but only the server should set this information. You should not set the value of this variable manually.
     Permitted Values
    Typestring

    The collation used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as collation_server.

  • collation_server

    Command-Line Format--collation-server
    Option-File Formatcollation-server
    Option Sets VariableYes, collation_server
    Variable Namecollation_server
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring

    The server's default collation.

  • completion_type

    Command-Line Format--completion_type=#
    Option-File Formatcompletion_type
    Option Sets VariableYes, completion_type
    Variable Namecompletion_type
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values (<= 5.5.2)
    Typenumeric
    Default0
    Valid Values

    0

    1

    2

     Permitted Values (>= 5.5.3)
    Typeenumeration
    DefaultNO_CHAIN
    Valid Values

    NO_CHAIN

    CHAIN

    RELEASE

    0

    1

    2

    The transaction completion type. This variable can take the values shown in the following table. As of MySQL 5.5.3, the variable can be assigned using either the name values or corresponding integer values. Before 5.5.3, only the integer values can be used.

    ValueОписание
    NO_CHAIN (or 0)COMMIT and ROLLBACK are unaffected. This is the default value.
    CHAIN (or 1)COMMIT and ROLLBACK are equivalent to COMMIT AND CHAIN and ROLLBACK AND CHAIN, respectively. (A new transaction starts immediately with the same isolation level as the just-terminated transaction.)
    RELEASE (or 2)COMMIT and ROLLBACK are equivalent to COMMIT RELEASE and ROLLBACK RELEASE, respectively. (The server disconnects after terminating the transaction.)

    completion_type affects transactions that begin with START TRANSACTION or BEGIN and end with COMMIT or ROLLBACK. It does not apply to implicit commits resulting from execution of the statements listed in Section 12.3.3, “Statements That Cause an Implicit Commit”. It also does not apply for XA COMMIT, XA ROLLBACK, or when autocommit=1.

  • concurrent_insert

    Command-Line Format--concurrent_insert[=#]
    Option-File Formatconcurrent_insert
    Option Sets VariableYes, concurrent_insert
    Variable Nameconcurrent_insert
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values (<= 5.5.2)
    Typenumeric
    Default1
    Valid Values

    0

    1

    2

     Permitted Values (>= 5.5.3)
    Typeenumeration
    DefaultAUTO
    Valid Values

    NEVER

    AUTO

    ALWAYS

    0

    1

    2

    If AUTO (the default), MySQL permits INSERT and SELECT statements to run concurrently for MyISAM tables that have no free blocks in the middle of the data file. If you start mysqld with --skip-new, this variable is set to NEVER.

    This variable can take the values shown in the following table. As of MySQL 5.5.3, the variable can be assigned using either the name values or corresponding integer values. Before 5.5.3, only the integer values can be used.

    ValueОписание
    NEVER (or 0)Disables concurrent inserts
    AUTO (or 1)(Default) Enables concurrent insert for MyISAM tables that do not have holes
    ALWAYS (or 2)Enables concurrent inserts for all MyISAM tables, even those that have holes. For a table with a hole, new rows are inserted at the end of the table if it is in use by another thread. Otherwise, MySQL acquires a normal write lock and inserts the row into the hole.

    See also Section 7.10.3, “Concurrent Inserts”.

  • connect_timeout

    Command-Line Format--connect_timeout=#
    Option-File Formatconnect_timeout
    Option Sets VariableYes, connect_timeout
    Variable Nameconnect_timeout
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default10

    The number of seconds that the mysqld server waits for a connect packet before responding with Bad handshake. The default value is 10 seconds.

    Increasing the connect_timeout value might help if clients frequently encounter errors of the form Lost connection to MySQL server at 'XXX', system error: errno.

  • datadir

    Command-Line Format--datadir=path
    -h
    Option-File Formatdatadir
    Option Sets VariableYes, datadir
    Variable Namedatadir
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

    The MySQL data directory. This variable can be set with the --datadir option.

  • date_format

    This variable is unused.

  • datetime_format

    This variable is unused.

  • debug

    Command-Line Format--debug[=debug_options]
    Option-File Formatdebug
    Variable Namedebug
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring
    Default'd:t:o,/tmp/mysqld.trace'

    This variable indicates the current debugging settings. It is available only for servers built with debugging support. The initial value comes from the value of instances of the --debug option given at server startup. The global and session values may be set at runtime; the SUPER privilege is required, even for the session value.

    Assigning a value that begins with + or - cause the value to added to or subtracted from the current value:

    mysql> SET debug = 'T';
    mysql> SELECT @@debug;
    +---------+
    | @@debug |
    +---------+
    | T       |
    +---------+
    
    mysql> SET debug = '+P';
    mysql> SELECT @@debug;
    +---------+
    | @@debug |
    +---------+
    | P:T     |
    +---------+
    
    mysql> SET debug = '-P';
    mysql> SELECT @@debug;
    +---------+
    | @@debug |
    +---------+
    | T       |
    +---------+
    
  • debug_sync

    Variable Namedebug_sync
    Variable ScopeSession
    Dynamic VariableYes
     Permitted Values
    Typestring

    This variable is the user interface to the Debug Sync facility. Use of Debug Sync requires that MySQL be configured with the -DENABLE_DEBUG_SYNC=1 option (see Section 2.9.4, “MySQL Source-Configuration Options”). If Debug Sync is not compiled in, this system variable is not available.

    The global variable value is read only and indicates whether the facility is enabled. By default, Debug Sync is disabled and the value of debug_sync is OFF. If the server is started with --debug-sync-timeout=N, where N is a timeout value greater than 0, Debug Sync is enabled and the value of debug_sync is ON - current signal followed by the signal name. Also, N becomes the default timeout for individual synchronization points.

    The session value can be read by any user and will have the same value as the global variable. The session value can be set by users that have the SUPER privilege to control synchronization points.

    For a description of the Debug Sync facility and how to use synchronization points, see MySQL Internals: Test Synchronization.

  • default_storage_engine

    Command-Line Format--default-storage-engine=name
    Option-File Formatdefault-storage-engine
    Option Sets VariableYes, default_storage_engine
    Variable Namedefault_storage_engine
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values (<= 5.5.4)
    Typeenumeration
    DefaultMyISAM
     Permitted Values (>= 5.5.5)
    Typeenumeration
    DefaultInnoDB

    The default storage engine. To set the storage engine at server startup, use the --default-storage-engine option. See Section 5.1.2, “Server Command Options”.

    This variable was added in MySQL 5.5.3 to be used in preference to storage_engine, which is now deprecated.

  • default_week_format

    Command-Line Format--default_week_format=#
    Option-File Formatdefault_week_format
    Option Sets VariableYes, default_week_format
    Variable Namedefault_week_format
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default0
    Range0 .. 7

    The default mode value to use for the WEEK() function. See Section 11.7, “Date and Time Functions”.

  • delay_key_write

    Command-Line Format--delay-key-write[=name]
    Option-File Formatdelay-key-write
    Option Sets VariableYes, delay_key_write
    Variable Namedelay-key-write
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeenumeration
    DefaultON
    Valid Values

    ON

    OFF

    ALL

    This option applies only to MyISAM tables. It can have one of the following values to affect handling of the DELAY_KEY_WRITE table option that can be used in CREATE TABLE statements.

    OptionОписание
    OFFDELAY_KEY_WRITE is ignored.
    ONMySQL honors any DELAY_KEY_WRITE option specified in CREATE TABLE statements. This is the default value.
    ALLAll new opened tables are treated as if they were created with the DELAY_KEY_WRITE option enabled.

    If DELAY_KEY_WRITE is enabled for a table, the key buffer is not flushed for the table on every index update, but only when the table is closed. This speeds up writes on keys a lot, but if you use this feature, you should add automatic checking of all MyISAM tables by starting the server with the --myisam-recover-options option (for example, --myisam-recover-options=BACKUP,FORCE). See Section 5.1.2, “Server Command Options”, and Section 13.5.1, “MyISAM Startup Options”.

    Warning

    If you enable external locking with --external-locking, there is no protection against index corruption for tables that use delayed key writes.

  • delayed_insert_limit

    Command-Line Format--delayed_insert_limit=#
    Option-File Formatdelayed_insert_limit
    Option Sets VariableYes, delayed_insert_limit
    Variable Namedelayed_insert_limit
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default100
    Range1 .. 4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default100
    Range1 .. 18446744073709547520

    After inserting delayed_insert_limit delayed rows, the INSERT DELAYED handler thread checks whether there are any SELECT statements pending. If so, it permits them to execute before continuing to insert delayed rows.

  • delayed_insert_timeout

    Command-Line Format--delayed_insert_timeout=#
    Option-File Formatdelayed_insert_timeout
    Option Sets VariableYes, delayed_insert_timeout
    Variable Namedelayed_insert_timeout
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default300

    How many seconds an INSERT DELAYED handler thread should wait for INSERT statements before terminating.

  • delayed_queue_size

    Command-Line Format--delayed_queue_size=#
    Option-File Formatdelayed_queue_size
    Option Sets VariableYes, delayed_queue_size
    Variable Namedelayed_queue_size
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default1000
    Range1 .. 4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default1000
    Range1 .. 18446744073709547520

    This is a per-table limit on the number of rows to queue when handling INSERT DELAYED statements. If the queue becomes full, any client that issues an INSERT DELAYED statement waits until there is room in the queue again.

  • div_precision_increment

    Command-Line Format--div_precision_increment=#
    Option-File Formatdiv_precision_increment
    Option Sets VariableYes, div_precision_increment
    Variable Namediv_precision_increment
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default4
    Range0 .. 30

    This variable indicates the number of digits by which to increase the scale of the result of division operations performed with the / operator. The default value is 4. The minimum and maximum values are 0 and 30, respectively. The following example illustrates the effect of increasing the default value.

    mysql> SELECT 1/7;
    +--------+
    | 1/7    |
    +--------+
    | 0.1429 |
    +--------+
    mysql> SET div_precision_increment = 12;
    mysql> SELECT 1/7;
    +----------------+
    | 1/7            |
    +----------------+
    | 0.142857142857 |
    +----------------+
    
  • engine_condition_pushdown

    Version Deprecated5.5.3
    Command-Line Format--engine-condition-pushdown
    Option-File Formatengine-condition-pushdown
    Option Sets VariableYes, engine_condition_pushdown
    Variable Nameengine_condition_pushdown
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Deprecated5.5.3, by optimizer_switch
     Permitted Values
    Typeboolean
    DefaultON

    The engine condition pushdown optimization enables processing for certain comparisons to be “pushed down” to the storage engine level for more efficient execution. For more information, see Section 7.13.3, “Engine Condition Pushdown Optimization”.

    Engine condition pushdown is used only by the NDBCLUSTER storage engine. Enabling this optimization on a MySQL Server acting as a MySQL Cluster SQL node causes WHERE conditions on unindexed columns to be evaluated on the cluster's data nodes and only the rows that match to be sent back to the SQL node that issued the query. This greatly reduces the amount of cluster data that must be sent over the network, increasing the efficiency with which results are returned.

    The engine_condition_pushdown variable controls whether engine condition pushdown is enabled. By default, this variable is ON (1). Setting it to OFF (0) disables pushdown.

    This variable is deprecated as of MySQL 5.5.3 and is removed in MySQL 5.6. Use the engine_condition_pushdown flag of the optimizer_switch variable instead. See Section 7.8.4.2, “Controlling Switchable Optimizations”.

  • error_count

    The number of errors that resulted from the last statement that generated messages. This variable is read only. See Section 12.7.5.18, “SHOW ERRORS Синтаксис”.

  • event_scheduler

    Command-Line Format--event-scheduler[=value]
    Option-File Formatevent-scheduler
    Option Sets VariableYes, event_scheduler
    Variable Nameevent_scheduler
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeenumeration
    DefaultOFF
    Valid Values

    ON

    OFF

    DISABLED

    This variable indicates the status of the Event Scheduler; possible values are ON, OFF, and DISABLED, with the default being OFF. This variable and its effects on the Event Scheduler's operation are discussed in greater detail in the Overview section of the Events chapter.

  • expire_logs_days

    Command-Line Format--expire_logs_days=#
    Option-File Formatexpire_logs_days
    Option Sets VariableYes, expire_logs_days
    Variable Nameexpire_logs_days
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default0
    Range0 .. 99

    The number of days for automatic binary log file removal. The default is 0, which means “no automatic removal.” Possible removals happen at startup and when the binary log is flushed. Log flushing occurs as indicated in Section 5.2, “MySQL Server Logs”.

    To remove binary log files manually, use the PURGE BINARY LOGS statement. See Section 12.4.1.1, “PURGE BINARY LOGS Синтаксис”.

  • external_user

    Version Introduced5.5.7
    Variable Nameexternal_user
    Variable ScopeSession
    Dynamic VariableNo
     Permitted Values
    Typestring

    The external user name used during the authentication process, as set by the plugin used to authenticate the client. With native (built-in) MySQL authentication, or if the plugin does not set the value, this variable is NULL. See Section 5.5.7, “Proxy Users”.

    This variable was added in MySQL 5.5.7.

  • flush

    Command-Line Format--flush
    Option-File Formatflush
    Variable Nameflush
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    If ON, the server flushes (synchronizes) all changes to disk after each SQL statement. Normally, MySQL does a write of all changes to disk only after each SQL statement and lets the operating system handle the synchronizing to disk. See Section C.5.4.2, “What to Do If MySQL Keeps Crashing”. This variable is set to ON if you start mysqld with the --flush option.

  • flush_time

    Command-Line Format--flush_time=#
    Option-File Formatflush_time
    Option Sets VariableYes, flush_time
    Variable Nameflush_time
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default0
    Min Value0
     Permitted Values
    Type (windows)numeric
    Default1800
    Min Value0

    If this is set to a nonzero value, all tables are closed every flush_time seconds to free up resources and synchronize unflushed data to disk. This option is best used only on Windows 9x or Me, or on systems with minimal resources.

  • foreign_key_checks

    If set to 1 (the default), foreign key constraints for InnoDB tables are checked. If set to 0, they are ignored. Disabling foreign key checking can be useful for reloading InnoDB tables in an order different from that required by their parent/child relationships. See Section 13.3.5.4, “FOREIGN KEY Constraints”.

    Setting foreign_key_checks to 0 also affects data definition statements: DROP SCHEMA drops a schema even if it contains tables that have foreign keys that are referred to by tables outside the schema, and DROP TABLE drops tables that have foreign keys that are referred to by other tables.

    Замечание

    Setting foreign_key_checks to 1 does not trigger a scan of the existing table data. Therefore, rows added to the table while foreign_key_checks = 0 will not be verified for consistency.

  • ft_boolean_syntax

    Command-Line Format--ft_boolean_syntax=name
    Option-File Formatft_boolean_syntax
    Variable Nameft_boolean_syntax
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typestring
    Default+-><()~*:""&

    The list of operators supported by boolean full-text searches performed using IN BOOLEAN MODE. See Section 11.9.2, “Boolean Full-Text Searches”.

    The default variable value is '+ -><()~*:""&|'. The rules for changing the value are as follows:

    • Operator function is determined by position within the string.

    • The replacement value must be 14 characters.

    • Each character must be an ASCII nonalphanumeric character.

    • Either the first or second character must be a space.

    • No duplicates are permitted except the phrase quoting operators in positions 11 and 12. These two characters are not required to be the same, but they are the only two that may be.

    • Positions 10, 13, and 14 (which by default are set to “:”, “&”, and “|”) are reserved for future extensions.

  • ft_max_word_len

    Command-Line Format--ft_max_word_len=#
    Option-File Formatft_max_word_len
    Option Sets VariableYes, ft_max_word_len
    Variable Nameft_max_word_len
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Min Value10

    The maximum length of the word to be included in a FULLTEXT index.

    Замечание

    FULLTEXT indexes must be rebuilt after changing this variable. Use REPAIR TABLE tbl_name QUICK.

  • ft_min_word_len

    Command-Line Format--ft_min_word_len=#
    Option-File Formatft_min_word_len
    Option Sets VariableYes, ft_min_word_len
    Variable Nameft_min_word_len
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default4
    Min Value1

    The minimum length of the word to be included in a FULLTEXT index.

    Замечание

    FULLTEXT indexes must be rebuilt after changing this variable. Use REPAIR TABLE tbl_name QUICK.

  • ft_query_expansion_limit

    Command-Line Format--ft_query_expansion_limit=#
    Option-File Formatft_query_expansion_limit
    Option Sets VariableYes, ft_query_expansion_limit
    Variable Nameft_query_expansion_limit
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default20
    Range0 .. 1000

    The number of top matches to use for full-text searches performed using WITH QUERY EXPANSION.

  • ft_stopword_file

    Command-Line Format--ft_stopword_file=file_name
    Option-File Formatft_stopword_file=file_name
    Option Sets VariableYes, ft_stopword_file
    Variable Nameft_stopword_file
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

    The file from which to read the list of stopwords for full-text searches. The server looks for the file in the data directory unless an absolute path name is given to specify a different directory. All the words from the file are used; comments are not honored. By default, a built-in list of stopwords is used (as defined in the storage/myisam/ft_static.c file). Setting this variable to the empty string ('') disables stopword filtering. See also Section 11.9.4, “Full-Text Stopwords”.

    Замечание

    FULLTEXT indexes must be rebuilt after changing this variable or the contents of the stopword file. Use REPAIR TABLE tbl_name QUICK.

  • general_log

    Command-Line Format--general-log
    Option-File Formatgeneral-log
    Option Sets VariableYes, general_log
    Variable Namegeneral_log
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    Whether the general query log is enabled. The value can be 0 (or OFF) to disable the log or 1 (or ON) to enable the log. The default value depends on whether the --general_log option is given. The destination for log output is controlled by the log_output system variable; if that value is NONE, no log entries are written even if the log is enabled.

  • general_log_file

    Command-Line Format--general-log-file=file_name
    Option-File Formatgeneral_log_file
    Option Sets VariableYes, general_log_file
    Variable Namegeneral_log_file
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typefile name
    Defaulthost_name.log

    The name of the general query log file. The default value is host_name.log, but the initial value can be changed with the --general_log_file option.

  • group_concat_max_len

    Command-Line Format--group_concat_max_len=#
    Option-File Formatgroup_concat_max_len
    Option Sets VariableYes, group_concat_max_len
    Variable Namegroup_concat_max_len
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default1024
    Range4 .. 4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default1024
    Range4 .. 18446744073709547520

    The maximum permitted result length in bytes for the GROUP_CONCAT() function. The default is 1024.

  • have_compress

    YES if the zlib compression library is available to the server, NO if not. If not, the COMPRESS() and UNCOMPRESS() functions cannot be used.

  • have_crypt

    YES if the crypt() system call is available to the server, NO if not. If not, the ENCRYPT() function cannot be used.

  • have_csv

    YES if mysqld supports CSV tables, NO if not.

    This variable is deprecated and is removed in MySQL 5.6. Use SHOW ENGINES instead.

  • have_dynamic_loading

    YES if mysqld supports dynamic loading of plugins, NO if not.

  • have_geometry

    YES if the server supports spatial data types, NO if not.

  • have_innodb

    YES if mysqld supports InnoDB tables. DISABLED if --skip-innodb is used.

    This variable is deprecated and is removed in MySQL 5.6. Use SHOW ENGINES instead.

  • have_openssl

    This variable is an alias for have_ssl.

  • have_partitioning

    YES if mysqld supports partitioning.

  • have_profiling

    YES if statement profiling is enabled, NO if not. See Section 12.7.5.31, “SHOW PROFILE Синтаксис”.

  • have_query_cache

    YES if mysqld supports the query cache, NO if not.

    This variable is deprecated and is removed in MySQL 5.6. Use SHOW ENGINES instead.

  • have_rtree_keys

    YES if RTREE indexes are available, NO if not. (These are used for spatial indexes in MyISAM tables.)

  • have_ssl

    YES if mysqld supports SSL connections, NO if not. DISABLED indicates that the server was compiled with SSL support, but but was not started with the appropriate --ssl-xxx options. See Section 5.5.8.2, “Using SSL Connections”, for more information.

  • have_symlink

    YES if symbolic link support is enabled, NO if not. This is required on Unix for support of the DATA DIRECTORY and INDEX DIRECTORY table options, and on Windows for support of data directory symlinks.

  • hostname

    Variable Namehostname
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring

    The server sets this variable to the server host name at startup.

  • identity

    This variable is a synonym for the last_insert_id variable. It exists for compatibility with other database systems. You can read its value with SELECT @@identity, and set it using SET identity.

  • init_connect

    Command-Line Format--init-connect=name
    Option-File Formatinit_connect
    Option Sets VariableYes, init_connect
    Variable Nameinit_connect
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typestring

    A string to be executed by the server for each client that connects. The string consists of one or more SQL statements, separated by semicolon characters. For example, each client session begins by default with autocommit mode enabled. For older servers (before MySQL 5.5.8), there is no global autocommit system variable to specify that autocommit should be disabled by default, but as a workaround init_connect can be used to achieve the same effect:

    SET GLOBAL init_connect='SET autocommit=0';

    The init_connect variable can also be set on the command line or in an option file. To set the variable as just shown using an option file, include these lines:

    [mysqld]
    init_connect='SET autocommit=0'

    The content of init_connect is not executed for users that have the SUPER privilege. This is done so that an erroneous value for init_connect does not prevent all clients from connecting. For example, the value might contain a statement that has a syntax error, thus causing client connections to fail. Not executing init_connect for users that have the SUPER privilege enables them to open a connection and fix the init_connect value.

  • init_file

    Command-Line Format--init-file=file_name
    Option-File Formatinit-file=file_name
    Option Sets VariableYes, init_file
    Variable Nameinit_file
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

    The name of the file specified with the --init-file option when you start the server. This should be a file containing SQL statements that you want the server to execute when it starts. Each statement must be on a single line and should not include comments. No statement terminator such as ;, \g, or \G should be given at the end of each statement.

    Note that the --init-file option is unavailable if MySQL was configured with the DISABLE_GRANT_OPTIONS compiler flag. See Section 2.9.4, “MySQL Source-Configuration Options”.

  • innodb_xxx

    InnoDB system variables are listed in Section 13.3.4, “InnoDB Startup Options and System Variables”.

  • insert_id

    The value to be used by the following INSERT or ALTER TABLE statement when inserting an AUTO_INCREMENT value. This is mainly used with the binary log.

  • interactive_timeout

    Command-Line Format--interactive_timeout=#
    Option-File Formatinteractive_timeout
    Option Sets VariableYes, interactive_timeout
    Variable Nameinteractive_timeout
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default28800
    Min Value1

    The number of seconds the server waits for activity on an interactive connection before closing it. An interactive client is defined as a client that uses the CLIENT_INTERACTIVE option to mysql_real_connect(). See also wait_timeout.

  • join_buffer_size

    Command-Line Format--join_buffer_size=#
    Option-File Formatjoin_buffer_size
    Option Sets VariableYes, join_buffer_size
    Variable Namejoin_buffer_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes

    The minimum size of the buffer that is used for plain index scans, range index scans, and joins that do not use indexes and thus perform full table scans. Normally, the best way to get fast joins is to add indexes. Increase the value of join_buffer_size to get a faster full join when adding indexes is not possible. One join buffer is allocated for each full join between two tables. For a complex join between several tables for which indexes are not used, multiple join buffers might be necessary. There is no gain from setting the buffer larger than required to hold each matching row, and all joins allocate at least the minimum size, so use caution in setting this variable to a large value globally. It is better to keep the global setting small and change to a larger setting only in sessions that are doing large joins. Memory allocation time can cause substantial performance drops if the global size is larger than needed by most queries that use it.

    The maximum permissible setting for join_buffer_size is 4GB. Values larger than 4GB are permitted for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB with a warning).

  • keep_files_on_create

    Command-Line Format--keep_files_on_create=#
    Option-File Formatkeep_files_on_create
    Option Sets VariableYes, keep_files_on_create
    Variable Namekeep_files_on_create
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    If a MyISAM table is created with no DATA DIRECTORY option, the .MYD file is created in the database directory. By default, if MyISAM finds an existing .MYD file in this case, it overwrites it. The same applies to .MYI files for tables created with no INDEX DIRECTORY option. To suppress this behavior, set the keep_files_on_create variable to ON (1), in which case MyISAM will not overwrite existing files and returns an error instead. The default value is OFF (0).

    If a MyISAM table is created with a DATA DIRECTORY or INDEX DIRECTORY option and an existing .MYD or .MYI file is found, MyISAM always returns an error. It will not overwrite a file in the specified directory.

  • key_buffer_size

    Command-Line Format--key_buffer_size=#
    Option-File Formatkey_buffer_size
    Option Sets VariableYes, key_buffer_size
    Variable Namekey_buffer_size
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default8388608
    Range8 .. 4294967295

    Index blocks for MyISAM tables are buffered and are shared by all threads. key_buffer_size is the size of the buffer used for index blocks. The key buffer is also known as the key cache.

    The maximum permissible setting for key_buffer_size is 4GB on 32-bit platforms. Values larger than 4GB are permitted for 64-bit platforms. The effective maximum size might be less, depending on your available physical RAM and per-process RAM limits imposed by your operating system or hardware platform. The value of this variable indicates the amount of memory requested. Internally, the server allocates as much memory as possible up to this amount, but the actual allocation might be less.

    You can increase the value to get better index handling for all reads and multiple writes; on a system whose primary function is to run MySQL using the MyISAM storage engine, 25% of the machine's total memory is an acceptable value for this variable. However, you should be aware that, if you make the value too large (for example, more than 50% of the machine's total memory), your system might start to page and become extremely slow. This is because MySQL relies on the operating system to perform file system caching for data reads, so you must leave some room for the file system cache. You should also consider the memory requirements of any other storage engines that you may be using in addition to MyISAM.

    For even more speed when writing many rows at the same time, use LOCK TABLES. See Section 7.2.2.1, “Speed of INSERT Statements”.

    You can check the performance of the key buffer by issuing a SHOW STATUS statement and examining the Key_read_requests, Key_reads, Key_write_requests, and Key_writes status variables. (See Section 12.7.5, “SHOW Синтаксис”.) The Key_reads/Key_read_requests ratio should normally be less than 0.01. The Key_writes/Key_write_requests ratio is usually near 1 if you are using mostly updates and deletes, but might be much smaller if you tend to do updates that affect many rows at the same time or if you are using the DELAY_KEY_WRITE table option.

    The fraction of the key buffer in use can be determined using key_buffer_size in conjunction with the Key_blocks_unused status variable and the buffer block size, which is available from the key_cache_block_size system variable:

    1 - ((Key_blocks_unused * key_cache_block_size) / key_buffer_size)

    This value is an approximation because some space in the key buffer is allocated internally for administrative structures. Factors that influence the amount of overhead for these structures include block size and pointer size. As block size increases, the percentage of the key buffer lost to overhead tends to decrease. Larger blocks results in a smaller number of read operations (because more keys are obtained per read), but conversely an increase in reads of keys that are not examined (if not all keys in a block are relevant to a query).

    It is possible to create multiple MyISAM key caches. The size limit of 4GB applies to each cache individually, not as a group. See Section 7.9.2, “The MyISAM Key Cache”.

  • key_cache_age_threshold

    Command-Line Format--key_cache_age_threshold=#
    Option-File Formatkey_cache_age_threshold
    Option Sets VariableYes, key_cache_age_threshold
    Variable Namekey_cache_age_threshold
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default300
    Range100 .. 4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default300
    Range100 .. 18446744073709547520

    This value controls the demotion of buffers from the hot sublist of a key cache to the warm sublist. Lower values cause demotion to happen more quickly. The minimum value is 100. The default value is 300. See Section 7.9.2, “The MyISAM Key Cache”.

  • key_cache_block_size

    Command-Line Format--key_cache_block_size=#
    Option-File Formatkey_cache_block_size
    Option Sets VariableYes, key_cache_block_size
    Variable Namekey_cache_block_size
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default1024
    Range512 .. 16384

    The size in bytes of blocks in the key cache. The default value is 1024. See Section 7.9.2, “The MyISAM Key Cache”.

  • key_cache_division_limit

    Command-Line Format--key_cache_division_limit=#
    Option-File Formatkey_cache_division_limit
    Option Sets VariableYes, key_cache_division_limit
    Variable Namekey_cache_division_limit
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default100
    Range1 .. 100

    The division point between the hot and warm sublists of the key cache buffer list. The value is the percentage of the buffer list to use for the warm sublist. Permissible values range from 1 to 100. The default value is 100. See Section 7.9.2, “The MyISAM Key Cache”.

  • language

    Command-Line Format--language=name
    -L
    Option-File Formatlanguage
    Option Sets VariableYes, language
    Variable Namelanguage
    Variable ScopeGlobal
    Dynamic VariableNo
    Deprecated5.6.1
     Permitted Values
    Typedirectory name
    Default/usr/local/mysql/share/mysql/english/

    The directory where error messages are located. See Section 9.2, “Setting the Error Message Language”.

    language is removed as of MySQL 5.5.0. Similar information is available from the lc_messages_dir and lc_messages variables.

  • large_files_support

    Variable Namelarge_files_support
    Variable ScopeGlobal
    Dynamic VariableNo

    Whether mysqld was compiled with options for large file support.

  • large_pages

    Command-Line Format--large-pages
    Option-File Formatlarge-pages
    Option Sets VariableYes, large_pages
    Variable Namelarge_pages
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform Specificlinux
     Permitted Values
    Type (linux)boolean
    DefaultFALSE

    Whether large page support is enabled (via the --large-pages option). See Section 7.11.4.2, “Enabling Large Page Support”.

  • large_page_size

    Variable Namelarge_page_size
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Type (linux)numeric
    Default0

    If large page support is enabled, this shows the size of memory pages. Currently, large memory pages are supported only on Linux; on other platforms, the value of this variable is always 0. See Section 7.11.4.2, “Enabling Large Page Support”.

  • last_insert_id

    The value to be returned from LAST_INSERT_ID(). This is stored in the binary log when you use LAST_INSERT_ID() in a statement that updates a table. Setting this variable does not update the value returned by the mysql_insert_id() C API function.

  • lc_messages

    Command-Line Format--lc-messages=name
    Option-File Formatlc-messages
    Option Sets VariableYes, lc_messages
    Variable Namelc-messages
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring

    The locale to use for error messages. The server converts the value to a language name and combines it with the value of the lc_messages_dir to produce the location for the error message file. See Section 9.2, “Setting the Error Message Language”.

  • lc_messages_dir

    Command-Line Format--lc-messages-dir=path
    Option-File Formatlc-messages-dir
    Option Sets VariableYes, lc_messages_dir
    Variable Namelc-messages-dir
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typedirectory name

    The directory where error messages are located. The value is used together with the value of lc_messages to produce the location for the error message file. See Section 9.2, “Setting the Error Message Language”.

  • lc_time_names

    Variable Namelc_time_names
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring

    This variable specifies the locale that controls the language used to display day and month names and abbreviations. This variable affects the output from the DATE_FORMAT(), DAYNAME() and MONTHNAME() functions. Locale names are POSIX-style values such as 'ja_JP' or 'pt_BR'. The default value is 'en_US' regardless of your system's locale setting. For further information, see Section 9.7, “MySQL Server Locale Support”.

  • license

    Variable Namelicense
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring
    DefaultGPL

    The type of license the server has.

  • local_infile

    Variable Namelocal_infile
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean

    Whether LOCAL is supported for LOAD DATA INFILE statements. See Section 5.3.5, “Security Issues with LOAD DATA LOCAL.

  • lock_wait_timeout

    Version Introduced5.5.3
    Command-Line Format--lock_wait_timeout=#
    Option-File Formatlock_wait_timeout
    Option Sets VariableYes, lock_wait_timeout
    Variable Namelock_wait_timeout
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default31536000
    Range1 .. 31536000

    This variable specifies the timeout in seconds for attempts to acquire metadata locks. The permissible values range from 1 to 31536000 (1 year). The default is 31536000.

    This timeout applies to all statements that use metadata locks. These include DML and DDL operations on tables, views, stored procedures, and stored functions, as well as LOCK TABLES, FLUSH TABLES WITH READ LOCK, and HANDLER statements.

    The timeout value applies separately for each metadata lock attempt. A given statement can require more than one lock, so it is possible for the statement to block for longer than the lock_wait_timeout value before reporting a timeout error. When lock timeout occurs, ER_LOCK_WAIT_TIMEOUT is reported.

    lock_wait_timeout does not apply to delayed inserts, which always execute with a timeout of 1 year. This is done to avoid unnecessary timeouts because a session that issues a delayed insert receives no notification of delayed insert timeouts.

    This variable was added in MySQL 5.5.3.

  • locked_in_memory

    Variable Namelocked_in_memory
    Variable ScopeGlobal
    Dynamic VariableNo

    Whether mysqld was locked in memory with --memlock.

  • log

    Whether logging of all statements to the general query log is enabled. See Section 5.2.3, “The General Query Log”.

    This variable is deprecated and is removed in MySQL 5.6. Use general_log instead.

  • log_bin

    Variable Namelog_bin
    Variable ScopeGlobal
    Dynamic VariableNo

    Whether the binary log is enabled. If the --log-bin option is used, then the value of this variable is ON; otherwise it is OFF. This variable reports only on the status of binary logging (enabled or disabled); it does not actually report the value to which --log-bin is set.

    See Section 5.2.4, “The Binary Log”.

  • log_bin_trust_function_creators

    Version Removed5.5.3
    Command-Line Format--log-bin-trust-function-creators
    Option-File Formatlog-bin-trust-function-creators
    Option Sets VariableYes, log_bin_trust_function_creators
    Variable Namelog_bin_trust_function_creators
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultFALSE

    This variable applies when binary logging is enabled. It controls whether stored function creators can be trusted not to create stored functions that will cause unsafe events to be written to the binary log. If set to 0 (the default), users are not permitted to create or alter stored functions unless they have the SUPER privilege in addition to the CREATE ROUTINE or ALTER ROUTINE privilege. A setting of 0 also enforces the restriction that a function must be declared with the DETERMINISTIC characteristic, or with the READS SQL DATA or NO SQL characteristic. If the variable is set to 1, MySQL does not enforce these restrictions on stored function creation. This variable also applies to trigger creation. See Section 18.7, “Binary Logging of Stored Programs”.

  • log_error

    Command-Line Format--log-error[=name]
    Option-File Formatlog-error
    Option Sets VariableYes, log_error
    Variable Namelog_error
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

    The location of the error log.

  • log_output

    Command-Line Format--log-output[=name]
    Option-File Formatlog-output
    Option Sets VariableYes, log_output
    Variable Namelog_output
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeset
    DefaultFILE
    Valid Values

    TABLE

    FILE

    NONE

    The destination for general query log and slow query log output. The value can be a comma-separated list of one or more of the words TABLE (log to tables), FILE (log to files), or NONE (do not log to tables or files). The default value is TABLE. NONE, if present, takes precedence over any other specifiers. If the value is NONE log entries are not written even if the logs are enabled. If the logs are not enabled, no logging occurs even if the value of log_output is not NONE. For more information, see Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”.

  • log_queries_not_using_indexes

    Command-Line Format--log-queries-not-using-indexes
    Option-File Formatlog-queries-not-using-indexes
    Option Sets VariableYes, log_queries_not_using_indexes
    Variable Namelog_queries_not_using_indexes
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    Whether queries that do not use indexes are logged to the slow query log. See Section 5.2.5, “The Slow Query Log”.

  • log_slave_updates

    Whether updates received by a slave server from a master server should be logged to the slave's own binary log. Binary logging must be enabled on the slave for this variable to have any effect. See Section 15.1.3, “Replication and Binary Logging Options and Variables”.

  • log_slow_admin_statements

    Command-Line Format--log-slow-admin-statements
    Option-File Formatlog-slow-admin-statements
     Permitted Values
    Typeboolean
    DefaultFALSE

    When the slow query log is enabled, whether to log slow administrative statements such as OPTIMIZE TABLE, ANALYZE TABLE, and ALTER TABLE to the slow query log.

  • log_slow_slave_statements

    Command-Line Format--log-slow-slave-statements
    Option-File Formatlog-slow-slave-statements
     Permitted Values
    Typeboolean
    Defaultoff

    When the slow query log is enabled, whether to log queries that have taken more than long_query_time seconds to execute on the slave.

  • log_slow_queries

    Command-Line Format--log-slow-queries[=name]
    Option-File Formatlog-slow-queries
    Option Sets VariableYes, log_slow_queries
    Variable Namelog_slow_queries
    Variable ScopeGlobal
    Dynamic VariableYes
    Deprecated5.1.29, by slow-query-log
     Permitted Values
    Typeboolean

    Whether slow queries should be logged. “Slow” is determined by the value of the long_query_time variable. See Section 5.2.5, “The Slow Query Log”.

    This variable is deprecated and is removed in MySQL 5.6. Use slow_query_log instead.

  • log_warnings

    Command-Line Format--log-warnings[=#]
    -W [#]
    Option-File Formatlog-warnings
    Option Sets VariableYes, log_warnings
    Variable Namelog_warnings
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Disabled byskip-log-warnings
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default1
    Range0 .. 18446744073709547520

    Whether to produce additional warning messages to the error log. It is enabled (1) by default and can be disabled by setting it to 0. Aborted connections and access-denied errors for new connection attempts are logged if the value is greater than 1. The server logs messages about statements that are unsafe for statement-based logging only if the value is greater than 0.

  • long_query_time

    Command-Line Format--long_query_time=#
    Option-File Formatlong_query_time
    Option Sets VariableYes, long_query_time
    Variable Namelong_query_time
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default10
    Min Value0

    If a query takes longer than this many seconds, the server increments the Slow_queries status variable. If the slow query log is enabled, the query is logged to the slow query log file. This value is measured in real time, not CPU time, so a query that is under the threshold on a lightly loaded system might be above the threshold on a heavily loaded one. The minimum and default values of long_query_time are 0 and 10, respectively. The value can be specified to a resolution of microseconds. For logging to a file, times are written including the microseconds part. For logging to tables, only integer times are written; the microseconds part is ignored. See Section 5.2.5, “The Slow Query Log”.

  • low_priority_updates

    Command-Line Format--low-priority-updates
    Option-File Formatlow-priority-updates
    Option Sets VariableYes, low_priority_updates
    Variable Namelow_priority_updates
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultFALSE

    If set to 1, all INSERT, UPDATE, DELETE, and LOCK TABLE WRITE statements wait until there is no pending SELECT or LOCK TABLE READ on the affected table. This affects only storage engines that use only table-level locking (such as MyISAM, MEMORY, and MERGE). This variable previously was named sql_low_priority_updates.

  • lower_case_file_system

    Command-Line Format--lower_case_file_system[=#]
    Option-File Formatlower_case_file_system
    Option Sets VariableYes, lower_case_file_system
    Variable Namelower_case_file_system
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typeboolean

    This variable describes the case sensitivity of file names on the file system where the data directory is located. OFF means file names are case sensitive, ON means they are not case sensitive. This variable is read only because it reflects a file system attribute and setting it would have no effect on the file system.

  • lower_case_table_names

    Command-Line Format--lower_case_table_names[=#]
    Option-File Formatlower_case_table_names
    Option Sets VariableYes, lower_case_table_names
    Variable Namelower_case_table_names
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default0
    Range0 .. 2

    If set to 0, table names are stored as specified and comparisons are case sensitive. If set to 1, table names are stored in lowercase on disk and comparisons are not case sensitive. If set to 2, table names are stored as given but compared in lowercase. This option also applies to database names and table aliases. For additional information, see Section 8.2.2, “Identifier Case Sensitivity”.

    You should not set this variable to 0 if you are running MySQL on a system that has case-insensitive file names (such as Windows or Mac OS X). If you set this variable to 0 on such a system and access MyISAM tablenames using different lettercases, index corruption may result. On Windows the default value is 1. On Mac OS X, the default value is 2.

    If you are using InnoDB tables, you should set this variable to 1 on all platforms to force names to be converted to lowercase.

    The setting of this variable has no effect on replication filtering options. This is a known issue which is fixed in MySQL 5.6. See Section 15.2.3, “How Servers Evaluate Replication Filtering Rules”, for more information.

    You should not use different settings for lower_case_table_names on replication masters and slaves. In particular, you should not do this when the slave uses a case-sensitive file system, as this can cause replication to fail. This is a known issue which is fixed in MySQL 5.6. For more information, see Section 15.4.1.33, “Replication and Variables”.

  • max_allowed_packet

    Command-Line Format--max_allowed_packet=#
    Option-File Formatmax_allowed_packet
    Option Sets VariableYes, max_allowed_packet
    Variable Namemax_allowed_packet
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default1048576
    Range1024 .. 1073741824

    The maximum size of one packet or any generated/intermediate string.

    The packet message buffer is initialized to net_buffer_length bytes, but can grow up to max_allowed_packet bytes when needed. This value by default is small, to catch large (possibly incorrect) packets.

    You must increase this value if you are using large BLOB columns or long strings. It should be as big as the largest BLOB you want to use. The protocol limit for max_allowed_packet is 1GB. The value should be a multiple of 1024; nonmultiples are rounded down to the nearest multiple.

    When you change the message buffer size by changing the value of the max_allowed_packet variable, you should also change the buffer size on the client side if your client program permits it. On the client side, max_allowed_packet has a default of 1GB. Some programs such as mysql and mysqldump enable you to change the client-side value by setting max_allowed_packet on the command line or in an option file.

    The session value of this variable is read only.

  • max_connect_errors

    Command-Line Format--max_connect_errors=#
    Option-File Formatmax_connect_errors
    Option Sets VariableYes, max_connect_errors
    Variable Namemax_connect_errors
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default10
    Range1 .. 4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default10
    Range1 .. 18446744073709547520

    If there are more than this number of interrupted connections from a host, that host is blocked from further connections. You can unblock blocked hosts with the FLUSH HOSTS statement. If a connection is established successfully within fewer than max_connect_errors attempts after a previous connection was interrupted, the error count for the host is cleared to zero. However, once a host is blocked, the FLUSH HOSTS statement is the only way to unblock it.

  • max_connections

    Command-Line Format--max_connections=#
    Option-File Formatmax_connections
    Option Sets VariableYes, max_connections
    Variable Namemax_connections
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default151
    Range1 .. 100000

    The maximum permitted number of simultaneous client connections. By default, this is 151. See Section C.5.2.7, “Too many connections, for more information.

    Increasing this value increases the number of file descriptors that mysqld requires. See Section 7.4.3.1, “How MySQL Opens and Closes Tables”, for comments on file descriptor limits.

  • max_delayed_threads

    Command-Line Format--max_delayed_threads=#
    Option-File Formatmax_delayed_threads
    Option Sets VariableYes, max_delayed_threads
    Variable Namemax_delayed_threads
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default20
    Range0 .. 16384

    Do not start more than this number of threads to handle INSERT DELAYED statements. If you try to insert data into a new table after all INSERT DELAYED threads are in use, the row is inserted as if the DELAYED attribute was not specified. If you set this to 0, MySQL never creates a thread to handle DELAYED rows; in effect, this disables DELAYED entirely.

    For the SESSION value of this variable, the only valid values are 0 or the GLOBAL value.

  • max_error_count

    Command-Line Format--max_error_count=#
    Option-File Formatmax_error_count
    Option Sets VariableYes, max_error_count
    Variable Namemax_error_count
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default64
    Range0 .. 65535

    The maximum number of error, warning, and note messages to be stored for display by the SHOW ERRORS and SHOW WARNINGS statements.

  • max_heap_table_size

    Command-Line Format--max_heap_table_size=#
    Option-File Formatmax_heap_table_size
    Option Sets VariableYes, max_heap_table_size
    Variable Namemax_heap_table_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default16777216
    Range16384 .. 4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default16777216
    Range16384 .. 1844674407370954752

    This variable sets the maximum size to which user-created MEMORY tables are permitted to grow. The value of the variable is used to calculate MEMORY table MAX_ROWS values. Setting this variable has no effect on any existing MEMORY table, unless the table is re-created with a statement such as CREATE TABLE or altered with ALTER TABLE or TRUNCATE TABLE. A server restart also sets the maximum size of existing MEMORY tables to the global max_heap_table_size value.

    This variable is also used in conjunction with tmp_table_size to limit the size of internal in-memory tables. See Section 7.4.3.3, “How MySQL Uses Internal Temporary Tables”.

  • max_insert_delayed_threads

    Variable Namemax_insert_delayed_threads
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric

    This variable is a synonym for max_delayed_threads.

  • max_join_size

    Command-Line Format--max_join_size=#
    Option-File Formatmax_join_size
    Option Sets VariableYes, max_join_size
    Variable Namemax_join_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values (>= 5.5.0)
    Typenumeric
    Default18446744073709551615
    Range1 .. 18446744073709551615

    Do not permit SELECT statements that probably need to examine more than max_join_size rows (for single-table statements) or row combinations (for multiple-table statements) or that are likely to do more than max_join_size disk seeks. By setting this value, you can catch SELECT statements where keys are not used properly and that would probably take a long time. Set it if your users tend to perform joins that lack a WHERE clause, that take a long time, or that return millions of rows.

    Setting this variable to a value other than DEFAULT resets the value of sql_big_selects to 0. If you set the sql_big_selects value again, the max_join_size variable is ignored.

    If a query result is in the query cache, no result size check is performed, because the result has previously been computed and it does not burden the server to send it to the client.

    This variable previously was named sql_max_join_size.

  • max_length_for_sort_data

    Command-Line Format--max_length_for_sort_data=#
    Option-File Formatmax_length_for_sort_data
    Option Sets VariableYes, max_length_for_sort_data
    Variable Namemax_length_for_sort_data
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default1024
    Range4 .. 8388608

    The cutoff on the size of index values that determines which filesort algorithm to use. See Section 7.13.9, “ORDER BY Optimization”.

  • max_long_data_size

    Version Introduced5.5.11
    Version Deprecated5.5.11
    Command-Line Format--max_long_data_size=#
    Option-File Formatmax_long_data_size
    Option Sets VariableYes, max_long_data_size
    Variable Namemax_long_data_size
    Variable ScopeGlobal
    Dynamic VariableNo
    Deprecated5.5.11
     Permitted Values
    Typenumeric
    Default1048576
    Range1024 .. 4294967295

    The maximum size of parameter values that can be sent with the mysql_stmt_send_long_data() C API function. If not set at server startup, the default is the value of the max_allowed_packet system variable. This variable is deprecated. In MySQL 5.6, it is removed and the maximum parameter size is controlled by max_allowed_packet.

  • max_prepared_stmt_count

    Command-Line Format--max_prepared_stmt_count=#
    Option-File Formatmax_prepared_stmt_count
    Option Sets VariableYes, max_prepared_stmt_count
    Variable Namemax_prepared_stmt_count
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default16382
    Range0 .. 1048576

    This variable limits the total number of prepared statements in the server. It can be used in environments where there is the potential for denial-of-service attacks based on running the server out of memory by preparing huge numbers of statements. If the value is set lower than the current number of prepared statements, existing statements are not affected and can be used, but no new statements can be prepared until the current number drops below the limit. The default value is 16,382. The permissible range of values is from 0 to 1 million. Setting the value to 0 disables prepared statements.

  • max_relay_log_size

    Command-Line Format--max_relay_log_size=#
    Option-File Formatmax_relay_log_size
    Option Sets VariableYes, max_relay_log_size
    Variable Namemax_relay_log_size
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default0
    Range0 .. 1073741824

    If a write by a replication slave to its relay log causes the current log file size to exceed the value of this variable, the slave rotates the relay logs (closes the current file and opens the next one). If max_relay_log_size is 0, the server uses max_binlog_size for both the binary log and the relay log. If max_relay_log_size is greater than 0, it constrains the size of the relay log, which enables you to have different sizes for the two logs. You must set max_relay_log_size to between 4096 bytes and 1GB (inclusive), or to 0. The default value is 0. See Section 15.2.1, “Replication Implementation Details”.

  • max_seeks_for_key

    Command-Line Format--max_seeks_for_key=#
    Option-File Formatmax_seeks_for_key
    Option Sets VariableYes, max_seeks_for_key
    Variable Namemax_seeks_for_key
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default4294967295
    Range1 .. 4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default18446744073709547520
    Range1 .. 18446744073709547520

    Limit the assumed maximum number of seeks when looking up rows based on a key. The MySQL optimizer assumes that no more than this number of key seeks are required when searching for matching rows in a table by scanning an index, regardless of the actual cardinality of the index (see Section 12.7.5.23, “SHOW INDEX Синтаксис”). By setting this to a low value (say, 100), you can force MySQL to prefer indexes instead of table scans.

  • max_sort_length

    Command-Line Format--max_sort_length=#
    Option-File Formatmax_sort_length
    Option Sets VariableYes, max_sort_length
    Variable Namemax_sort_length
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default1024
    Range4 .. 8388608

    The number of bytes to use when sorting BLOB or TEXT values. Only the first max_sort_length bytes of each value are used; the rest are ignored.

  • max_sp_recursion_depth

    Command-Line Format--max_sp_recursion_depth[=#]
    Option-File Formatmax_sp_recursion_depth
    Option Sets VariableYes, max_sp_recursion_depth
    Variable Namemax_sp_recursion_depth
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default0
    Max Value255

    The number of times that any given stored procedure may be called recursively. The default value for this option is 0, which completely disables recursion in stored procedures. The maximum value is 255.

    Stored procedure recursion increases the demand on thread stack space. If you increase the value of max_sp_recursion_depth, it may be necessary to increase thread stack size by increasing the value of thread_stack at server startup.

  • max_tmp_tables

    Command-Line Format--max_tmp_tables=#
    Option-File Formatmax_tmp_tables
    Option Sets VariableYes, max_tmp_tables
    Variable Namemax_tmp_tables
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default32
    Range1 .. 4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default32
    Range1 .. 18446744073709547520

    The maximum number of temporary tables a client can keep open at the same time. (This variable does not yet do anything.)

  • max_user_connections

    Command-Line Format--max_user_connections=#
    Option-File Formatmax_user_connections
    Option Sets VariableYes, max_user_connections
    Variable Namemax_user_connections
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default0
    Range0 .. 4294967295

    The maximum number of simultaneous connections permitted to any given MySQL user account. A value of 0 (the default) means “no limit.

    This variable has a global value that can be set at server startup or runtime. It also has a read-only session value that indicates the effective simultaneous-connection limit that applies to the account associated with the current session. The session value is initialized as follows:

    • If the user account has a nonzero MAX_USER_CONNECTIONS resource limit, the session max_user_connections value is set to that limit.

    • Otherwise, the session max_user_connections value is set to the global value.

    Account resource limits are specified using the GRANT statement. See Section 5.5.4, “Setting Account Resource Limits”, and Section 12.7.1.3, “GRANT Синтаксис”.

  • max_write_lock_count

    Command-Line Format--max_write_lock_count=#
    Option-File Formatmax_write_lock_count
    Option Sets VariableYes, max_write_lock_count
    Variable Namemax_write_lock_count
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default4294967295
    Range1 .. 4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default18446744073709547520
    Range1 .. 18446744073709547520

    After this many write locks, permit some pending read lock requests to be processed in between.

  • metadata_locks_cache_size

    Version Introduced5.5.19
    Variable Namemetadata_locks_cache_size
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default1024
    Range1 .. 1048576

    The size of the metadata locks cache. The server uses this cache to avoid creation and destruction of synchronization objects. This is particularly helpful on systems where such operations are expensive, such as Windows XP. This variable was added in MySQL 5.5.19.

  • min_examined_row_limit

    Command-Line Format--min-examined-row-limit=#
    Option-File Formatmin-examined-row-limit
    Variable Namemin_examined_row_limit
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default0
    Range0 .. 4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default0
    Range0 .. 18446744073709547520

    Queries that examine fewer than this number of rows are not logged to the slow query log.

  • myisam_data_pointer_size

    Command-Line Format--myisam_data_pointer_size=#
    Option-File Formatmyisam_data_pointer_size
    Option Sets VariableYes, myisam_data_pointer_size
    Variable Namemyisam_data_pointer_size
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default6
    Range2 .. 7

    The default pointer size in bytes, to be used by CREATE TABLE for MyISAM tables when no MAX_ROWS option is specified. This variable cannot be less than 2 or larger than 7. The default value is 6. See Section C.5.2.12, “The table is full.

  • myisam_max_sort_file_size

    Command-Line Format--myisam_max_sort_file_size=#
    Option-File Formatmyisam_max_sort_file_size
    Option Sets VariableYes, myisam_max_sort_file_size
    Variable Namemyisam_max_sort_file_size
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default2147483648

    The maximum size of the temporary file that MySQL is permitted to use while re-creating a MyISAM index (during REPAIR TABLE, ALTER TABLE, or LOAD DATA INFILE). If the file size would be larger than this value, the index is created using the key cache instead, which is slower. The value is given in bytes.

    The default value is 2GB. If MyISAM index files exceed this size and disk space is available, increasing the value may help performance. The space must be available in the file system containing the directory where the original index file is located.

  • myisam_mmap_size

    Version Introduced5.5.1
    Command-Line Format--myisam_mmap_size=#
    Option-File Formatmyisam_mmap_size
    Option Sets VariableYes, myisam_mmap_size
    Variable Namemyisam_mmap_size
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default4294967295
    Range7 .. 4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default18446744073709547520
    Range7 .. 18446744073709547520

    The maximum amount of memory to use for memory mapping compressed MyISAM files. If many compressed MyISAM tables are used, the value can be decreased to reduce the likelihood of memory-swapping problems. This variable was added in MySQL 5.5.1.

  • myisam_recover_options

    Variable Namemyisam_recover_options
    Variable ScopeGlobal
    Dynamic VariableNo

    The value of the --myisam-recover-options option. See Section 5.1.2, “Server Command Options”.

  • myisam_repair_threads

    Command-Line Format--myisam_repair_threads=#
    Option-File Formatmyisam_repair_threads
    Option Sets VariableYes, myisam_repair_threads
    Variable Namemyisam_repair_threads
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default1
    Range1 .. 4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default1
    Range1 .. 18446744073709547520

    If this value is greater than 1, MyISAM table indexes are created in parallel (each index in its own thread) during the Repair by sorting process. The default value is 1.

    Замечание

    Multi-threaded repair is still beta-quality code.

  • myisam_sort_buffer_size

    Command-Line Format--myisam_sort_buffer_size=#
    Option-File Formatmyisam_sort_buffer_size
    Option Sets VariableYes, myisam_sort_buffer_size
    Variable Namemyisam_sort_buffer_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default8388608
    Range4 .. 4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default8388608
    Range4 .. 18446744073709547520

    The size of the buffer that is allocated when sorting MyISAM indexes during a REPAIR TABLE or when creating indexes with CREATE INDEX or ALTER TABLE.

    The maximum permissible setting for myisam_sort_buffer_size is 4GB. Values larger than 4GB are permitted for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB with a warning).

  • myisam_stats_method

    Command-Line Format--myisam_stats_method=name
    Option-File Formatmyisam_stats_method
    Option Sets VariableYes, myisam_stats_method
    Variable Namemyisam_stats_method
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeenumeration
    Valid Values

    nulls_equal

    nulls_unequal

    nulls_ignored

    How the server treats NULL values when collecting statistics about the distribution of index values for MyISAM tables. This variable has three possible values, nulls_equal, nulls_unequal, and nulls_ignored. For nulls_equal, all NULL index values are considered equal and form a single value group that has a size equal to the number of NULL values. For nulls_unequal, NULL values are considered unequal, and each NULL forms a distinct value group of size 1. For nulls_ignored, NULL values are ignored.

    The method that is used for generating table statistics influences how the optimizer chooses indexes for query execution, as described in Section 7.3.7, “InnoDB and MyISAM Index Statistics Collection”.

  • myisam_use_mmap

    Command-Line Format--myisam_use_mmap
    Option-File Formatmyisam_use_mmap
    Option Sets VariableYes, myisam_use_mmap
    Variable Namemyisam_use_mmap
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    Use memory mapping for reading and writing MyISAM tables.

  • named_pipe

    Variable Namenamed_pipe
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform Specificwindows
     Permitted Values
    Type (windows)boolean
    DefaultOFF

    (Windows only.) Indicates whether the server supports connections over named pipes.

  • net_buffer_length

    Command-Line Format--net_buffer_length=#
    Option-File Formatnet_buffer_length
    Option Sets VariableYes, net_buffer_length
    Variable Namenet_buffer_length
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default16384
    Range1024 .. 1048576

    Each client thread is associated with a connection buffer and result buffer. Both begin with a size given by net_buffer_length but are dynamically enlarged up to max_allowed_packet bytes as needed. The result buffer shrinks to net_buffer_length after each SQL statement.

    This variable should not normally be changed, but if you have very little memory, you can set it to the expected length of statements sent by clients. If statements exceed this length, the connection buffer is automatically enlarged. The maximum value to which net_buffer_length can be set is 1MB.

    The session value of this variable is read only.

  • net_read_timeout

    Command-Line Format--net_read_timeout=#
    Option-File Formatnet_read_timeout
    Option Sets VariableYes, net_read_timeout
    Variable Namenet_read_timeout
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default30
    Min Value1

    The number of seconds to wait for more data from a connection before aborting the read. When the server is reading from the client, net_read_timeout is the timeout value controlling when to abort. When the server is writing to the client, net_write_timeout is the timeout value controlling when to abort. See also slave_net_timeout.

  • net_retry_count

    Command-Line Format--net_retry_count=#
    Option-File Formatnet_retry_count
    Option Sets VariableYes, net_retry_count
    Variable Namenet_retry_count
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default10
    Range1 .. 4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default10
    Range1 .. 18446744073709547520

    If a read or write on a communication port is interrupted, retry this many times before giving up. This value should be set quite high on FreeBSD because internal interrupts are sent to all threads.

  • net_write_timeout

    Command-Line Format--net_write_timeout=#
    Option-File Formatnet_write_timeout
    Option Sets VariableYes, net_write_timeout
    Variable Namenet_write_timeout
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default60
    Min Value1

    The number of seconds to wait for a block to be written to a connection before aborting the write. See also net_read_timeout.

  • new

    Command-Line Format--new
    -n
    Option-File Formatnew
    Option Sets VariableYes, new
    Variable Namenew
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Disabled byskip-new
     Permitted Values
    Typeboolean
    DefaultFALSE

    This variable was used in MySQL 4.0 to turn on some 4.1 behaviors, and is retained for backward compatibility. In MySQL 5.5, its value is always OFF.

  • old

    Command-Line Format--old
    Option-File Formatold
    Variable Nameold
    Variable ScopeGlobal
    Dynamic VariableNo

    old is a compatibility variable. It is disabled by default, but can be enabled at startup to revert the server to behaviors present in older versions.

    Currently, when old is enabled, it changes the default scope of index hints to that used prior to MySQL 5.1.17. That is, index hints with no FOR clause apply only to how indexes are used for row retrieval and not to resolution of ORDER BY or GROUP BY clauses. (See Section 12.2.9.3, “Index Hint Синтаксис”.) Take care about enabling this in a replication setup. With statement-based binary logging, having different modes for the master and slaves might lead to replication errors.

  • old_alter_table

    Command-Line Format--old-alter-table
    Option-File Formatold-alter-table
    Option Sets VariableYes, old_alter_table
    Variable Nameold_alter_table
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    When this variable is enabled, the server does not use the optimized method of processing an ALTER TABLE operation. It reverts to using a temporary table, copying over the data, and then renaming the temporary table to the original, as used by MySQL 5.0 and earlier. For more information on the operation of ALTER TABLE, see Section 12.1.7, “ALTER TABLE Синтаксис”.

  • old_passwords

    Command-Line Format--old_passwords
    Option-File Formatold-passwords
    Option Sets VariableYes, old_passwords
    Variable Nameold_passwords
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultFALSE

    Whether the server should use pre-4.1-style passwords for MySQL user accounts. See Section C.5.2.4, “Client does not support authentication protocol.

  • one_shot

    This is not a variable, but it can be used when setting some variables. It is described in Section 12.7.4, “SET Синтаксис”.

  • open_files_limit

    Command-Line Format--open-files-limit=#
    Option-File Formatopen-files-limit
    Option Sets VariableYes, open_files_limit
    Variable Nameopen_files_limit
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default0
    Range0 .. 65535

    The number of files that the operating system permits mysqld to open. This is the real value permitted by the system and might be different from the value you gave using the --open-files-limit option to mysqld or mysqld_safe. The value is 0 on systems where MySQL cannot change the number of open files.

  • optimizer_prune_level

    Command-Line Format--optimizer_prune_level[=#]
    Option-File Formatoptimizer_prune_level
    Option Sets VariableYes, optimizer_prune_level
    Variable Nameoptimizer_prune_level
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    Default1

    Controls the heuristics applied during query optimization to prune less-promising partial plans from the optimizer search space. A value of 0 disables heuristics so that the optimizer performs an exhaustive search. A value of 1 causes the optimizer to prune plans based on the number of rows retrieved by intermediate plans.

  • optimizer_search_depth

    Command-Line Format--optimizer_search_depth[=#]
    Option-File Formatoptimizer_search_depth
    Option Sets VariableYes, optimizer_search_depth
    Variable Nameoptimizer_search_depth
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values (<= 5.5.99)
    Typenumeric
    Default62
    Range0 .. 63

    The maximum depth of search performed by the query optimizer. Values larger than the number of relations in a query result in better query plans, but take longer to generate an execution plan for a query. Values smaller than the number of relations in a query return an execution plan quicker, but the resulting plan may be far from being optimal. If set to 0, the system automatically picks a reasonable value. If set to 63, the optimizer switches to the algorithm used in MySQL 5.0.0 (and previous versions) for performing searches. The value of 63 is deprecated and will be treated as invalid in a future MySQL release.

  • optimizer_switch

    Command-Line Format--optimizer_switch=value
    Option-File Formatoptimizer_switch
    optimizer_switch
    optimizer_switch
    Option Sets VariableYes, optimizer_switch
    Variable Nameoptimizer_switch
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values (<= 5.5.2)
    Typeset
    Valid Values

    index_merge={on|off}

    index_merge_intersection={on|off}

    index_merge_sort_union={on|off}

    index_merge_union={on|off}

     Permitted Values (>= 5.5.3)
    Typeset
    Valid Values

    engine_condition_pushdown={on|off}

    index_merge={on|off}

    index_merge_intersection={on|off}

    index_merge_sort_union={on|off}

    index_merge_union={on|off}

    The optimizer_switch system variable enables control over optimizer behavior. The value of this variable is a set of flags, each of which has a value of on or off to indicate whether the corresponding optimizer behavior is enabled or disabled. This variable has global and session values and can be changed at runtime. The global default can be set at server startup.

    To see the current set of optimizer flags, select the variable value:

    mysql> SELECT @@optimizer_switch\G
    *************************** 1. row ***************************
    @@optimizer_switch: index_merge=on,index_merge_union=on,
                        index_merge_sort_union=on,
                        index_merge_intersection=on,
                        engine_condition_pushdown=on
    

    For more information about the syntax of this variable and the optimizer behaviors that it controls, see Section 7.8.4.2, “Controlling Switchable Optimizations”.

  • performance_schema_xxx

    Performance Schema system variables are listed in Section 20.8, “Performance Schema System Variables”.

  • pid_file

    Command-Line Format--pid-file=file_name
    Option-File Formatpid-file=file_name
    Option Sets VariableYes, pid_file
    Variable Namepid_file
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

    The path name of the process ID (PID) file. This variable can be set with the --pid-file option.

  • plugin_dir

    Command-Line Format--plugin_dir=path
    Option-File Formatplugin_dir
    Option Sets VariableYes, plugin_dir
    Variable Nameplugin_dir
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values (>= 5.5.0, <= 5.5.4)
    Type (other)directory name
    DefaultBASEDIR/lib/mysql/plugin
     Permitted Values (>= 5.5.0, <= 5.5.4)
    Type (windows)directory name
    DefaultBASEDIR/lib/plugin
     Permitted Values (>= 5.5.5)
    Typedirectory name
    DefaultBASEDIR/lib/plugin

    The path name of the plugin directory.

    If the plugin directory is writable by the server, it may be possible for a user to write executable code to a file in the directory using SELECT ... INTO DUMPFILE. This can be prevented by making plugin_dir read only to the server or by setting --secure-file-priv to a directory where SELECT writes can be made safely.

  • port

    Command-Line Format--port=#
    -P
    Option-File Formatport
    Option Sets VariableYes, port
    Variable Nameport
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default3306

    The number of the port on which the server listens for TCP/IP connections. This variable can be set with the --port option.

  • preload_buffer_size

    Command-Line Format--preload_buffer_size=#
    Option-File Formatpreload_buffer_size
    Option Sets VariableYes, preload_buffer_size
    Variable Namepreload_buffer_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default32768
    Range1024 .. 1073741824

    The size of the buffer that is allocated when preloading indexes.

  • profiling

    If set to 0 (the default), statement profiling is disabled. If set to 1, statement profiling is enabled and the SHOW PROFILES and SHOW PROFILE statements provide access to profiling information. See Section 12.7.5.32, “SHOW PROFILES Синтаксис”.

  • profiling_history_size

    The number of statements for which to maintain profiling information if profiling is enabled. The default value is 15. The maximum value is 100. Setting the value to 0 effectively disables profiling. See Section 12.7.5.32, “SHOW PROFILES Синтаксис”.

  • protocol_version

    Variable Nameprotocol_version
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric

    The version of the client/server protocol used by the MySQL server.

  • proxy_user

    Version Introduced5.5.7
    Variable Nameproxy_user
    Variable ScopeSession
    Dynamic VariableNo
     Permitted Values
    Typestring

    If the current client is a proxy for another user, this variable is the proxy user account name. Otherwise, this variable is NULL. See Section 5.5.7, “Proxy Users”.

    This variable was added in MySQL 5.5.7.

  • pseudo_thread_id

    Variable Namepseudo_thread_id
    Variable ScopeSession
    Dynamic VariableYes
     Permitted Values
    Typenumeric

    This variable is for internal server use.

  • query_alloc_block_size

    Command-Line Format--query_alloc_block_size=#
    Option-File Formatquery_alloc_block_size
    Option Sets VariableYes, query_alloc_block_size
    Variable Namequery_alloc_block_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default8192
    Range1024 .. 4294967295
    Block Size1024
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default8192
    Range1024 .. 18446744073709547520
    Block Size1024

    The allocation size of memory blocks that are allocated for objects created during statement parsing and execution. If you have problems with memory fragmentation, it might help to increase this parameter.

  • query_cache_limit

    Command-Line Format--query_cache_limit=#
    Option-File Formatquery_cache_limit
    Option Sets VariableYes, query_cache_limit
    Variable Namequery_cache_limit
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default1048576
    Range0 .. 4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default1048576
    Range0 .. 18446744073709547520

    Do not cache results that are larger than this number of bytes. The default value is 1MB.

  • query_cache_min_res_unit

    Command-Line Format--query_cache_min_res_unit=#
    Option-File Formatquery_cache_min_res_unit
    Option Sets VariableYes, query_cache_min_res_unit
    Variable Namequery_cache_min_res_unit
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default4096
    Range512 .. 4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default4096
    Range512 .. 18446744073709547520

    The minimum size (in bytes) for blocks allocated by the query cache. The default value is 4096 (4KB). Tuning information for this variable is given in Section 7.9.3.3, “Query Cache Configuration”.

  • query_cache_size

    Command-Line Format--query_cache_size=#
    Option-File Formatquery_cache_size
    Option Sets VariableYes, query_cache_size
    Variable Namequery_cache_size
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default0
    Range0 .. 4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default0
    Range0 .. 18446744073709547520

    The amount of memory allocated for caching query results. The default value is 0, which disables the query cache. To reduce overhead significantly, you should also start the server with query_cache_type=0 if you will not be using the query cache. The permissible values are multiples of 1024; other values are rounded down to the nearest multiple. Note that query_cache_size bytes of memory are allocated even if query_cache_type is set to 0. See Section 7.9.3.3, “Query Cache Configuration”, for more information.

    The query cache needs a minimum size of about 40KB to allocate its structures. (The exact size depends on system architecture.) If you set the value of query_cache_size too small, a warning will occur, as described in Section 7.9.3.3, “Query Cache Configuration”.

  • query_cache_type

    Command-Line Format--query_cache_type=#
    Option-File Formatquery_cache_type
    Option Sets VariableYes, query_cache_type
    Variable Namequery_cache_type
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeenumeration
    Default1
    Valid Values

    0

    1

    2

    Set the query cache type. Setting the GLOBAL value sets the type for all clients that connect thereafter. Individual clients can set the SESSION value to affect their own use of the query cache. Possible values are shown in the following table.

    OptionОписание
    0 or OFFDo not cache results in or retrieve results from the query cache. Note that this does not deallocate the query cache buffer. To do that, you should set query_cache_size to 0.
    1 or ONCache all cacheable query results except for those that begin with SELECT SQL_NO_CACHE.
    2 or DEMANDCache results only for cacheable queries that begin with SELECT SQL_CACHE.

    This variable defaults to ON.

    If the server is started with query_cache_type set to 0, it does not acquire the query cache mutex at all, which means that the query cache cannot be enabled at runtime and there is reduced overhead in query execution.

  • query_cache_wlock_invalidate

    Command-Line Format--query_cache_wlock_invalidate
    Option-File Formatquery_cache_wlock_invalidate
    Option Sets VariableYes, query_cache_wlock_invalidate
    Variable Namequery_cache_wlock_invalidate
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultFALSE

    Normally, when one client acquires a WRITE lock on a MyISAM table, other clients are not blocked from issuing statements that read from the table if the query results are present in the query cache. Setting this variable to 1 causes acquisition of a WRITE lock for a table to invalidate any queries in the query cache that refer to the table. This forces other clients that attempt to access the table to wait while the lock is in effect.

  • query_prealloc_size

    Command-Line Format--query_prealloc_size=#
    Option-File Formatquery_prealloc_size
    Option Sets VariableYes, query_prealloc_size
    Variable Namequery_prealloc_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default8192
    Range8192 .. 4294967295
    Block Size1024
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default8192
    Range8192 .. 18446744073709547520
    Block Size1024

    The size of the persistent buffer used for statement parsing and execution. This buffer is not freed between statements. If you are running complex queries, a larger query_prealloc_size value might be helpful in improving performance, because it can reduce the need for the server to perform memory allocation during query execution operations.

  • rand_seed1

    The rand_seed1 and rand_seed2 variables exist as session variables only, and can be set but not read. The variables—but not their values—are shown in the output of SHOW VARIABLES.

    The purpose of these variables is to support replication of the RAND() function. For statements that invoke RAND(), the master passes two values to the slave, where they are used to seed the random number generator. The slave uses these values to set the session variables rand_seed1 and rand_seed2 so that RAND() on the slave generates the same value as on the master.

  • rand_seed2

    See the description for rand_seed1.

  • range_alloc_block_size

    Command-Line Format--range_alloc_block_size=#
    Option-File Formatrange_alloc_block_size
    Option Sets VariableYes, range_alloc_block_size
    Variable Namerange_alloc_block_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default4096
    Range4096 .. 4294967295
    Block Size1024

    The size of blocks that are allocated when doing range optimization.

  • read_buffer_size

    Command-Line Format--read_buffer_size=#
    Option-File Formatread_buffer_size
    Option Sets VariableYes, read_buffer_size
    Variable Nameread_buffer_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default131072
    Range8200 .. 2147479552

    Each thread that does a sequential scan allocates a buffer of this size (in bytes) for each table it scans. If you do many sequential scans, you might want to increase this value, which defaults to 131072. The value of this variable should be a multiple of 4KB. If it is set to a value that is not a multiple of 4KB, its value will be rounded down to the nearest multiple of 4KB.

    The maximum permissible setting for read_buffer_size is 2GB.

    read_buffer_size and read_rnd_buffer_size are not specific to any storage engine and apply in a general manner for optimization. See Section 7.11.4.1, “How MySQL Uses Memory”, for example.

  • read_only

    Command-Line Format--read-only
    Option-File Formatread_only
    Option Sets VariableYes, read_only
    Variable Nameread_only
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default0

    This variable is off by default. When it is enabled, the server permits no updates except from users that have the SUPER privilege or (on a slave server) from updates performed by slave threads. In replication setups, it can be useful to enable read_only on slave servers to ensure that slaves accept updates only from the master server and not from clients.

    read_only does not apply to TEMPORARY tables, nor does it prevent the server from inserting rows into the log tables (see Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”). This variable does not prevent the use of ANALYZE TABLE or OPTIMIZE TABLE statements because its purpose is to prevent changes to table structure or contents. Analysis and optimization do not qualify as such changes. This means, for example, that consistency checks on read-only slaves can be performed with mysqlcheck --all-databases --analyze.

    read_only exists only as a GLOBAL variable, so changes to its value require the SUPER privilege. Changes to read_only on a master server are not replicated to slave servers. The value can be set on a slave server independent of the setting on the master.

    Important

    In MySQL 5.5, enabling read_only prevents the use of the SET PASSWORD statement by any user not having the SUPER privilege. This is not necessarily the case for all MySQL release series. When replicating from one MySQL release series to another (for example, from a MySQL 5.0 master to a MySQL 5.1 or later slave), you should check the documentation for the versions running on both master and slave to determine whether the behavior of read_only in this regard is or is not the same, and, if it is different, whether this has an impact on your applications.

    The following conditions apply:

    • If you attempt to enable read_only while you have any explicit locks (acquired with LOCK TABLES) or have a pending transaction, an error occurs.

    • If you attempt to enable read_only while other clients hold explicit table locks or have pending transactions, the attempt blocks until the locks are released and the transactions end. While the attempt to enable read_only is pending, requests by other clients for table locks or to begin transactions also block until read_only has been set.

    • read_only can be enabled while you hold a global read lock (acquired with FLUSH TABLES WITH READ LOCK) because that does not involve table locks.

    As of MySQL 5.5.3, attempts to set read_only block for active transactions that hold metadata locks until those transactions end.

  • read_rnd_buffer_size

    Command-Line Format--read_rnd_buffer_size=#
    Option-File Formatread_rnd_buffer_size
    Option Sets VariableYes, read_rnd_buffer_size
    Variable Nameread_rnd_buffer_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default262144
    Range8200 .. 4294967295

    When reading rows in sorted order following a key-sorting operation, the rows are read through this buffer to avoid disk seeks. See Section 7.13.9, “ORDER BY Optimization”. Setting the variable to a large value can improve ORDER BY performance by a lot. However, this is a buffer allocated for each client, so you should not set the global variable to a large value. Instead, change the session variable only from within those clients that need to run large queries.

    The maximum permissible setting for read_rnd_buffer_size is 2GB.

    read_buffer_size and read_rnd_buffer_size are not specific to any storage engine and apply in a general manner for optimization. See Section 7.11.4.1, “How MySQL Uses Memory”, for example.

  • relay_log_purge

    Command-Line Format--relay_log_purge
    Option-File Formatrelay_log_purge
    Option Sets VariableYes, relay_log_purge
    Variable Namerelay_log_purge
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultTRUE

    Disables or enables automatic purging of relay log files as soon as they are not needed any more. The default value is 1 (ON).

  • relay_log_space_limit

    Command-Line Format--relay_log_space_limit=#
    Option-File Formatrelay_log_space_limit
    Option Sets VariableYes, relay_log_space_limit
    Variable Namerelay_log_space_limit
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default0
    Range0 .. 4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default0
    Range0 .. 18446744073709547520

    The maximum amount of space to use for all relay logs.

  • report_host

    Command-Line Format--report-host=host_name
    Option-File Formatreport-host
    Option Sets VariableYes, report_host
    Variable Namereport-host
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring

    The value of the --report-host option.

  • report_password

    Command-Line Format--report-password=name
    Option-File Formatreport-password
    Option Sets VariableYes, report_password
    Variable Namereport-password
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring

    The value of the --report-password option. Not the same as the password used for the MySQL replication user account.

  • report_port

    Command-Line Format--report-port=#
    Option-File Formatreport-port
    Option Sets VariableYes, report_port
    Variable Namereport-port
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default3306

    The value of the --report-port option.

  • report_user

    Command-Line Format--report-user=name
    Option-File Formatreport-user
    Option Sets VariableYes, report_user
    Variable Namereport-user
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring

    The value of the --report-user option. Not the same as the name for the MySQL replication user account.

  • rpl_semi_sync_master_enabled

    Variable Namerpl_semi_sync_master_enabled
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    Controls whether semisynchronous replication is enabled on the master. To enable or disable the plugin, set this variable to ON or OFF (or 1 or 0), respectively. The default is OFF.

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_master_timeout

    Variable Namerpl_semi_sync_master_timeout
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values (>= 5.5.0)
    Typenumeric
    Default10000

    A value in milliseconds that controls how long the master waits on a commit for acknowledgment from a slave before timing out and reverting to asynchronous replication. The default value is 10000 (10 seconds).

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_master_trace_level

    Variable Namerpl_semi_sync_master_trace_level
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default32

    The semisynchronous replication debug trace level on the master. Currently, four levels are defined:

    • 1 = general level (for example, time function failures)

    • 16 = detail level (more verbose information)

    • 32 = net wait level (more information about network waits)

    • 64 = function level (information about function entry and exit)

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_master_wait_no_slave

    Variable Namerpl_semi_sync_master_wait_no_slave
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultON

    With semisynchronous replication, for each transaction, the master waits until timeout for acknowledgment of receipt from some semisynchronous slave. If no response occurs during this period, the master reverts to normal replication. This variable controls whether the master waits for the timeout to expire before reverting to normal replication even if the slave count drops to zero during the timeout period.

    If the value is ON (the default), it is permissible for the slave count to drop to zero during the timeout period (for example, if slaves disconnect). The master still waits for the timeout, so as long as some slave reconnects and acknowledges the transaction within the timeout interval, semisynchronous replication continues.

    If the value is OFF, the master reverts to normal replication if the slave count drops to zero during the timeout period.

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_slave_enabled

    Variable Namerpl_semi_sync_slave_enabled
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    Controls whether semisynchronous replication is enabled on the slave. To enable or disable the plugin, set this variable to ON or OFF (or 1 or 0), respectively. The default is OFF.

    This variable is available only if the slave-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_slave_trace_level

    Variable Namerpl_semi_sync_slave_trace_level
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default32

    The semisynchronous replication debug trace level on the slave. See rpl_semi_sync_master_trace_level for the permissible values.

    This variable is available only if the slave-side semisynchronous replication plugin is installed.

  • secure_auth

    Command-Line Format--secure-auth
    Option-File Formatsecure-auth
    Option Sets VariableYes, secure_auth
    Variable Namesecure_auth
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultFALSE

    If the MySQL server has been started with the --secure-auth option, it blocks connections from all accounts that have passwords stored in the old (pre-4.1) format. In that case, the value of this variable is ON, otherwise it is OFF.

    You should enable this option if you want to prevent all use of passwords employing the old format (and hence insecure communication over the network).

    Server startup fails with an error if this option is enabled and the privilege tables are in pre-4.1 format. See Section C.5.2.4, “Client does not support authentication protocol.

  • secure_file_priv

    Command-Line Format--secure-file-priv=path
    Option-File Formatsecure-file-priv=path
    Option Sets VariableYes, secure_file_priv
    Variable Namesecure-file-priv
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring

    By default, this variable is empty. If set to the name of a directory, it limits the effect of the LOAD_FILE() function and the LOAD DATA and SELECT ... INTO OUTFILE statements to work only with files in that directory.

  • server_id

    Command-Line Format--server-id=#
    Option-File Formatserver-id
    Option Sets VariableYes, server_id
    Variable Nameserver_id
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default0
    Range0 .. 4294967295

    The server ID, used in replication to give each master and slave a unique identity. This variable is set by the --server-id option. For each server participating in replication, you should pick a positive integer in the range from 1 to 232 – 1 to act as that server's ID.

  • shared_memory

    Variable Nameshared_memory
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform Specificwindows

    (Windows only.) Whether the server permits shared-memory connections.

  • shared_memory_base_name

    Variable Nameshared_memory_base_name
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform Specificwindows

    (Windows only.) The name of shared memory to use for shared-memory connections. This is useful when running multiple MySQL instances on a single physical machine. The default name is MYSQL. The name is case sensitive.

  • skip_external_locking

    This is OFF if mysqld uses external locking, ON if external locking is disabled. This affects only MyISAM table access.

  • skip_name_resolve

    This variable is set from the value of the --skip-name-resolve option. If it is ON, mysqld resolves host names when checking client connections. If OFF, mysqld uses only IP numbers and all Host column values in the grant tables must be IP addresses or localhost. See Section 7.11.5.2, “How MySQL Uses DNS”.

    This variable was added in MySQL 5.5.5.

  • skip_networking

    This is ON if the server permits only local (non-TCP/IP) connections. On Unix, local connections use a Unix socket file. On Windows, local connections use a named pipe or shared memory. This variable can be set to ON with the --skip-networking option.

  • skip_show_database

    This prevents people from using the SHOW DATABASES statement if they do not have the SHOW DATABASES privilege. This can improve security if you have concerns about users being able to see databases belonging to other users. Its effect depends on the SHOW DATABASES privilege: If the variable value is ON, the SHOW DATABASES statement is permitted only to users who have the SHOW DATABASES privilege, and the statement displays all database names. If the value is OFF, SHOW DATABASES is permitted to all users, but displays the names of only those databases for which the user has the SHOW DATABASES or other privilege.

  • slow_launch_time

    Command-Line Format--slow_launch_time=#
    Option-File Formatslow_launch_time
    Option Sets VariableYes, slow_launch_time
    Variable Nameslow_launch_time
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default2

    If creating a thread takes longer than this many seconds, the server increments the Slow_launch_threads status variable.

  • slow_query_log

    Command-Line Format--slow-query-log
    Option-File Formatslow-query-log
    Option Sets VariableYes, slow_query_log
    Variable Nameslow_query_log
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    Whether the slow query log is enabled. The value can be 0 (or OFF) to disable the log or 1 (or ON) to enable the log. The default value depends on whether the --slow_query_log option is given. The destination for log output is controlled by the log_output system variable; if that value is NONE, no log entries are written even if the log is enabled.

    Slow” is determined by the value of the long_query_time variable. See Section 5.2.5, “The Slow Query Log”.

  • slow_query_log_file

    Command-Line Format--slow-query-log-file=file_name
    Option-File Formatslow_query_log_file
    Option Sets VariableYes, slow_query_log_file
    Variable Nameslow_query_log_file
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typefile name

    The name of the slow query log file. The default value is host_name-slow.log, but the initial value can be changed with the --slow_query_log_file option.

  • socket

    Command-Line Format--socket=name
    Option-File Formatsocket
    Option Sets VariableYes, socket
    Variable Namesocket
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name
    Default/tmp/mysql.sock

    On Unix platforms, this variable is the name of the socket file that is used for local client connections. The default is /tmp/mysql.sock. (For some distribution formats, the directory might be different, such as /var/lib/mysql for RPMs.)

    On Windows, this variable is the name of the named pipe that is used for local client connections. The default value is MySQL (not case sensitive).

  • sort_buffer_size

    Command-Line Format--sort_buffer_size=#
    Option-File Formatsort_buffer_size
    Option Sets VariableYes, sort_buffer_size
    Variable Namesort_buffer_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default2097144
    Max Value4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default2097144
    Max Value18446744073709547520

    Each session that needs to do a sort allocates a buffer of this size. sort_buffer_size is not specific to any storage engine and applies in a general manner for optimization. See Section 7.13.9, “ORDER BY Optimization”, for example.

    If you see many Sort_merge_passes per second in SHOW GLOBAL STATUS output, you can consider increasing the sort_buffer_size value to speed up ORDER BY or GROUP BY operations that cannot be improved with query optimization or improved indexing. The entire buffer is allocated even if it is not all needed, so setting it larger than required globally will slow down most queries that sort. It is best to increase it as a session setting, and only for the sessions that need a larger size. On Linux, there are thresholds of 256KB and 2MB where larger values may significantly slow down memory allocation, so you should consider staying below one of those values. Experiment to find the best value for your workload. See Section C.5.4.4, “Where MySQL Stores Temporary Files”.

    The maximum permissible setting for sort_buffer_size is 4GB. Values larger than 4GB are permitted for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB with a warning).

  • sql_auto_is_null

    Variable Namesql_auto_is_null
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values (<= 5.5.2)
    Typeboolean
    Default1
     Permitted Values (>= 5.5.3)
    Typeboolean
    Default0

    If this variable is set to 1, then after a statement that successfully inserts an automatically generated AUTO_INCREMENT value, you can find that value by issuing a statement of the following form:

    SELECT * FROM tbl_name WHERE auto_col IS NULL
    

    If the statement returns a row, the value returned is the same as if you invoked the LAST_INSERT_ID() function. For details, including the return value after a multiple-row insert, see Section 11.14, “Information Functions”. If no AUTO_INCREMENT value was successfully inserted, the SELECT statement returns no row.

    The behavior of retrieving an AUTO_INCREMENT value by using an IS NULL comparison is used by some ODBC programs, such as Access. See Section 21.1.7.1.1, “Obtaining Auto-Increment Values”. This behavior can be disabled by setting sql_auto_is_null to 0.

    The default value of sql_auto_is_null is 0 as of MySQL 5.5.3, and 1 for earlier versions.

  • sql_big_selects

    Variable Namesql_big_selects
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    Default1

    If set to 0, MySQL aborts SELECT statements that are likely to take a very long time to execute (that is, statements for which the optimizer estimates that the number of examined rows exceeds the value of max_join_size). This is useful when an inadvisable WHERE statement has been issued. The default value for a new connection is 1, which permits all SELECT statements.

    If you set the max_join_size system variable to a value other than DEFAULT, sql_big_selects is set to 0.

  • sql_buffer_result

    Variable Namesql_buffer_result
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    Default0

    If set to 1, sql_buffer_result forces results from SELECT statements to be put into temporary tables. This helps MySQL free the table locks early and can be beneficial in cases where it takes a long time to send results to the client. The default value is 0.

  • sql_log_bin

    Variable Namesql_log_bin
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean

    This variable controls whether logging to the binary log is done. The default value is 1 (do logging). To change logging for the current session, change the session value of this variable. The session user must have the SUPER privilege to set this variable.

    Beginning with MySQL 5.5.5, it is no longer possible to set @@session.sql_log_bin within a transaction or subquery. (Bug #53437)

  • sql_log_off

    Variable Namesql_log_off
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    Default0

    This variable controls whether logging to the general query log is done. The default value is 0 (do logging). To change logging for the current session, change the session value of this variable. The session user must have the SUPER privilege to set this option. The default value is 0.

  • sql_log_update

    Version Removed5.5.3
    Variable Namesql_log_update
    Variable ScopeSession
    Dynamic VariableYes
    Deprecated5.0, by sql_log_bin
     Permitted Values
    Typeboolean

    This variable is deprecated, and is mapped to sql_log_bin. It was removed in MySQL 5.5.3.

  • sql_mode

    Command-Line Format--sql-mode=name
    Option-File Formatsql-mode
    Option Sets VariableYes, sql_mode
    Variable Namesql_mode
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeset
    Default''
    Valid Values

    ALLOW_INVALID_DATES

    ANSI_QUOTES

    ERROR_FOR_DIVISION_BY_ZERO

    HIGH_NOT_PRECEDENCE

    IGNORE_SPACE

    NO_AUTO_CREATE_USER

    NO_AUTO_VALUE_ON_ZERO

    NO_BACKSLASH_ESCAPES

    NO_DIR_IN_CREATE

    NO_ENGINE_SUBSTITUTION

    NO_FIELD_OPTIONS

    NO_KEY_OPTIONS

    NO_TABLE_OPTIONS

    NO_UNSIGNED_SUBTRACTION

    NO_ZERO_DATE

    NO_ZERO_IN_DATE

    ONLY_FULL_GROUP_BY

    PAD_CHAR_TO_FULL_LENGTH

    PIPES_AS_CONCAT

    REAL_AS_FLOAT

    STRICT_ALL_TABLES

    STRICT_TRANS_TABLES

    The current server SQL mode, which can be set dynamically. See Section 5.1.6, “Server SQL Modes”.

  • sql_notes

    If set to 1 (the default), warnings of Замечание level increment warning_count and the server records them. If set to 0, Замечание warnings do not increment warning_count and the server does not record them. mysqldump includes output to set this variable to 0 so that reloading the dump file does not produce warnings for events that do not affect the integrity of the reload operation.

  • sql_quote_show_create

    If set to 1 (the default), the server quotes identifiers for SHOW CREATE TABLE and SHOW CREATE DATABASE statements. If set to 0, quoting is disabled. This option is enabled by default so that replication works for identifiers that require quoting. See Section 12.7.5.12, “SHOW CREATE TABLE Синтаксис”, and Section 12.7.5.8, “SHOW CREATE DATABASE Синтаксис”.

  • sql_safe_updates

    If set to 1, MySQL aborts UPDATE or DELETE statements that do not use a key in the WHERE clause or a LIMIT clause. This makes it possible to catch UPDATE or DELETE statements where keys are not used properly and that would probably change or delete a large number of rows. The default value is 0.

  • sql_select_limit

    Variable Namesql_select_limit
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric

    The maximum number of rows to return from SELECT statements. The default value for a new connection is the maximum number of rows that the server permits per table. Typical default values are (232)–1 or (264)–1. If you have changed the limit, the default value can be restored by assigning a value of DEFAULT.

    If a SELECT has a LIMIT clause, the LIMIT takes precedence over the value of sql_select_limit.

    sql_select_limit does not apply to SELECT statements executed within stored routines. It also does not apply to SELECT statements that do not produce a result set to be returned to the client. These include SELECT statements in subqueries, CREATE TABLE ... SELECT, and INSERT INTO ... SELECT.

  • sql_warnings

    This variable controls whether single-row INSERT statements produce an information string if warnings occur. The default is 0. Set the value to 1 to produce an information string.

  • ssl_ca

    Command-Line Format--ssl-ca=name
    Option-File Formatssl-ca
    Option Sets VariableYes, ssl_ca
    Variable Namessl-ca
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

    The path to a file with a list of trusted SSL CAs.

  • ssl_capath

    Command-Line Format--ssl-capath=name
    Option-File Formatssl-capath
    Option Sets VariableYes, ssl_capath
    Variable Namessl-capath
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typedirectory name

    The path to a directory that contains trusted SSL CA certificates in PEM format.

  • ssl_cert

    Command-Line Format--ssl-cert=name
    Option-File Formatssl-cert
    Option Sets VariableYes, ssl_cert
    Variable Namessl-cert
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

    The name of the SSL certificate file to use for establishing a secure connection.

  • ssl_cipher

    Command-Line Format--ssl-cipher=name
    Option-File Formatssl-cipher
    Option Sets VariableYes, ssl_cipher
    Variable Namessl-cipher
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

    A list of permissible ciphers to use for SSL encryption.

  • ssl_key

    Command-Line Format--ssl-key=name
    Option-File Formatssl-key
    Option Sets VariableYes, ssl_key
    Variable Namessl-key
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring

    The name of the SSL key file to use for establishing a secure connection.

  • storage_engine

    Variable Namestorage_engine
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values (>= 5.5.3, <= 5.5.4)
    Typeenumeration
    DefaultMyISAM
     Permitted Values (>= 5.5.5)
    Typeenumeration
    DefaultInnoDB

    The default storage engine (table type). To set the storage engine at server startup, use the --default-storage-engine option. See Section 5.1.2, “Server Command Options”.

    This variable is deprecated as of MySQL 5.5.3. Use default_storage_engine instead.

  • sync_frm

    Command-Line Format--sync-frm
    Option-File Formatsync_frm
    Option Sets VariableYes, sync_frm
    Variable Namesync_frm
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultTRUE

    If this variable is set to 1, when any nontemporary table is created its .frm file is synchronized to disk (using fdatasync()). This is slower but safer in case of a crash. The default is 1.

  • system_time_zone

    Variable Namesystem_time_zone
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring

    The server system time zone. When the server begins executing, it inherits a time zone setting from the machine defaults, possibly modified by the environment of the account used for running the server or the startup script. The value is used to set system_time_zone. Typically the time zone is specified by the TZ environment variable. It also can be specified using the --timezone option of the mysqld_safe script.

    The system_time_zone variable differs from time_zone. Although they might have the same value, the latter variable is used to initialize the time zone for each client that connects. See Section 9.6, “MySQL Server Time Zone Support”.

  • table_definition_cache

    Command-Line Format--table_definition_cache=#
    Option-File Formattable_definition_cache
    Option Sets VariableYes, table_definition_cache
    Variable Nametable_definition_cache
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default400
    Range400 .. 524288

    The number of table definitions that can be stored in the definition cache. If you use a large number of tables, you can create a large table definition cache to speed up opening of tables. The table definition cache takes less space and does not use file descriptors, unlike the normal table cache. The minimum and default values are both 400.

  • table_lock_wait_timeout

    Version Removed5.5.3
    Command-Line Format--table_lock_wait_timeout=#
    Option-File Formattable_lock_wait_timeout
    Option Sets VariableYes, table_lock_wait_timeout
    Variable Nametable_lock_wait_timeout
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default50
    Range1 .. 1073741824

    This variable is unused. It was removed in 5.5.3.

  • table_open_cache

    Command-Line Format--table-open-cache=#
    Option-File Formattable_open_cache
    Variable Nametable_open_cache
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default400
    Range400 .. 524288

    The number of open tables for all threads. Increasing this value increases the number of file descriptors that mysqld requires. You can check whether you need to increase the table cache by checking the Opened_tables status variable. See Section 5.1.5, “Server Status Variables”. If the value of Opened_tables is large and you do not use FLUSH TABLES often (which just forces all tables to be closed and reopened), then you should increase the value of the table_open_cache variable. For more information about the table cache, see Section 7.4.3.1, “How MySQL Opens and Closes Tables”.

  • table_type

    This variable was removed in MySQL 5.5.3. Use storage_engine instead.

  • thread_cache_size

    Command-Line Format--thread_cache_size=#
    Option-File Formatthread_cache_size
    Option Sets VariableYes, thread_cache_size
    Variable Namethread_cache_size
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default0
    Range0 .. 16384

    How many threads the server should cache for reuse. When a client disconnects, the client's threads are put in the cache if there are fewer than thread_cache_size threads there. Requests for threads are satisfied by reusing threads taken from the cache if possible, and only when the cache is empty is a new thread created. This variable can be increased to improve performance if you have a lot of new connections. Normally, this does not provide a notable performance improvement if you have a good thread implementation. However, if your server sees hundreds of connections per second you should normally set thread_cache_size high enough so that most new connections use cached threads. By examining the difference between the Connections and Threads_created status variables, you can see how efficient the thread cache is. For details, see Section 5.1.5, “Server Status Variables”.

  • thread_concurrency

    Command-Line Format--thread_concurrency=#
    Option-File Formatthread_concurrency
    Option Sets VariableYes, thread_concurrency
    Variable Namethread_concurrency
    Variable ScopeGlobal
    Dynamic VariableNo
    Deprecated5.6.1
     Permitted Values
    Typenumeric
    Default10
    Range1 .. 512

    This variable is specific to Solaris systems, for which mysqld invokes the thr_setconcurrency() with the variable value. This function enables applications to give the threads system a hint about the desired number of threads that should be run at the same time.

  • thread_handling

    Command-Line Format--thread_handling=name
    Option-File Formatthread_handling=name
    Option Sets VariableYes, thread_handling
    Variable Namethread_handling
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values (<= 5.5.13)
    Typeenumeration
    Valid Values

    no-threads

    one-thread-per-connection

     Permitted Values (>= 5.5.16)
    Typeenumeration
    Valid Values

    no-threads

    one-thread-per-connection

    dynamically-loaded

    The thread-handling model used by the server for connection threads. The permissible user-settable values are no-threads (the server uses a single thread) and one-thread-per-connection (the server uses one thread to handle each client connection; this is the default). no-threads is useful for debugging under Linux; see the Porting chapter of the MySQL Internals manual.

    If the thread pool plugin is enabled, the server sets the thread_handling value to dynamically-loaded. See Section 7.11.6.1, “Thread Pool Components and Installation”.

  • thread_pool_algorithm

    Version Introduced5.5.16
    Command-Line Format--thread_pool_algorithm=#
    Option-File Formatthread_pool_algorithm=#
    Option Sets VariableYes, thread_pool_algorithm
    Variable Namethread_pool_algorithm
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default0
    Range0 .. 1

    This variable controls which algorithm the thread pool plugin uses:

    • A value of 0 (the default) uses a conservative low-concurrency algorithm which is most well tested and is known to produce very good results.

    • A value of 1 increases the concurrency and uses a more aggressive algorithm which at times has been known to perform 5–10% better on optimal thread counts, but has degrading performance as the number of connections increases. Its use should be considered as experimental and not supported.

      This variable was added in MySQL 5.5.16. It is available only if the thread pool plugin is enabled. See Section 7.11.6, “The Thread Pool Plugin”

  • thread_pool_high_priority_connection

    Version Introduced5.5.16
    Command-Line Format--thread_pool_high_priority_connection=#
    Option-File Formatthread_pool_high_priority_connection=#
    Option Sets VariableYes, thread_pool_high_priority_connection
    Variable Namethread_pool_high_priority_connection
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default0
    Range0 .. 1

    This variable affects queuing of new statements prior to execution. If the value is 0 (false, the default), statement queuing uses both the low-priority and high-priority queues. If the value is 1 (true), queued statements always go to the high-priority queue.

    This variable was added in MySQL 5.5.16. It is available only if the thread pool plugin is enabled. See Section 7.11.6, “The Thread Pool Plugin”

  • thread_pool_max_unused_threads

    Version Introduced5.5.16
    Command-Line Format--thread_pool_max_unused_threads=#
    Option-File Formatthread_pool_max_unused_threads=#
    Option Sets VariableYes, thread_pool_max_unused_threads
    Variable Namethread_pool_max_unused_threads
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default0
    Range0 .. 4096

    The maximum permitted number of unused threads in the thread pool. This variable makes it possible to limit the amount of memory used by sleeping threads.

    A value of 0 (the default) means no limit on the number of sleeping threads. A value of N where N is greater than 0 means 1 consumer thread and N–1 reserve threads. In this case, if a thread is ready to sleep but the number of sleeping threads is already at the maximum, the thread exits rather than going to sleep.

    A sleeping thread is either sleeping as a consumer thread or a reserve thread. The thread pool permits one thread to be the consumer thread when sleeping. If a thread goes to sleep and there is no existing consumer thread, it will sleep as a consumer thread. When a thread must be woken up, a consumer thread is selected if there is one. A reserve thread is selected only when there is no consumer thread to wake up.

    This variable was added in MySQL 5.5.16. It is available only if the thread pool plugin is enabled. See Section 7.11.6, “The Thread Pool Plugin”

  • thread_pool_prio_kickup_timer

    Version Introduced5.5.16
    Command-Line Format--thread_pool_prio_kickup_timer=#
    Option-File Formatthread_pool_prio_kickup_timer=#
    Option Sets VariableYes, thread_pool_prio_kickup_timer
    Variable Namethread_pool_prio_kickup_timer
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default1000
    Range0 .. 4294967294

    This variable affects statements waiting for execution in the low-priority queue. The value is the number of milliseconds before a waiting statement is moved to the high-priority queue. The default is 1000 (1 second). The range of values is 0 to 232 – 2.

    This variable was added in MySQL 5.5.16. It is available only if the thread pool plugin is enabled. See Section 7.11.6, “The Thread Pool Plugin”

  • thread_pool_size

    Version Introduced5.5.16
    Command-Line Format--thread_pool_size=#
    Option-File Formatthread_pool_size=#
    Option Sets VariableYes, thread_pool_size
    Variable Namethread_pool_size
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default16
    Range1 .. 64

    The number of thread groups in the thread pool. This is the most important parameter controlling thread pool performance. It affects how many statements can execute simultaneously. The default value is 16, with a range from 1 to 64 of permissible values. If a value outside this range is specified, the thread pool plugin does not load and the server writes a message to the error log.

    This variable was added in MySQL 5.5.16. It is available only if the thread pool plugin is enabled. See Section 7.11.6, “The Thread Pool Plugin”

  • thread_pool_stall_limit

    Version Introduced5.5.16
    Command-Line Format--thread_pool_stall_limit=#
    Option-File Formatthread_pool_stall_limit=#
    Option Sets VariableYes, thread_pool_stall_limit
    Variable Namethread_pool_stall_limit
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default6
    Range4 .. 600

    This variable affects executing statements. The value is the amount of time a statement has to finish after starting to execute before it becomes defined as stalled, at which point the thread pool permits the thread group to begin executing another statement. The value is measured in 10 millisecond units, so a value of 6 (the default) means 60ms. The range of values is 4 to 600 (40ms to 6s). Short wait values permit threads to start more quickly. Short values are also better for avoiding deadlock situations. Long wait values are useful for workloads that include long-running statements, to avoid starting too many new statements while the current ones execute.

    This variable was added in MySQL 5.5.16. It is available only if the thread pool plugin is enabled. See Section 7.11.6, “The Thread Pool Plugin”

  • thread_stack

    Command-Line Format--thread_stack=#
    Option-File Formatthread_stack
    Option Sets VariableYes, thread_stack
    Variable Namethread_stack
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default196608
    Range131072 .. 4294967295
    Block Size1024
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default262144
    Range131072 .. 18446744073709547520
    Block Size1024

    The stack size for each thread. Many of the limits detected by the crash-me test are dependent on this value. See Section 7.12.2, “The MySQL Benchmark Suite”. The default of 192KB (256KB for 64-bit systems) is large enough for normal operation. If the thread stack size is too small, it limits the complexity of the SQL statements that the server can handle, the recursion depth of stored procedures, and other memory-consuming actions.

  • time_format

    This variable is unused.

  • time_zone

    Command-Line Format--default_time_zone=string
    Option-File Formatdefault_time_zone
    Variable Nametime_zone
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring

    The current time zone. This variable is used to initialize the time zone for each client that connects. By default, the initial value of this is 'SYSTEM' (which means, “use the value of system_time_zone”). The value can be specified explicitly at server startup with the --default-time-zone option. See Section 9.6, “MySQL Server Time Zone Support”.

  • timed_mutexes

    Command-Line Format--timed_mutexes
    Option-File Formattimed_mutexes
    Option Sets VariableYes, timed_mutexes
    Variable Nametimed_mutexes
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    This variable controls whether InnoDB mutexes are timed. If this variable is set to 0 or OFF (the default), mutex timing is disabled. If the variable is set to 1 or ON, mutex timing is enabled. With timing enabled, the os_wait_times value in the output from SHOW ENGINE INNODB MUTEX indicates the amount of time (in ms) spent in operating system waits. Otherwise, the value is 0.

  • timestamp = {timestamp_value | DEFAULT}

    Set the time for this client. This is used to get the original timestamp if you use the binary log to restore rows. timestamp_value should be a Unix epoch timestamp, not a MySQL timestamp.

    SET timestamp affects the value returned by NOW() but not by SYSDATE(). This means that timestamp settings in the binary log have no effect on invocations of SYSDATE(). The server can be started with the --sysdate-is-now option to cause SYSDATE() to be an alias for NOW(), in which case SET timestamp affects both functions.

  • tmp_table_size

    Command-Line Format--tmp_table_size=#
    Option-File Formattmp_table_size
    Option Sets VariableYes, tmp_table_size
    Variable Nametmp_table_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Defaultsystem dependent
    Range1024 .. 4294967295

    The maximum size of internal in-memory temporary tables. (The actual limit is determined as the minimum of tmp_table_size and max_heap_table_size.) If an in-memory temporary table exceeds the limit, MySQL automatically converts it to an on-disk MyISAM table. Increase the value of tmp_table_size (and max_heap_table_size if necessary) if you do many advanced GROUP BY queries and you have lots of memory. This variable does not apply to user-created MEMORY tables.

    You can compare the number of internal on-disk temporary tables created to the total number of internal temporary tables created by comparing the values of the Created_tmp_disk_tables and Created_tmp_tables variables.

    See also Section 7.4.3.3, “How MySQL Uses Internal Temporary Tables”.

  • tmpdir

    Command-Line Format--tmpdir=path
    -t
    Option-File Formattmpdir
    Option Sets VariableYes, tmpdir
    Variable Nametmpdir
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

    The directory used for temporary files and temporary tables. This variable can be set to a list of several paths that are used in round-robin fashion. Paths should be separated by colon characters (“:”) on Unix and semicolon characters (“;”) on Windows.

    The multiple-directory feature can be used to spread the load between several physical disks. If the MySQL server is acting as a replication slave, you should not set tmpdir to point to a directory on a memory-based file system or to a directory that is cleared when the server host restarts. A replication slave needs some of its temporary files to survive a machine restart so that it can replicate temporary tables or LOAD DATA INFILE operations. If files in the temporary file directory are lost when the server restarts, replication fails. You can set the slave's temporary directory using the slave_load_tmpdir variable. In that case, the slave will not use the general tmpdir value and you can set tmpdir to a nonpermanent location.

  • transaction_alloc_block_size

    Command-Line Format--transaction_alloc_block_size=#
    Option-File Formattransaction_alloc_block_size
    Option Sets VariableYes, transaction_alloc_block_size
    Variable Nametransaction_alloc_block_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default8192
    Range1024 .. 4294967295
    Block Size1024
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default8192
    Range1024 .. 18446744073709547520
    Block Size1024

    The amount in bytes by which to increase a per-transaction memory pool which needs memory. See the description of transaction_prealloc_size.

  • transaction_prealloc_size

    Command-Line Format--transaction_prealloc_size=#
    Option-File Formattransaction_prealloc_size
    Option Sets VariableYes, transaction_prealloc_size
    Variable Nametransaction_prealloc_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default4096
    Range1024 .. 4294967295
    Block Size1024
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default4096
    Range1024 .. 18446744073709547520
    Block Size1024

    There is a per-transaction memory pool from which various transaction-related allocations take memory. The initial size of the pool in bytes is transaction_prealloc_size. For every allocation that cannot be satisfied from the pool because it has insufficient memory available, the pool is increased by transaction_alloc_block_size bytes. When the transaction ends, the pool is truncated to transaction_prealloc_size bytes.

    By making transaction_prealloc_size sufficiently large to contain all statements within a single transaction, you can avoid many malloc() calls.

  • tx_isolation

    Variable Nametx_isolation
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeenumeration
    DefaultREPEATABLE-READ
    Valid Values

    READ-UNCOMMITTED

    READ-COMMITTED

    REPEATABLE-READ

    SERIALIZABLE

    The default transaction isolation level. Defaults to REPEATABLE-READ.

    This variable is set by the SET TRANSACTION ISOLATION LEVEL statement. See Section 12.3.6, “SET TRANSACTION Синтаксис”. If you set tx_isolation directly to an isolation level name that contains a space, the name should be enclosed within quotation marks, with the space replaced by a dash. For example:

    SET tx_isolation = 'READ-COMMITTED';

    Any unique prefix of a valid value may be used to set the value of this variable.

    The default transactional isolation level can also be set at startup using the --transaction-isolation server option.

  • unique_checks

    Variable Nameunique_checks
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    Default1

    If set to 1 (the default), uniqueness checks for secondary indexes in InnoDB tables are performed. If set to 0, storage engines are permitted to assume that duplicate keys are not present in input data. If you know for certain that your data does not contain uniqueness violations, you can set this to 0 to speed up large table imports to InnoDB.

    Note that setting this variable to 0 does not require storage engines to ignore duplicate keys. An engine is still permitted to check for them and issue duplicate-key errors if it detects them.

  • updatable_views_with_limit

    Command-Line Format--updatable_views_with_limit=#
    Option-File Formatupdatable_views_with_limit
    Option Sets VariableYes, updatable_views_with_limit
    Variable Nameupdatable_views_with_limit
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    Default1

    This variable controls whether updates to a view can be made when the view does not contain all columns of the primary key defined in the underlying table, if the update statement contains a LIMIT clause. (Such updates often are generated by GUI tools.) An update is an UPDATE or DELETE statement. Primary key here means a PRIMARY KEY, or a UNIQUE index in which no column can contain NULL.

    The variable can have two values:

    • 1 or YES: Issue a warning only (not an error message). This is the default value.

    • 0 or NO: Prohibit the update.

  • version

    The version number for the server. The value might also include a suffix indicating server build or configuration information. -log indicates that one or more of the general log, slow query log, or binary log are enabled. -debug indicates that the server was built with debugging support enabled.

  • version_comment

    Variable Nameversion_comment
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring

    The CMake configuration program has a WITH_COMMENT option that permits a comment to be specified when building MySQL. This variable contains the value of that comment. See Section 2.9.4, “MySQL Source-Configuration Options”.

  • version_compile_machine

    Variable Nameversion_compile_machine
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring

    The type of machine or architecture on which MySQL was built.

  • version_compile_os

    Variable Nameversion_compile_os
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring

    The type of operating system on which MySQL was built.

  • wait_timeout

    Command-Line Format--wait_timeout=#
    Option-File Formatwait_timeout
    Option Sets VariableYes, wait_timeout
    Variable Namewait_timeout
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default28800
    Range1 .. 31536000
     Permitted Values
    Type (windows)numeric
    Default28800
    Range1 .. 2147483

    The number of seconds the server waits for activity on a noninteractive connection before closing it.

    On thread startup, the session wait_timeout value is initialized from the global wait_timeout value or from the global interactive_timeout value, depending on the type of client (as defined by the CLIENT_INTERACTIVE connect option to mysql_real_connect()). See also interactive_timeout.

  • warning_count

    The number of errors, warnings, and notes that resulted from the last statement that generated messages. This variable is read only. See Section 12.7.5.41, “SHOW WARNINGS Синтаксис”.

5.1.4. Using System Variables

The MySQL server maintains many system variables that indicate how it is configured. Section 5.1.3, “Server System Variables”, describes the meaning of these variables. Each system variable has a default value. System variables can be set at server startup using options on the command line or in an option file. Most of them can be changed dynamically while the server is running by means of the SET statement, which enables you to modify operation of the server without having to stop and restart it. You can refer to system variable values in expressions.

The server maintains two kinds of system variables. Global variables affect the overall operation of the server. Session variables affect its operation for individual client connections. A given system variable can have both a global and a session value. Global and session system variables are related as follows:

  • When the server starts, it initializes all global variables to their default values. These defaults can be changed by options specified on the command line or in an option file. (See Section 4.2.3, “Specifying Program Options”.)

  • The server also maintains a set of session variables for each client that connects. The client's session variables are initialized at connect time using the current values of the corresponding global variables. For example, the client's SQL mode is controlled by the session sql_mode value, which is initialized when the client connects to the value of the global sql_mode value.

System variable values can be set globally at server startup by using options on the command line or in an option file. When you use a startup option to set a variable that takes a numeric value, the value can be given with a suffix of K, M, or G (either uppercase or lowercase) to indicate a multiplier of 1024, 10242 or 10243; that is, units of kilobytes, megabytes, or gigabytes, respectively. Thus, the following command starts the server with a query cache size of 16 megabytes and a maximum packet size of one gigabyte:

mysqld --query_cache_size=16M --max_allowed_packet=1G

Within an option file, those variables are set like this:

[mysqld]
query_cache_size=16M
max_allowed_packet=1G

The lettercase of suffix letters does not matter; 16M and 16m are equivalent, as are 1G and 1g.

If you want to restrict the maximum value to which a system variable can be set at runtime with the SET statement, you can specify this maximum by using an option of the form --maximum-var_name=value at server startup. For example, to prevent the value of query_cache_size from being increased to more than 32MB at runtime, use the option --maximum-query_cache_size=32M.

Many system variables are dynamic and can be changed while the server runs by using the SET statement. For a list, see Section 5.1.4.2, “Dynamic System Variables”. To change a system variable with SET, refer to it as var_name, optionally preceded by a modifier:

  • To indicate explicitly that a variable is a global variable, precede its name by GLOBAL or @@global.. The SUPER privilege is required to set global variables.

  • To indicate explicitly that a variable is a session variable, precede its name by SESSION, @@session., or @@. Setting a session variable requires no special privilege, but a client can change only its own session variables, not those of any other client.

  • LOCAL and @@local. are synonyms for SESSION and @@session..

  • If no modifier is present, SET changes the session variable.

A SET statement can contain multiple variable assignments, separated by commas. If you set several system variables, the most recent GLOBAL or SESSION modifier in the statement is used for following variables that have no modifier specified.

Examples:

SET sort_buffer_size=10000;
SET @@local.sort_buffer_size=10000;
SET GLOBAL sort_buffer_size=1000000, SESSION sort_buffer_size=1000000;
SET @@sort_buffer_size=1000000;
SET @@global.sort_buffer_size=1000000, @@local.sort_buffer_size=1000000;

The @@var_name syntax for system variables is supported for compatibility with some other database systems.

If you change a session system variable, the value remains in effect until your session ends or until you change the variable to a different value. The change is not visible to other clients.

If you change a global system variable, the value is remembered and used for new connections until the server restarts. (To make a global system variable setting permanent, you should set it in an option file.) The change is visible to any client that accesses that global variable. However, the change affects the corresponding session variable only for clients that connect after the change. The global variable change does not affect the session variable for any client that is currently connected (not even that of the client that issues the SET GLOBAL statement).

To prevent incorrect usage, MySQL produces an error if you use SET GLOBAL with a variable that can only be used with SET SESSION or if you do not specify GLOBAL (or @@global.) when setting a global variable.

To set a SESSION variable to the GLOBAL value or a GLOBAL value to the compiled-in MySQL default value, use the DEFAULT keyword. For example, the following two statements are identical in setting the session value of max_join_size to the global value:

SET max_join_size=DEFAULT;
SET @@session.max_join_size=@@global.max_join_size;

Not all system variables can be set to DEFAULT. In such cases, use of DEFAULT results in an error.

You can refer to the values of specific global or session system variables in expressions by using one of the @@-modifiers. For example, you can retrieve values in a SELECT statement like this:

SELECT @@global.sql_mode, @@session.sql_mode, @@sql_mode;

When you refer to a system variable in an expression as @@var_name (that is, when you do not specify @@global. or @@session.), MySQL returns the session value if it exists and the global value otherwise. (This differs from SET @@var_name = value, which always refers to the session value.)

Замечание

Some variables displayed by SHOW VARIABLES may not be available using SELECT @@var_name syntax; an Unknown system variable occurs. As a workaround in such cases, you can use SHOW VARIABLES LIKE 'var_name'.

Suffixes for specifying a value multiplier can be used when setting a variable at server startup, but not to set the value with SET at runtime. On the other hand, with SET you can assign a variable's value using an expression, which is not true when you set a variable at server startup. For example, the first of the following lines is legal at server startup, but the second is not:

shell> mysql --max_allowed_packet=16M
shell> mysql --max_allowed_packet=16*1024*1024

Conversely, the second of the following lines is legal at runtime, but the first is not:

mysql> SET GLOBAL max_allowed_packet=16M;
mysql> SET GLOBAL max_allowed_packet=16*1024*1024;
Замечание

Some system variables can be enabled with the SET statement by setting them to ON or 1, or disabled by setting them to OFF or 0. However, to set such a variable on the command line or in an option file, you must set it to 1 or 0; setting it to ON or OFF will not work. For example, on the command line, --delay_key_write=1 works but --delay_key_write=ON does not.

To display system variable names and values, use the SHOW VARIABLES statement:

mysql> SHOW VARIABLES;
+---------------------------------+-----------------------------------+
| Variable_name                   | Value                             |
+---------------------------------+-----------------------------------+
| auto_increment_increment        | 1                                 |
| auto_increment_offset           | 1                                 |
| automatic_sp_privileges         | ON                                |
| back_log                        | 50                                |
| basedir                         | /home/mysql/                      |
| binlog_cache_size               | 32768                             |
| bulk_insert_buffer_size         | 8388608                           |
| character_set_client            | latin1                            |
| character_set_connection        | latin1                            |
| character_set_database          | latin1                            |
| character_set_results           | latin1                            |
| character_set_server            | latin1                            |
| character_set_system            | utf8                              |
| character_sets_dir              | /home/mysql/share/mysql/charsets/ |
| collation_connection            | latin1_swedish_ci                 |
| collation_database              | latin1_swedish_ci                 |
| collation_server                | latin1_swedish_ci                 |
...
| innodb_additional_mem_pool_size | 1048576                           |
| innodb_autoextend_increment     | 8                                 |
| innodb_buffer_pool_size         | 8388608                           |
| innodb_checksums                | ON                                |
| innodb_commit_concurrency       | 0                                 |
| innodb_concurrency_tickets      | 500                               |
| innodb_data_file_path           | ibdata1:10M:autoextend            |
| innodb_data_home_dir            |                                   |
...
| version                         | 5.1.6-alpha-log                   |
| version_comment                 | Source distribution               |
| version_compile_machine         | i686                              |
| version_compile_os              | suse-linux                        |
| wait_timeout                    | 28800                             |
+---------------------------------+-----------------------------------+

With a LIKE clause, the statement displays only those variables that match the pattern. To obtain a specific variable name, use a LIKE clause as shown:

SHOW VARIABLES LIKE 'max_join_size';
SHOW SESSION VARIABLES LIKE 'max_join_size';

To get a list of variables whose name match a pattern, use the “%” wildcard character in a LIKE clause:

SHOW VARIABLES LIKE '%size%';
SHOW GLOBAL VARIABLES LIKE '%size%';

Wildcard characters can be used in any position within the pattern to be matched. Strictly speaking, because “_” is a wildcard that matches any single character, you should escape it as “\_” to match it literally. In practice, this is rarely necessary.

For SHOW VARIABLES, if you specify neither GLOBAL nor SESSION, MySQL returns SESSION values.

The reason for requiring the GLOBAL keyword when setting GLOBAL-only variables but not when retrieving them is to prevent problems in the future. If we were to remove a SESSION variable that has the same name as a GLOBAL variable, a client with the SUPER privilege might accidentally change the GLOBAL variable rather than just the SESSION variable for its own connection. If we add a SESSION variable with the same name as a GLOBAL variable, a client that intends to change the GLOBAL variable might find only its own SESSION variable changed.

5.1.4.1. Structured System Variables

A structured variable differs from a regular system variable in two respects:

  • Its value is a structure with components that specify server parameters considered to be closely related.

  • There might be several instances of a given type of structured variable. Each one has a different name and refers to a different resource maintained by the server.

MySQL 5.5 supports one structured variable type, which specifies parameters governing the operation of key caches. A key cache structured variable has these components:

This section describes the syntax for referring to structured variables. Key cache variables are used for syntax examples, but specific details about how key caches operate are found elsewhere, in Section 7.9.2, “The MyISAM Key Cache”.

To refer to a component of a structured variable instance, you can use a compound name in instance_name.component_name format. Examples:

hot_cache.key_buffer_size
hot_cache.key_cache_block_size
cold_cache.key_cache_block_size

For each structured system variable, an instance with the name of default is always predefined. If you refer to a component of a structured variable without any instance name, the default instance is used. Thus, default.key_buffer_size and key_buffer_size both refer to the same system variable.

Structured variable instances and components follow these naming rules:

  • For a given type of structured variable, each instance must have a name that is unique within variables of that type. However, instance names need not be unique across structured variable types. For example, each structured variable has an instance named default, so default is not unique across variable types.

  • The names of the components of each structured variable type must be unique across all system variable names. If this were not true (that is, if two different types of structured variables could share component member names), it would not be clear which default structured variable to use for references to member names that are not qualified by an instance name.

  • If a structured variable instance name is not legal as an unquoted identifier, refer to it as a quoted identifier using backticks. For example, hot-cache is not legal, but `hot-cache` is.

  • global, session, and local are not legal instance names. This avoids a conflict with notation such as @@global.var_name for referring to nonstructured system variables.

Currently, the first two rules have no possibility of being violated because the only structured variable type is the one for key caches. These rules will assume greater significance if some other type of structured variable is created in the future.

With one exception, you can refer to structured variable components using compound names in any context where simple variable names can occur. For example, you can assign a value to a structured variable using a command-line option:

shell> mysqld --hot_cache.key_buffer_size=64K

In an option file, use this syntax:

[mysqld]
hot_cache.key_buffer_size=64K

If you start the server with this option, it creates a key cache named hot_cache with a size of 64KB in addition to the default key cache that has a default size of 8MB.

Suppose that you start the server as follows:

shell> mysqld --key_buffer_size=256K \
         --extra_cache.key_buffer_size=128K \
         --extra_cache.key_cache_block_size=2048

In this case, the server sets the size of the default key cache to 256KB. (You could also have written --default.key_buffer_size=256K.) In addition, the server creates a second key cache named extra_cache that has a size of 128KB, with the size of block buffers for caching table index blocks set to 2048 bytes.

The following example starts the server with three different key caches having sizes in a 3:1:1 ratio:

shell> mysqld --key_buffer_size=6M \
         --hot_cache.key_buffer_size=2M \
         --cold_cache.key_buffer_size=2M

Structured variable values may be set and retrieved at runtime as well. For example, to set a key cache named hot_cache to a size of 10MB, use either of these statements:

mysql> SET GLOBAL hot_cache.key_buffer_size = 10*1024*1024;
mysql> SET @@global.hot_cache.key_buffer_size = 10*1024*1024;

To retrieve the cache size, do this:

mysql> SELECT @@global.hot_cache.key_buffer_size;

However, the following statement does not work. The variable is not interpreted as a compound name, but as a simple string for a LIKE pattern-matching operation:

mysql> SHOW GLOBAL VARIABLES LIKE 'hot_cache.key_buffer_size';

This is the exception to being able to use structured variable names anywhere a simple variable name may occur.

5.1.4.2. Dynamic System Variables

Many server system variables are dynamic and can be set at runtime using SET GLOBAL or SET SESSION. You can also obtain their values using SELECT. See Section 5.1.4, “Using System Variables”.

The following table shows the full list of all dynamic system variables. The last column indicates for each variable whether GLOBAL or SESSION (or both) apply. The table also lists session options that can be set with the SET statement. Section 5.1.3, “Server System Variables”, discusses these options.

Variables that have a type of “string” take a string value. Variables that have a type of “numeric” take a numeric value. Variables that have a type of “boolean” can be set to 0, 1, ON or OFF. (If you set them on the command line or in an option file, use the numeric values.) Variables that are marked as “enumeration” normally should be set to one of the available values for the variable, but can also be set to the number that corresponds to the desired enumeration value. For enumerated system variables, the first enumeration value corresponds to 0. This differs from ENUM columns, for which the first enumeration value corresponds to 1.

Table 5.3. Dynamic Variable Summary

Variable NameVariable TypeVariable Scope
auto_increment_incrementnumericGLOBAL | SESSION
auto_increment_offsetnumericGLOBAL | SESSION
autocommitbooleanGLOBAL | SESSION
automatic_sp_privilegesbooleanGLOBAL
big_tablesbooleanGLOBAL | SESSION
binlog_cache_sizenumericGLOBAL
binlog_direct_non_transactional_updatesbooleanGLOBAL | SESSION
binlog_formatenumerationGLOBAL | SESSION
binlog_stmt_cache_sizenumericGLOBAL
bulk_insert_buffer_sizenumericGLOBAL | SESSION
character_set_clientstringGLOBAL | SESSION
character_set_connectionstringGLOBAL | SESSION
character_set_databasestringGLOBAL | SESSION
character_set_filesystemstringGLOBAL | SESSION
character_set_resultsstringGLOBAL | SESSION
character_set_serverstringGLOBAL | SESSION
collation_connectionstringGLOBAL | SESSION
collation_databasestringGLOBAL | SESSION
collation_serverstringGLOBAL | SESSION
completion_typenumericGLOBAL | SESSION
concurrent_insertbooleanGLOBAL
connect_timeoutnumericGLOBAL
debugstringGLOBAL | SESSION
debug_syncstringSESSION
default_storage_engineenumerationGLOBAL | SESSION
default_week_formatnumericGLOBAL | SESSION
delay_key_writeenumerationGLOBAL
delayed_insert_limitnumericGLOBAL
delayed_insert_timeoutnumericGLOBAL
delayed_queue_sizenumericGLOBAL
div_precision_incrementnumericGLOBAL | SESSION
engine_condition_pushdownbooleanGLOBAL | SESSION
event_schedulerenumerationGLOBAL
expire_logs_daysnumericGLOBAL
flushbooleanGLOBAL
flush_timenumericGLOBAL
foreign_key_checksbooleanGLOBAL | SESSION
ft_boolean_syntaxstringGLOBAL
general_logbooleanGLOBAL
general_log_filefilenameGLOBAL
group_concat_max_lennumericGLOBAL | SESSION
identitynumericSESSION
init_connectstringGLOBAL
init_slavestringGLOBAL
innodb_adaptive_flushingbooleanGLOBAL
innodb_adaptive_hash_indexbooleanGLOBAL
innodb_autoextend_incrementnumericGLOBAL
innodb_change_bufferingenumerationGLOBAL
innodb_commit_concurrencynumericGLOBAL
innodb_concurrency_ticketsnumericGLOBAL
innodb_fast_shutdownnumericGLOBAL
innodb_file_formatstringGLOBAL
innodb_file_format_maxstringGLOBAL
innodb_file_per_tablebooleanGLOBAL
innodb_flush_log_at_trx_commitenumerationGLOBAL
innodb_io_capacitynumericGLOBAL
innodb_large_prefixbooleanGLOBAL
innodb_lock_wait_timeoutnumericGLOBAL | SESSION
innodb_max_dirty_pages_pctnumericGLOBAL
innodb_max_purge_lagnumericGLOBAL
innodb_old_blocks_pctnumericGLOBAL
innodb_old_blocks_timenumericGLOBAL
innodb_read_ahead_thresholdnumericGLOBAL
innodb_replication_delaynumericGLOBAL
innodb_rollback_segmentsnumericGLOBAL
innodb_spin_wait_delaynumericGLOBAL
innodb_stats_methodenumerationGLOBAL | SESSION
innodb_stats_on_metadatabooleanGLOBAL
innodb_stats_sample_pagesnumericGLOBAL
innodb_strict_modebooleanGLOBAL | SESSION
innodb_support_xabooleanGLOBAL | SESSION
innodb_sync_spin_loopsnumericGLOBAL
innodb_table_locksbooleanGLOBAL | SESSION
innodb_thread_concurrencynumericGLOBAL
innodb_thread_sleep_delaynumericGLOBAL
insert_idnumericSESSION
interactive_timeoutnumericGLOBAL | SESSION
join_buffer_sizenumericGLOBAL | SESSION
keep_files_on_createbooleanGLOBAL | SESSION
key_buffer_sizenumericGLOBAL
key_cache_age_thresholdnumericGLOBAL
key_cache_block_sizenumericGLOBAL
key_cache_division_limitnumericGLOBAL
last_insert_idnumericSESSION
lc_messagesstringGLOBAL | SESSION
lc_time_namesstringGLOBAL | SESSION
local_infilebooleanGLOBAL
lock_wait_timeoutnumericGLOBAL | SESSION
logstringGLOBAL
log_bin_trust_function_creatorsbooleanGLOBAL
log_bin_trust_routine_creatorsbooleanGLOBAL
log_outputsetGLOBAL
log_queries_not_using_indexesbooleanGLOBAL
log_slow_queriesbooleanGLOBAL
log_warningsnumericGLOBAL | SESSION
long_query_timenumericGLOBAL | SESSION
low_priority_updatesbooleanGLOBAL | SESSION
max_allowed_packetnumericGLOBAL
max_binlog_cache_sizenumericGLOBAL
max_binlog_sizenumericGLOBAL
max_binlog_stmt_cache_sizenumericGLOBAL
max_connect_errorsnumericGLOBAL
max_connectionsnumericGLOBAL
max_delayed_threadsnumericGLOBAL | SESSION
max_error_countnumericGLOBAL | SESSION
max_heap_table_sizenumericGLOBAL | SESSION
max_insert_delayed_threadsnumericGLOBAL | SESSION
max_join_sizenumericGLOBAL | SESSION
max_length_for_sort_datanumericGLOBAL | SESSION
max_prepared_stmt_countnumericGLOBAL
max_relay_log_sizenumericGLOBAL
max_seeks_for_keynumericGLOBAL | SESSION
max_sort_lengthnumericGLOBAL | SESSION
max_sp_recursion_depthnumericGLOBAL | SESSION
max_tmp_tablesnumericGLOBAL | SESSION
max_user_connectionsnumericGLOBAL | SESSION
max_write_lock_countnumericGLOBAL
min_examined_row_limitnumericGLOBAL | SESSION
myisam_data_pointer_sizenumericGLOBAL
myisam_max_sort_file_sizenumericGLOBAL
myisam_repair_threadsnumericGLOBAL | SESSION
myisam_sort_buffer_sizenumericGLOBAL | SESSION
myisam_stats_methodenumerationGLOBAL | SESSION
myisam_use_mmapbooleanGLOBAL
ndb_autoincrement_prefetch_sznumericGLOBAL | SESSION
ndb_blob_read_batch_bytesnumericGLOBAL | SESSION
ndb_blob_write_batch_bytesnumericGLOBAL | SESSION
ndb_cache_check_timenumericGLOBAL
ndb_deferred_constraintsbooleanGLOBAL | SESSION
ndb_deferred_constraintsbooleanGLOBAL | SESSION
ndb_distribution={KEYHASH|LINHASH}enumerationGLOBAL | SESSION
ndb_distributionenumerationGLOBAL | SESSION
ndb_extra_loggingnumericGLOBAL
ndb_force_sendbooleanGLOBAL | SESSION
ndb_log_binbooleanGLOBAL | SESSION
ndb_log_binlog_indexbooleanGLOBAL
ndb_log_empty_epochsbooleanGLOBAL
ndb_log_empty_epochsbooleanGLOBAL
ndb_log_update_as_writebooleanGLOBAL
ndb_log_updated_onlybooleanGLOBAL
ndb_optimization_delaynumericGLOBAL
ndb_table_no_loggingbooleanSESSION
ndb_table_temporarybooleanSESSION
ndb_use_exact_countbooleanGLOBAL | SESSION
ndb_use_transactionsbooleanGLOBAL | SESSION
ndbinfo_max_bytesnumericGLOBAL | SESSION
ndbinfo_max_rowsnumericGLOBAL | SESSION
ndbinfo_show_hiddenbooleanGLOBAL | SESSION
ndbinfo_table_prefixstringGLOBAL | SESSION
net_buffer_lengthnumericGLOBAL | SESSION
net_read_timeoutnumericGLOBAL | SESSION
net_retry_countnumericGLOBAL | SESSION
net_write_timeoutnumericGLOBAL | SESSION
newbooleanGLOBAL | SESSION
old_alter_tablebooleanGLOBAL | SESSION
old_passwordsbooleanGLOBAL | SESSION
optimizer_prune_levelbooleanGLOBAL | SESSION
optimizer_search_depthnumericGLOBAL | SESSION
optimizer_switchsetGLOBAL | SESSION
preload_buffer_sizenumericGLOBAL | SESSION
profilingbooleanGLOBAL | SESSION
profiling_history_sizenumericGLOBAL | SESSION
pseudo_thread_idnumericSESSION
query_alloc_block_sizenumericGLOBAL | SESSION
query_cache_limitnumericGLOBAL
query_cache_min_res_unitnumericGLOBAL
query_cache_sizenumericGLOBAL
query_cache_typeenumerationGLOBAL | SESSION
query_cache_wlock_invalidatebooleanGLOBAL | SESSION
query_prealloc_sizenumericGLOBAL | SESSION
rand_seed1numericSESSION
rand_seed2numericSESSION
range_alloc_block_sizenumericGLOBAL | SESSION
read_buffer_sizenumericGLOBAL | SESSION
read_onlynumericGLOBAL
read_rnd_buffer_sizenumericGLOBAL | SESSION
relay_log_purgebooleanGLOBAL
relay_log_recoverybooleanGLOBAL
rpl_recovery_ranknumericGLOBAL
rpl_semi_sync_master_enabledbooleanGLOBAL
rpl_semi_sync_master_timeoutnumericGLOBAL
rpl_semi_sync_master_trace_levelnumericGLOBAL
rpl_semi_sync_master_wait_no_slavebooleanGLOBAL
rpl_semi_sync_slave_enabledbooleanGLOBAL
rpl_semi_sync_slave_trace_levelnumericGLOBAL
safe_show_databasebooleanGLOBAL
secure_authbooleanGLOBAL
server_idnumericGLOBAL
slave_allow_batchingbooleanGLOBAL
slave_compressed_protocolbooleanGLOBAL
slave_exec_modeenumerationGLOBAL
slave_net_timeoutnumericGLOBAL
slave_transaction_retriesnumericGLOBAL
slow_launch_timenumericGLOBAL
slow_query_logbooleanGLOBAL
slow_query_log_filefilenameGLOBAL
sort_buffer_sizenumericGLOBAL | SESSION
sql_auto_is_nullbooleanGLOBAL | SESSION
sql_big_selectsbooleanGLOBAL | SESSION
sql_big_tablesbooleanGLOBAL | SESSION
sql_buffer_resultbooleanGLOBAL | SESSION
sql_log_binbooleanGLOBAL | SESSION
sql_log_offbooleanGLOBAL | SESSION
sql_log_updatebooleanSESSION
sql_low_priority_updatesbooleanGLOBAL | SESSION
sql_max_join_sizenumericGLOBAL | SESSION
sql_modesetGLOBAL | SESSION
sql_notesbooleanGLOBAL | SESSION
sql_quote_show_createbooleanGLOBAL | SESSION
sql_safe_updatesbooleanGLOBAL | SESSION
sql_select_limitnumericGLOBAL | SESSION
sql_slave_skip_counternumericGLOBAL
sql_warningsbooleanGLOBAL | SESSION
storage_engineenumerationGLOBAL | SESSION
sync_binlognumericGLOBAL
sync_frmbooleanGLOBAL
sync_master_infonumericGLOBAL
sync_relay_lognumericGLOBAL
sync_relay_log_infonumericGLOBAL
table_definition_cachenumericGLOBAL
table_lock_wait_timeoutnumericGLOBAL
table_open_cachenumericGLOBAL
table_typeenumerationGLOBAL | SESSION
thread_cache_sizenumericGLOBAL
thread_pool_high_priority_connectionnumericGLOBAL | SESSION
thread_pool_max_unused_threadsnumericGLOBAL
thread_pool_prio_kickup_timernumericGLOBAL | SESSION
thread_pool_stall_limitnumericGLOBAL
time_zonestringGLOBAL | SESSION
timed_mutexesbooleanGLOBAL
timestampnumericSESSION
tmp_table_sizenumericGLOBAL | SESSION
transaction_alloc_block_sizenumericGLOBAL | SESSION
transaction_prealloc_sizenumericGLOBAL | SESSION
tx_isolationenumerationGLOBAL | SESSION
unique_checksbooleanGLOBAL | SESSION
updatable_views_with_limitbooleanGLOBAL | SESSION
wait_timeoutnumericGLOBAL | SESSION

5.1.5. Server Status Variables

The server maintains many status variables that provide information about its operation. You can view these variables and their values by using the SHOW [GLOBAL | SESSION] STATUS statement (see Section 12.7.5.36, “SHOW STATUS Синтаксис”). The optional GLOBAL keyword aggregates the values over all connections, and SESSION shows the values for the current connection.

mysql> SHOW GLOBAL STATUS;
+-----------------------------------+------------+
| Variable_name                     | Value      |
+-----------------------------------+------------+
| Aborted_clients                   | 0          |
| Aborted_connects                  | 0          |
| Bytes_received                    | 155372598  |
| Bytes_sent                        | 1176560426 |
...
| Connections                       | 30023      |
| Created_tmp_disk_tables           | 0          |
| Created_tmp_files                 | 3          |
| Created_tmp_tables                | 2          |
...
| Threads_created                   | 217        |
| Threads_running                   | 88         |
| Uptime                            | 1389872    |
+-----------------------------------+------------+

The following table lists all available server status variables:

Table 5.4. Status Variable Summary

Variable NameVariable TypeVariable Scope
Aborted_clientsnumericGLOBAL
Aborted_connectsnumericGLOBAL
Binlog_cache_disk_usenumericGLOBAL
Binlog_cache_usenumericGLOBAL
Binlog_stmt_cache_disk_usenumericGLOBAL
Binlog_stmt_cache_usenumericGLOBAL
Bytes_receivednumericGLOBAL | SESSION
Bytes_sentnumericGLOBAL | SESSION
Com_admin_commandsnumericGLOBAL | SESSION
Com_alter_dbnumericGLOBAL | SESSION
Com_alter_db_upgradenumericGLOBAL | SESSION
Com_alter_eventnumericGLOBAL | SESSION
Com_alter_functionnumericGLOBAL | SESSION
Com_alter_procedurenumericGLOBAL | SESSION
Com_alter_servernumericGLOBAL | SESSION
Com_alter_tablenumericGLOBAL | SESSION
Com_alter_tablespacenumericGLOBAL | SESSION
Com_analyzenumericGLOBAL | SESSION
Com_assign_to_keycachenumericGLOBAL | SESSION
Com_beginnumericGLOBAL | SESSION
Com_binlognumericGLOBAL | SESSION
Com_call_procedurenumericGLOBAL | SESSION
Com_change_dbnumericGLOBAL | SESSION
Com_change_masternumericGLOBAL | SESSION
Com_checknumericGLOBAL | SESSION
Com_checksumnumericGLOBAL | SESSION
Com_commitnumericGLOBAL | SESSION
Com_create_dbnumericGLOBAL | SESSION
Com_create_eventnumericGLOBAL | SESSION
Com_create_functionnumericGLOBAL | SESSION
Com_create_indexnumericGLOBAL | SESSION
Com_create_procedurenumericGLOBAL | SESSION
Com_create_servernumericGLOBAL | SESSION
Com_create_tablenumericGLOBAL | SESSION
Com_create_triggernumericGLOBAL | SESSION
Com_create_udfnumericGLOBAL | SESSION
Com_create_usernumericGLOBAL | SESSION
Com_create_viewnumericGLOBAL | SESSION
Com_dealloc_sqlnumericGLOBAL | SESSION
Com_deletenumericGLOBAL | SESSION
Com_delete_multinumericGLOBAL | SESSION
Com_donumericGLOBAL | SESSION
Com_drop_dbnumericGLOBAL | SESSION
Com_drop_eventnumericGLOBAL | SESSION
Com_drop_functionnumericGLOBAL | SESSION
Com_drop_indexnumericGLOBAL | SESSION
Com_drop_procedurenumericGLOBAL | SESSION
Com_drop_servernumericGLOBAL | SESSION
Com_drop_tablenumericGLOBAL | SESSION
Com_drop_triggernumericGLOBAL | SESSION
Com_drop_usernumericGLOBAL | SESSION
Com_drop_viewnumericGLOBAL | SESSION
Com_empty_querynumericGLOBAL | SESSION
Com_execute_sqlnumericGLOBAL | SESSION
Com_flushnumericGLOBAL | SESSION
Com_grantnumericGLOBAL | SESSION
Com_ha_closenumericGLOBAL | SESSION
Com_ha_opennumericGLOBAL | SESSION
Com_ha_readnumericGLOBAL | SESSION
Com_helpnumericGLOBAL | SESSION
Com_insertnumericGLOBAL | SESSION
Com_insert_selectnumericGLOBAL | SESSION
Com_install_pluginnumericGLOBAL | SESSION
Com_killnumericGLOBAL | SESSION
Com_loadnumericGLOBAL | SESSION
Com_lock_tablesnumericGLOBAL | SESSION
Com_optimizenumericGLOBAL | SESSION
Com_preload_keysnumericGLOBAL | SESSION
Com_prepare_sqlnumericGLOBAL | SESSION
Com_purgenumericGLOBAL | SESSION
Com_purge_before_datenumericGLOBAL | SESSION
Com_release_savepointnumericGLOBAL | SESSION
Com_rename_tablenumericGLOBAL | SESSION
Com_rename_usernumericGLOBAL | SESSION
Com_repairnumericGLOBAL | SESSION
Com_replacenumericGLOBAL | SESSION
Com_replace_selectnumericGLOBAL | SESSION
Com_resetnumericGLOBAL | SESSION
Com_resignalnumericGLOBAL | SESSION
Com_revokenumericGLOBAL | SESSION
Com_revoke_allnumericGLOBAL | SESSION
Com_rollbacknumericGLOBAL | SESSION
Com_rollback_to_savepointnumericGLOBAL | SESSION
Com_savepointnumericGLOBAL | SESSION
Com_selectnumericGLOBAL | SESSION
Com_set_optionnumericGLOBAL | SESSION
Com_show_authorsnumericGLOBAL | SESSION
Com_show_binlog_eventsnumericGLOBAL | SESSION
Com_show_binlogsnumericGLOBAL | SESSION
Com_show_charsetsnumericGLOBAL | SESSION
Com_show_collationsnumericGLOBAL | SESSION
Com_show_contributorsnumericGLOBAL | SESSION
Com_show_create_dbnumericGLOBAL | SESSION
Com_show_create_eventnumericGLOBAL | SESSION
Com_show_create_funcnumericGLOBAL | SESSION
Com_show_create_procnumericGLOBAL | SESSION
Com_show_create_tablenumericGLOBAL | SESSION
Com_show_create_triggernumericGLOBAL | SESSION
Com_show_databasesnumericGLOBAL | SESSION
Com_show_engine_logsnumericGLOBAL | SESSION
Com_show_engine_mutexnumericGLOBAL | SESSION
Com_show_engine_statusnumericGLOBAL | SESSION
Com_show_errorsnumericGLOBAL | SESSION
Com_show_eventsnumericGLOBAL | SESSION
Com_show_fieldsnumericGLOBAL | SESSION
Com_show_function_codenumericGLOBAL | SESSION
Com_show_function_statusnumericGLOBAL | SESSION
Com_show_grantsnumericGLOBAL | SESSION
Com_show_keysnumericGLOBAL | SESSION
Com_show_logsnumericGLOBAL | SESSION
Com_show_master_statusnumericGLOBAL | SESSION
Com_show_new_masternumericGLOBAL | SESSION
Com_show_open_tablesnumericGLOBAL | SESSION
Com_show_pluginsnumericGLOBAL | SESSION
Com_show_privilegesnumericGLOBAL | SESSION
Com_show_procedure_codenumericGLOBAL | SESSION
Com_show_procedure_statusnumericGLOBAL | SESSION
Com_show_processlistnumericGLOBAL | SESSION
Com_show_profilenumericGLOBAL | SESSION
Com_show_profilesnumericGLOBAL | SESSION
Com_show_relaylog_eventsnumericGLOBAL | SESSION
Com_show_slave_hostsnumericGLOBAL | SESSION
Com_show_slave_statusnumericGLOBAL | SESSION
Com_show_statusnumericGLOBAL | SESSION
Com_show_storage_enginesnumericGLOBAL | SESSION
Com_show_table_statusnumericGLOBAL | SESSION
Com_show_tablesnumericGLOBAL | SESSION
Com_show_triggersnumericGLOBAL | SESSION
Com_show_variablesnumericGLOBAL | SESSION
Com_show_warningsnumericGLOBAL | SESSION
Com_signalnumericGLOBAL | SESSION
Com_slave_startnumericGLOBAL | SESSION
Com_slave_stopnumericGLOBAL | SESSION
Com_stmt_closenumericGLOBAL | SESSION
Com_stmt_executenumericGLOBAL | SESSION
Com_stmt_fetchnumericGLOBAL | SESSION
Com_stmt_preparenumericGLOBAL | SESSION
Com_stmt_repreparenumericGLOBAL | SESSION
Com_stmt_resetnumericGLOBAL | SESSION
Com_stmt_send_long_datanumericGLOBAL | SESSION
Com_truncatenumericGLOBAL | SESSION
Com_uninstall_pluginnumericGLOBAL | SESSION
Com_unlock_tablesnumericGLOBAL | SESSION
Com_updatenumericGLOBAL | SESSION
Com_update_multinumericGLOBAL | SESSION
Com_xa_commitnumericGLOBAL | SESSION
Com_xa_endnumericGLOBAL | SESSION
Com_xa_preparenumericGLOBAL | SESSION
Com_xa_recovernumericGLOBAL | SESSION
Com_xa_rollbacknumericGLOBAL | SESSION
Com_xa_startnumericGLOBAL | SESSION
CompressionnumericSESSION
ConnectionsnumericGLOBAL
Created_tmp_disk_tablesnumericGLOBAL | SESSION
Created_tmp_filesnumericGLOBAL
Created_tmp_tablesnumericGLOBAL | SESSION
Delayed_errorsnumericGLOBAL
Delayed_insert_threadsnumericGLOBAL
Delayed_writesnumericGLOBAL
Flush_commandsnumericGLOBAL
Handler_commitnumericGLOBAL | SESSION
Handler_deletenumericGLOBAL | SESSION
Handler_discovernumericGLOBAL | SESSION
Handler_preparenumericGLOBAL | SESSION
Handler_read_firstnumericGLOBAL | SESSION
Handler_read_keynumericGLOBAL | SESSION
Handler_read_lastnumericGLOBAL | SESSION
Handler_read_nextnumericGLOBAL | SESSION
Handler_read_prevnumericGLOBAL | SESSION
Handler_read_rndnumericGLOBAL | SESSION
Handler_read_rnd_nextnumericGLOBAL | SESSION
Handler_rollbacknumericGLOBAL | SESSION
Handler_savepointnumericGLOBAL | SESSION
Handler_savepoint_rollbacknumericGLOBAL | SESSION
Handler_updatenumericGLOBAL | SESSION
Handler_writenumericGLOBAL | SESSION
Innodb_buffer_pool_pages_datanumericGLOBAL
Innodb_buffer_pool_pages_dirtynumericGLOBAL
Innodb_buffer_pool_pages_flushednumericGLOBAL
Innodb_buffer_pool_pages_freenumericGLOBAL
Innodb_buffer_pool_pages_latchednumericGLOBAL
Innodb_buffer_pool_pages_miscnumericGLOBAL
Innodb_buffer_pool_pages_totalnumericGLOBAL
Innodb_buffer_pool_read_aheadnumericGLOBAL
Innodb_buffer_pool_read_ahead_evictednumericGLOBAL
Innodb_buffer_pool_read_requestsnumericGLOBAL
Innodb_buffer_pool_readsnumericGLOBAL
Innodb_buffer_pool_wait_freenumericGLOBAL
Innodb_buffer_pool_write_requestsnumericGLOBAL
Innodb_data_fsyncsnumericGLOBAL
Innodb_data_pending_fsyncsnumericGLOBAL
Innodb_data_pending_readsnumericGLOBAL
Innodb_data_pending_writesnumericGLOBAL
Innodb_data_readnumericGLOBAL
Innodb_data_readsnumericGLOBAL
Innodb_data_writesnumericGLOBAL
Innodb_data_writtennumericGLOBAL
Innodb_dblwr_pages_writtennumericGLOBAL
Innodb_dblwr_writesnumericGLOBAL
Innodb_have_atomic_builtinsnumericGLOBAL
Innodb_log_waitsnumericGLOBAL
Innodb_log_write_requestsnumericGLOBAL
Innodb_log_writesnumericGLOBAL
Innodb_os_log_fsyncsnumericGLOBAL
Innodb_os_log_pending_fsyncsnumericGLOBAL
Innodb_os_log_pending_writesnumericGLOBAL
Innodb_os_log_writtennumericGLOBAL
Innodb_page_sizenumericGLOBAL
Innodb_pages_creatednumericGLOBAL
Innodb_pages_readnumericGLOBAL
Innodb_pages_writtennumericGLOBAL
Innodb_row_lock_current_waitsnumericGLOBAL
Innodb_row_lock_timenumericGLOBAL
Innodb_row_lock_time_avgnumericGLOBAL
Innodb_row_lock_time_maxnumericGLOBAL
Innodb_row_lock_waitsnumericGLOBAL
Innodb_rows_deletednumericGLOBAL
Innodb_rows_insertednumericGLOBAL
Innodb_rows_readnumericGLOBAL
Innodb_rows_updatednumericGLOBAL
Innodb_truncated_status_writesnumericGLOBAL
Key_blocks_not_flushednumericGLOBAL
Key_blocks_unusednumericGLOBAL
Key_blocks_usednumericGLOBAL
Key_read_requestsnumericGLOBAL
Key_readsnumericGLOBAL
Key_write_requestsnumericGLOBAL
Key_writesnumericGLOBAL
Last_query_costnumericSESSION
Max_used_connectionsnumericGLOBAL
Ndb_api_bytes_received_countnumericGLOBAL
Ndb_api_bytes_received_count_sessionnumericSESSION
Ndb_api_bytes_received_count_slavenumericGLOBAL
Ndb_api_bytes_sent_countnumericGLOBAL
Ndb_api_bytes_sent_count_sessionnumericSESSION
Ndb_api_bytes_sent_count_slavenumericGLOBAL
Ndb_api_event_bytes_countnumericGLOBAL
Ndb_api_event_bytes_count_injectornumericGLOBAL
Ndb_api_event_data_countnumericGLOBAL
Ndb_api_event_data_count_injectornumericGLOBAL
Ndb_api_event_nondata_countnumericGLOBAL
Ndb_api_event_nondata_count_injectornumericGLOBAL
Ndb_api_pk_op_countnumericGLOBAL
Ndb_api_pk_op_count_sessionnumericSESSION
Ndb_api_pk_op_count_slavenumericGLOBAL
Ndb_api_pruned_scan_countnumericGLOBAL
Ndb_api_pruned_scan_count_sessionnumericSESSION
Ndb_api_pruned_scan_count_slavenumericGLOBAL
Ndb_api_range_scan_countnumericGLOBAL
Ndb_api_range_scan_count_sessionnumericSESSION
Ndb_api_range_scan_count_slavenumericGLOBAL
Ndb_api_read_row_countnumericGLOBAL
Ndb_api_read_row_count_sessionnumericSESSION
Ndb_api_read_row_count_slavenumericGLOBAL
Ndb_api_scan_batch_countnumericGLOBAL
Ndb_api_scan_batch_count_sessionnumericSESSION
Ndb_api_scan_batch_count_slavenumericGLOBAL
Ndb_api_table_scan_countnumericGLOBAL
Ndb_api_table_scan_count_sessionnumericSESSION
Ndb_api_table_scan_count_slavenumericGLOBAL
Ndb_api_trans_abort_countnumericGLOBAL
Ndb_api_trans_abort_count_sessionnumericSESSION
Ndb_api_trans_abort_count_slavenumericGLOBAL
Ndb_api_trans_close_countnumericGLOBAL
Ndb_api_trans_close_count_sessionnumericSESSION
Ndb_api_trans_close_count_slavenumericGLOBAL
Ndb_api_trans_commit_countnumericGLOBAL
Ndb_api_trans_commit_count_sessionnumericSESSION
Ndb_api_trans_commit_count_slavenumericGLOBAL
Ndb_api_trans_local_read_row_countnumericGLOBAL
Ndb_api_trans_local_read_row_count_sessionnumericSESSION
Ndb_api_trans_local_read_row_count_slavenumericGLOBAL
Ndb_api_trans_start_countnumericGLOBAL
Ndb_api_trans_start_count_sessionnumericSESSION
Ndb_api_trans_start_count_slavenumericGLOBAL
Ndb_api_uk_op_countnumericGLOBAL
Ndb_api_uk_op_count_sessionnumericSESSION
Ndb_api_uk_op_count_slavenumericGLOBAL
Ndb_api_wait_exec_complete_countnumericGLOBAL
Ndb_api_wait_exec_complete_count_sessionnumericSESSION
Ndb_api_wait_exec_complete_count_slavenumericGLOBAL
Ndb_api_wait_meta_request_countnumericGLOBAL
Ndb_api_wait_meta_request_count_sessionnumericSESSION
Ndb_api_wait_meta_request_count_slavenumericGLOBAL
Ndb_api_wait_nanos_countnumericGLOBAL
Ndb_api_wait_nanos_count_sessionnumericSESSION
Ndb_api_wait_nanos_count_slavenumericGLOBAL
Ndb_api_wait_scan_result_countnumericGLOBAL
Ndb_api_wait_scan_result_count_sessionnumericSESSION
Ndb_api_wait_scan_result_count_slavenumericGLOBAL
ndb_cluster_connection_poolnumericGLOBAL
Ndb_cluster_node_idnumericGLOBAL | SESSION
Ndb_config_from_hostnumericGLOBAL | SESSION
Ndb_conflict_fn_epochnumericGLOBAL
Ndb_conflict_fn_epoch_transnumericGLOBAL
Ndb_conflict_fn_maxnumericGLOBAL
Ndb_conflict_fn_oldnumericGLOBAL
Ndb_conflict_trans_conflict_commit_countnumericGLOBAL
Ndb_conflict_trans_detect_iter_countnumericGLOBAL
Ndb_conflict_trans_reject_countnumericGLOBAL
Ndb_conflict_trans_row_conflict_countnumericGLOBAL
Ndb_conflict_trans_row_reject_countnumericGLOBAL
ndb_execute_countnumericGLOBAL
ndb-nodeidnumericGLOBAL
Ndb_number_of_data_nodesnumericGLOBAL
ndb_pruned_scan_countnumericGLOBAL
Ndb_pushed_queries_definednumericGLOBAL
Ndb_pushed_queries_droppednumericGLOBAL
Ndb_pushed_queries_executednumericGLOBAL
ndb_pushed_readsnumericGLOBAL
ndb_scan_countnumericGLOBAL
Not_flushed_delayed_rowsnumericGLOBAL
Open_filesnumericGLOBAL
Open_streamsnumericGLOBAL
Open_table_definitionsnumericGLOBAL
Open_tablesnumericGLOBAL | SESSION
Opened_filesnumericGLOBAL
Opened_table_definitionsnumericGLOBAL | SESSION
Opened_tablesnumericGLOBAL | SESSION
Performance_schema_cond_classes_lostnumericGLOBAL
Performance_schema_cond_instances_lostnumericGLOBAL
Performance_schema_file_classes_lostnumericGLOBAL
Performance_schema_file_handles_lostnumericGLOBAL
Performance_schema_file_instances_lostnumericGLOBAL
Performance_schema_locker_lostnumericGLOBAL
Performance_schema_mutex_classes_lostnumericGLOBAL
Performance_schema_mutex_instances_lostnumericGLOBAL
Performance_schema_rwlock_classes_lostnumericGLOBAL
Performance_schema_rwlock_instances_lostnumericGLOBAL
Performance_schema_table_handles_lostnumericGLOBAL
Performance_schema_table_instances_lostnumericGLOBAL
Performance_schema_thread_classes_lostnumericGLOBAL
Performance_schema_thread_instances_lostnumericGLOBAL
Prepared_stmt_countnumericGLOBAL
Qcache_free_blocksnumericGLOBAL
Qcache_free_memorynumericGLOBAL
Qcache_hitsnumericGLOBAL
Qcache_insertsnumericGLOBAL
Qcache_lowmem_prunesnumericGLOBAL
Qcache_not_cachednumericGLOBAL
Qcache_queries_in_cachenumericGLOBAL
Qcache_total_blocksnumericGLOBAL
QueriesnumericGLOBAL | SESSION
QuestionsnumericGLOBAL | SESSION
Rpl_semi_sync_master_clientsnumericGLOBAL
Rpl_semi_sync_master_net_avg_wait_timenumericGLOBAL
Rpl_semi_sync_master_net_wait_timenumericGLOBAL
Rpl_semi_sync_master_net_waitsnumericGLOBAL
Rpl_semi_sync_master_no_timesnumericGLOBAL
Rpl_semi_sync_master_no_txnumericGLOBAL
Rpl_semi_sync_master_statusbooleanGLOBAL
Rpl_semi_sync_master_timefunc_failuresnumericGLOBAL
Rpl_semi_sync_master_tx_avg_wait_timenumericGLOBAL
Rpl_semi_sync_master_tx_wait_timenumericGLOBAL
Rpl_semi_sync_master_tx_waitsnumericGLOBAL
Rpl_semi_sync_master_wait_pos_backtraversenumericGLOBAL
Rpl_semi_sync_master_wait_sessionsnumericGLOBAL
Rpl_semi_sync_master_yes_txnumericGLOBAL
Rpl_semi_sync_slave_statusbooleanGLOBAL
Rpl_statusstringGLOBAL
Select_full_joinnumericGLOBAL | SESSION
Select_full_range_joinnumericGLOBAL | SESSION
Select_rangenumericGLOBAL | SESSION
Select_range_checknumericGLOBAL | SESSION
Select_scannumericGLOBAL | SESSION
Slave_heartbeat_period GLOBAL
Slave_open_temp_tablesnumericGLOBAL
Slave_received_heartbeats GLOBAL
Slave_retried_transactionsnumericGLOBAL
Slave_runningbooleanGLOBAL
Slow_launch_threadsnumericGLOBAL | SESSION
Slow_queriesnumericGLOBAL | SESSION
Sort_merge_passesnumericGLOBAL | SESSION
Sort_rangenumericGLOBAL | SESSION
Sort_rowsnumericGLOBAL | SESSION
Sort_scannumericGLOBAL | SESSION
Ssl_accept_renegotiatesnumericGLOBAL
Ssl_acceptsnumericGLOBAL
Ssl_callback_cache_hitsnumericGLOBAL
Ssl_cipherstringGLOBAL | SESSION
Ssl_cipher_liststringGLOBAL | SESSION
Ssl_client_connectsnumericGLOBAL
Ssl_connect_renegotiatesnumericGLOBAL
Ssl_ctx_verify_depthnumericGLOBAL
Ssl_ctx_verify_modenumericGLOBAL
Ssl_default_timeoutnumericGLOBAL | SESSION
Ssl_finished_acceptsnumericGLOBAL
Ssl_finished_connectsnumericGLOBAL
Ssl_session_cache_hitsnumericGLOBAL
Ssl_session_cache_missesnumericGLOBAL
Ssl_session_cache_modestringGLOBAL
Ssl_session_cache_overflowsnumericGLOBAL
Ssl_session_cache_sizenumericGLOBAL
Ssl_session_cache_timeoutsnumericGLOBAL
Ssl_sessions_reusednumericGLOBAL | SESSION
Ssl_used_session_cache_entriesnumericGLOBAL
Ssl_verify_depthnumericGLOBAL | SESSION
Ssl_verify_modenumericGLOBAL | SESSION
Ssl_versionstringGLOBAL | SESSION
Table_locks_immediatenumericGLOBAL
Table_locks_waitednumericGLOBAL
Tc_log_max_pages_usednumericGLOBAL
Tc_log_page_sizenumericGLOBAL
Tc_log_page_waitsnumericGLOBAL
Threads_cachednumericGLOBAL
Threads_connectednumericGLOBAL
Threads_creatednumericGLOBAL
Threads_runningnumericGLOBAL
UptimenumericGLOBAL
Uptime_since_flush_statusnumericGLOBAL

Many status variables are reset to 0 by the FLUSH STATUS statement.

The status variables have the following meanings. Variables with no version indicated were already present prior to MySQL 5.5. For information regarding their implementation history, see MySQL 5.1 Справочное Руководство.

  • Aborted_clients

    The number of connections that were aborted because the client died without closing the connection properly. See Section C.5.2.11, “Communication Ошибки and Aborted Connections”.

  • Aborted_connects

    The number of failed attempts to connect to the MySQL server. See Section C.5.2.11, “Communication Ошибки and Aborted Connections”.

  • Binlog_cache_disk_use

    The number of transactions that used the binary log cache but that exceeded the value of binlog_cache_size and used a temporary file to store changes from the transaction.

    In MySQL versions 5.5.3 through 5.5.8, this variable also included the number of nontransactional statements that caused the binary log transaction cache to be written to disk. Beginning with MySQL 5.5.9, the number of such nontransactional statements is tracked separately in the Binlog_stmt_cache_disk_use status variable.

  • Binlog_cache_use

    The number of transactions that used the binary log cache.

  • Binlog_stmt_cache_disk_use

    The number of nontransaction statements that used the binary log statement cache but that exceeded the value of binlog_stmt_cache_size and used a temporary file to store those statements.

  • Binlog_stmt_cache_use

    The number of nontransactional statements that used the binary log statement cache.

  • Bytes_received

    The number of bytes received from all clients.

  • Bytes_sent

    The number of bytes sent to all clients.

  • Com_xxx

    The Com_xxx statement counter variables indicate the number of times each xxx statement has been executed. There is one status variable for each type of statement. For example, Com_delete and Com_insert count DELETE and INSERT statements, respectively. However, if a query result is returned from query cache, the server increments the Qcache_hits status variable, not Com_select. See Section 7.9.3.4, “Query Cache Status and Maintenance”.

    All of the Com_stmt_xxx variables are increased even if a prepared statement argument is unknown or an error occurred during execution. In other words, their values correspond to the number of requests issued, not to the number of requests successfully completed.

    The Com_stmt_xxx status variables are as follows:

    • Com_stmt_prepare

    • Com_stmt_execute

    • Com_stmt_fetch

    • Com_stmt_send_long_data

    • Com_stmt_reset

    • Com_stmt_close

    Those variables stand for prepared statement commands. Their names refer to the COM_xxx command set used in the network layer. In other words, their values increase whenever prepared statement API calls such as mysql_stmt_prepare(), mysql_stmt_execute(), and so forth are executed. However, Com_stmt_prepare, Com_stmt_execute and Com_stmt_close also increase for PREPARE, EXECUTE, or DEALLOCATE PREPARE, respectively. Additionally, the values of the older statement counter variables Com_prepare_sql, Com_execute_sql, and Com_dealloc_sql increase for the PREPARE, EXECUTE, and DEALLOCATE PREPARE statements. Com_stmt_fetch stands for the total number of network round-trips issued when fetching from cursors.

    Com_stmt_reprepare indicated the number of times statements were automatically reprepared by the server after metadata changes to tables or views referred to by the statement. A reprepare operation increments Com_stmt_reprepare is incremented, and also Com_stmt_prepare.

  • Compression

    Whether the client connection uses compression in the client/server protocol.

  • Connections

    The number of connection attempts (successful or not) to the MySQL server.

  • Created_tmp_disk_tables

    The number of internal on-disk temporary tables created by the server while executing statements.

    If an internal temporary table is created initially as an in-memory table but becomes too large, MySQL automatically converts it to an on-disk table. The maximum size for in-memory temporary tables is the minimum of the tmp_table_size and max_heap_table_size values. If Created_tmp_disk_tables is large, you may want to increase the tmp_table_size or max_heap_table_size values. value to lessen the likelihood that internal temporary tables in memory will be converted to on-disk tables.

    You can compare the number of internal on-disk temporary tables created to the total number of internal temporary tables created by comparing the values of the Created_tmp_disk_tables and Created_tmp_tables variables.

    See also Section 7.4.3.3, “How MySQL Uses Internal Temporary Tables”.

  • Created_tmp_files

    How many temporary files mysqld has created.

  • Created_tmp_tables

    The number of internal temporary tables created by the server while executing statements.

    You can compare the number of internal on-disk temporary tables created to the total number of internal temporary tables created by comparing the values of the Created_tmp_disk_tables and Created_tmp_tables variables.

    See also Section 7.4.3.3, “How MySQL Uses Internal Temporary Tables”.

    Each invocation of the SHOW STATUS statement uses an internal temporary table and increments the global Created_tmp_tables value.

  • Delayed_errors

    The number of rows written with INSERT DELAYED for which some error occurred (probably duplicate key).

  • Delayed_insert_threads

    The number of INSERT DELAYED handler threads in use.

  • Delayed_writes

    The number of INSERT DELAYED rows written.

  • Flush_commands

    The number of times the server flushes tables, whether because a user executed a FLUSH TABLES statement or due to internal server operation. It is also incremented by receipt of a COM_REFRESH packet. This is in contrast to Com_flush, which indicates how many FLUSH statements have been executed, whether FLUSH TABLES, FLUSH LOGS, and so forth.

  • Handler_commit

    The number of internal COMMIT statements.

  • Handler_delete

    The number of times that rows have been deleted from tables.

  • Handler_prepare

    A counter for the prepare phase of two-phase commit operations.

  • Handler_read_first

    The number of times the first entry in an index was read. If this value is high, it suggests that the server is doing a lot of full index scans; for example, SELECT col1 FROM foo, assuming that col1 is indexed.

  • Handler_read_key

    The number of requests to read a row based on a key. If this value is high, it is a good indication that your tables are properly indexed for your queries.

  • Handler_read_last

    The number of requests to read the last key in an index. With ORDER BY, the server will issue a first-key request followed by several next-key requests, whereas with With ORDER BY DESC, the server will issue a last-key request followed by several previous-key requests. This variable was added in MySQL 5.5.7.

  • Handler_read_next

    The number of requests to read the next row in key order. This value is incremented if you are querying an index column with a range constraint or if you are doing an index scan.

  • Handler_read_prev

    The number of requests to read the previous row in key order. This read method is mainly used to optimize ORDER BY ... DESC.

  • Handler_read_rnd

    The number of requests to read a row based on a fixed position. This value is high if you are doing a lot of queries that require sorting of the result. You probably have a lot of queries that require MySQL to scan entire tables or you have joins that do not use keys properly.

  • Handler_read_rnd_next

    The number of requests to read the next row in the data file. This value is high if you are doing a lot of table scans. Generally this suggests that your tables are not properly indexed or that your queries are not written to take advantage of the indexes you have.

  • Handler_rollback

    The number of requests for a storage engine to perform a rollback operation.

  • Handler_savepoint

    The number of requests for a storage engine to place a savepoint.

  • Handler_savepoint_rollback

    The number of requests for a storage engine to roll back to a savepoint.

  • Handler_update

    The number of requests to update a row in a table.

  • Handler_write

    The number of requests to insert a row in a table.

  • Innodb_buffer_pool_pages_data

    The number of pages containing data (dirty or clean).

  • Innodb_buffer_pool_pages_dirty

    The number of pages currently dirty.

  • Innodb_buffer_pool_pages_flushed

    The number of buffer pool page-flush requests.

  • Innodb_buffer_pool_pages_free

    The number of free pages.

  • Innodb_buffer_pool_pages_latched

    The number of latched pages in InnoDB buffer pool. These are pages currently being read or written or that cannot be flushed or removed for some other reason. Calculation of this variable is expensive, so it is available only when the UNIV_DEBUG system is defined at server build time.

  • Innodb_buffer_pool_pages_misc

    The number of pages that are busy because they have been allocated for administrative overhead such as row locks or the adaptive hash index. This value can also be calculated as Innodb_buffer_pool_pages_totalInnodb_buffer_pool_pages_freeInnodb_buffer_pool_pages_data.

  • Innodb_buffer_pool_pages_total

    The total size of the buffer pool, in pages.

  • Innodb_buffer_pool_read_ahead

    The number of pages read into the InnoDB buffer pool by the read-ahead background thread.

  • Innodb_buffer_pool_read_ahead_evicted

    The number of pages read into the InnoDB buffer pool by the read-ahead background thread that were subsequently evicted without having been accessed by queries.

  • Innodb_buffer_pool_read_requests

    The number of logical read requests InnoDB has done.

  • Innodb_buffer_pool_reads

    The number of logical reads that InnoDB could not satisfy from the buffer pool, and had to read directly from the disk.

  • Innodb_buffer_pool_wait_free

    Normally, writes to the InnoDB buffer pool happen in the background. However, if it is necessary to read or create a page and no clean pages are available, it is also necessary to wait for pages to be flushed first. This counter counts instances of these waits. If the buffer pool size has been set properly, this value should be small.

  • Innodb_buffer_pool_write_requests

    The number writes done to the InnoDB buffer pool.

  • Innodb_data_fsyncs

    The number of fsync() operations so far.

  • Innodb_data_pending_fsyncs

    The current number of pending fsync() operations.

  • Innodb_data_pending_reads

    The current number of pending reads.

  • Innodb_data_pending_writes

    The current number of pending writes.

  • Innodb_data_read

    The amount of data read since the server was started.

  • Innodb_data_reads

    The total number of data reads.

  • Innodb_data_writes

    The total number of data writes.

  • Innodb_data_written

    The amount of data written so far, in bytes.

  • Innodb_dblwr_pages_written

    The number of pages that have been written for doublewrite operations. See Section 13.3.12.1, “InnoDB Disk I/O”.

  • Innodb_dblwr_writes

    The number of doublewrite operations that have been performed. See Section 13.3.12.1, “InnoDB Disk I/O”.

  • Innodb_have_atomic_builtins

    Indicates whether the server was built with atomic instructions.

  • Innodb_log_waits

    The number of times that the log buffer was too small and a wait was required for it to be flushed before continuing.

  • Innodb_log_write_requests

    The number of log write requests.

  • Innodb_log_writes

    The number of physical writes to the log file.

  • Innodb_os_log_fsyncs

    The number of fsync() writes done to the log file.

  • Innodb_os_log_pending_fsyncs

    The number of pending log file fsync() operations.

  • Innodb_os_log_pending_writes

    The number of pending log file writes.

  • Innodb_os_log_written

    The number of bytes written to the log file.

  • Innodb_page_size

    The compiled-in InnoDB page size (default 16KB). Many values are counted in pages; the page size enables them to be easily converted to bytes.

  • Innodb_pages_created

    The number of pages created.

  • Innodb_pages_read

    The number of pages read.

  • Innodb_pages_written

    The number of pages written.

  • Innodb_row_lock_current_waits

    The number of row locks currently being waited for.

  • Innodb_row_lock_time

    The total time spent in acquiring row locks, in milliseconds.

  • Innodb_row_lock_time_avg

    The average time to acquire a row lock, in milliseconds.

  • Innodb_row_lock_time_max

    The maximum time to acquire a row lock, in milliseconds.

  • Innodb_row_lock_waits

    The number of times a row lock had to be waited for.

  • Innodb_rows_deleted

    The number of rows deleted from InnoDB tables.

  • Innodb_rows_inserted

    The number of rows inserted into InnoDB tables.

  • Innodb_rows_read

    The number of rows read from InnoDB tables.

  • Innodb_rows_updated

    The number of rows updated in InnoDB tables.

  • Innodb_truncated_status_writes

    The number of times output from the SHOW ENGINE INNODB STATUS is truncated. Monitoring applications that parse the output from this command can test this value before and after issuing the SHOW ENGINE command, to confirm if the output is complete or not.

  • Key_blocks_not_flushed

    The number of key blocks in the key cache that have changed but have not yet been flushed to disk.

  • Key_blocks_unused

    The number of unused blocks in the key cache. You can use this value to determine how much of the key cache is in use; see the discussion of key_buffer_size in Section 5.1.3, “Server System Variables”.

  • Key_blocks_used

    The number of used blocks in the key cache. This value is a high-water mark that indicates the maximum number of blocks that have ever been in use at one time.

  • Key_read_requests

    The number of requests to read a key block from the cache.

  • Key_reads

    The number of physical reads of a key block from disk. If Key_reads is large, then your key_buffer_size value is probably too small. The cache miss rate can be calculated as Key_reads/Key_read_requests.

  • Key_write_requests

    The number of requests to write a key block to the cache.

  • Key_writes

    The number of physical writes of a key block to disk.

  • Last_query_cost

    The total cost of the last compiled query as computed by the query optimizer. This is useful for comparing the cost of different query plans for the same query. The default value of 0 means that no query has been compiled yet. The default value is 0. Last_query_cost has session scope.

    The Last_query_cost value can be computed accurately only for simple “flat” queries, not complex queries such as those with subqueries or UNION. For the latter, the value is set to 0.

  • Max_used_connections

    The maximum number of connections that have been in use simultaneously since the server started.

  • Not_flushed_delayed_rows

    The number of rows waiting to be written in INSERT DELAYED queues.

  • Open_files

    The number of files that are open. This count includes regular files opened by the server. It does not include other types of files such as sockets or pipes. Also, the count does not include files that storage engines open using their own internal functions rather than asking the server level to do so.

  • Open_streams

    The number of streams that are open (used mainly for logging).

  • Open_table_definitions

    The number of cached .frm files.

  • Open_tables

    The number of tables that are open.

  • Opened_files

    The number of files that have been opened with my_open() (a mysys library function). Parts of the server that open files without using this function do not increment the count.

  • Opened_table_definitions

    The number of .frm files that have been cached.

  • Opened_tables

    The number of tables that have been opened. If Opened_tables is big, your table_open_cache value is probably too small.

  • Performance_schema_xxx

    Performance Schema status variables are listed in Section 20.9, “Performance Schema Status Variables”.

  • Prepared_stmt_count

    The current number of prepared statements. (The maximum number of statements is given by the max_prepared_stmt_count system variable.)

  • Qcache_free_blocks

    The number of free memory blocks in the query cache.

  • Qcache_free_memory

    The amount of free memory for the query cache.

  • Qcache_hits

    The number of query cache hits.

  • Qcache_inserts

    The number of queries added to the query cache.

  • Qcache_lowmem_prunes

    The number of queries that were deleted from the query cache because of low memory.

  • Qcache_not_cached

    The number of noncached queries (not cacheable, or not cached due to the query_cache_type setting).

  • Qcache_queries_in_cache

    The number of queries registered in the query cache.

  • Qcache_total_blocks

    The total number of blocks in the query cache.

  • Queries

    The number of statements executed by the server. This variable includes statements executed within stored programs, unlike the Questions variable. It does not count COM_PING or COM_STATISTICS commands.

  • Questions

    The number of statements executed by the server. This includes only statements sent to the server by clients and not statements executed within stored programs, unlike the Queries variable. This variable does not count COM_PING, COM_STATISTICS, COM_STMT_PREPARE, COM_STMT_CLOSE, or COM_STMT_RESET commands.

  • Rpl_semi_sync_master_clients

    The number of semisynchronous slaves.

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • Rpl_semi_sync_master_net_avg_wait_time

    The average time in microseconds the master waited for a slave reply.

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • Rpl_semi_sync_master_net_wait_time

    The total time in microseconds the master waited for slave replies.

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • Rpl_semi_sync_master_net_waits

    The total number of times the master waited for slave replies.

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • Rpl_semi_sync_master_no_times

    The number of times the master turned off semisynchronous replication.

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • Rpl_semi_sync_master_no_tx

    The number of commits that were not acknowledged successfully by a slave.

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • Rpl_semi_sync_master_status

    Whether semisynchronous replication currently is operational on the master. The value is ON if the plugin has been enabled and a commit acknowledgment has occurred. It is OFF if the plugin is not enabled or the master has fallen back to asynchronous replication due to commit acknowledgment timeout.

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • Rpl_semi_sync_master_timefunc_failures

    The number of times the master failed when calling time functions such as gettimeofday().

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • Rpl_semi_sync_master_tx_avg_wait_time

    The average time in microseconds the master waited for each transaction.

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • Rpl_semi_sync_master_tx_wait_time

    The total time in microseconds the master waited for transactions.

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • Rpl_semi_sync_master_tx_waits

    The total number of times the master waited for transactions.

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • Rpl_semi_sync_master_wait_pos_backtraverse

    The total number of times the master waited for an event with binary coordinates lower than events waited for previously. This can occur when the order in which transactions start waiting for a reply is different from the order in which their binary log events are written.

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • Rpl_semi_sync_master_wait_sessions

    The number of sessions currently waiting for slave replies.

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • Rpl_semi_sync_master_yes_tx

    The number of commits that were acknowledged successfully by a slave.

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • Rpl_semi_sync_slave_status

    Whether semisynchronous replication currently is operational on the slave. This is ON if the plugin has been enabled and the slave I/O thread is running, OFF otherwise.

    This variable is available only if the slave-side semisynchronous replication plugin is installed.

  • Rpl_status

    The status of fail-safe replication (not implemented). This variable is unused and is removed in MySQL 5.6.

  • Select_full_join

    The number of joins that perform table scans because they do not use indexes. If this value is not 0, you should carefully check the indexes of your tables.

  • Select_full_range_join

    The number of joins that used a range search on a reference table.

  • Select_range

    The number of joins that used ranges on the first table. This is normally not a critical issue even if the value is quite large.

  • Select_range_check

    The number of joins without keys that check for key usage after each row. If this is not 0, you should carefully check the indexes of your tables.

  • Select_scan

    The number of joins that did a full scan of the first table.

  • Slave_heartbeat_period

    Shows the replication heartbeat interval (in seconds) on a replication slave.

  • Slave_open_temp_tables

    The number of temporary tables that the slave SQL thread currently has open. If the value is greater than zero, it is not safe to shut down the slave; see Section 15.4.1.19, “Replication and Temporary Tables”.

  • Slave_received_heartbeats

    This counter increments with each replication heartbeat received by a replication slave since the last time that the slave was restarted or reset, or a CHANGE MASTER TO statement was issued.

  • Slave_retried_transactions

    The total number of times since startup that the replication slave SQL thread has retried transactions.

  • Slave_running

    This is ON if this server is a replication slave that is connected to a replication master, and both the I/O and SQL threads are running; otherwise, it is OFF.

  • Slow_launch_threads

    The number of threads that have taken more than slow_launch_time seconds to create.

  • Slow_queries

    The number of queries that have taken more than long_query_time seconds. See Section 5.2.5, “The Slow Query Log”.

  • Sort_merge_passes

    The number of merge passes that the sort algorithm has had to do. If this value is large, you should consider increasing the value of the sort_buffer_size system variable.

  • Sort_range

    The number of sorts that were done using ranges.

  • Sort_rows

    The number of sorted rows.

  • Sort_scan

    The number of sorts that were done by scanning the table.

  • Ssl_accept_renegotiates

    The number of negotiates needed to establish the connection.

  • Ssl_accepts

    The number of accepted SSL connections.

  • Ssl_callback_cache_hits

    The number of callback cache hits.

  • Ssl_cipher

    The current SSL cipher (empty for non-SSL connections).

  • Ssl_cipher_list

    The list of possible SSL ciphers.

  • Ssl_client_connects

    The number of SSL connection attempts to an SSL-enabled master.

  • Ssl_connect_renegotiates

    The number of negotiates needed to establish the connection to an SSL-enabled master.

  • Ssl_ctx_verify_depth

    The SSL context verification depth (how many certificates in the chain are tested).

  • Ssl_ctx_verify_mode

    The SSL context verification mode.

  • Ssl_default_timeout

    The default SSL timeout.

  • Ssl_finished_accepts

    The number of successful SSL connections to the server.

  • Ssl_finished_connects

    The number of successful slave connections to an SSL-enabled master.

  • Ssl_session_cache_hits

    The number of SSL session cache hits.

  • Ssl_session_cache_misses

    The number of SSL session cache misses.

  • Ssl_session_cache_mode

    The SSL session cache mode.

  • Ssl_session_cache_overflows

    The number of SSL session cache overflows.

  • Ssl_session_cache_size

    The SSL session cache size.

  • Ssl_session_cache_timeouts

    The number of SSL session cache timeouts.

  • Ssl_sessions_reused

    How many SSL connections were reused from the cache.

  • Ssl_used_session_cache_entries

    How many SSL session cache entries were used.

  • Ssl_verify_depth

    The verification depth for replication SSL connections.

  • Ssl_verify_mode

    The verification mode for replication SSL connections.

  • Ssl_version

    The SSL version number.

  • Table_locks_immediate

    The number of times that a request for a table lock could be granted immediately.

  • Table_locks_waited

    The number of times that a request for a table lock could not be granted immediately and a wait was needed. If this is high and you have performance problems, you should first optimize your queries, and then either split your table or tables or use replication.

  • Tc_log_max_pages_used

    For the memory-mapped implementation of the log that is used by mysqld when it acts as the transaction coordinator for recovery of internal XA transactions, this variable indicates the largest number of pages used for the log since the server started. If the product of Tc_log_max_pages_used and Tc_log_page_size is always significantly less than the log size, the size is larger than necessary and can be reduced. (The size is set by the --log-tc-size option. Currently, this variable is unused: It is unneeded for binary log-based recovery, and the memory-mapped recovery log method is not used unless the number of storage engines capable of two-phase commit is greater than one. (InnoDB is the only applicable engine.)

  • Tc_log_page_size

    The page size used for the memory-mapped implementation of the XA recovery log. The default value is determined using getpagesize(). Currently, this variable is unused for the same reasons as described for Tc_log_max_pages_used.

  • Tc_log_page_waits

    For the memory-mapped implementation of the recovery log, this variable increments each time the server was not able to commit a transaction and had to wait for a free page in the log. If this value is large, you might want to increase the log size (with the --log-tc-size option). For binary log-based recovery, this variable increments each time the binary log cannot be closed because there are two-phase commits in progress. (The close operation waits until all such transactions are finished.)

  • Threads_cached

    The number of threads in the thread cache.

  • Threads_connected

    The number of currently open connections.

  • Threads_created

    The number of threads created to handle connections. If Threads_created is big, you may want to increase the thread_cache_size value. The cache miss rate can be calculated as Threads_created/Connections.

  • Threads_running

    The number of threads that are not sleeping.

  • Uptime

    The number of seconds that the server has been up.

  • Uptime_since_flush_status

    The number of seconds since the most recent FLUSH STATUS statement.

5.1.6. Server SQL Modes

The MySQL server can operate in different SQL modes, and can apply these modes differently for different clients. This capability enables each application to tailor the server's operating mode to its own requirements.

For answers to some questions that are often asked about server SQL modes in MySQL, see Section B.3, “MySQL 5.5 FAQ: Server SQL Mode”.

Modes define what SQL syntax MySQL should support and what kind of data validation checks it should perform. This makes it easier to use MySQL in different environments and to use MySQL together with other database servers.

You can set the default SQL mode by starting mysqld with the --sql-mode="modes" option, or by using sql-mode="modes" in my.cnf (Unix operating systems) or my.ini (Windows). modes is a list of different modes separated by comma (“,”) characters. The default value is empty (no modes set). The modes value also can be empty (--sql-mode="" on the command line, or sql-mode="" in my.cnf on Unix systems or in my.ini on Windows) if you want to clear it explicitly.

You can change the SQL mode at runtime by using a SET [GLOBAL|SESSION] sql_mode='modes' statement to set the sql_mode system value. Setting the GLOBAL variable requires the SUPER privilege and affects the operation of all clients that connect from that time on. Setting the SESSION variable affects only the current client. Any client can change its own session sql_mode value at any time.

Important

SQL mode and user-defined partitioning.  Changing the server SQL mode after creating and inserting data into partitioned tables can cause major changes in the behavior of such tables, and could lead to loss or corruption of data. It is strongly recommended that you never change the SQL mode once you have created tables employing user-defined partitioning.

When replicating partitioned tables, differing SQL modes on master and slave can also lead to problems. For best results, you should always use the same server SQL mode on the master and on the slave.

See Section 17.5, “Restrictions and Limitations on Partitioning”, for more information.

You can retrieve the current global or session sql_mode value with the following statements:

SELECT @@GLOBAL.sql_mode;
SELECT @@SESSION.sql_mode;

The most important sql_mode values are probably these:

  • ANSI

    This mode changes syntax and behavior to conform more closely to standard SQL.

  • STRICT_TRANS_TABLES

    If a value could not be inserted as given into a transactional table, abort the statement. For a nontransactional table, abort the statement if the value occurs in a single-row statement or the first row of a multiple-row statement. More detail is given later in this section.

  • TRADITIONAL

    Make MySQL behave like a “traditional” SQL database system. A simple description of this mode is “give an error instead of a warning” when inserting an incorrect value into a column.

    Замечание

    The INSERT/UPDATE aborts as soon as the error is noticed. This may not be what you want if you are using a nontransactional storage engine, because data changes made prior to the error may not be rolled back, resulting in a “partially done” update.

When this manual refers to “strict mode,” it means a mode where at least one of STRICT_TRANS_TABLES or STRICT_ALL_TABLES is enabled.

The following list describes all supported modes:

  • ALLOW_INVALID_DATES

    Do not perform full checking of dates. Check only that the month is in the range from 1 to 12 and the day is in the range from 1 to 31. This is very convenient for Web applications where you obtain year, month, and day in three different fields and you want to store exactly what the user inserted (without date validation). This mode applies to DATE and DATETIME columns. It does not apply TIMESTAMP columns, which always require a valid date.

    The server requires that month and day values be legal, and not merely in the range 1 to 12 and 1 to 31, respectively. With strict mode disabled, invalid dates such as '2004-04-31' are converted to '0000-00-00' and a warning is generated. With strict mode enabled, invalid dates generate an error. To permit such dates, enable ALLOW_INVALID_DATES.

  • ANSI_QUOTES

    Treat “"” as an identifier quote character (like the “`” quote character) and not as a string quote character. You can still use “`” to quote identifiers with this mode enabled. With ANSI_QUOTES enabled, you cannot use double quotation marks to quote literal strings, because it is interpreted as an identifier.

  • ERROR_FOR_DIVISION_BY_ZERO

    Produce an error in strict mode (otherwise a warning) when a division by zero (or MOD(X,0)) occurs during an INSERT or UPDATE. If this mode is not enabled, MySQL instead returns NULL for divisions by zero. For INSERT IGNORE or UPDATE IGNORE, MySQL generates a warning for divisions by zero, but the result of the operation is NULL.

  • HIGH_NOT_PRECEDENCE

    The precedence of the NOT operator is such that expressions such as NOT a BETWEEN b AND c are parsed as NOT (a BETWEEN b AND c). In some older versions of MySQL, the expression was parsed as (NOT a) BETWEEN b AND c. The old higher-precedence behavior can be obtained by enabling the HIGH_NOT_PRECEDENCE SQL mode.

    mysql> SET sql_mode = '';
    mysql> SELECT NOT 1 BETWEEN -5 AND 5;
            -> 0
    mysql> SET sql_mode = 'HIGH_NOT_PRECEDENCE';
    mysql> SELECT NOT 1 BETWEEN -5 AND 5;
            -> 1
    
  • IGNORE_SPACE

    Permit spaces between a function name and the “(” character. This causes built-in function names to be treated as reserved words. As a result, identifiers that are the same as function names must be quoted as described in Section 8.2, “Schema Object Names”. For example, because there is a COUNT() function, the use of count as a table name in the following statement causes an error:

    mysql> CREATE TABLE count (i INT);
    ERROR 1064 (42000): You have an error in your SQL syntax
    

    The table name should be quoted:

    mysql> CREATE TABLE `count` (i INT);
    Query OK, 0 rows affected (0.00 sec)
    

    The IGNORE_SPACE SQL mode applies to built-in functions, not to user-defined functions or stored functions. It is always permissible to have spaces after a UDF or stored function name, regardless of whether IGNORE_SPACE is enabled.

    For further discussion of IGNORE_SPACE, see Section 8.2.4, “Function Name Parsing and Resolution”.

  • NO_AUTO_CREATE_USER

    Prevent the GRANT statement from automatically creating new users if it would otherwise do so, unless a nonempty password also is specified.

    This mode has no effect for GRANT statements that include an IDENTIFIED WITH clause. That is, GRANT ... IDENTIFIED WITH creates nonexistent users regardless of the mode setting.

  • NO_AUTO_VALUE_ON_ZERO

    NO_AUTO_VALUE_ON_ZERO affects handling of AUTO_INCREMENT columns. Normally, you generate the next sequence number for the column by inserting either NULL or 0 into it. NO_AUTO_VALUE_ON_ZERO suppresses this behavior for 0 so that only NULL generates the next sequence number.

    This mode can be useful if 0 has been stored in a table's AUTO_INCREMENT column. (Storing 0 is not a recommended practice, by the way.) For example, if you dump the table with mysqldump and then reload it, MySQL normally generates new sequence numbers when it encounters the 0 values, resulting in a table with contents different from the one that was dumped. Enabling NO_AUTO_VALUE_ON_ZERO before reloading the dump file solves this problem. mysqldump now automatically includes in its output a statement that enables NO_AUTO_VALUE_ON_ZERO, to avoid this problem.

  • NO_BACKSLASH_ESCAPES

    Disable the use of the backslash character (“\”) as an escape character within strings. With this mode enabled, backslash becomes an ordinary character like any other.

  • NO_DIR_IN_CREATE

    When creating a table, ignore all INDEX DIRECTORY and DATA DIRECTORY directives. This option is useful on slave replication servers.

  • NO_ENGINE_SUBSTITUTION

    Control automatic substitution of the default storage engine when a statement such as CREATE TABLE or ALTER TABLE specifies a storage engine that is disabled or not compiled in.

    Because storage engines can be pluggable at runtime, unavailable engines are treated the same way:

    With NO_ENGINE_SUBSTITUTION disabled, for CREATE TABLE the default engine is used and a warning occurs if the desired engine is unavailable. For ALTER TABLE, a warning occurs and the table is not altered.

    With NO_ENGINE_SUBSTITUTION enabled, an error occurs and the table is not created or altered if the desired engine is unavailable.

  • NO_FIELD_OPTIONS

    Do not print MySQL-specific column options in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode.

  • NO_KEY_OPTIONS

    Do not print MySQL-specific index options in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode.

  • NO_TABLE_OPTIONS

    Do not print MySQL-specific table options (such as ENGINE) in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode.

  • NO_UNSIGNED_SUBTRACTION

    By default, subtraction between integer operands produces an UNSIGNED result if any operand isUNSIGNED. When NO_UNSIGNED_SUBTRACTION is enabled, the subtraction result is signed, even if any operand is unsigned. For example, compare the type of column c2 in table t1 with that of column c2 in table t2:

    mysql> SET sql_mode='';
    mysql> CREATE TABLE test (c1 BIGINT UNSIGNED NOT NULL);
    mysql> CREATE TABLE t1 SELECT c1 - 1 AS c2 FROM test;
    mysql> DESCRIBE t1;
    +-------+---------------------+------+-----+---------+-------+
    | Field | Type                | Null | Key | Default | Extra |
    +-------+---------------------+------+-----+---------+-------+
    | c2    | bigint(21) unsigned |      |     | 0       |       |
    +-------+---------------------+------+-----+---------+-------+
    
    mysql> SET sql_mode='NO_UNSIGNED_SUBTRACTION';
    mysql> CREATE TABLE t2 SELECT c1 - 1 AS c2 FROM test;
    mysql> DESCRIBE t2;
    +-------+------------+------+-----+---------+-------+
    | Field | Type       | Null | Key | Default | Extra |
    +-------+------------+------+-----+---------+-------+
    | c2    | bigint(21) |      |     | 0       |       |
    +-------+------------+------+-----+---------+-------+
    

    Note that this means that BIGINT UNSIGNED is not 100% usable in all contexts. See Section 11.10, “Cast Functions and Operators”.

    mysql> SET sql_mode = '';
    mysql> SELECT CAST(0 AS UNSIGNED) - 1;
    +-------------------------+
    | CAST(0 AS UNSIGNED) - 1 |
    +-------------------------+
    |    18446744073709551615 |
    +-------------------------+
    
    mysql> SET sql_mode = 'NO_UNSIGNED_SUBTRACTION';
    mysql> SELECT CAST(0 AS UNSIGNED) - 1;
    +-------------------------+
    | CAST(0 AS UNSIGNED) - 1 |
    +-------------------------+
    |                      -1 |
    +-------------------------+
    
  • NO_ZERO_DATE

    In strict mode, do not permit '0000-00-00' as a valid date. You can still insert zero dates with the IGNORE option. When not in strict mode, the date is accepted but a warning is generated.

  • NO_ZERO_IN_DATE

    In strict mode, do not accept dates where the year part is nonzero but the month or day part is 0 (for example, '0000-00-00' is legal but '2010-00-01' and '2010-01-00' are not). If used with the IGNORE option, MySQL inserts a '0000-00-00' date for any such date. When not in strict mode, the date is accepted but a warning is generated.

  • ONLY_FULL_GROUP_BY

    Do not permit queries for which the select list refers to nonaggregated columns that are not named in the GROUP BY clause. The following query is invalid with this mode enabled because address is not named in the GROUP BY clause:

    SELECT name, address, MAX(age) FROM t GROUP BY name;

    This mode also restricts references to nonaggregated columns in the HAVING clause that are not named in the GROUP BY clause.

  • PAD_CHAR_TO_FULL_LENGTH

    By default, trailing spaces are trimmed from CHAR column values on retrieval. If PAD_CHAR_TO_FULL_LENGTH is enabled, trimming does not occur and retrieved CHAR values are padded to their full length. This mode does not apply to VARCHAR columns, for which trailing spaces are retained on retrieval.

    mysql> CREATE TABLE t1 (c1 CHAR(10));
    Query OK, 0 rows affected (0.37 sec)
    
    mysql> INSERT INTO t1 (c1) VALUES('xy');
    Query OK, 1 row affected (0.01 sec)
    
    mysql> SET sql_mode = '';
    Query OK, 0 rows affected (0.00 sec)
    
    mysql> SELECT c1, CHAR_LENGTH(c1) FROM t1;
    +------+-----------------+
    | c1   | CHAR_LENGTH(c1) |
    +------+-----------------+
    | xy   |               2 |
    +------+-----------------+
    1 row in set (0.00 sec)
    
    mysql> SET sql_mode = 'PAD_CHAR_TO_FULL_LENGTH';
    Query OK, 0 rows affected (0.00 sec)
    
    mysql> SELECT c1, CHAR_LENGTH(c1) FROM t1;
    +------------+-----------------+
    | c1         | CHAR_LENGTH(c1) |
    +------------+-----------------+
    | xy         |              10 |
    +------------+-----------------+
    1 row in set (0.00 sec)
    
  • PIPES_AS_CONCAT

    Treat || as a string concatenation operator (same as CONCAT()) rather than as a synonym for OR.

  • REAL_AS_FLOAT

    Treat REAL as a synonym for FLOAT. By default, MySQL treats REAL as a synonym for DOUBLE.

  • STRICT_ALL_TABLES

    Enable strict mode for all storage engines. Invalid data values are rejected. Additional detail follows.

  • STRICT_TRANS_TABLES

    Enable strict mode for transactional storage engines, and when possible for nontransactional storage engines. Additional details follow.

Strict mode controls how MySQL handles input values that are invalid or missing. A value can be invalid for several reasons. For example, it might have the wrong data type for the column, or it might be out of range. A value is missing when a new row to be inserted does not contain a value for a non-NULL column that has no explicit DEFAULT clause in its definition. (For a NULL column, NULL is inserted if the value is missing.)

For transactional tables, an error occurs for invalid or missing values in a statement when either of the STRICT_ALL_TABLES or STRICT_TRANS_TABLES modes are enabled. The statement is aborted and rolled back.

For nontransactional tables, the behavior is the same for either mode, if the bad value occurs in the first row to be inserted or updated. The statement is aborted and the table remains unchanged. If the statement inserts or modifies multiple rows and the bad value occurs in the second or later row, the result depends on which strict option is enabled:

  • For STRICT_ALL_TABLES, MySQL returns an error and ignores the rest of the rows. However, in this case, the earlier rows still have been inserted or updated. This means that you might get a partial update, which might not be what you want. To avoid this, it is best to use single-row statements because these can be aborted without changing the table.

  • For STRICT_TRANS_TABLES, MySQL converts an invalid value to the closest valid value for the column and insert the adjusted value. If a value is missing, MySQL inserts the implicit default value for the column data type. In either case, MySQL generates a warning rather than an error and continues processing the statement. Implicit defaults are described in Section 10.1.4, “Data Type Default Values”.

Strict mode disallows invalid date values such as '2004-04-31'. It does not disallow dates with zero month or day parts such as '2004-04-00' or “zero” dates. To disallow these as well, enable the NO_ZERO_IN_DATE and NO_ZERO_DATE SQL modes in addition to strict mode.

If you are not using strict mode (that is, neither STRICT_TRANS_TABLES nor STRICT_ALL_TABLES is enabled), MySQL inserts adjusted values for invalid or missing values and produces warnings. In strict mode, you can produce this behavior by using INSERT IGNORE or UPDATE IGNORE. See Section 12.7.5.41, “SHOW WARNINGS Синтаксис”.

Strict mode does not affect whether foreign key constraints are checked. foreign_key_checks can be used for that. (See Section 5.1.3, “Server System Variables”.)

The following special modes are provided as shorthand for combinations of mode values from the preceding list.

The descriptions include all mode values that are available in the most recent version of MySQL. For older versions, a combination mode does not include individual mode values that are not available except in newer versions.

5.1.7. Server Plugins

MySQL supports a plugin API that enables creation of server components. Plugins can be loaded at server startup, or loaded and unloaded at runtime without restarting the server. The components supported by this interface include, but are not limited to, storage engines, full-text parser plugins, partitioning support, and server extensions.

5.1.7.1. Installing and Uninstalling Plugins

Server plugins must be loaded in to the server before they can be used. MySQL enables you to load a plugin at server startup or at runtime. It is also possible to control the activation of loaded plugins at startup, and to unload them at runtime.

Installing Plugins

Server plugins must be known to the server before they can be used. A plugin can be made known several ways, as described here. In the following descriptions, plugin_name stands for a plugin name such as innodb or csv.

Built-in plugins:

A plugin that is built in to the server is known by the server automatically. Normally, the server enables the plugin at startup, although this can be changed with the --plugin_name option.

Plugins registered in the mysql.plugin table:

The mysql.plugin table serves as a registry of plugins. The server normally enables each plugin listed in the table at startup, although whether a given plugin is enabled can be changed with the --plugin_name option. If the server is started with the --skip-grant-tables option, it does not consult this table and does not load the plugins listed there.

Plugins named with the --plugin-load option:

A plugin that is located in a plugin library file can be loaded at server startup with the --plugin-load option. Normally, the server enables the plugin at startup, although this can be changed with the --plugin_name option.

The option value is a semicolon-separated list of name=plugin_library pairs. Each name is the name of the plugin, and plugin_library is the name of the shared library that contains the plugin code. If a plugin library is named without any preceding plugin name, the server loads all plugins in the library. Each library file must be located in the directory named by the plugin_dir system variable.

This option does not register any plugin in the mysql.plugin table. For subsequent restarts, the server loads the plugin again only if --plugin-load is given again. That is, this option effects a one-time installation that persists only for one server invocation.

--plugin-load enables plugins to be loaded even when --skip-grant-tables is given (which causes the server to ignore the mysql.plugin table). --plugin-load also enables plugins to be loaded at startup under configurations when plugins cannot be loaded at runtime.

Plugins installed with the INSTALL PLUGIN statement:

A plugin that is located in a plugin library file can be loaded at runtime with the INSTALL PLUGIN statement. The statement also registers the plugin in the mysql.plugin table to cause the server to load it on subsequent restarts. For this reason, INSTALL PLUGIN requires the INSERT privilege for the mysql.plugin table.

If a plugin is named both using a --plugin-load option and in the mysql.plugin table, the server starts but writes these messages to the error log:

100310 19:15:44 [ERROR] Function 'plugin_name' already exists
100310 19:15:44 [Warning] Couldn't load plugin named 'plugin_name'
with soname 'plugin_object_file'.

Пример: The --plugin-load option installs a plugin at server startup. To install a plugin named myplugin in a plugin library file named somepluglib.so, use these lines in a my.cnf file:

[mysqld]
plugin-load=myplugin=somepluglib.so

In this case, the plugin is not registered in mysql.plugin. Restarting the server without the --plugin-load option causes the plugin not to be loaded at startup.

Alternatively, the INSTALL PLUGIN statement causes the server to load the plugin code from the library file at runtime:

mysql> INSTALL PLUGIN myplugin SONAME 'somepluglib.so';

INSTALL PLUGIN also causes “permanent” plugin registration: The server lists the plugin in the mysql.plugin table to ensure that it is loaded on subsequent server restarts.

Many plugins can be loaded either at server startup or at runtime. However, if a plugin is designed such that it must be loaded and initialized during server startup, use --plugin-load rather than INSTALL PLUGIN.

While a plugin is loaded, information about it is available at runtime from several sources, such as the INFORMATION_SCHEMA.PLUGINS table and the SHOW PLUGINS statement. For more information, see Section 5.1.7.2, “Obtaining Server Plugin Information”.

Controlling Plugin Activation

If the server knows about a plugin when it starts (for example, because the plugin is named using a --plugin-load option or registered in the mysql.plugin table), the server loads and enables the plugin by default. It is possible to control activation for such a plugin using a --plugin_name[=value] startup option named after the plugin. In the following descriptions, plugin_name stands for a plugin name such as innodb or csv. As with other options, dashes and underscores are interchangeable in option names. For example, --my_plugin=ON and --my-plugin=ON are equivalent.

  • --plugin_name=OFF

    Tells the server to disable the plugin.

  • --plugin_name[=ON]

    Tells the server to enable the plugin. (Specifying the option as --plugin_name without a value has the same effect.) If the plugin fails to initialize, the server runs with the plugin disabled.

  • --plugin_name=FORCE

    Tells the server to enable the plugin, but if plugin initialization fails, the server does not start. In other words, this option forces the server to run with the plugin enabled or not at all.

  • --plugin_name=FORCE_PLUS_PERMANENT

    Like FORCE, but in addition prevents the plugin from being unloaded at runtime. If a user attempts to do so with UNINSTALL PLUGIN, an error occurs. This value is available as of MySQL 5.5.7.

The values OFF, ON, FORCE, and FORCE_PLUS_PERMANENT are not case sensitive.

The activation state for plugins is visible in the LOAD_OPTION column of the INFORMATION_SCHEMA.PLUGINS table.

Suppose that CSV, BLACKHOLE, and ARCHIVE are built-in pluggable storage engines and that you want the server to load them at startup, subject to these conditions: The server is permitted to run if CSV initialization fails, but must require that BLACKHOLE initialization succeeds, and ARCHIVE should be disabled. To accomplish that, use these lines in an option file:

[mysqld]
csv=ON
blackhole=FORCE
archive=OFF

The --enable-plugin_name option format is supported as a synonym for --plugin_name=ON. The --disable-plugin_name and --skip-plugin_name option formats are supported as synonyms for --plugin_name=OFF.

Before MySQL 5.1.36, plugin options are boolean options (see Section 4.2.3.2, “Program Option Modifiers”). That is, any of these options enable the plugin:

--plugin_name
--plugin_name=1
--enable-plugin_name

And these options disable the plugin:

--plugin_name=0
--disable-plugin_name
--skip-plugin_name

If you upgrade to MySQL 5.5 from a version older than 5.1.36 and previously used options of the form --plugin_name=0 or --plugin_name=1, the equivalent options are now --plugin_name=OFF and --plugin_name=ON, respectively. You also have the choice of requiring plugins to start successfully by using --plugin_name=FORCE or --plugin_name=FORCE_PLUS_PERMANENT.

If a plugin is disabled, either explicitly with OFF or implicitly because it was enabled with ON but failed to initialize, aspects of server operation that require the plugin will change. For example, if the plugin implements a storage engine, existing tables for the storage engine become inaccessible, and attempts to create new tables for the storage engine result in tables that use the default storage engine unless the NO_ENGINE_SUBSTITUTION SQL mode has been enabled to cause an error to occur instead.

Disabling a plugin may require adjustment to other options. For example, if you start the server using --skip-innodb to disable InnoDB, other innodb_xxx options likely will need to be omitted from the startup command. In addition, because InnoDB is the default storage engine, it will not start unless you specify another available storage engine with --default-storage-engine.

Uninstalling Plugins

A plugin known to the server can be uninstalled to disable it at runtime with the UNINSTALL PLUGIN statement. The statement unloads the plugin and removes it from the mysql.plugin table if it is registered there. For this reason, UNINSTALL PLUGIN statement requires the DELETE privilege for the mysql.plugin table. With the plugin no longer registered in the table, the server will not load the plugin automatically for subsequent restarts.

UNINSTALL PLUGIN can unload plugins regardless of whether they were loaded with INSTALL PLUGIN or --plugin-load.

UNINSTALL PLUGIN is subject to these exceptions:

  • It cannot unload plugins that are built in to the server. These can be identified as those that have a library name of NULL in the output from INFORMATION_SCHEMA.PLUGINS or SHOW PLUGINS.

  • It cannot unload plugins for which the server was started with --plugin_name=FORCE_PLUS_PERMANENT, which prevents plugin unloading at runtime. These can be identified from the LOAD_OPTION column of the INFORMATION_SCHEMA.PLUGINS table.

5.1.7.2. Obtaining Server Plugin Information

There are several ways to determine which plugins are installed in the server:

  • The INFORMATION_SCHEMA.PLUGINS table contains a row for each loaded plugin. Any that have a PLUGIN_LIBRARY value of NULL are built in and cannot be unloaded.

    mysql> SELECT * FROM information_schema.PLUGINS\G
    *************************** 1. row ***************************
               PLUGIN_NAME: binlog
            PLUGIN_VERSION: 1.0
             PLUGIN_STATUS: ACTIVE
               PLUGIN_TYPE: STORAGE ENGINE
       PLUGIN_TYPE_VERSION: 50158.0
            PLUGIN_LIBRARY: NULL
    PLUGIN_LIBRARY_VERSION: NULL
             PLUGIN_AUTHOR: MySQL AB
        PLUGIN_DESCRIPTION: This is a pseudo storage engine to represent the binlog in a transaction
            PLUGIN_LICENSE: GPL
               LOAD_OPTION: FORCE
    ...
    *************************** 10. row ***************************
               PLUGIN_NAME: InnoDB
            PLUGIN_VERSION: 1.0
             PLUGIN_STATUS: ACTIVE
               PLUGIN_TYPE: STORAGE ENGINE
       PLUGIN_TYPE_VERSION: 50158.0
            PLUGIN_LIBRARY: ha_innodb_plugin.so
    PLUGIN_LIBRARY_VERSION: 1.0
             PLUGIN_AUTHOR: Innobase Oy
        PLUGIN_DESCRIPTION: Supports transactions, row-level locking,
                            and foreign keys
            PLUGIN_LICENSE: GPL
               LOAD_OPTION: ON
    ...
    
  • The SHOW PLUGINS statement displays a row for each loaded plugin. Any that have a Library value of NULL are built in and cannot be unloaded.

    mysql> SHOW PLUGINS\G
    *************************** 1. row ***************************
       Name: binlog
     Status: ACTIVE
       Type: STORAGE ENGINE
    Library: NULL
    License: GPL
    ...
    *************************** 10. row ***************************
       Name: InnoDB
     Status: ACTIVE
       Type: STORAGE ENGINE
    Library: ha_innodb_plugin.so
    License: GPL
    ...
    
  • The mysql.plugin table shows which plugins have been registered with INSTALL PLUGIN. The table contains only plugin names and library file names, so it does not provide as much information as the PLUGINS table or the SHOW PLUGINS statement.

5.1.8. Server-Side Help

MySQL Server supports a HELP statement that returns online information from the MySQL Reference manual (see Section 12.8.3, “HELP Синтаксис”). The proper operation of this statement requires that the help tables in the mysql database be initialized with help topic information, which is done by processing the contents of the fill_help_tables.sql script.

If you install MySQL using a binary or source distribution on Unix, help table setup occurs when you run mysql_install_db. For an RPM distribution on Linux or binary distribution on Windows, help table setup occurs as part of the MySQL installation process.

If you upgrade MySQL using a binary distribution, the help tables are not upgraded automatically, but you can upgrade them manually. Locate the fill_help_tables.sql file in the share or share/mysql directory. Change location into that directory and process the file with the mysql client as follows:

shell> mysql -u root mysql < fill_help_tables.sql

You can also obtain the latest fill_help_tables.sql at any time to upgrade your help tables. Download the proper file for your version of MySQL from http://dev.mysql.com/doc/index-other.html. After downloading and uncompressing the file, process it with mysql as described previously.

If you are working with Bazaar and a MySQL development source tree, you will need to download the fill_help_tables.sql file because the tree contains only a “stub” version.

5.1.9. Server Response to Signals

On Unix, signals can be sent to processes. mysqld responds to signals sent to it as follows:

  • SIGTERM causes the server to shut down.

  • SIGHUP causes the server to reload the grant tables and flush the logs (like FLUSH PRIVILEGES and FLUSH LOGS). It also writes a status report to the error log that has this format:

    Status information:
    
    Current dir: /var/mysql/data/
    Running threads: 0  Stack size: 196608
    Current locks:
    
    Key caches:
    default
    Buffer_size:       8388600
    Block_size:           1024
    Division_limit:        100
    Age_limit:             300
    blocks used:             0
    not flushed:             0
    w_requests:              0
    writes:                  0
    r_requests:              0
    reads:                   0
    
    handler status:
    read_key:            0
    read_next:           0
    read_rnd             0
    read_first:          1
    write:               0
    delete               0
    update:              0
    
    Table status:
    Opened tables:          5
    Open tables:            0
    Open files:             7
    Open streams:           0
    
    Alarm status:
    Active alarms:   1
    Max used alarms: 2
    Next alarm time: 67

On some Mac OS X 10.3 versions, mysqld ignores SIGHUP and SIGQUIT.

5.1.10. The Shutdown Process

The server shutdown process takes place as follows:

  1. The shutdown process is initiated.

    This can occur initiated several ways. For example, a user with the SHUTDOWN privilege can execute a mysqladmin shutdown command. mysqladmin can be used on any platform supported by MySQL. Other operating system-specific shutdown initiation methods are possible as well: The server shuts down on Unix when it receives a SIGTERM signal. A server running as a service on Windows shuts down when the services manager tells it to.

  2. The server creates a shutdown thread if necessary.

    Depending on how shutdown was initiated, the server might create a thread to handle the shutdown process. If shutdown was requested by a client, a shutdown thread is created. If shutdown is the result of receiving a SIGTERM signal, the signal thread might handle shutdown itself, or it might create a separate thread to do so. If the server tries to create a shutdown thread and cannot (for example, if memory is exhausted), it issues a diagnostic message that appears in the error log:

    Error: Can't create thread to kill server
  3. The server stops accepting new connections.

    To prevent new activity from being initiated during shutdown, the server stops accepting new client connections by closing the handlers for the network interfaces to which it normally listens for connections: the TCP/IP port, the Unix socket file, the Windows named pipe, and shared memory on Windows.

  4. The server terminates current activity.

    For each thread associated with a client connection, the server breaks the connection to the client and marks the thread as killed. Threads die when they notice that they are so marked. Threads for idle connections die quickly. Threads that currently are processing statements check their state periodically and take longer to die. For additional information about thread termination, see Section 12.7.6.4, “KILL Синтаксис”, in particular for the instructions about killed REPAIR TABLE or OPTIMIZE TABLE operations on MyISAM tables.

    For threads that have an open transaction, the transaction is rolled back. Note that if a thread is updating a nontransactional table, an operation such as a multiple-row UPDATE or INSERT may leave the table partially updated because the operation can terminate before completion.

    If the server is a master replication server, it treats threads associated with currently connected slaves like other client threads. That is, each one is marked as killed and exits when it next checks its state.

    If the server is a slave replication server, it stops the I/O and SQL threads, if they are active, before marking client threads as killed. The SQL thread is permitted to finish its current statement (to avoid causing replication problems), and then stops. If the SQL thread was in the middle of a transaction at this point, the transaction is rolled back.

    If the slave is updating a non-transactional table when it is forcibly killed, the slave's data may become inconsistent with the master.

  5. The server shuts down or closes storage engines.

    At this stage, the server flushes the table cache and closes all open tables.

    Each storage engine performs any actions necessary for tables that it manages. For example, MyISAM flushes any pending index writes for a table. InnoDB flushes its buffer pool to disk (unless innodb_fast_shutdown is 2), writes the current LSN to the tablespace, and terminates its own internal threads.

  6. The server exits.

5.2. MySQL Server Logs

MySQL Server has several logs that can help you find out what activity is taking place.

Log TypeInformation Written to Log
Error logProblems encountered starting, running, or stopping mysqld
General query logEstablished client connections and statements received from clients
Binary logStatements that change data (also used for replication)
Relay logData changes received from a replication master server
Slow query logQueries that took more than long_query_time seconds to execute

By default, no logs are enabled. The following log-specific sections provide information about the server options that enable logging.

By default, the server writes files for all enabled logs in the data directory. You can force the server to close and reopen the log files (or in some cases switch to a new log file) by flushing the logs. Log flushing occurs when you issue a FLUSH LOGS statement; execute mysqladmin with a flush-logs or refresh argument; or execute mysqldump with a --flush-logs or --master-data option. See Section 12.7.6.3, “FLUSH Синтаксис”, Section 4.5.2, “mysqladmin — Client for Administering a MySQL Server”, and Section 4.5.4, “mysqldump — A Database Backup Program”. In addition, the binary log is flushed when its size reaches the value of the max_binlog_size system variable.

You can control the general query and slow query logs during runtime. You can enable or disable logging, or change the log file name. You can tell the server to write general query and slow query entries to log tables, log files, or both. For details, see Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”, Section 5.2.3, “The General Query Log”, and Section 5.2.5, “The Slow Query Log”.

The relay log is used only on slave replication servers, to hold data changes from the master server that must also be made on the slave. For discussion of relay log contents and configuration, see Section 15.2.2.1, “The Slave Relay Log”.

For information about log maintenance operations such as expiration of old log files, see Section 5.2.6, “Server Log Maintenance”.

For information about keeping logs secure, see Section 5.3.2.1, “Administrator Guidelines for Password Security”.

5.2.1. Selecting General Query and Slow Query Log Output Destinations

MySQL Server provides flexible control over the destination of output to the general query log and the slow query log, if those logs are enabled. Possible destinations for log entries are log files or the general_log and slow_log tables in the mysql database. Either or both destinations can be selected.

Currently, logging to tables incurs significantly more server overhead than logging to files. If you enable the general log or slow query log and require highest performance, you should use file logging, not table logging.

Log control at server startup. The --log-output option specifies the destination for log output. This option does not in itself enable the logs. Its syntax is --log-output[=value,...]:

  • If --log-output is given with a value, the value should be a comma-separated list of one or more of the words TABLE (log to tables), FILE (log to files), or NONE (do not log to tables or files). NONE, if present, takes precedence over any other specifiers.

  • If --log-output is omitted or given without a value, the default logging destination is FILE.

The general_log system variable controls logging to the general query log for the selected log destinations. If specified at server startup, general_log takes an optional argument of 1 or 0 to enable or disable the log. To specify a file name other than the default for file logging, set the general_log_file variable. Similarly, the slow_query_log variable controls logging to the slow query log for the selected destinations and setting slow_query_log_file specifies a file name for file logging. If either log is enabled, the server opens the corresponding log file and writes startup messages to it. However, further logging of queries to the file does not occur unless the FILE log destination is selected.

Examples:

  • To write general query log entries to the log table and the log file, use --log-output=TABLE,FILE to select both log destinations and --general_log to enable the general query log.

  • To write general and slow query log entries only to the log tables, use --log-output=TABLE to select tables as the log destination and --general_log and --slow_query_log to enable both logs.

  • To write slow query log entries only to the log file, use --log-output=FILE to select files as the log destination and --slow_query_log to enable the slow query log. (In this case, because the default log destination is FILE, you could omit the --log-output option.)

Log control at runtime. The system variables associated with log tables and files enable runtime control over logging:

  • The global log_output system variable indicates the current logging destination. It can be modified at runtime to change the destination.

  • The global general_log and slow_query_log variables indicate whether the general query log and slow query log are enabled (ON) or disabled (OFF). You can set these variables at runtime to control whether the logs are enabled.

  • The global general_log_file and slow_query_log_file variables indicate the names of the general query log and slow query log files. You can set these variables at server startup or at runtime to change the names of the log files.

  • To disable or enable general query logging for the current connection, set the session sql_log_off variable to ON or OFF.

The use of tables for log output offers the following benefits:

  • Log entries have a standard format. To display the current structure of the log tables, use these statements:

    SHOW CREATE TABLE mysql.general_log;
    SHOW CREATE TABLE mysql.slow_log;
  • Log contents are accessible through SQL statements. This enables the use of queries that select only those log entries that satisfy specific criteria. For example, to select log contents associated with a particular client (which can be useful for identifying problematic queries from that client), it is easier to do this using a log table than a log file.

  • Logs are accessible remotely through any client that can connect to the server and issue queries (if the client has the appropriate log table privileges). It is not necessary to log in to the server host and directly access the file system.

The log table implementation has the following characteristics:

  • In general, the primary purpose of log tables is to provide an interface for users to observe the runtime execution of the server, not to interfere with its runtime execution.

  • CREATE TABLE, ALTER TABLE, and DROP TABLE are valid operations on a log table. For ALTER TABLE and DROP TABLE, the log table cannot be in use and must be disabled, as described later.

  • By default, the log tables use the CSV storage engine that writes data in comma-separated values format. For users who have access to the .CSV files that contain log table data, the files are easy to import into other programs such as spreadsheets that can process CSV input.

    The log tables can be altered to use the MyISAM storage engine. You cannot use ALTER TABLE to alter a log table that is in use. The log must be disabled first. No engines other than CSV or MyISAM are legal for the log tables.

  • To disable logging so that you can alter (or drop) a log table, you can use the following strategy. The example uses the general query log; the procedure for the slow query log is similar but uses the slow_log table and slow_query_log system variable.

    SET @old_log_state = @@global.general_log;
    SET GLOBAL general_log = 'OFF';
    ALTER TABLE mysql.general_log ENGINE = MyISAM;
    SET GLOBAL general_log = @old_log_state;
  • TRUNCATE TABLE is a valid operation on a log table. It can be used to expire log entries.

  • RENAME TABLE is a valid operation on a log table. You can atomically rename a log table (to perform log rotation, for example) using the following strategy:

    USE mysql;
    DROP TABLE IF EXISTS general_log2;
    CREATE TABLE general_log2 LIKE general_log;
    RENAME TABLE general_log TO general_log_backup, general_log2 TO general_log;
  • As of MySQL 5.5.7, CHECK TABLE is a valid operation on a log table.

  • LOCK TABLES cannot be used on a log table.

  • INSERT, DELETE, and UPDATE cannot be used on a log table. These operations are permitted only internally to the server itself.

  • FLUSH TABLES WITH READ LOCK and the state of the global read_only system variable have no effect on log tables. The server can always write to the log tables.

  • Entries written to the log tables are not written to the binary log and thus are not replicated to slave servers.

  • To flush the log tables or log files, use FLUSH TABLES or FLUSH LOGS, respectively.

  • Partitioning of log tables is not permitted.

5.2.2. The Error Log

The error log contains information indicating when mysqld was started and stopped and also any critical errors that occur while the server is running. If mysqld notices a table that needs to be automatically checked or repaired, it writes a message to the error log.

On some operating systems, the error log contains a stack trace if mysqld dies. The trace can be used to determine where mysqld died. See MySQL Internals: Porting.

You can specify where mysqld writes the error log with the --log-error[=file_name] option. If the option is given with no file_name value, mysqld uses the name host_name.err by default. The server creates the file in the data directory unless an absolute path name is given to specify a different directory.

If you do not specify --log-error, or (on Windows) if you use the --console option, errors are written to stderr, the standard error output. Usually this is your terminal.

On Windows, error output is always written to the error log if --console is not given.

In addition, on Windows, events and error messages are written to the Windows Event Log within the Application log. Entries marked as Warning and Замечание are written to the Event Log, but informational messages (such as information statements from individual storage engines) are not copied to the Event Log. The log entries have a source of MySQL. You cannot disable writing information to the Windows Event Log.

If you flush the logs using FLUSH LOGS or mysqladmin flush-logs and mysqld is writing the error log to a file (for example, if it was started with the --log-error option), the effect is version dependent:

  • As of MySQL 5.5.7, the server closes and reopens the log file. To rename the file, you can do so manually before flushing. Then flushing the logs reopens a new file with the original file name. For example, you can rename the file and create a new one using the following commands:

    shell> mv host_name.err host_name.err-old
    shell> mysqladmin flush-logs
    shell> mv host_name.err-old backup-directory
    

    On Windows, use rename rather than mv.

  • Prior to MySQL 5.5.7, the server renames the current log file with the suffix -old, then creates a new empty log file. Be aware that a second log-flushing operation thus causes the original error log file to be lost unless you save it under a different name. On Windows, you cannot rename the error log while the server has it open before MySQL 5.5.7. To avoid a restart, flush the logs first to cause the server to rename the original file and create a new one, then save the renamed file. That also works on Unix, or you can use the commands shown earlier.

No error log renaming occurs when the logs are flushed in any case if the server is not writing to a named file.

If you use mysqld_safe to start mysqld, mysqld_safe arranges for mysqld to write error messages to a log file or to syslog mysqld_safe has three error-logging options, --syslog, --skip-syslog, and --log-error. The default with no logging options or with --skip-syslog is to use the default log file. To explicitly specify use of an error log file, specify --log-error=file_name to mysqld_safe, and mysqld_safe will arrange for mysqld to write messages to a log file. To use syslog instead, specify the --syslog option.

If you specify --log-error in an option file in a section that mysqld reads, mysqld_safe also will find and use the option.

If mysqld_safe is used to start mysqld and mysqld dies unexpectedly, mysqld_safe notices that it needs to restart mysqld and writes a restarted mysqld message to the error log.

The --log-warnings option or log_warnings system variable can be used to control warning logging to the error log. The default value is enabled (1). Warning logging can be disabled using a value of 0. If the value is greater than 1, aborted connections are written to the error log, and access-denied errors for new connection attempts are written. See Section C.5.2.11, “Communication Ошибки and Aborted Connections”.

5.2.3. The General Query Log

The general query log is a general record of what mysqld is doing. The server writes information to this log when clients connect or disconnect, and it logs each SQL statement received from clients. The general query log can be very useful when you suspect an error in a client and want to know exactly what the client sent to mysqld.

mysqld writes statements to the query log in the order that it receives them, which might differ from the order in which they are executed. This logging order contrasts to the binary log, for which statements are written after they are executed but before any locks are released. (Also, the query log contains all statements, whereas the binary log does not contain statements that only select data.)

By default, the general query log is disabled. To specify the initial general query log state explicitly, use --general_log[={0|1}]. With no argument or an argument of 1, --general_log enables the log. With an argument of 0, this option disables the log. To specify a log file name, use --general_log_file=file_name. To specify the log destination, use --log-output (as described in Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”). The older options to enable the general query log, --log and -l, are deprecated.

If you specify no name for the general query log file, the default name is host_name.log. The server creates the file in the data directory unless an absolute path name is given to specify a different directory.

To disable or enable the general query log or change the log file name at runtime, use the global general_log and general_log_file system variables. Set general_log to 0 (or OFF) to disable the log or to 1 (or ON) to enable it. Set general_log_file to specify the name of the log file. If a log file already is open, it is closed and the new file is opened.

When the general query log is enabled, the server writes output to any destinations specified by the --log-output option or log_output system variable. If you enable the log, the server opens the log file and writes startup messages to it. However, further logging of queries to the file does not occur unless the FILE log destination is selected. If the destination is NONE, the server writes no queries even if the general log is enabled. Setting the log file name has no effect on logging if the log destination value does not contain FILE.

Server restarts and log flushing do not cause a new general query log file to be generated (although flushing closes and reopens it). You can rename the file and create a new one by using the following commands:

shell> mv host_name.log host_name-old.log
shell> mysqladmin flush-logs
shell> mv host_name-old.log backup-directory

On Windows, use rename rather than mv.

You can also rename the general query log file at runtime by disabling the log:

SET GLOBAL general_log = 'OFF';

With the log disabled, rename the log file externally; for example, from the command line. Then enable the log again:

SET GLOBAL general_log = 'ON';

This method works on any platform and does not require a server restart.

The session sql_log_off variable can be set to ON or OFF to disable or enable general query logging for the current connection.

The general query log should be protected because logged statements might contain passwords. See Section 5.3.2.1, “Administrator Guidelines for Password Security”.

5.2.4. The Binary Log

The binary log contains “events” that describe database changes such as table creation operations or changes to table data. It also contains events for statements that potentially could have made changes (for example, a DELETE which matched no rows), unless row-based logging is used. The binary log also contains information about how long each statement took that updated data. The binary log has two important purposes:

  • For replication, the binary log is used on master replication servers as a record of the statements to be sent to slave servers. The master server sends the events contained in its binary log to its slaves, which execute those events to make the same data changes that were made on the master. See Section 15.2, “Replication Implementation”.

  • Certain data recovery operations require use of the binary log. After a backup has been restored, the events in the binary log that were recorded after the backup was made are re-executed. These events bring databases up to date from the point of the backup. See Section 6.5, “Point-in-Time (Incremental) Recovery Using the Binary Log”.

Running a server with binary logging enabled makes performance slightly slower. However, the benefits of the binary log in enabling you to set up replication and for restore operations generally outweigh this minor performance decrement.

For information about server options and variables affecting the operation of binary logging, see Section 15.1.3.4, “Binary Log Options and Variables”.

The binary log is not used for statements such as SELECT or SHOW that do not modify data. If you want to log all statements (for example, to identify a problem query), use the general query log. See Section 5.2.3, “The General Query Log”.

The binary log should be protected because logged statements might contain passwords. See Section 5.3.2.1, “Administrator Guidelines for Password Security”.

The format of the events recorded in the binary log is dependent on the binary logging format. Three format types are supported, row-based logging, statement-based logging and mixed-base logging. The binary logging format used depends on the MySQL version. For more information on logging formats, see Section 5.2.4.1, “Binary Logging Formats”.

For information about the format of the binary log itself, see http://forge.mysql.com/wiki/MySQL_Internals_Binary_Log.

To enable the binary log, start the server with the --log-bin[=base_name] option. If no base_name value is given, the default name is the value of the pid-file option (which by default is the name of host machine) followed by -bin. If the basename is given, the server writes the file in the data directory unless the basename is given with a leading absolute path name to specify a different directory. It is recommended that you specify a basename; see Section C.5.8, “Known Issues in MySQL”, for the reason.

If you supply an extension in the log name (for example, --log-bin=base_name.extension), the extension is silently removed and ignored.

mysqld appends a numeric extension to the binary log basename to generate binary log file names. The number increases each time the server creates a new log file, thus creating an ordered series of files. The server creates a new file in the series each time it starts or flushes the logs. The server also creates a new binary log file automatically after the current log's size reaches max_binlog_size. A binary log file may become larger than max_binlog_size if you are using large transactions because a transaction is written to the file in one piece, never split between files.

To keep track of which binary log files have been used, mysqld also creates a binary log index file that contains the names of all used binary log files. By default, this has the same basename as the binary log file, with the extension '.index'. You can change the name of the binary log index file with the --log-bin-index[=file_name] option. You should not manually edit this file while mysqld is running; doing so would confuse mysqld.

The term “binary log file” generally denotes an individual numbered file containing database events. The term “binary log” collectively denotes the set of numbered binary log files plus the index file.

The server evaluates the --binlog-do-db and --binlog-ignore-db options in the same way as it does the --replicate-do-db and --replicate-ignore-db options. For information about how this is done, see Section 15.2.3.1, “Evaluation of Database-Level Replication and Binary Logging Options”.

If you are replicating from a MySQL Cluster to a standalone MySQL Server, you should be aware that the the NDB storage engine uses default values for some binary logging options (including options specific to NDB such as --ndb-log-update-as-write) that differ from those used by other storage engines. If not corrected for, these differences can lead to divergence of the master's and slave's binary logs. For more information, see Replication from NDB to other storage engines. In particular, if you are using a nontransactional storage engine such as MyISAM on the slave, see Replication from NDB to a nontransactional storage engine.

A replication slave server by default does not write to its own binary log any data modifications that are received from the replication master. To log these modifications, start the slave with the --log-slave-updates option in addition to the --log-bin option (see Section 15.1.3.3, “Replication Slave Options and Variables”). This is done when a slave is also to act as a master to other slaves in chained replication.

You can delete all binary log files with the RESET MASTER statement, or a subset of them with PURGE BINARY LOGS. See Section 12.7.6.6, “RESET Синтаксис”, and Section 12.4.1.1, “PURGE BINARY LOGS Синтаксис”.

If you are using replication, you should not delete old binary log files on the master until you are sure that no slave still needs to use them. For example, if your slaves never run more than three days behind, once a day you can execute mysqladmin flush-logs on the master and then remove any logs that are more than three days old. You can remove the files manually, but it is preferable to use PURGE BINARY LOGS, which also safely updates the binary log index file for you (and which can take a date argument). See Section 12.4.1.1, “PURGE BINARY LOGS Синтаксис”.

A client that has the SUPER privilege can disable binary logging of its own statements by using a SET sql_log_bin=0 statement. See Section 5.1.3, “Server System Variables”.

You can display the contents of binary log files with the mysqlbinlog utility. This can be useful when you want to reprocess statements in the log for a recovery operation. For example, you can update a MySQL server from the binary log as follows:

shell> mysqlbinlog log_file | mysql -h server_name

mysqlbinlog also can be used to display replication slave relay log file contents because they are written using the same format as binary log files. For more information on the mysqlbinlog utility and how to use it, see Section 4.6.7, “mysqlbinlog — Utility for Processing Binary Log Files”. For more information about the binary log and recovery operations, see Section 6.5, “Point-in-Time (Incremental) Recovery Using the Binary Log”.

Binary logging is done immediately after a statement completes but before any locks are released or any commit is done. This ensures that the log is logged in execution order.

Updates to nontransactional tables are stored in the binary log immediately after execution.

Within an uncommitted transaction, all updates (UPDATE, DELETE, or INSERT) that change transactional tables such as InnoDB tables are cached until a COMMIT statement is received by the server. At that point, mysqld writes the entire transaction to the binary log before the COMMIT is executed.

Modifications to nontransactional tables cannot be rolled back. If a transaction that is rolled back includes modifications to nontransactional tables, the entire transaction is logged with a ROLLBACK statement at the end to ensure that the modifications to those tables are replicated.

When a thread that handles the transaction starts, it allocates a buffer of binlog_cache_size to buffer statements. If a statement is bigger than this, the thread opens a temporary file to store the transaction. The temporary file is deleted when the thread ends.

The Binlog_cache_use status variable shows the number of transactions that used this buffer (and possibly a temporary file) for storing statements. The Binlog_cache_disk_use status variable shows how many of those transactions actually had to use a temporary file. These two variables can be used for tuning binlog_cache_size to a large enough value that avoids the use of temporary files.

The max_binlog_cache_size system variable (default 4GB, which is also the maximum) can be used to restrict the total size used to cache a multiple-statement transaction. If a transaction is larger than this many bytes, it fails and rolls back. The minimum value is 4096.

If you are using the binary log and row based logging, concurrent inserts are converted to normal inserts for CREATE ... SELECT or INSERT ... SELECT statements. This is done to ensure that you can re-create an exact copy of your tables by applying the log during a backup operation. If you are using statement-based logging, the original statement is written to the log.

The binary log format has some known limitations that can affect recovery from backups. See Section 15.4.1, “Replication Features and Issues”.

Binary logging for stored programs is done as described in Section 18.7, “Binary Logging of Stored Programs”.

Note that the binary log format differs in MySQL 5.5 from previous versions of MySQL, due to enhancements in replication. See Section 15.4.2, “Replication Compatibility Between MySQL Versions”.

Writes to the binary log file and binary log index file are handled in the same way as writes to MyISAM tables. See Section C.5.4.3, “How MySQL Handles a Full Disk”.

By default, the binary log is not synchronized to disk at each write. So if the operating system or machine (not only the MySQL server) crashes, there is a chance that the last statements of the binary log are lost. To prevent this, you can make the binary log be synchronized to disk after every N writes to the binary log, with the sync_binlog system variable. See Section 5.1.3, “Server System Variables”. 1 is the safest value for sync_binlog, but also the slowest. Even with sync_binlog set to 1, there is still the chance of an inconsistency between the table content and binary log content in case of a crash. For example, if you are using InnoDB tables and the MySQL server processes a COMMIT statement, it writes the whole transaction to the binary log and then commits this transaction into InnoDB. If the server crashes between those two operations, the transaction is rolled back by InnoDB at restart but still exists in the binary log. To resolve this, you should set --innodb_support_xa to 1. Although this option is related to the support of XA transactions in InnoDB, it also ensures that the binary log and InnoDB data files are synchronized.

For this option to provide a greater degree of safety, the MySQL server should also be configured to synchronize the binary log and the InnoDB logs to disk at every transaction. The InnoDB logs are synchronized by default, and sync_binlog=1 can be used to synchronize the binary log. The effect of this option is that at restart after a crash, after doing a rollback of transactions, the MySQL server cuts rolled back InnoDB transactions from the binary log. This ensures that the binary log reflects the exact data of InnoDB tables, and so, that the slave remains in synchrony with the master (not receiving a statement which has been rolled back).

If the MySQL server discovers at crash recovery that the binary log is shorter than it should have been, it lacks at least one successfully committed InnoDB transaction. This should not happen if sync_binlog=1 and the disk/file system do an actual sync when they are requested to (some do not), so the server prints an error message The binary log file_name is shorter than its expected size. In this case, this binary log is not correct and replication should be restarted from a fresh snapshot of the master's data.

The session values of the following system variables are written to the binary log and honored by the replication slave when parsing the binary log:

5.2.4.1. Binary Logging Formats

The server uses several logging formats to record information in the binary log. The exact format employed depends on the version of MySQL being used. There are three logging formats:

  • Replication capabilities in MySQL originally were based on propagation of SQL statements from master to slave. This is called statement-based logging. You can cause this format to be used by starting the server with --binlog-format=STATEMENT.

  • In row-based logging, the master writes events to the binary log that indicate how individual table rows are affected. You can cause the server to use row-based logging by starting it with --binlog-format=ROW.

  • A third option is also available: mixed logging. With mixed logging, statement-based logging is used by default, but the logging mode switches automatically to row-based in certain cases as described below. You can cause MySQL to use mixed logging explicitly by starting mysqld with the option --binlog-format=MIXED.

In MySQL 5.5, the default binary logging format is STATEMENT.

The logging format can also be set or limited by the storage engine being used. This helps to eliminate issues when replicating certain statements between a master and slave which are using different storage engines.

With statement-based replication, there may be issues with replicating nondeterministic statements. In deciding whether or not a given statement is safe for statement-based replication, MySQL determines whether it can guarantee that the statement can be replicated using statement-based logging. If MySQL cannot make this guarantee, it marks the statement as potentially unreliable and issues the warning, Statement may not be safe to log in statement format.

You can avoid these issues by using MySQL's row-based replication instead.

5.2.4.2. Setting The Binary Log Format

You can select the binary logging format explicitly by starting the MySQL server with --binlog-format=type. The supported values for type are:

  • STATEMENT causes logging to be statement based.

  • ROW causes logging to be row based.

  • MIXED causes logging to use mixed format.

In MySQL 5.5, the default binary logging format is STATEMENT.

Exception.  For all MySQL Cluster releases using the NDBCLUSTER storage engine, the default binary log format is MIXED. See Section 16.6, “MySQL Cluster Replication”.

The logging format also can be switched at runtime. To specify the format globally for all clients, set the global value of the binlog_format system variable:

mysql> SET GLOBAL binlog_format = 'STATEMENT';
mysql> SET GLOBAL binlog_format = 'ROW';
mysql> SET GLOBAL binlog_format = 'MIXED';

An individual client can control the logging format for its own statements by setting the session value of binlog_format:

mysql> SET SESSION binlog_format = 'STATEMENT';
mysql> SET SESSION binlog_format = 'ROW';
mysql> SET SESSION binlog_format = 'MIXED';
Замечание

Each MySQL Server can set its own and only its own binary logging format (true whether binlog_format is set with global or session scope). This means that changing the logging format on a replication master does not cause a slave to change its logging format to match. (When using STATEMENT mode, the binlog_format system variable is not replicated; when using MIXED or ROW logging mode, it is replicated but is ignored by the slave.) Changing the binary logging format on the master while replication is ongoing, or without also changing it on the slave can thus cause unexpected results, or even cause replication to fail altogether.

To change the global or session binlog_format value, you must have the SUPER privilege.

In addition to switching the logging format manually, a slave server may switch the format automatically. This happens when the server is running in either STATEMENT or MIXED format and encounters an event in the binary log that is written in ROW logging format. In that case, the slave switches to row-based replication temporarily for that event, and switches back to the previous format afterward.

There are several reasons why a client might want to set binary logging on a per-session basis:

  • A session that makes many small changes to the database might want to use row-based logging.

  • A session that performs updates that match many rows in the WHERE clause might want to use statement-based logging because it will be more efficient to log a few statements than many rows.

  • Some statements require a lot of execution time on the master, but result in just a few rows being modified. It might therefore be beneficial to replicate them using row-based logging.

There are exceptions when you cannot switch the replication format at runtime:

  • From within a stored function or a trigger

  • If the NDBCLUSTER storage engine is enabled

  • If the session is currently in row-based replication mode and has open temporary tables

Trying to switch the format in any of these cases results in an error.

Switching the replication format at runtime is not recommended when any temporary tables exist, because temporary tables are logged only when using statement-based replication, whereas with row-based replication they are not logged. With mixed replication, temporary tables are usually logged; exceptions happen with user-defined functions (UDFs) and with the UUID() function.

With the binary log format set to ROW, many changes are written to the binary log using the row-based format. Some changes, however, still use the statement-based format. Examples include all DDL (data definition language) statements such as CREATE TABLE, ALTER TABLE, or DROP TABLE.

The --binlog-row-event-max-size option is available for servers that are capable of row-based replication. Rows are stored into the binary log in chunks having a size in bytes not exceeding the value of this option. The value must be a multiple of 256. The default value is 1024.

Warning

When using statement-based logging for replication, it is possible for the data on the master and slave to become different if a statement is designed in such a way that the data modification is nondeterministic; that is, it is left to the will of the query optimizer. In general, this is not a good practice even outside of replication. For a detailed explanation of this issue, see Section C.5.8, “Known Issues in MySQL”.

5.2.4.3. Mixed Binary Logging Format

When running in MIXED logging format, the server automatically switches from statement-based to row-based logging under the following conditions:

Замечание

A warning is generated if you try to execute a statement using statement-based logging that should be written using row-based logging. The warning is shown both in the client (in the output of SHOW WARNINGS) and through the mysqld error log. A warning is added to the SHOW WARNINGS table each time such a statement is executed. However, only the first statement that generated the warning for each client session is written to the error log to prevent flooding the log.

In addition to the decisions above, individual engines can also determine the logging format used when information in a table is updated. The logging capabilities of an individual engine can be defined as follows:

  • If an engine supports row-based logging, the engine is said to be row-logging capable.

  • If an engine supports statement-based logging, the engine is said to be statement-logging capable.

A given storage engine can support either or both logging formats. The following table lists the formats supported by each engine.

Storage EngineRow Logging SupportedStatement Logging Supported
ARCHIVEYesYes
BLACKHOLEYesYes
CSVYesYes
EXAMPLEYesNo
FEDERATEDYesYes
HEAPYesYes
InnoDBYesYes when the transaction isolation level is REPEATABLE READ or SERIALIZABLE; No otherwise.
MyISAMYesYes
MERGEYesYes
NDBCLUSTERYesNo

In MySQL 5.5.3 and later, whether a statement is to be logged and the logging mode to be used is determined according to the type of statement (safe, unsafe, or binary injected), the binary logging format (STATEMENT, ROW, or MIXED), and the logging capabilities of the storage engine (statement capable, row capable, both, or neither). Statements may be logged with or without a warning; failed statements are not logged, but generate errors in the log. This is shown in the following decision table, where SLC stands for “statement-logging capable” and RLC stands for “row-logging capable”.

ConditionAction
Typebinlog_formatSLCRLCError / WarningLogged as
**NoNoError: Cannot execute statement: Binary logging is impossible since at least one engine is involved that is both row-incapable and statement-incapable.-
SafeSTATEMENTYesNo-STATEMENT
SafeMIXEDYesNo-STATEMENT
SafeROWYesNoError: Cannot execute statement: Binary logging is impossible since BINLOG_FORMAT = ROW and at least one table uses a storage engine that is not capable of row-based logging.-
UnsafeSTATEMENTYesNoWarning: Unsafe statement binlogged in statement format, since BINLOG_FORMAT = STATEMENTSTATEMENT
UnsafeMIXEDYesNoError: Cannot execute statement: Binary logging of an unsafe statement is impossible when the storage engine is limited to statement-based logging, even if BINLOG_FORMAT = MIXED.-
UnsafeROWYesNoError: Cannot execute statement: Binary logging is impossible since BINLOG_FORMAT = ROW and at least one table uses a storage engine that is not capable of row-based logging.-
Row InjectionSTATEMENTYesNoError: Cannot execute row injection: Binary logging is not possible since at least one table uses a storage engine that is not capable of row-based logging.-
Row InjectionMIXEDYesNoError: Cannot execute row injection: Binary logging is not possible since at least one table uses a storage engine that is not capable of row-based logging.-
Row InjectionROWYesNoError: Cannot execute row injection: Binary logging is not possible since at least one table uses a storage engine that is not capable of row-based logging.-
SafeSTATEMENTNoYesError: Cannot execute statement: Binary logging is impossible since BINLOG_FORMAT = STATEMENT and at least one table uses a storage engine that is not capable of statement-based logging.-
SafeMIXEDNoYes-ROW
SafeROWNoYes-ROW
UnsafeSTATEMENTNoYesError: Cannot execute statement: Binary logging is impossible since BINLOG_FORMAT = STATEMENT and at least one table uses a storage engine that is not capable of statement-based logging.-
UnsafeMIXEDNoYes-ROW
UnsafeROWNoYes-ROW
Row InjectionSTATEMENTNoYesError: Cannot execute row injection: Binary logging is not possible since BINLOG_FORMAT = STATEMENT.-
Row InjectionMIXEDNoYes-ROW
Row InjectionROWNoYes-ROW
SafeSTATEMENTYesYes-STATEMENT
SafeMIXEDYesYes-ROW
SafeROWYesYes-ROW
UnsafeSTATEMENTYesYesWarning: Unsafe statement binlogged in statement format since BINLOG_FORMAT = STATEMENT.STATEMENT
UnsafeMIXEDYesYes-ROW
UnsafeROWYesYes-ROW
Row InjectionSTATEMENTYesYesError: Cannot execute row injection: Binary logging is not possible because BINLOG_FORMAT = STATEMENT.-
Row InjectionMIXEDYesYes-ROW
Row InjectionROWYesYes-ROW

Handling of mixed-format logging in MySQL 5.5.2 and earlier.  The decision-making process for binary logging changed in MySQL 5.5.3, due to the fix for Bug #39934. Prior to MySQL 5.5.3, when determining the logging mode to be used, the capabilities of all the tables affected by the event are combined, and the set of affected tables is then marked according to these rules:

  • A set of tables is defined as row-logging restricted if the tables are row-logging capable but not statement-logging capable.

  • A set of tables is defined as statement-logging restricted if the tables are statement-logging capable but not row-logging capable.

Once the determination of the possible logging formats required by the statement is complete it is compared to the current binlog_format setting. The following table is used in MySQL 5.5.2 and earlier to decide how the information is recorded in the binary log or, if appropriate, whether an error is raised. In the table, a safe operation is defined as one that is deterministic.

In MySQL 5.5.2 and earlier, several rules decide whether the statement is deterministic, as shown in the following table, where SLR stands for “statement-logging restricted” and RLR stands for “row-logging restricted”. A statement is statement-logging restricted if one or more of the tables it accesses is not row-logging capable. Similarly, a statement is row-logging restricted if any table accessed by the statement is not statement-logging capable.

ConditionAction
Safe/unsafebinlog_formatSLRRLRError/WarningLogged as
SafeSTATEMENTYesYesError: not loggable 
SafeSTATEMENTYesNo STATEMENT
SafeSTATEMENTNoYesError: not loggable 
SafeSTATEMENTNoNo STATEMENT
SafeMIXEDYesYesError: not loggable 
SafeMIXEDYesNo STATEMENT
SafeMIXEDNoYes ROW
SafeMIXEDNoNo STATEMENT
SafeROWYesYesError: not loggable 
SafeROWYesNoError: not loggable 
SafeROWNoYes ROW
SafeROWNoNo ROW
UnsafeSTATEMENTYesYesError: not loggable 
UnsafeSTATEMENTYesNoWarning: unsafeSTATEMENT
UnsafeSTATEMENTNoYesError: not loggable 
UnsafeSTATEMENTNoNoWarning: unsafeSTATEMENT
UnsafeMIXEDYesYesError: not loggable 
UnsafeMIXEDYesNoError: not loggable 
UnsafeMIXEDNoYes ROW
UnsafeMIXEDNoNo ROW
UnsafeROWYesYesError: not loggable 
UnsafeROWYesNoError: not loggable 
UnsafeROWNoYes ROW
UnsafeROWNoNo ROW

In all MySQL 5.5 releases, when a warning is produced by the determination, a standard MySQL warning is produced (and is available using SHOW WARNINGS). The information is also written to the mysqld error log. Only one error for each error instance per client connection is logged to prevent flooding the log. The log message includes the SQL statement that was attempted.

If a slave server was started with --log-warnings enabled, the slave prints messages to the error log to provide information about its status, such as the binary log and relay log coordinates where it starts its job, when it is switching to another relay log, when it reconnects after a disconnect, and so forth.

5.2.4.4. Logging Format for Changes to mysql Database Tables

The contents of the grant tables in the mysql database can be modified directly (for example, with INSERT or DELETE) or indirectly (for example, with GRANT or CREATE USER). Statements that affect mysql database tables are written to the binary log using the following rules:

CREATE TABLE ... SELECT is a combination of data definition and data manipulation. The CREATE TABLE part is logged using statement format and the SELECT part is logged according to the value of binlog_format.

5.2.5. The Slow Query Log

The slow query log consists of SQL statements that took more than long_query_time seconds to execute and required at least min_examined_row_limit rows to be examined. The minimum and default values of long_query_time are 0 and 10, respectively. The value can be specified to a resolution of microseconds. For logging to a file, times are written including the microseconds part. For logging to tables, only integer times are written; the microseconds part is ignored.

The time to acquire the initial table locks is not counted as execution time. mysqld writes a statement to the slow query log after it has been executed and after all locks have been released, so log order might differ from execution order.

By default, the slow query log is disabled. To specify the initial slow query log state explicitly, use --slow_query_log[={0|1}]. With no argument or an argument of 1, --slow_query_log enables the log. With an argument of 0, this option disables the log. To specify a log file name, use --slow_query_log_file=file_name. To specify the log destination, use --log-output (as described in Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”). The older option to enable the slow query log file, --log-slow-queries, is deprecated.

If you specify no name for the slow query log file, the default name is host_name-slow.log. The server creates the file in the data directory unless an absolute path name is given to specify a different directory.

To disable or enable the slow query log or change the log file name at runtime, use the global slow_query_log and slow_query_log_file system variables. Set slow_query_log to 0 (or OFF) to disable the log or to 1 (or ON) to enable it. Set slow_query_log_file to specify the name of the log file. If a log file already is open, it is closed and the new file is opened.

When the slow query log is enabled, the server writes output to any destinations specified by the --log-output option or log_output system variable. If you enable the log, the server opens the log file and writes startup messages to it. However, further logging of queries to the file does not occur unless the FILE log destination is selected. If the destination is NONE, the server writes no queries even if the slow query log is enabled. Setting the log file name has no effect on logging if the log destination value does not contain FILE.

The server writes less information to the slow query log (and binary log) if you use the --log-short-format option.

To include slow administrative statements such as OPTIMIZE TABLE, ANALYZE TABLE, and ALTER TABLE in the statements written to the slow query log, enable the log_slow_admin_statements system variable.

To include queries that do not use indexes for row lookups in the statements written to the slow query log, enable the log_queries_not_using_indexes system variable. When such queries are logged, the slow query log may grow quickly.

The server uses the controlling parameters in the following order to determine whether to write a query to the slow query log:

  1. The query must either not be an administrative statement, or log_slow_admin_statements must be enabled.

  2. The query must have taken at least long_query_time seconds, or log_queries_not_using_indexes must be enabled and the query used no indexes for row lookups.

  3. The query must have examined at least min_examined_row_limit rows.

The server does not write queries handled by the query cache to the slow query log, nor queries that would not benefit from the presence of an index because the table has zero rows or one row.

By default, a replication slave does not write replicated queries to the slow query log. To change this, enable the log_slow_slave_statements system variable.

The slow query log should be protected because logged statements might contain passwords. See Section 5.3.2.1, “Administrator Guidelines for Password Security”.

The slow query log can be used to find queries that take a long time to execute and are therefore candidates for optimization. However, examining a long slow query log can become a difficult task. To make this easier, you can process a slow query log file using the mysqldumpslow command to summarize the queries that appear in the log. See Section 4.6.8, “mysqldumpslow — Summarize Slow Query Log Files”.

5.2.6. Server Log Maintenance

As described in Section 5.2, “MySQL Server Logs”, MySQL Server can create several different log files to help you see what activity is taking place. However, you must clean up these files regularly to ensure that the logs do not take up too much disk space.

When using MySQL with logging enabled, you may want to back up and remove old log files from time to time and tell MySQL to start logging to new files. See Section 6.2, “Database Backup Methods”.

On a Linux (Red Hat) installation, you can use the mysql-log-rotate script for this. If you installed MySQL from an RPM distribution, this script should have been installed automatically. Be careful with this script if you are using the binary log for replication. You should not remove binary logs until you are certain that their contents have been processed by all slaves.

On other systems, you must install a short script yourself that you start from cron (or its equivalent) for handling log files.

For the binary log, you can set the expire_logs_days system variable to expire binary log files automatically after a given number of days (see Section 5.1.3, “Server System Variables”). If you are using replication, you should set the variable no lower than the maximum number of days your slaves might lag behind the master. To remove binary logs on demand, use the PURGE BINARY LOGS statement (see Section 12.4.1.1, “PURGE BINARY LOGS Синтаксис”).

You can force MySQL to start using new log files by flushing the logs. Log flushing occurs when you issue a FLUSH LOGS statement or execute a mysqladmin flush-logs, mysqladmin refresh, mysqldump --flush-logs, or mysqldump --master-data command. See Section 12.7.6.3, “FLUSH Синтаксис”, Section 4.5.2, “mysqladmin — Client for Administering a MySQL Server”, and Section 4.5.4, “mysqldump — A Database Backup Program”. In addition, the binary log is flushed when its size reaches the value of the max_binlog_size system variable.

As of MySQL 5.5.3, FLUSH LOGS supports optional modifiers to enable selective flushing of individual logs (for example, FLUSH BINARY LOGS).

A log-flushing operation does the following:

  • If general query logging or slow query logging to a log file is enabled, the server closes and reopens the general query log file or slow query log file.

  • If binary logging is enabled, the server closes the current binary log file and opens a new log file with the next sequence number.

  • If the server was started with the --log-error option to cause the error log to be written to a file, the result of a log-flushing operation is version dependent:

    • As of MySQL 5.5.7, the server closes and reopens the log file.

    • Prior to MySQL 5.5.7, the server renames the current log file with the suffix -old, then creates a new empty log file.

The server creates a new binary log file when you flush the logs. However, it just closes and reopens the general and slow query log files. To cause new files to be created on Unix, rename the current log files before flushing them. At flush time, the server opens new log files with the original names. For example, if the general and slow query log files are named mysql.log and mysql-slow.log, you can use a series of commands like this:

shell> cd mysql-data-directory
shell> mv mysql.log mysql.old
shell> mv mysql-slow.log mysql-slow.old
shell> mysqladmin flush-logs

On Windows, use rename rather than mv.

At this point, you can make a backup of mysql.old and mysql-slow.old and then remove them from disk.

A similar strategy can be used to back up the error log file, if there is one, except that, on Windows, you cannot rename the error log file while the server has it open before MySQL 5.5.7. To rename the error log file, a stop and restart can be avoided by flushing the logs to cause the server to rename the current log file with the suffix -old and create a new empty error log file. For further information, see Section 5.2.2, “The Error Log”.

You can rename the general query log or slow query log at runtime by disabling the log:

SET GLOBAL general_log = 'OFF';
SET GLOBAL slow_query_log = 'OFF';

With the logs disabled, rename the log files externally; for example, from the command line. Then enable the logs again:

SET GLOBAL general_log = 'ON';
SET GLOBAL slow_query_log = 'ON';

This method works on any platform and does not require a server restart.

5.3. General Security Issues

This section describes some general security issues to be aware of and what you can do to make your MySQL installation more secure against attack or misuse. For information specifically about the access control system that MySQL uses for setting up user accounts and checking database access, see Section 5.4, “The MySQL Access Privilege System”.

For answers to some questions that are often asked about MySQL Server security issues, see Section B.9, “MySQL 5.5 FAQ: Security”.

5.3.1. General Security Guidelines

Anyone using MySQL on a computer connected to the Internet should read this section to avoid the most common security mistakes.

In discussing security, we emphasize the necessity of fully protecting the entire server host (not just the MySQL server) against all types of applicable attacks: eavesdropping, altering, playback, and denial of service. We do not cover all aspects of availability and fault tolerance here.

MySQL uses security based on Access Control Lists (ACLs) for all connections, queries, and other operations that users can attempt to perform. There is also support for SSL-encrypted connections between MySQL clients and servers. Many of the concepts discussed here are not specific to MySQL at all; the same general ideas apply to almost all applications.

When running MySQL, follow these guidelines whenever possible:

  • Do not ever give anyone (except MySQL root accounts) access to the user table in the mysql database! This is critical.

  • Learn the MySQL access privilege system. The GRANT and REVOKE statements are used for controlling access to MySQL. Do not grant more privileges than necessary. Never grant privileges to all hosts.

    Checklist:

    • Try mysql -u root. If you are able to connect successfully to the server without being asked for a password, anyone can connect to your MySQL server as the MySQL root user with full privileges! Review the MySQL installation instructions, paying particular attention to the information about setting a root password. See Section 2.10.2, “Securing the Initial MySQL Accounts”.

    • Use the SHOW GRANTS statement to check which accounts have access to what. Then use the REVOKE statement to remove those privileges that are not necessary.

  • Do not store any plaintext passwords in your database. If your computer becomes compromised, the intruder can take the full list of passwords and use them. Instead, use MD5(), SHA1(), SHA2(), or some other one-way hashing function and store the hash value.

  • Do not choose passwords from dictionaries. Special programs exist to break passwords. Even passwords like “xfish98” are very bad. Much better is “duag98” which contains the same word “fish” but typed one key to the left on a standard QWERTY keyboard. Another method is to use a password that is taken from the first characters of each word in a sentence (for example, “Mary had a little lamb” results in a password of “Mhall”). The password is easy to remember and type, but difficult to guess for someone who does not know the sentence.

  • Invest in a firewall. This protects you from at least 50% of all types of exploits in any software. Put MySQL behind the firewall or in a demilitarized zone (DMZ).

    Checklist:

    • Try to scan your ports from the Internet using a tool such as nmap. MySQL uses port 3306 by default. This port should not be accessible from untrusted hosts. Another simple way to check whether or not your MySQL port is open is to try the following command from some remote machine, where server_host is the host name or IP address of the host on which your MySQL server runs:

      shell> telnet server_host 3306
      

      If you get a connection and some garbage characters, the port is open, and should be closed on your firewall or router, unless you really have a good reason to keep it open. If telnet hangs or the connection is refused, the port is blocked, which is how you want it to be.

  • Do not trust any data entered by users of your applications. They can try to trick your code by entering special or escaped character sequences in Web forms, URLs, or whatever application you have built. Be sure that your application remains secure if a user enters something like “; DROP DATABASE mysql;”. This is an extreme example, but large security leaks and data loss might occur as a result of hackers using similar techniques, if you do not prepare for them.

    A common mistake is to protect only string data values. Remember to check numeric data as well. If an application generates a query such as SELECT * FROM table WHERE ID=234 when a user enters the value 234, the user can enter the value 234 OR 1=1 to cause the application to generate the query SELECT * FROM table WHERE ID=234 OR 1=1. As a result, the server retrieves every row in the table. This exposes every row and causes excessive server load. The simplest way to protect from this type of attack is to use single quotation marks around the numeric constants: SELECT * FROM table WHERE ID='234'. If the user enters extra information, it all becomes part of the string. In a numeric context, MySQL automatically converts this string to a number and strips any trailing nonnumeric characters from it.

    Sometimes people think that if a database contains only publicly available data, it need not be protected. This is incorrect. Even if it is permissible to display any row in the database, you should still protect against denial of service attacks (for example, those that are based on the technique in the preceding paragraph that causes the server to waste resources). Otherwise, your server becomes unresponsive to legitimate users.

    Checklist:

    • Try to enter single and double quotation marks (“'” and “"”) in all of your Web forms. If you get any kind of MySQL error, investigate the problem right away.

    • Try to modify dynamic URLs by adding %22 (“"”), %23 (“#”), and %27 (“'”) to them.

    • Try to modify data types in dynamic URLs from numeric to character types using the characters shown in the previous examples. Your application should be safe against these and similar attacks.

    • Try to enter characters, spaces, and special symbols rather than numbers in numeric fields. Your application should remove them before passing them to MySQL or else generate an error. Passing unchecked values to MySQL is very dangerous!

    • Check the size of data before passing it to MySQL.

    • Have your application connect to the database using a user name different from the one you use for administrative purposes. Do not give your applications any access privileges they do not need.

  • Many application programming interfaces provide a means of escaping special characters in data values. Properly used, this prevents application users from entering values that cause the application to generate statements that have a different effect than you intend:

    • MySQL C API: Use the mysql_real_escape_string() API call.

    • MySQL++: Use the escape and quote modifiers for query streams.

    • PHP: Use the mysql_real_escape_string() function (available as of PHP 4.3.0, prior to that PHP version use mysql_escape_string(), and prior to PHP 4.0.3, use addslashes() ). Note that only mysql_real_escape_string() is character set-aware; the other functions can be “bypassed” when using (invalid) multi-byte character sets. In PHP 5, you can use the mysqli extension, which supports the improved MySQL authentication protocol and passwords, as well as prepared statements with placeholders.

    • Perl DBI: Use placeholders or the quote() method.

    • Ruby DBI: Use placeholders or the quote() method.

    • Java JDBC: Use a PreparedStatement object and placeholders.

    Other programming interfaces might have similar capabilities.

  • Do not transmit plain (unencrypted) data over the Internet. This information is accessible to everyone who has the time and ability to intercept it and use it for their own purposes. Instead, use an encrypted protocol such as SSL or SSH. MySQL supports internal SSL connections as of version 4.0. Another technique is to use SSH port-forwarding to create an encrypted (and compressed) tunnel for the communication.

  • Learn to use the tcpdump and strings utilities. In most cases, you can check whether MySQL data streams are unencrypted by issuing a command like the following:

    shell> tcpdump -l -i eth0 -w - src or dst port 3306 | strings
    

    This works under Linux and should work with small modifications under other systems.

    Warning

    If you do not see plaintext data, this does not always mean that the information actually is encrypted. If you need high security, you should consult with a security expert.

5.3.2. Password Security in MySQL

Passwords occur in several contexts within MySQL. The following sections provide guidelines that enable administrators and end users to keep these passwords secure and avoid exposing them. There is also a discussion of how MySQL uses password hashing internally.

5.3.2.1. Administrator Guidelines for Password Security

Database administrators should use the following guidelines to keep passwords secure.

MySQL stores passwords for user accounts in the mysql.user table. Access to this table should never be granted to any nonadministrative accounts.

A user who has access to modify the plugin directory (the value of the plugin_dir system variable) or the my.cnf file that specifies the location of the plugin directory can replace plugins and modify the capabilities provided by plugins.

Passwords can appear as plain text in SQL statements such as CREATE USER, GRANT, and SET PASSWORD, or statements that invoke the PASSWORD() function. If these statements are logged by the MySQL server, the passwords become available to anyone with access to the logs. This applies to the general query log, the slow query log, and the binary log (see Section 5.2, “MySQL Server Logs”). To guard against unwarranted exposure to log files, they should be located in a directory that restricts access to only the server and the database administrator. If you log to tables in the mysql database, access to the tables should never be granted to any nonadministrative accounts.

Replication slaves store the password for the replication master in the master.info file. Access to this file should be restricted to the database administrator.

Database backups that include tables or log files containing passwords should be protected using a restricted access mode.

5.3.2.2. End-User Guidelines for Password Security

MySQL users should use the following guidelines to keep passwords secure.

When you run a client program to connect to the MySQL server, it is inadvisable to specify your password in a way that exposes it to discovery by other users. The methods you can use to specify your password when you run client programs are listed here, along with an assessment of the risks of each method. In short, the safest methods are to have the client program prompt for the password or to specify the password in a properly protected option file.

  • Use a -pyour_pass or --password=your_pass option on the command line. For example:

    shell> mysql -u francis -pfrank db_name
    

    This is convenient but insecure, because your password becomes visible to system status programs such as ps that may be invoked by other users to display command lines. MySQL clients typically overwrite the command-line password argument with zeros during their initialization sequence. However, there is still a brief interval during which the value is visible. Also, on some systems this overwriting strategy is ineffective and the password remains visible to ps. (SystemV Unix systems and perhaps others are subject to this problem.)

    If your operating environment is set up to display your current command in the title bar of your terminal window, the password remains visible as long as the command is running, even if the command has scrolled out of view in the window content area.

  • Use the -p or --password option on the command line with no password value specified. In this case, the client program solicits the password interactively:

    shell> mysql -u francis -p db_name
    Enter password: ********
    

    The “*” characters indicate where you enter your password. The password is not displayed as you enter it.

    It is more secure to enter your password this way than to specify it on the command line because it is not visible to other users. However, this method of entering a password is suitable only for programs that you run interactively. If you want to invoke a client from a script that runs noninteractively, there is no opportunity to enter the password from the keyboard. On some systems, you may even find that the first line of your script is read and interpreted (incorrectly) as your password.

  • Store your password in an option file. For example, on Unix you can list your password in the [client] section of the .my.cnf file in your home directory:

    [client]
    password=your_pass

    To keep the password safe, the file should not be accessible to anyone but yourself. To ensure this, set the file access mode to 400 or 600. For example:

    shell> chmod 600 .my.cnf
    

    To name from the command line a specific option file containing the password, use the --defaults-file=file_name option, where file_name is the full path name to the file. For example:

    shell> mysql --defaults-file=/home/francis/mysql-opts
    

    Section 4.2.3.3, “Using Option Files”, discusses option files in more detail.

  • Store your password in the MYSQL_PWD environment variable. See Section 2.12, “Environment Variables”.

    This method of specifying your MySQL password must be considered extremely insecure and should not be used. Some versions of ps include an option to display the environment of running processes. If you set MYSQL_PWD, your password is exposed to any other user who runs ps. Even on systems without such a version of ps, it is unwise to assume that there are no other methods by which users can examine process environments.

On Unix, the mysql client writes a record of executed statements to a history file (see Section 4.5.1.3, “mysql History File”). By default, this file is named .mysql_history and is created in your home directory. Passwords can appear as plain text in SQL statements such as CREATE USER, GRANT, and SET PASSWORD, so if you use these statements, they are logged in the history file. To keep this file safe, use a restrictive access mode, the same way as described earlier for the .my.cnf file.

If your command interpreter is configured to maintain a history, any file in which the commands are saved will contain MySQL passwords entered on the command line. For example, bash uses ~/.bash_history. Any such file should have a restrictive access mode.

5.3.2.3. Password Hashing in MySQL

MySQL user accounts are listed in the user table of the mysql database. Each MySQL account is assigned a password, although what is stored in the Password column of the user table is not the plaintext version of the password, but a hash value computed from it. Password hash values are computed by the PASSWORD() function.

MySQL uses passwords in two phases of client/server communication:

  • When a client attempts to connect to the server, there is an initial authentication step in which the client must present a password that has a hash value matching the hash value stored in the user table for the account that the client wants to use.

  • After the client connects, it can (if it has sufficient privileges) set or change the password hashes for accounts listed in the user table. The client can do this by using the PASSWORD() function to generate a password hash, or by using the GRANT or SET PASSWORD statements.

In other words, the server uses hash values during authentication when a client first attempts to connect. The server generates hash values if a connected client invokes the PASSWORD() function or uses a GRANT or SET PASSWORD statement to set or change a password.

The password hashing mechanism was updated in MySQL 4.1 to provide better security and to reduce the risk of passwords being intercepted. However, this new mechanism is understood only by MySQL 4.1 (and newer) servers and clients, which can result in some compatibility problems. A 4.1 or newer client can connect to a pre-4.1 server, because the client understands both the old and new password hashing mechanisms. However, a pre-4.1 client that attempts to connect to a 4.1 or newer server may run into difficulties. For example, a 3.23 mysql client that attempts to connect to a 5.5 server may fail with the following error message:

shell> mysql -h localhost -u root
Client does not support authentication protocol requested
by server; consider upgrading MySQL client

Another common example of this phenomenon occurs for attempts to use the older PHP mysql extension after upgrading to MySQL 4.1 or newer. (See Section 21.10.6, “Common Problems with MySQL and PHP”.)

The following discussion describes the differences between the old and new password mechanisms, and what you should do if you upgrade your server but need to maintain backward compatibility with pre-4.1 clients. Additional information can be found in Section C.5.2.4, “Client does not support authentication protocol. This information is of particular importance to PHP programmers migrating MySQL databases from version 4.0 or lower to version 4.1 or higher.

Замечание

This discussion contrasts 4.1 behavior with pre-4.1 behavior, but the 4.1 behavior described here actually begins with 4.1.1. MySQL 4.1.0 is an “odd” release because it has a slightly different mechanism than that implemented in 4.1.1 and up. Differences between 4.1.0 and more recent versions are described further in MySQL 5.1 Справочное Руководство.

Prior to MySQL 4.1, password hashes computed by the PASSWORD() function are 16 bytes long. Such hashes look like this:

mysql> SELECT PASSWORD('mypass');
+--------------------+
| PASSWORD('mypass') |
+--------------------+
| 6f8c114b58f2ce9e   |
+--------------------+

The Password column of the user table (in which these hashes are stored) also is 16 bytes long before MySQL 4.1.

As of MySQL 4.1, the PASSWORD() function has been modified to produce a longer 41-byte hash value:

mysql> SELECT PASSWORD('mypass');
+-------------------------------------------+
| PASSWORD('mypass')                        |
+-------------------------------------------+
| *6C8989366EAF75BB670AD8EA7A7FC1176A95CEF4 |
+-------------------------------------------+

Accordingly, the Password column in the user table also must be 41 bytes long to store these values:

  • If you perform a new installation of MySQL 5.5, the Password column is made 41 bytes long automatically.

  • Upgrading from MySQL 4.1 (4.1.1 or later in the 4.1 series) to MySQL 5.5 should not give rise to any issues in this regard because both versions use the same password hashing mechanism. If you wish to upgrade an older release of MySQL to version 5.5, you should upgrade to version 4.1 first, then upgrade the 4.1 installation to 5.5.

A widened Password column can store password hashes in both the old and new formats. The format of any given password hash value can be determined two ways:

  • The obvious difference is the length (16 bytes versus 41 bytes).

  • A second difference is that password hashes in the new format always begin with a “*” character, whereas passwords in the old format never do.

The longer password hash format has better cryptographic properties, and client authentication based on long hashes is more secure than that based on the older short hashes.

The differences between short and long password hashes are relevant both for how the server uses passwords during authentication and for how it generates password hashes for connected clients that perform password-changing operations.

The way in which the server uses password hashes during authentication is affected by the width of the Password column:

  • If the column is short, only short-hash authentication is used.

  • If the column is long, it can hold either short or long hashes, and the server can use either format:

    • Pre-4.1 clients can connect, although because they know only about the old hashing mechanism, they can authenticate only using accounts that have short hashes.

    • 4.1 and later clients can authenticate using accounts that have short or long hashes.

Even for short-hash accounts, the authentication process is actually a bit more secure for 4.1 and later clients than for older clients. In terms of security, the gradient from least to most secure is:

  • Pre-4.1 client authenticating with short password hash

  • 4.1 or later client authenticating with short password hash

  • 4.1 or later client authenticating with long password hash

The way in which the server generates password hashes for connected clients is affected by the width of the Password column and by the --old-passwords option. A 4.1 or later server generates long hashes only if certain conditions are met: The Password column must be wide enough to hold long values and the --old-passwords option must not be given. These conditions apply as follows:

  • The Password column must be wide enough to hold long hashes (41 bytes). If the column has not been updated and still has the pre-4.1 width of 16 bytes, the server notices that long hashes cannot fit into it and generates only short hashes when a client performs password-changing operations using PASSWORD(), GRANT, or SET PASSWORD. This is the behavior that occurs if you have upgraded to 4.1 but have not yet run the mysql_upgrade program to widen the Password column.

  • If the Password column is wide, it can store either short or long password hashes. In this case, PASSWORD(), GRANT, and SET PASSWORD generate long hashes unless the server was started with the --old-passwords option. That option forces the server to generate short password hashes instead.

The purpose of the --old-passwords option is to enable you to maintain backward compatibility with pre-4.1 clients under circumstances where the server would otherwise generate long password hashes. The option does not affect authentication (4.1 and later clients can still use accounts that have long password hashes), but it does prevent creation of a long password hash in the user table as the result of a password-changing operation. Were that to occur, the account no longer could be used by pre-4.1 clients. Without the --old-passwords option, the following undesirable scenario is possible:

  • An old client connects to an account that has a short password hash.

  • The client changes its own password. Without --old-passwords, this results in the account having a long password hash.

  • The next time the old client attempts to connect to the account, it cannot, because the account has a long password hash that requires the new hashing mechanism during authentication. (Once an account has a long password hash in the user table, only 4.1 and later clients can authenticate for it, because pre-4.1 clients do not understand long hashes.)

This scenario illustrates that, if you must support older pre-4.1 clients, it is dangerous to run a 4.1 or newer server without using the --old-passwords option. By running the server with --old-passwords, password-changing operations do not generate long password hashes and thus do not cause accounts to become inaccessible to older clients. (Those clients cannot inadvertently lock themselves out by changing their password and ending up with a long password hash.)

The downside of the --old-passwords option is that any passwords you create or change use short hashes, even for 4.1 clients. Thus, you lose the additional security provided by long password hashes. If you want to create an account that has a long hash (for example, for use by 4.1 clients), you must do so while running the server without --old-passwords.

The following scenarios are possible for running a 4.1 or later server:

Scenario 1: Short Password column in user table:

  • Only short hashes can be stored in the Password column.

  • The server uses only short hashes during client authentication.

  • For connected clients, password hash-generating operations involving PASSWORD(), GRANT, or SET PASSWORD use short hashes exclusively. Any change to an account's password results in that account having a short password hash.

  • The --old-passwords option can be used but is superfluous because with a short Password column, the server generates only short password hashes anyway.

Scenario 2: Long Password column; server not started with --old-passwords option:

  • Short or long hashes can be stored in the Password column.

  • 4.1 and later clients can authenticate using accounts that have short or long hashes.

  • Pre-4.1 clients can authenticate only using accounts that have short hashes.

  • For connected clients, password hash-generating operations involving PASSWORD(), GRANT, or SET PASSWORD use long hashes exclusively. A change to an account's password results in that account having a long password hash.

As indicated earlier, a danger in this scenario is that it is possible for accounts that have a short password hash to become inaccessible to pre-4.1 clients. A change to such an account's password made using GRANT, PASSWORD(), or SET PASSWORD results in the account being given a long password hash. From that point on, no pre-4.1 client can authenticate to that account until the client upgrades to 4.1.

To deal with this problem, you can change a password in a special way. For example, normally you use SET PASSWORD as follows to change an account password:

SET PASSWORD FOR 'some_user'@'some_host' = PASSWORD('mypass');

To change the password but create a short hash, use the OLD_PASSWORD() function instead:

SET PASSWORD FOR 'some_user'@'some_host' = OLD_PASSWORD('mypass');

OLD_PASSWORD() is useful for situations in which you explicitly want to generate a short hash.

Scenario 3: Long Password column; 4.1 or newer server started with --old-passwords option:

  • Short or long hashes can be stored in the Password column.

  • 4.1 and later clients can authenticate for accounts that have short or long hashes (but note that it is possible to create long hashes only when the server is started without --old-passwords).

  • Pre-4.1 clients can authenticate only for accounts that have short hashes.

  • For connected clients, password hash-generating operations involving PASSWORD(), GRANT, or SET PASSWORD use short hashes exclusively. Any change to an account's password results in that account having a short password hash.

In this scenario, you cannot create accounts that have long password hashes, because the --old-passwords option prevents generation of long hashes. Also, if you create an account with a long hash before using the --old-passwords option, changing the account's password while --old-passwords is in effect results in the account being given a short password, causing it to lose the security benefits of a longer hash.

The disadvantages for these scenarios may be summarized as follows:

In scenario 1, you cannot take advantage of longer hashes that provide more secure authentication.

In scenario 2, accounts with short hashes become inaccessible to pre-4.1 clients if you change their passwords without explicitly using OLD_PASSWORD().

In scenario 3, --old-passwords prevents accounts with short hashes from becoming inaccessible, but password-changing operations cause accounts with long hashes to revert to short hashes, and you cannot change them back to long hashes while --old-passwords is in effect.

5.3.2.4. Implications of Password Hashing Changes in MySQL 4.1 for Application Programs

An upgrade to MySQL version 4.1 or later can cause compatibility issues for applications that use PASSWORD() to generate passwords for their own purposes. Applications really should not do this, because PASSWORD() should be used only to manage passwords for MySQL accounts. But some applications use PASSWORD() for their own purposes anyway.

If you upgrade to 4.1 or later from a pre-4.1 version of MySQL and run the server under conditions where it generates long password hashes, an application using PASSWORD() for its own passwords breaks. The recommended course of action in such cases is to modify the application to use another function, such as SHA1() or MD5(), to produce hashed values. If that is not possible, you can use the OLD_PASSWORD() function, which is provided for generate short hashes in the old format. However, you should note that OLD_PASSWORD() may one day no longer be supported.

If the server is running under circumstances where it generates short hashes, OLD_PASSWORD() is available but is equivalent to PASSWORD().

PHP programmers migrating their MySQL databases from version 4.0 or lower to version 4.1 or higher should see Section 21.10, “MySQL PHP API”.

5.3.3. Making MySQL Secure Against Attackers

When you connect to a MySQL server, you should use a password. The password is not transmitted in clear text over the connection. Password handling during the client connection sequence was upgraded in MySQL 4.1.1 to be very secure. If you are still using pre-4.1.1-style passwords, the encryption algorithm is not as strong as the newer algorithm. With some effort, a clever attacker who can sniff the traffic between the client and the server can crack the password. (See Section 5.3.2.3, “Password Hashing in MySQL”, for a discussion of the different password handling methods.)

All other information is transferred as text, and can be read by anyone who is able to watch the connection. If the connection between the client and the server goes through an untrusted network, and you are concerned about this, you can use the compressed protocol to make traffic much more difficult to decipher. You can also use MySQL's internal SSL support to make the connection even more secure. See Section 5.5.8, “Using SSL for Secure Connections”. Alternatively, use SSH to get an encrypted TCP/IP connection between a MySQL server and a MySQL client. You can find an Open Source SSH client at http://www.openssh.org/, and a commercial SSH client at http://www.ssh.com/.

To make a MySQL system secure, you should strongly consider the following suggestions:

  • Require all MySQL accounts to have a password. A client program does not necessarily know the identity of the person running it. It is common for client/server applications that the user can specify any user name to the client program. For example, anyone can use the mysql program to connect as any other person simply by invoking it as mysql -u other_user db_name if other_user has no password. If all accounts have a password, connecting using another user's account becomes much more difficult.

    For a discussion of methods for setting passwords, see Section 5.5.5, “Assigning Account Passwords”.

  • Never run the MySQL server as the Unix root user. This is extremely dangerous, because any user with the FILE privilege is able to cause the server to create files as root (for example, ~root/.bashrc). To prevent this, mysqld refuses to run as root unless that is specified explicitly using the --user=root option.

    mysqld can (and should) be run as an ordinary, unprivileged user instead. You can create a separate Unix account named mysql to make everything even more secure. Use this account only for administering MySQL. To start mysqld as a different Unix user, add a user option that specifies the user name in the [mysqld] group of the my.cnf option file where you specify server options. For example:

    [mysqld]
    user=mysql

    This causes the server to start as the designated user whether you start it manually or by using mysqld_safe or mysql.server. For more details, see Section 5.3.6, “How to Run MySQL as a Normal User”.

    Running mysqld as a Unix user other than root does not mean that you need to change the root user name in the user table. User names for MySQL accounts have nothing to do with user names for Unix accounts.

  • Do not permit the use of symlinks to tables. (This capability can be disabled with the --skip-symbolic-links option.) This is especially important if you run mysqld as root, because anyone that has write access to the server's data directory then could delete any file in the system! See Section 7.11.3.1.2, “Using Symbolic Links for Tables on Unix”.

  • Make sure that the only Unix user account with read or write privileges in the database directories is the account that is used for running mysqld.

  • Do not grant the PROCESS or SUPER privilege to nonadministrative users. The output of mysqladmin processlist and SHOW PROCESSLIST shows the text of any statements currently being executed, so any user who is permitted to see the server process list might be able to see statements issued by other users such as UPDATE user SET password=PASSWORD('not_secure').

    mysqld reserves an extra connection for users who have the SUPER privilege, so that a MySQL root user can log in and check server activity even if all normal connections are in use.

    The SUPER privilege can be used to terminate client connections, change server operation by changing the value of system variables, and control replication servers.

  • Do not grant the FILE privilege to nonadministrative users. Any user that has this privilege can write a file anywhere in the file system with the privileges of the mysqld daemon. To make this a bit safer, files generated with SELECT ... INTO OUTFILE do not overwrite existing files and are writable by everyone.

    The FILE privilege may also be used to read any file that is world-readable or accessible to the Unix user that the server runs as. With this privilege, you can read any file into a database table. This could be abused, for example, by using LOAD DATA to load /etc/passwd into a table, which then can be displayed with SELECT.

  • Stored programs and views should be written using the security guidelines discussed in Section 18.6, “Access Control for Stored Programs and Views”.

  • If you do not trust your DNS, you should use IP addresses rather than host names in the grant tables. In any case, you should be very careful about creating grant table entries using host name values that contain wildcards.

  • If you want to restrict the number of connections permitted to a single account, you can do so by setting the max_user_connections variable in mysqld. The GRANT statement also supports resource control options for limiting the extent of server use permitted to an account. See Section 12.7.1.3, “GRANT Синтаксис”.

  • If the plugin directory is writable by the server, it may be possible for a user to write executable code to a file in the directory using SELECT ... INTO DUMPFILE. This can be prevented by making plugin_dir read only to the server or by setting --secure-file-priv to a directory where SELECT writes can be made safely.

5.3.4. Security-Related mysqld Options

The following mysqld options affect security:

Table 5.5. Security Option/Variable Summary

NameCmd-LineOption fileSystem VarStatus VarVar ScopeDynamic
allow-suspicious-udfsYesYes    
automatic_sp_privileges  Yes GlobalYes
chrootYesYes    
des-key-fileYesYes    
local_infile  Yes GlobalYes
local-infileYesYes    
- Variable: local_infile      
old-passwordsYesYes  BothYes
- Variable: old_passwords  Yes BothYes
safe-show-databaseYesYesYes GlobalYes
safe-user-createYesYes    
secure-authYesYes  GlobalYes
- Variable: secure_auth  Yes GlobalYes
secure-file-privYesYes  GlobalNo
- Variable: secure_file_priv  Yes GlobalNo
skip-grant-tablesYesYes    
skip-name-resolveYesYes  GlobalNo
- Variable: skip_name_resolve  Yes GlobalNo
skip-networkingYesYes  GlobalNo
- Variable: skip_networking  Yes GlobalNo
skip-show-databaseYesYes  GlobalNo
- Variable: skip_show_database  Yes GlobalNo

5.3.5. Security Issues with LOAD DATA LOCAL

The LOAD DATA statement can load a file that is located on the server host, or it can load a file that is located on the client host when the LOCAL keyword is specified.

There are two potential security issues with supporting the LOCAL version of LOAD DATA statements:

  • The transfer of the file from the client host to the server host is initiated by the MySQL server. In theory, a patched server could be built that would tell the client program to transfer a file of the server's choosing rather than the file named by the client in the LOAD DATA statement. Such a server could access any file on the client host to which the client user has read access.

  • In a Web environment where the clients are connecting from a Web server, a user could use LOAD DATA LOCAL to read any files that the Web server process has read access to (assuming that a user could run any command against the SQL server). In this environment, the client with respect to the MySQL server actually is the Web server, not the remote program being run by the user who connects to the Web server.

To deal with these problems, we changed how LOAD DATA LOCAL is handled as of MySQL 3.23.49 and MySQL 4.0.2 (4.0.13 on Windows):

  • By default, all MySQL clients and libraries in binary distributions are compiled with the -DENABLED_LOCAL_INFILE=1 option, to be compatible with MySQL 3.23.48 and before.

  • If you build MySQL from source but do not invoke CMake with the -DENABLED_LOCAL_INFILE=1 option, LOAD DATA LOCAL cannot be used by any client unless it is written explicitly to invoke mysql_options(... MYSQL_OPT_LOCAL_INFILE, 0). See Section 21.9.3.49, “mysql_options().

  • You can disable all LOAD DATA LOCAL statements from the server side by starting mysqld with the --local-infile=0 option.

  • For the mysql command-line client, enable LOAD DATA LOCAL by specifying the --local-infile[=1] option, or disable it with the --local-infile=0 option. For mysqlimport, local data file loading is off by default; enable it with the --local or -L option. In any case, successful use of a local load operation requires that the server permits it.

  • If you use LOAD DATA LOCAL in Perl scripts or other programs that read the [client] group from option files, you can add the local-infile=1 option to that group. However, to keep this from causing problems for programs that do not understand local-infile, specify it using the loose- prefix:

    [client]
    loose-local-infile=1
  • If LOAD DATA LOCAL is disabled, either in the server or the client, a client that attempts to issue such a statement receives the following error message:

    ERROR 1148: The used command is not allowed with this MySQL version

5.3.6. How to Run MySQL as a Normal User

On Windows, you can run the server as a Windows service using a normal user account.

On Unix, the MySQL server mysqld can be started and run by any user. However, you should avoid running the server as the Unix root user for security reasons. To change mysqld to run as a normal unprivileged Unix user user_name, you must do the following:

  1. Stop the server if it is running (use mysqladmin shutdown).

  2. Change the database directories and files so that user_name has privileges to read and write files in them (you might need to do this as the Unix root user):

    shell> chown -R user_name /path/to/mysql/datadir
    

    If you do not do this, the server will not be able to access databases or tables when it runs as user_name.

    If directories or files within the MySQL data directory are symbolic links, chown -R might not follow symbolic links for you. If it does not, you will also need to follow those links and change the directories and files they point to.

  3. Start the server as user user_name. Another alternative is to start mysqld as the Unix root user and use the --user=user_name option. mysqld starts up, then switches to run as the Unix user user_name before accepting any connections.

  4. To start the server as the given user automatically at system startup time, specify the user name by adding a user option to the [mysqld] group of the /etc/my.cnf option file or the my.cnf option file in the server's data directory. For example:

    [mysqld]
    user=user_name
    

If your Unix machine itself is not secured, you should assign passwords to the MySQL root accounts in the grant tables. Otherwise, any user with a login account on that machine can run the mysql client with a --user=root option and perform any operation. (It is a good idea to assign passwords to MySQL accounts in any case, but especially so when other login accounts exist on the server host.) See Section 2.10, “Postinstallation Setup and Testing”.

5.4. The MySQL Access Privilege System

The primary function of the MySQL privilege system is to authenticate a user who connects from a given host and to associate that user with privileges on a database such as SELECT, INSERT, UPDATE, and DELETE. Additional functionality includes the ability to have anonymous users and to grant privileges for MySQL-specific functions such as LOAD DATA INFILE and administrative operations.

There are some things that you cannot do with the MySQL privilege system:

  • You cannot explicitly specify that a given user should be denied access. That is, you cannot explicitly match a user and then refuse the connection.

  • You cannot specify that a user has privileges to create or drop tables in a database but not to create or drop the database itself.

  • A password applies globally to an account. You cannot associate a password with a specific object such as a database, table, or routine.

The user interface to the MySQL privilege system consists of SQL statements such as CREATE USER, GRANT, and REVOKE. See Section 12.7.1, “Account Management Statements”.

Internally, the server stores privilege information in the grant tables of the mysql database (that is, in the database named mysql). The MySQL server reads the contents of these tables into memory when it starts and bases access-control decisions on the in-memory copies of the grant tables.

The MySQL privilege system ensures that all users may perform only the operations permitted to them. As a user, when you connect to a MySQL server, your identity is determined by the host from which you connect and the user name you specify. When you issue requests after connecting, the system grants privileges according to your identity and what you want to do.

MySQL considers both your host name and user name in identifying you because there is no reason to assume that a given user name belongs to the same person on all hosts. For example, the user joe who connects from office.example.com need not be the same person as the user joe who connects from home.example.com. MySQL handles this by enabling you to distinguish users on different hosts that happen to have the same name: You can grant one set of privileges for connections by joe from office.example.com, and a different set of privileges for connections by joe from home.example.com. To see what privileges a given account has, use the SHOW GRANTS statement. For example:

SHOW GRANTS FOR 'joe'@'office.example.com';
SHOW GRANTS FOR 'joe'@'home.example.com';

MySQL access control involves two stages when you run a client program that connects to the server:

Stage 1: The server accepts or rejects the connection based on your identity and whether you can verify your identity by supplying the correct password.

Stage 2: Assuming that you can connect, the server checks each statement you issue to determine whether you have sufficient privileges to perform it. For example, if you try to select rows from a table in a database or drop a table from the database, the server verifies that you have the SELECT privilege for the table or the DROP privilege for the database.

For a more detailed description of what happens during each stage, see Section 5.4.4, “Access Control, Stage 1: Connection Verification”, and Section 5.4.5, “Access Control, Stage 2: Request Verification”.

If your privileges are changed (either by yourself or someone else) while you are connected, those changes do not necessarily take effect immediately for the next statement that you issue. For details about the conditions under which the server reloads the grant tables, see Section 5.4.6, “When Privilege Changes Take Effect”.

For general security-related advice, see Section 5.3, “General Security Issues”. For help in diagnosing privilege-related problems, see Section 5.4.7, “Causes of Access-Denied Ошибки”.

5.4.1. Privileges Provided by MySQL

MySQL provides privileges that apply in different contexts and at different levels of operation:

  • Administrative privileges enable users to manage operation of the MySQL server. These privileges are global because they are not specific to a particular database.

  • Database privileges apply to a database and to all objects within it. These privileges can be granted for specific databases, or globally so that they apply to all databases.

  • Privileges for database objects such as tables, indexes, views, and stored routines can be granted for specific objects within a database, for all objects of a given type within a database (for example, all tables in a database), or globally for all objects of a given type in all databases).

Information about account privileges is stored in the user, db, host, tables_priv, columns_priv, and procs_priv tables in the mysql database (see Section 5.4.2, “Privilege System Grant Tables”). The MySQL server reads the contents of these tables into memory when it starts and reloads them under the circumstances indicated in Section 5.4.6, “When Privilege Changes Take Effect”. Access-control decisions are based on the in-memory copies of the grant tables.

Some releases of MySQL introduce changes to the structure of the grant tables to add new access privileges or features. Whenever you update to a new version of MySQL, you should update your grant tables to make sure that they have the current structure so that you can take advantage of any new capabilities. See Section 4.4.7, “mysql_upgrade — Check Tables for MySQL Upgrade”.

The following table shows the privilege names used at the SQL level in the GRANT and REVOKE statements, along with the column name associated with each privilege in the grant tables and the context in which the privilege applies.

Table 5.6. Permissible Privileges for GRANT and REVOKE

PrivilegeColumnContext
CREATECreate_privdatabases, tables, or indexes
DROPDrop_privdatabases, tables, or views
GRANT OPTIONGrant_privdatabases, tables, or stored routines
LOCK TABLESLock_tables_privdatabases
REFERENCESReferences_privdatabases or tables
EVENTEvent_privdatabases
ALTERAlter_privtables
DELETEDelete_privtables
INDEXIndex_privtables
INSERTInsert_privtables or columns
SELECTSelect_privtables or columns
UPDATEUpdate_privtables or columns
CREATE TEMPORARY TABLESCreate_tmp_table_privtables
TRIGGERTrigger_privtables
CREATE VIEWCreate_view_privviews
SHOW VIEWShow_view_privviews
ALTER ROUTINEAlter_routine_privstored routines
CREATE ROUTINECreate_routine_privstored routines
EXECUTEExecute_privstored routines
FILEFile_privfile access on server host
CREATE TABLESPACECreate_tablespace_privserver administration
CREATE USERCreate_user_privserver administration
PROCESSProcess_privserver administration
PROXYsee proxies_priv tableserver administration
RELOADReload_privserver administration
REPLICATION CLIENTRepl_client_privserver administration
REPLICATION SLAVERepl_slave_privserver administration
SHOW DATABASESShow_db_privserver administration
SHUTDOWNShutdown_privserver administration
SUPERSuper_privserver administration
ALL [PRIVILEGES] server administration
USAGE server administration

The following list provides a general description of each privilege available in MySQL. Particular SQL statements might have more specific privilege requirements than indicated here. If so, the description for the statement in question provides the details.

  • The ALL or ALL PRIVILEGES privilege specifier is shorthand. It stands for “all privileges available at a given privilege level” (except GRANT OPTION). For example, granting ALL at the global or table level grants all global privileges or all table-level privileges.

  • The ALTER privilege enables use of ALTER TABLE to change the structure of tables. ALTER TABLE also requires the CREATE and INSERT privileges. Renaming a table requires ALTER and DROP on the old table, ALTER, CREATE, and INSERT on the new table.

  • The ALTER ROUTINE privilege is needed to alter or drop stored routines (procedures and functions).

  • The CREATE privilege enables creation of new databases and tables.

  • The CREATE ROUTINE privilege is needed to create stored routines (procedures and functions).

  • The CREATE TABLESPACE privilege is needed to create, alter, or drop tablespaces and log file groups.

  • The CREATE TEMPORARY TABLES privilege enables the creation of temporary tables using the CREATE TEMPORARY TABLE statement.

    However, other operations on a temporary table, such as INSERT, UPDATE, or SELECT, require additional privileges for those operations for the database containing the temporary table, or for the nontemporary table of the same name.

    To keep privileges for temporary and nontemporary tables separate, a common workaround for this situation is to create a database dedicated to the use of temporary tables. Then for that database, a user can be granted the CREATE TEMPORARY TABLES privilege, along with any other privileges required for temporary table operations done by that user.

  • The CREATE USER privilege enables use of CREATE USER, DROP USER, RENAME USER, and REVOKE ALL PRIVILEGES.

  • The CREATE VIEW privilege enables use of CREATE VIEW.

  • The DELETE privilege enables rows to be deleted from tables in a database.

  • The DROP privilege enables you to drop (remove) existing databases, tables, and views. The DROP privilege is required in order to use the statement ALTER TABLE ... DROP PARTITION on a partitioned table. The DROP privilege is also required for TRUNCATE TABLE. If you grant the DROP privilege for the mysql database to a user, that user can drop the database in which the MySQL access privileges are stored.

  • The EVENT privilege is required to create, alter, drop, or see events for the Event Scheduler.

  • The EXECUTE privilege is required to execute stored routines (procedures and functions).

  • The FILE privilege gives you permission to read and write files on the server host using the LOAD DATA INFILE and SELECT ... INTO OUTFILE statements and the LOAD_FILE() function. A user who has the FILE privilege can read any file on the server host that is either world-readable or readable by the MySQL server. (This implies the user can read any file in any database directory, because the server can access any of those files.) The FILE privilege also enables the user to create new files in any directory where the MySQL server has write access. As a security measure, the server will not overwrite existing files.

  • The GRANT OPTION privilege enables you to give to other users or remove from other users those privileges that you yourself possess.

  • The INDEX privilege enables you to create or drop (remove) indexes. INDEX applies to existing tables. If you have the CREATE privilege for a table, you can include index definitions in the CREATE TABLE statement.

  • The INSERT privilege enables rows to be inserted into tables in a database. INSERT is also required for the ANALYZE TABLE, OPTIMIZE TABLE, and REPAIR TABLE table-maintenance statements.

  • The LOCK TABLES privilege enables the use of explicit LOCK TABLES statements to lock tables for which you have the SELECT privilege. This includes the use of write locks, which prevents other sessions from reading the locked table.

  • The PROCESS privilege pertains to display of information about the threads executing within the server (that is, information about the statements being executed by sessions). The privilege enables use of SHOW PROCESSLIST or mysqladmin processlist to see threads belonging to other accounts; you can always see your own threads.

  • The PROXY privilege enables a user to impersonate or become known as another user. See Section 5.5.7, “Proxy Users”. This privilege was added in MySQL 5.5.7.

  • The REFERENCES privilege currently is unused.

  • The RELOAD privilege enables use of the FLUSH statement. It also enables mysqladmin commands that are equivalent to FLUSH operations: flush-hosts, flush-logs, flush-privileges, flush-status, flush-tables, flush-threads, refresh, and reload.

    The reload command tells the server to reload the grant tables into memory. flush-privileges is a synonym for reload. The refresh command closes and reopens the log files and flushes all tables. The other flush-xxx commands perform functions similar to refresh, but are more specific and may be preferable in some instances. For example, if you want to flush just the log files, flush-logs is a better choice than refresh.

  • The REPLICATION CLIENT privilege enables the use of SHOW MASTER STATUS and SHOW SLAVE STATUS.

  • The REPLICATION SLAVE privilege should be granted to accounts that are used by slave servers to connect to the current server as their master. Without this privilege, the slave cannot request updates that have been made to databases on the master server.

  • The SELECT privilege enables you to select rows from tables in a database. SELECT statements require the SELECT privilege only if they actually retrieve rows from a table. Some SELECT statements do not access tables and can be executed without permission for any database. For example, you can use SELECT as a simple calculator to evaluate expressions that make no reference to tables:

    SELECT 1+1;
    SELECT PI()*2;

    The SELECT privilege is also needed for other statements that read column values. For example, SELECT is needed for columns referenced on the right hand side of col_name=expr assignment in UPDATE statements or for columns named in the WHERE clause of DELETE or UPDATE statements.

  • The SHOW DATABASES privilege enables the account to see database names by issuing the SHOW DATABASE statement. Accounts that do not have this privilege see only databases for which they have some privileges, and cannot use the statement at all if the server was started with the --skip-show-database option. Note that any global privilege is a privilege for the database.

  • The SHOW VIEW privilege enables use of SHOW CREATE VIEW.

  • The SHUTDOWN privilege enables use of the mysqladmin shutdown command. There is no corresponding SQL statement.

  • The SUPER privilege enables an account to use CHANGE MASTER TO, KILL or mysqladmin kill to kill threads belonging to other accounts (you can always kill your own threads), PURGE BINARY LOGS, configuration changes using SET GLOBAL to modify global system variables, the mysqladmin debug command, enabling or disabling logging, performing updates even if the read_only system variable is enabled, starting and stopping replication on slave servers, specification of any account in the DEFINER attribute of stored programs and views, and enables you to connect (once) even if the connection limit controlled by the max_connections system variable is reached.

    To create or alter stored functions if binary logging is enabled, you may also need the SUPER privilege, as described in Section 18.7, “Binary Logging of Stored Programs”.

  • The TRIGGER privilege enables trigger operations. You must have this privilege for a table to create, drop, or execute triggers for that table.

  • The UPDATE privilege enables rows to be updated in tables in a database.

  • The USAGE privilege specifier stands for “no privileges.” It is used at the global level with GRANT to modify account attributes such as resource limits or SSL characteristics without affecting existing account privileges.

It is a good idea to grant to an account only those privileges that it needs. You should exercise particular caution in granting the FILE and administrative privileges:

  • The FILE privilege can be abused to read into a database table any files that the MySQL server can read on the server host. This includes all world-readable files and files in the server's data directory. The table can then be accessed using SELECT to transfer its contents to the client host.

  • The GRANT OPTION privilege enables users to give their privileges to other users. Two users that have different privileges and with the GRANT OPTION privilege are able to combine privileges.

  • The ALTER privilege may be used to subvert the privilege system by renaming tables.

  • The SHUTDOWN privilege can be abused to deny service to other users entirely by terminating the server.

  • The PROCESS privilege can be used to view the plain text of currently executing statements, including statements that set or change passwords.

  • The SUPER privilege can be used to terminate other sessions or change how the server operates.

  • Privileges granted for the mysql database itself can be used to change passwords and other access privilege information. Passwords are stored encrypted, so a malicious user cannot simply read them to know the plain text password. However, a user with write access to the user table Password column can change an account's password, and then connect to the MySQL server using that account.

5.4.2. Privilege System Grant Tables

Normally, you manipulate the contents of the grant tables in the mysql database indirectly by using statements such as GRANT and REVOKE to set up accounts and control the privileges available to each one. See Section 12.7.1, “Account Management Statements”. The discussion here describes the underlying structure of the grant tables and how the server uses their contents when interacting with clients.

These mysql database tables contain grant information:

  • user: Contains user accounts, global privileges, and other non-privilege columns.

  • db: Contains database-level privileges.

  • host: Obsolete.

  • tables_priv: Contains table-level privileges.

  • columns_priv: Contains column-level privileges.

  • procs_priv: Contains stored procedure and function privileges.

  • proxies_priv: Contains proxy-user privileges.

Other tables in the mysql database do not hold grant information and are discussed elsewhere:

Each grant table contains scope columns and privilege columns:

  • Scope columns determine the scope of each row (entry) in the tables; that is, the context in which the row applies. For example, a user table row with Host and User values of 'thomas.loc.gov' and 'bob' would be used for authenticating connections made to the server from the host thomas.loc.gov by a client that specifies a user name of bob. Similarly, a db table row with Host, User, and Db column values of 'thomas.loc.gov', 'bob' and 'reports' would be used when bob connects from the host thomas.loc.gov to access the reports database. The tables_priv and columns_priv tables contain scope columns indicating tables or table/column combinations to which each row applies. The procs_priv scope columns indicate the stored routine to which each row applies.

  • Privilege columns indicate which privileges are granted by a table row; that is, what operations can be performed. The server combines the information in the various grant tables to form a complete description of a user's privileges. Section 5.4.5, “Access Control, Stage 2: Request Verification”, describes the rules that are used to do this.

The server uses the grant tables in the following manner:

  • The user table scope columns determine whether to reject or permit incoming connections. For permitted connections, any privileges granted in the user table indicate the user's global privileges. Any privilege granted in this table applies to all databases on the server.

    Замечание

    Because any global privilege is considered a privilege for all databases, any global privilege enables a user to see all database names with SHOW DATABASES or by examining the SCHEMATA table of INFORMATION_SCHEMA.

  • The db table scope columns determine which users can access which databases from which hosts. The privilege columns determine which operations are permitted. A privilege granted at the database level applies to the database and to all objects in the database, such as tables and stored programs.

  • The host table is used in conjunction with the db table when you want a given db table row to apply to several hosts. For example, if you want a user to be able to use a database from several hosts in your network, leave the Host value empty in the user's db table row, then populate the host table with a row for each of those hosts. This mechanism is described more detail in Section 5.4.5, “Access Control, Stage 2: Request Verification”.

    Замечание

    The host table must be modified directly with statements such as INSERT, UPDATE, and DELETE. It is not affected by statements such as GRANT and REVOKE that modify the grant tables indirectly. Most MySQL installations need not use this table at all.

  • The tables_priv and columns_priv tables are similar to the db table, but are more fine-grained: They apply at the table and column levels rather than at the database level. A privilege granted at the table level applies to the table and to all its columns. A privilege granted at the column level applies only to a specific column.

  • The procs_priv table applies to stored routines. A privilege granted at the routine level applies only to a single routine.

  • The proxies_priv table indicates which users can act as proxies for other users and whether proxy users can grant the PROXY privilege to other users.

The server uses the user, db, and host tables in the mysql database at both the first and second stages of access control (see Section 5.4, “The MySQL Access Privilege System”). The columns in the user and db tables are shown here. The host table is similar to the db table but has a specialized use as described in Section 5.4.5, “Access Control, Stage 2: Request Verification”.

Table 5.7. user and db Table Columns

Table Nameuserdb
Scope columnsHostHost
 UserDb
 PasswordUser
Privilege columnsSelect_privSelect_priv
 Insert_privInsert_priv
 Update_privUpdate_priv
 Delete_privDelete_priv
 Index_privIndex_priv
 Alter_privAlter_priv
 Create_privCreate_priv
 Drop_privDrop_priv
 Grant_privGrant_priv
 Create_view_privCreate_view_priv
 Show_view_privShow_view_priv
 Create_routine_privCreate_routine_priv
 Alter_routine_privAlter_routine_priv
 Execute_privExecute_priv
 Trigger_privTrigger_priv
 Event_privEvent_priv
 Create_tmp_table_privCreate_tmp_table_priv
 Lock_tables_privLock_tables_priv
 References_privReferences_priv
 Reload_priv 
 Shutdown_priv 
 Process_priv 
 File_priv 
 Show_db_priv 
 Super_priv 
 Repl_slave_priv 
 Repl_client_priv 
 Create_user_priv 
 Create_tablespace_priv 
Security columnsssl_type 
 ssl_cipher 
 x509_issuer 
 x509_subject 
 plugin 
 authentication_string 
Resource control columnsmax_questions 
 max_updates 
 max_connections 
 max_user_connections 

As of MySQL 5.5.7, the mysql.user table has plugin and authentication_string columns for storing authentication plugin information.

If the plugin column for an account row is empty, the server uses native authentication for connection attempts for the account: Clients must match the password in the Password column of the account row.

If an account row names a plugin in the plugin column, the server uses it to authenticate connection attempts for the account. Whether the plugin uses the value in the Password column is up to the plugin.

Prior to MySQL 5.5.11, the length of the plugin column was 60 characters. This was increased to 64 characters in MySQL 5.5.11 for compatibility with the mysql.plugin table's name column. (Bug #11766610, Bug #59752)

During the second stage of access control, the server performs request verification to make sure that each client has sufficient privileges for each request that it issues. In addition to the user, db, and host grant tables, the server may also consult the tables_priv and columns_priv tables for requests that involve tables. The latter tables provide finer privilege control at the table and column levels. They have the columns shown in the following table.

Table 5.8. tables_priv and columns_priv Table Columns

Table Nametables_privcolumns_priv
Scope columnsHostHost
 DbDb
 UserUser
 Table_nameTable_name
  Column_name
Privilege columnsTable_privColumn_priv
 Column_priv 
Other columnsTimestampTimestamp
 Grantor 

The Timestamp and Grantor columns currently are unused and are discussed no further here.

For verification of requests that involve stored routines, the server may consult the procs_priv table, which has the columns shown in the following table.

Table 5.9. procs_priv Table Columns

Table Nameprocs_priv
Scope columnsHost
 Db
 User
 Routine_name
 Routine_type
Privilege columnsProc_priv
Other columnsTimestamp
 Grantor

The Routine_type column is an ENUM column with values of 'FUNCTION' or 'PROCEDURE' to indicate the type of routine the row refers to. This column enables privileges to be granted separately for a function and a procedure with the same name.

The Timestamp and Grantor columns currently are unused and are discussed no further here.

The proxies_priv table was added in MySQL 5.5.7 and records information about proxy users. It has these columns:

  • Host, User: These columns indicate the user account that has the PROXY privilege for the proxied account.

  • Proxied_host, Proxied_user: These columns indicate the account of the proxied user.

  • Grantor: Currently unused.

  • Timestamp: Currently unused.

  • With_grant: This column indicates whether the proxy account can grant the PROXY privilege to other accounts.

Scope columns in the grant tables contain strings. They are declared as shown here; the default value for each is the empty string.

Table 5.10. Grant Table Scope Column Types

Column NameType
HostCHAR(60)
UserCHAR(16)
PasswordCHAR(41)
DbCHAR(64)
Table_nameCHAR(64)
Column_nameCHAR(64)
Routine_nameCHAR(64)

For access-checking purposes, comparisons of User, Password, Db, and Table_name values are case sensitive. Comparisons of Host, Column_name, and Routine_name values are not case sensitive.

In the user, db, and host tables, each privilege is listed in a separate column that is declared as ENUM('N','Y') DEFAULT 'N'. In other words, each privilege can be disabled or enabled, with the default being disabled.

In the tables_priv, columns_priv, and procs_priv tables, the privilege columns are declared as SET columns. Values in these columns can contain any combination of the privileges controlled by the table. Only those privileges listed in the column value are enabled.

Table 5.11. Set-Type Privilege Column Values

Table NameColumn NamePossible Set Elements
tables_privTable_priv'Select', 'Insert', 'Update', 'Delete', 'Create', 'Drop', 'Grant', 'References', 'Index', 'Alter', 'Create View', 'Show view', 'Trigger'
tables_privColumn_priv'Select', 'Insert', 'Update', 'References'
columns_privColumn_priv'Select', 'Insert', 'Update', 'References'
procs_privProc_priv'Execute', 'Alter Routine', 'Grant'

Administrative privileges (such as RELOAD or SHUTDOWN) are specified only in the user table. Administrative operations are operations on the server itself and are not database-specific, so there is no reason to list these privileges in the other grant tables. Consequently, to determine whether you can perform an administrative operation, the server need consult only the user table.

The FILE privilege also is specified only in the user table. It is not an administrative privilege as such, but your ability to read or write files on the server host is independent of the database you are accessing.

The mysqld server reads the contents of the grant tables into memory when it starts. You can tell it to reload the tables by issuing a FLUSH PRIVILEGES statement or executing a mysqladmin flush-privileges or mysqladmin reload command. Changes to the grant tables take effect as indicated in Section 5.4.6, “When Privilege Changes Take Effect”.

When you modify an account's privileges, it is a good idea to verify that the changes set up privileges the way you want. To check the privileges for a given account, use the SHOW GRANTS statement (see Section 12.7.5.22, “SHOW GRANTS Синтаксис”). For example, to determine the privileges that are granted to an account with user name and host name values of bob and pc84.example.com, use this statement:

SHOW GRANTS FOR 'bob'@'pc84.example.com';

5.4.3. Specifying Account Names

MySQL account names consist of a user name and a host name. This enables creation of accounts for users with the same name who can connect from different hosts. This section describes how to write account names, including special values and wildcard rules.

In SQL statements such as CREATE USER, GRANT, and SET PASSWORD, write account names using the following rules:

  • Синтаксис for account names is 'user_name'@'host_name'.

  • An account name consisting only of a user name is equivalent to 'user_name'@'%'. For example, 'me' is equivalent to 'me'@'%'.

  • The user name and host name need not be quoted if they are legal as unquoted identifiers. Quotes are necessary to specify a user_name string containing special characters (such as “-”), or a host_name string containing special characters or wildcard characters (such as “%”); for example, 'test-user'@'%.com'.

  • Quote user names and host names as identifiers or as strings, using either backticks (“`”), single quotation marks (“'”), or double quotation marks (“"”).

  • The user name and host name parts, if quoted, must be quoted separately. That is, write 'me'@'localhost', not 'me@localhost'; the latter is interpreted as 'me@localhost'@'%'.

  • A reference to the CURRENT_USER() (or CURRENT_USER) function is equivalent to specifying the current user's name and host name literally.

MySQL stores account names in grant tables in the mysql database using separate columns for the user name and host name parts:

  • The user table contains one row for each account. The User and Host columns store the user name and host name. This table also indicates which global privileges the account has.

  • Other grant tables indicate privileges an account has for databases and objects within databases. These tables have User and Host columns to store the account name. Each row in these tables associates with the account in the user table that has the same User and Host values.

For additional detail about grant table structure, see Section 5.4.2, “Privilege System Grant Tables”.

User names and host names have certain special values or wildcard conventions, as described following.

A user name is either a nonblank value that literally matches the user name for incoming connection attempts, or a blank value (empty string) that matches any user name. An account with a blank user name is an anonymous user. To specify an anonymous user in SQL statements, use a quoted empty user name part, such as ''@'localhost'.

The host name part of an account name can take many forms, and wildcards are permitted:

  • A host value can be a host name or an IP address. The name 'localhost' indicates the local host. The IP address '127.0.0.1' indicates the loopback interface. For the local host, the host value can be the IPv6 address '::1', which indicates the IPv6 loopback interface.

  • You can use the wildcard characters “%” and “_” in host values. These have the same meaning as for pattern-matching operations performed with the LIKE operator. For example, a host value of '%' matches any host name, whereas a value of '%.mysql.com' matches any host in the mysql.com domain. '192.168.1.%' matches any host in the 192.168.1 class C network.

    Because you can use IP wildcard values in host values (for example, '192.168.1.%' to match every host on a subnet), someone could try to exploit this capability by naming a host 192.168.1.somewhere.com. To foil such attempts, MySQL disallows matching on host names that start with digits and a dot. Thus, if you have a host named something like 1.2.example.com, its name never matches the host part of account names. An IP wildcard value can match only IP addresses, not host names.

  • For a host value specified as an IP address, you can specify a netmask indicating how many address bits to use for the network number. This applies only for IPv4 addresses, not IPv6 addresses. The syntax is host_ip/netmask. For example:

    CREATE USER 'david'@'192.58.197.0/255.255.255.0';

    This enables david to connect from any client host having an IP address client_ip for which the following condition is true:

    client_ip & netmask = host_ip
    

    That is, for the CREATE USER statement just shown:

    client_ip & 255.255.255.0 = 192.58.197.0
    

    IP addresses that satisfy this condition and can connect to the MySQL server are those in the range from 192.58.197.0 to 192.58.197.255.

    The netmask can only be used to tell the server to use 8, 16, 24, or 32 bits of the address. Examples:

    • 192.0.0.0/255.0.0.0: Any host on the 192 class A network

    • 192.168.0.0/255.255.0.0: Any host on the 192.168 class B network

    • 192.168.1.0/255.255.255.0: Any host on the 192.168.1 class C network

    • 192.168.1.1: Only the host with this specific IP address

    The following netmask will not work because it masks 28 bits, and 28 is not a multiple of 8:

    192.168.0.1/255.255.255.240

5.4.4. Access Control, Stage 1: Connection Verification

When you attempt to connect to a MySQL server, the server accepts or rejects the connection based on your identity and whether you can verify your identity by supplying the correct password. If not, the server denies access to you completely. Otherwise, the server accepts the connection, and then enters Stage 2 and waits for requests.

Your identity is based on two pieces of information:

  • The client host from which you connect

  • Your MySQL user name

Identity checking is performed using the three user table scope columns (Host, User, and Password). The server accepts the connection only if the Host and User columns in some user table row match the client host name and user name and the client supplies the password specified in that row. The rules for permissible Host and User values are given in Section 5.4.3, “Specifying Account Names”.

If the User column value is nonblank, the user name in an incoming connection must match exactly. If the User value is blank, it matches any user name. If the user table row that matches an incoming connection has a blank user name, the user is considered to be an anonymous user with no name, not a user with the name that the client actually specified. This means that a blank user name is used for all further access checking for the duration of the connection (that is, during Stage 2).

The Password column can be blank. This is not a wildcard and does not mean that any password matches. It means that the user must connect without specifying a password. If the server authenticates a client using a plugin, the authentication method that the plugin implements may or may not use the password in the Password column. In this case, it is possible that an external password is also used to authenticate to the MySQL server.

Nonblank Password values in the user table represent encrypted passwords. MySQL does not store passwords in plaintext form for anyone to see. Rather, the password supplied by a user who is attempting to connect is encrypted (using the PASSWORD() function). The encrypted password then is used during the connection process when checking whether the password is correct. This is done without the encrypted password ever traveling over the connection. See Section 5.5.1, “User Names and Passwords”.

From MySQL's point of view, the encrypted password is the real password, so you should never give anyone access to it. In particular, do not give nonadministrative users read access to tables in the mysql database.

The following table shows how various combinations of Host and User values in the user table apply to incoming connections.

Host ValueUser ValuePermissible Connections
'thomas.loc.gov''fred'fred, connecting from thomas.loc.gov
'thomas.loc.gov'''Any user, connecting from thomas.loc.gov
'%''fred'fred, connecting from any host
'%'''Any user, connecting from any host
'%.loc.gov''fred'fred, connecting from any host in the loc.gov domain
'x.y.%''fred'fred, connecting from x.y.net, x.y.com, x.y.edu, and so on; this is probably not useful
'144.155.166.177''fred'fred, connecting from the host with IP address 144.155.166.177
'144.155.166.%''fred'fred, connecting from any host in the 144.155.166 class C subnet
'144.155.166.0/255.255.255.0''fred'Same as previous example

It is possible for the client host name and user name of an incoming connection to match more than one row in the user table. The preceding set of examples demonstrates this: Several of the entries shown match a connection from thomas.loc.gov by fred.

When multiple matches are possible, the server must determine which of them to use. It resolves this issue as follows:

  • Whenever the server reads the user table into memory, it sorts the rows.

  • When a client attempts to connect, the server looks through the rows in sorted order.

  • The server uses the first row that matches the client host name and user name.

The server uses sorting rules that order rows with the most-specific Host values first. Literal host names and IP addresses are the most specific. (The specificity of a literal IP address is not affected by whether it has a netmask, so 192.168.1.13 and 192.168.1.0/255.255.255.0 are considered equally specific.) The pattern '%' means “any host” and is least specific. The empty string '' also means “any host” but sorts after '%'. Rows with the same Host value are ordered with the most-specific User values first (a blank User value means “any user” and is least specific).

To see how this works, suppose that the user table looks like this:

+-----------+----------+-
| Host      | User     | ...
+-----------+----------+-
| %         | root     | ...
| %         | jeffrey  | ...
| localhost | root     | ...
| localhost |          | ...
+-----------+----------+-

When the server reads the table into memory, it sorts the rows using the rules just described. The result after sorting looks like this:

+-----------+----------+-
| Host      | User     | ...
+-----------+----------+-
| localhost | root     | ...
| localhost |          | ...
| %         | jeffrey  | ...
| %         | root     | ...
+-----------+----------+-

When a client attempts to connect, the server looks through the sorted rows and uses the first match found. For a connection from localhost by jeffrey, two of the rows from the table match: the one with Host and User values of 'localhost' and '', and the one with values of '%' and 'jeffrey'. The 'localhost' row appears first in sorted order, so that is the one the server uses.

Here is another example. Suppose that the user table looks like this:

+----------------+----------+-
| Host           | User     | ...
+----------------+----------+-
| %              | jeffrey  | ...
| thomas.loc.gov |          | ...
+----------------+----------+-

The sorted table looks like this:

+----------------+----------+-
| Host           | User     | ...
+----------------+----------+-
| thomas.loc.gov |          | ...
| %              | jeffrey  | ...
+----------------+----------+-

A connection by jeffrey from thomas.loc.gov is matched by the first row, whereas a connection by jeffrey from any host is matched by the second.

Замечание

It is a common misconception to think that, for a given user name, all rows that explicitly name that user are used first when the server attempts to find a match for the connection. This is not true. The preceding example illustrates this, where a connection from thomas.loc.gov by jeffrey is first matched not by the row containing 'jeffrey' as the User column value, but by the row with no user name. As a result, jeffrey is authenticated as an anonymous user, even though he specified a user name when connecting.

If you are able to connect to the server, but your privileges are not what you expect, you probably are being authenticated as some other account. To find out what account the server used to authenticate you, use the CURRENT_USER() function. (See Section 11.14, “Information Functions”.) It returns a value in user_name@host_name format that indicates the User and Host values from the matching user table row. Suppose that jeffrey connects and issues the following query:

mysql> SELECT CURRENT_USER();
+----------------+
| CURRENT_USER() |
+----------------+
| @localhost     |
+----------------+

The result shown here indicates that the matching user table row had a blank User column value. In other words, the server is treating jeffrey as an anonymous user.

Another way to diagnose authentication problems is to print out the user table and sort it by hand to see where the first match is being made.

5.4.5. Access Control, Stage 2: Request Verification

After you establish a connection, the server enters Stage 2 of access control. For each request that you issue through that connection, the server determines what operation you want to perform, then checks whether you have sufficient privileges to do so. This is where the privilege columns in the grant tables come into play. These privileges can come from any of the user, db, host, tables_priv, columns_priv, or procs_priv tables. (You may find it helpful to refer to Section 5.4.2, “Privilege System Grant Tables”, which lists the columns present in each of the grant tables.)

The user table grants privileges that are assigned to you on a global basis and that apply no matter what the default database is. For example, if the user table grants you the DELETE privilege, you can delete rows from any table in any database on the server host! It is wise to grant privileges in the user table only to people who need them, such as database administrators. For other users, you should leave all privileges in the user table set to 'N' and grant privileges at more specific levels only. You can grant privileges for particular databases, tables, columns, or routines.

The db and host tables grant database-specific privileges. Values in the scope columns of these tables can take the following forms:

  • A blank User value in the db table matches the anonymous user. A nonblank value matches literally; there are no wildcards in user names.

  • The wildcard characters “%” and “_” can be used in the Host and Db columns of either table. These have the same meaning as for pattern-matching operations performed with the LIKE operator. If you want to use either character literally when granting privileges, you must escape it with a backslash. For example, to include the underscore character (“_”) as part of a database name, specify it as “\_” in the GRANT statement.

  • A '%' Host value in the db table means “any host.” A blank Host value in the db table means “consult the host table for further information” (a process that is described later in this section).

  • A '%' or blank Host value in the host table means “any host.

  • A '%' or blank Db value in either table means “any database.

The server reads the db and host tables into memory and sorts them at the same time that it reads the user table. The server sorts the db table based on the Host, Db, and User scope columns, and sorts the host table based on the Host and Db scope columns. As with the user table, sorting puts the most-specific values first and least-specific values last, and when the server looks for matching entries, it uses the first match that it finds.

The tables_priv, columns_priv, and procs_priv tables grant table-specific, column-specific, and routine-specific privileges. Values in the scope columns of these tables can take the following forms:

  • The wildcard characters “%” and “_” can be used in the Host column. These have the same meaning as for pattern-matching operations performed with the LIKE operator.

  • A '%' or blank Host value means “any host.

  • The Db, Table_name, Column_name, and Routine_name columns cannot contain wildcards or be blank.

The server sorts the tables_priv, columns_priv, and procs_priv tables based on the Host, Db, and User columns. This is similar to db table sorting, but simpler because only the Host column can contain wildcards.

The server uses the sorted tables to verify each request that it receives. For requests that require administrative privileges such as SHUTDOWN or RELOAD, the server checks only the user table row because that is the only table that specifies administrative privileges. The server grants access if the row permits the requested operation and denies access otherwise. For example, if you want to execute mysqladmin shutdown but your user table row does not grant the SHUTDOWN privilege to you, the server denies access without even checking the db or host tables. (They contain no Shutdown_priv column, so there is no need to do so.)

For database-related requests (INSERT, UPDATE, and so on), the server first checks the user's global privileges by looking in the user table row. If the row permits the requested operation, access is granted. If the global privileges in the user table are insufficient, the server determines the user's database-specific privileges by checking the db and host tables:

  1. The server looks in the db table for a match on the Host, Db, and User columns. The Host and User columns are matched to the connecting user's host name and MySQL user name. The Db column is matched to the database that the user wants to access. If there is no row for the Host and User, access is denied.

  2. If there is a matching db table row and its Host column is not blank, that row defines the user's database-specific privileges.

  3. If the matching db table row's Host column is blank, it signifies that the host table enumerates which hosts should be permitted access to the database. In this case, a further lookup is done in the host table to find a match on the Host and Db columns. If no host table row matches, access is denied. If there is a match, the user's database-specific privileges are computed as the intersection (not the union!) of the privileges in the db and host table entries; that is, the privileges that are 'Y' in both entries. (This way you can grant general privileges in the db table row and then selectively restrict them on a host-by-host basis using the host table entries.)

After determining the database-specific privileges granted by the db and host table entries, the server adds them to the global privileges granted by the user table. If the result permits the requested operation, access is granted. Otherwise, the server successively checks the user's table and column privileges in the tables_priv and columns_priv tables, adds those to the user's privileges, and permits or denies access based on the result. For stored-routine operations, the server uses the procs_priv table rather than tables_priv and columns_priv.

Expressed in boolean terms, the preceding description of how a user's privileges are calculated may be summarized like this:

global privileges
OR (database privileges AND host privileges)
OR table privileges
OR column privileges
OR routine privileges

It may not be apparent why, if the global user row privileges are initially found to be insufficient for the requested operation, the server adds those privileges to the database, table, and column privileges later. The reason is that a request might require more than one type of privilege. For example, if you execute an INSERT INTO ... SELECT statement, you need both the INSERT and the SELECT privileges. Your privileges might be such that the user table row grants one privilege and the db table row grants the other. In this case, you have the necessary privileges to perform the request, but the server cannot tell that from either table by itself; the privileges granted by the entries in both tables must be combined.

The host table is not affected by the GRANT or REVOKE statements, so it is unused in most MySQL installations. If you modify it directly, you can use it for some specialized purposes, such as to maintain a list of secure servers on the local network that are granted all privileges.

You can also use the host table to indicate hosts that are not secure. Suppose that you have a machine public.your.domain that is located in a public area that you do not consider secure. You can enable access to all hosts on your network except that machine by using host table entries like this:

+--------------------+----+-
| Host               | Db | ...
+--------------------+----+-
| public.your.domain | %  | ... (all privileges set to 'N')
| %.your.domain      | %  | ... (all privileges set to 'Y')
+--------------------+----+-

5.4.6. When Privilege Changes Take Effect

When mysqld starts, it reads all grant table contents into memory. The in-memory tables become effective for access control at that point.

If you modify the grant tables indirectly using account-management statements such as GRANT, REVOKE, SET PASSWORD, or RENAME USER, the server notices these changes and loads the grant tables into memory again immediately.

If you modify the grant tables directly using statements such as INSERT, UPDATE, or DELETE, your changes have no effect on privilege checking until you either restart the server or tell it to reload the tables. If you change the grant tables directly but forget to reload them, your changes have no effect until you restart the server. This may leave you wondering why your changes seem to make no difference!

To tell the server to reload the grant tables, perform a flush-privileges operation. This can be done by issuing a FLUSH PRIVILEGES statement or by executing a mysqladmin flush-privileges or mysqladmin reload command.

A grant table reload affects privileges for each existing client connection as follows:

  • Table and column privilege changes take effect with the client's next request.

  • Database privilege changes take effect the next time the client executes a USE db_name statement.

    Замечание

    Client applications may cache the database name; thus, this effect may not be visible to them without actually changing to a different database or flushing the privileges.

  • Global privileges and passwords are unaffected for a connected client. These changes take effect only for subsequent connections.

If the server is started with the --skip-grant-tables option, it does not read the grant tables or implement any access control. Anyone can connect and do anything, which is insecure. To cause a server thus started to read the tables and enable access checking, flush the privileges.

5.4.7. Causes of Access-Denied Ошибки

If you encounter problems when you try to connect to the MySQL server, the following items describe some courses of action you can take to correct the problem.

  • Make sure that the server is running. If it is not, clients cannot connect to it. For example, if an attempt to connect to the server fails with a message such as one of those following, one cause might be that the server is not running:

    shell> mysql
    ERROR 2003: Can't connect to MySQL server on 'host_name' (111)
    shell> mysql
    ERROR 2002: Can't connect to local MySQL server through socket
    '/tmp/mysql.sock' (111)
    
  • It might be that the server is running, but you are trying to connect using a TCP/IP port, named pipe, or Unix socket file different from the one on which the server is listening. To correct this when you invoke a client program, specify a --port option to indicate the proper port number, or a --socket option to indicate the proper named pipe or Unix socket file. To find out where the socket file is, you can use this command:

    shell> netstat -ln | grep mysql
    
  • Make sure that the server has not been configured to ignore network connections or (if you are attempting to connect remotely) that it has not been configured to listen only locally on its network interfaces. If the server was started with --skip-networking, it will not accept TCP/IP connections at all. If the server was started with --bind-address=127.0.0.1, it will listen for TCP/IP connections only locally on the loopback interface and will not accept remote connections.

  • Check to make sure that there is no firewall blocking access to MySQL. Your firewall may be configured on the basis of the application being executed, or the port number used by MySQL for communication (3306 by default). Under Linux or Unix, check your IP tables (or similar) configuration to ensure that the port has not been blocked. Under Windows, applications such as ZoneAlarm or the Windows XP personal firewall may need to be configured not to block the MySQL port.

  • The grant tables must be properly set up so that the server can use them for access control. For some distribution types (such as binary distributions on Windows, or RPM distributions on Linux), the installation process initializes the mysql database containing the grant tables. For distributions that do not do this, you must initialize the grant tables manually by running the mysql_install_db script. For details, see Section 2.10.1, “Unix Postinstallation Procedures”.

    To determine whether you need to initialize the grant tables, look for a mysql directory under the data directory. (The data directory normally is named data or var and is located under your MySQL installation directory.) Make sure that you have a file named user.MYD in the mysql database directory. If not, execute the mysql_install_db script. After running this script and starting the server, test the initial privileges by executing this command:

    shell> mysql -u root test
    

    The server should let you connect without error.

  • After a fresh installation, you should connect to the server and set up your users and their access permissions:

    shell> mysql -u root mysql
    

    The server should let you connect because the MySQL root user has no password initially. That is also a security risk, so setting the password for the root accounts is something you should do while you're setting up your other MySQL accounts. For instructions on setting the initial passwords, see Section 2.10.2, “Securing the Initial MySQL Accounts”.

  • If you have updated an existing MySQL installation to a newer version, did you run the mysql_upgrade script? If not, do so. The structure of the grant tables changes occasionally when new capabilities are added, so after an upgrade you should always make sure that your tables have the current structure. For instructions, see Section 4.4.7, “mysql_upgrade — Check Tables for MySQL Upgrade”.

  • If a client program receives the following error message when it tries to connect, it means that the server expects passwords in a newer format than the client is capable of generating:

    shell> mysql
    Client does not support authentication protocol requested
    by server; consider upgrading MySQL client
    

    For information on how to deal with this, see Section 5.3.2.3, “Password Hashing in MySQL”, and Section C.5.2.4, “Client does not support authentication protocol.

  • Remember that client programs use connection parameters specified in option files or environment variables. If a client program seems to be sending incorrect default connection parameters when you have not specified them on the command line, check any applicable option files and your environment. For example, if you get Access denied when you run a client without any options, make sure that you have not specified an old password in any of your option files!

    You can suppress the use of option files by a client program by invoking it with the --no-defaults option. For example:

    shell> mysqladmin --no-defaults -u root version
    

    The option files that clients use are listed in Section 4.2.3.3, “Using Option Files”. Environment variables are listed in Section 2.12, “Environment Variables”.

  • If you get the following error, it means that you are using an incorrect root password:

    shell> mysqladmin -u root -pxxxx ver
    Access denied for user 'root'@'localhost' (using password: YES)
    

    If the preceding error occurs even when you have not specified a password, it means that you have an incorrect password listed in some option file. Try the --no-defaults option as described in the previous item.

    For information on changing passwords, see Section 5.5.5, “Assigning Account Passwords”.

    If you have lost or forgotten the root password, see Section C.5.4.1, “How to Reset the Root Password”.

  • If you change a password by using SET PASSWORD, INSERT, or UPDATE, you must encrypt the password using the PASSWORD() function. If you do not use PASSWORD() for these statements, the password will not work. For example, the following statement assigns a password, but fails to encrypt it, so the user is not able to connect afterward:

    SET PASSWORD FOR 'abe'@'host_name' = 'eagle';
    

    Instead, set the password like this:

    SET PASSWORD FOR 'abe'@'host_name' = PASSWORD('eagle');
    

    The PASSWORD() function is unnecessary when you specify a password using the CREATE USER or GRANT statements or the mysqladmin password command. Each of those automatically uses PASSWORD() to encrypt the password. See Section 5.5.5, “Assigning Account Passwords”, and Section 12.7.1.1, “CREATE USER Синтаксис”.

  • localhost is a synonym for your local host name, and is also the default host to which clients try to connect if you specify no host explicitly.

    To avoid this problem on such systems, you can use a --host=127.0.0.1 option to name the server host explicitly. This will make a TCP/IP connection to the local mysqld server. You can also use TCP/IP by specifying a --host option that uses the actual host name of the local host. In this case, the host name must be specified in a user table row on the server host, even though you are running the client program on the same host as the server.

  • The Access denied error message tells you who you are trying to log in as, the client host from which you are trying to connect, and whether you were using a password. Normally, you should have one row in the user table that exactly matches the host name and user name that were given in the error message. For example, if you get an error message that contains using password: NO, it means that you tried to log in without a password.

  • If you get an Access denied error when trying to connect to the database with mysql -u user_name, you may have a problem with the user table. Check this by executing mysql -u root mysql and issuing this SQL statement:

    SELECT * FROM user;

    The result should include a row with the Host and User columns matching your client's host name and your MySQL user name.

  • If the following error occurs when you try to connect from a host other than the one on which the MySQL server is running, it means that there is no row in the user table with a Host value that matches the client host:

    Host ... is not allowed to connect to this MySQL server

    You can fix this by setting up an account for the combination of client host name and user name that you are using when trying to connect.

    If you do not know the IP address or host name of the machine from which you are connecting, you should put a row with '%' as the Host column value in the user table. After trying to connect from the client machine, use a SELECT USER() query to see how you really did connect. Then change the '%' in the user table row to the actual host name that shows up in the log. Otherwise, your system is left insecure because it permits connections from any host for the given user name.

    On Linux, another reason that this error might occur is that you are using a binary MySQL version that is compiled with a different version of the glibc library than the one you are using. In this case, you should either upgrade your operating system or glibc, or download a source distribution of MySQL version and compile it yourself. A source RPM is normally trivial to compile and install, so this is not a big problem.

  • If you specify a host name when trying to connect, but get an error message where the host name is not shown or is an IP address, it means that the MySQL server got an error when trying to resolve the IP address of the client host to a name:

    shell> mysqladmin -u root -pxxxx -h some_hostname ver
    Access denied for user 'root'@'' (using password: YES)
    

    If you try to connect as root and get the following error, it means that you do not have a row in the user table with a User column value of 'root' and that mysqld cannot resolve the host name for your client:

    Access denied for user ''@'unknown'

    These errors indicate a DNS problem. To fix it, execute mysqladmin flush-hosts to reset the internal DNS host name cache. See Section 7.11.5.2, “How MySQL Uses DNS”.

    Some permanent solutions are:

    • Determine what is wrong with your DNS server and fix it.

    • Specify IP addresses rather than host names in the MySQL grant tables.

    • Put an entry for the client machine name in /etc/hosts on Unix or \windows\hosts on Windows.

    • Start mysqld with the --skip-name-resolve option.

    • Start mysqld with the --skip-host-cache option.

    • On Unix, if you are running the server and the client on the same machine, connect to localhost. Unix connections to localhost use a Unix socket file rather than TCP/IP.

    • On Windows, if you are running the server and the client on the same machine and the server supports named pipe connections, connect to the host name . (period). Connections to . use a named pipe rather than TCP/IP.

  • If mysql -u root test works but mysql -h your_hostname -u root test results in Access denied (where your_hostname is the actual host name of the local host), you may not have the correct name for your host in the user table. A common problem here is that the Host value in the user table row specifies an unqualified host name, but your system's name resolution routines return a fully qualified domain name (or vice versa). For example, if you have an entry with host 'pluto' in the user table, but your DNS tells MySQL that your host name is 'pluto.example.com', the entry does not work. Try adding an entry to the user table that contains the IP address of your host as the Host column value. (Alternatively, you could add an entry to the user table with a Host value that contains a wildcard; for example, 'pluto.%'. However, use of Host values ending with “%” is insecure and is not recommended!)

  • If mysql -u user_name test works but mysql -u user_name other_db does not, you have not granted access to the given user for the database named other_db.

  • If mysql -u user_name works when executed on the server host, but mysql -h host_name -u user_name does not work when executed on a remote client host, you have not enabled access to the server for the given user name from the remote host.

  • If you cannot figure out why you get Access denied, remove from the user table all entries that have Host values containing wildcards (entries that contain '%' or '_' characters). A very common error is to insert a new entry with Host='%' and User='some_user', thinking that this enables you to specify localhost to connect from the same machine. The reason that this does not work is that the default privileges include an entry with Host='localhost' and User=''. Because that entry has a Host value 'localhost' that is more specific than '%', it is used in preference to the new entry when connecting from localhost! The correct procedure is to insert a second entry with Host='localhost' and User='some_user', or to delete the entry with Host='localhost' and User=''. After deleting the entry, remember to issue a FLUSH PRIVILEGES statement to reload the grant tables. See also Section 5.4.4, “Access Control, Stage 1: Connection Verification”.

  • If you are able to connect to the MySQL server, but get an Access denied message whenever you issue a SELECT ... INTO OUTFILE or LOAD DATA INFILE statement, your entry in the user table does not have the FILE privilege enabled.

  • If you change the grant tables directly (for example, by using INSERT, UPDATE, or DELETE statements) and your changes seem to be ignored, remember that you must execute a FLUSH PRIVILEGES statement or a mysqladmin flush-privileges command to cause the server to reload the privilege tables. Otherwise, your changes have no effect until the next time the server is restarted. Remember that after you change the root password with an UPDATE statement, you will not need to specify the new password until after you flush the privileges, because the server will not know you've changed the password yet!

  • If your privileges seem to have changed in the middle of a session, it may be that a MySQL administrator has changed them. Reloading the grant tables affects new client connections, but it also affects existing connections as indicated in Section 5.4.6, “When Privilege Changes Take Effect”.

  • If you have access problems with a Perl, PHP, Python, or ODBC program, try to connect to the server with mysql -u user_name db_name or mysql -u user_name -pyour_pass db_name. If you are able to connect using the mysql client, the problem lies with your program, not with the access privileges. (There is no space between -p and the password; you can also use the --password=your_pass syntax to specify the password. If you use the -p or --password option with no password value, MySQL prompts you for the password.)

  • For testing purposes, start the mysqld server with the --skip-grant-tables option. Then you can change the MySQL grant tables and use the mysqlaccess script to check whether your modifications have the desired effect. When you are satisfied with your changes, execute mysqladmin flush-privileges to tell the mysqld server to reload the privileges. This enables you to begin using the new grant table contents without stopping and restarting the server.

  • If you get the following error, you may have a problem with the db or host table:

    Access to database denied

    If the entry selected from the db table has an empty value in the Host column, make sure that there are one or more corresponding entries in the host table specifying which hosts the db table entry applies to. This problem occurs infrequently because the host table is rarely used.

  • If everything else fails, start the mysqld server with a debugging option (for example, --debug=d,general,query). This prints host and user information about attempted connections, as well as information about each command issued. See MySQL Internals: Porting.

  • If you have any other problems with the MySQL grant tables and feel you must post the problem to the mailing list, always provide a dump of the MySQL grant tables. You can dump the tables with the mysqldump mysql command. To file a bug report, see the instructions at Section 1.7, “How to Report Bugs or Problems”. In some cases, you may need to restart mysqld with --skip-grant-tables to run mysqldump.

5.5. MySQL User Account Management

This section describes how to set up accounts for clients of your MySQL server. It discusses the following topics:

  • The meaning of account names and passwords as used in MySQL and how that compares to names and passwords used by your operating system

  • How to set up new accounts and remove existing accounts

  • How to change passwords

  • Guidelines for using passwords securely

  • How to use secure connections with SSL

See also Section 12.7.1, “Account Management Statements”, which describes the syntax and use for all user-management SQL statements.

5.5.1. User Names and Passwords

MySQL stores accounts in the user table of the mysql database. An account is defined in terms of a user name and the client host or hosts from which the user can connect to the server. The account may also have a password. For information about account representation in the user table, see Section 5.4.2, “Privilege System Grant Tables”. MySQL 5.5 supports authentication plugins, so it is possible that an account authenticates using some external authentication method. See Section 5.5.6, “Pluggable Authentication”.

There are several distinctions between the way user names and passwords are used by MySQL and the way they are used by your operating system:

  • User names, as used by MySQL for authentication purposes, have nothing to do with user names (login names) as used by Windows or Unix. On Unix, most MySQL clients by default try to log in using the current Unix user name as the MySQL user name, but that is for convenience only. The default can be overridden easily, because client programs permit any user name to be specified with a -u or --user option. Because this means that anyone can attempt to connect to the server using any user name, you cannot make a database secure in any way unless all MySQL accounts have passwords. Anyone who specifies a user name for an account that has no password is able to connect successfully to the server.

  • MySQL user names can be up to 16 characters long. Operating system user names, because they are completely unrelated to MySQL user names, may be of a different maximum length. For example, Unix user names typically are limited to eight characters.

    Warning

    The limit on MySQL user name length is hard-coded in the MySQL servers and clients, and trying to circumvent it by modifying the definitions of the tables in the mysql database does not work.

    You should never alter any of the tables in the mysql database in any manner whatsoever except by means of the procedure that is described in Section 4.4.7, “mysql_upgrade — Check Tables for MySQL Upgrade”. Attempting to redefine MySQL's system tables in any other fashion results in undefined (and unsupported!) behavior.

  • The server uses MySQL passwords stored in the user table to authenticate client connections using MySQL native authentication (against passwords stored in the mysql.user table). These passwords have nothing to do with passwords for logging in to your operating system. There is no necessary connection between the “external” password you use to log in to a Windows or Unix machine and the password you use to access the MySQL server on that machine.

    If the server authenticates a client using a plugin, the authentication method that the plugin implements may or may not use the password in the user table. In this case, it is possible that an external password is also used to authenticate to the MySQL server.

  • MySQL encrypts passwords stored in the user table using its own algorithm. This encryption is the same as that implemented by the PASSWORD() SQL function but differs from that used during the Unix login process. Unix password encryption is the same as that implemented by the ENCRYPT() SQL function. See the descriptions of the PASSWORD() and ENCRYPT() functions in Section 11.13, “Encryption and Compression Functions”.

    From version 4.1 on, MySQL employs a stronger authentication method that has better password protection during the connection process than in earlier versions. It is secure even if TCP/IP packets are sniffed or the mysql database is captured. (In earlier versions, even though passwords are stored in encrypted form in the user table, knowledge of the encrypted password value could be used to connect to the MySQL server.) Section 5.3.2.3, “Password Hashing in MySQL”, discusses password encryption further.

  • It is possible to connect to the server regardless of character set settings if the user name and password contain only ASCII characters. To connect when the user name or password contain non-ASCII characters, the client should call the mysql_options() C API function with the MYSQL_SET_CHARSET_NAME option and appropriate character set name as arguments. This causes authentication to take place using the specified character set. Otherwise, authentication will fail unless the server default character set is the same as the encoding in the authentication defaults.

    Standard MySQL client programs support a --default-character-set option that causes mysql_options() to be called as just described. In addition, character set autodetection is supported as described in Section 9.1.4, “Connection Character Sets and Collations”. For programs that use a connector that is not based on the C API, the connector may provide an equivalent to mysql_options() that can be used instead. Check the connector documentation.

    The preceding notes do not apply for ucs2, utf16, and utf32, which are not permitted as client character sets.

When you install MySQL, the grant tables are populated with an initial set of accounts. The names and access privileges for these accounts are described in Section 2.10.2, “Securing the Initial MySQL Accounts”, which also discusses how to assign passwords to them. Thereafter, you normally set up, modify, and remove MySQL accounts using statements such as CREATE USER, GRANT, and REVOKE. See Section 12.7.1, “Account Management Statements”.

When you connect to a MySQL server with a command-line client, specify the user name and password as necessary for the account that you want to use:

shell> mysql --user=monty --password=password db_name

If you prefer short options, the command looks like this:

shell> mysql -u monty -ppassword db_name

There must be no space between the -p option and the following password value.

If you omit the password value following the --password or -p option on the command line, the client prompts for one.

Specifying a password on the command line should be considered insecure. See Section 5.3.2.2, “End-User Guidelines for Password Security”. You can use an option file to avoid giving the password on the command line.

For additional information about specifying user names, passwords, and other connection parameters, see Section 4.2.2, “Connecting to the MySQL Server”.

5.5.2. Adding User Accounts

You can create MySQL accounts in two ways:

  • By using statements intended for creating accounts, such as CREATE USER or GRANT. These statements cause the server to make appropriate modifications to the grant tables.

  • By manipulating the MySQL grant tables directly with statements such as INSERT, UPDATE, or DELETE.

The preferred method is to use account-creation statements because they are more concise and less error-prone than manipulating the grant tables directly. CREATE USER and GRANT are described in Section 12.7.1, “Account Management Statements”.

Another option for creating accounts is to use one of several available third-party programs that offer capabilities for MySQL account administration. phpMyAdmin is one such program.

The following examples show how to use the mysql client program to set up new accounts. These examples assume that privileges have been set up according to the defaults described in Section 2.10.2, “Securing the Initial MySQL Accounts”. This means that to make changes, you must connect to the MySQL server as the MySQL root user, and the root account must have the INSERT privilege for the mysql database and the RELOAD administrative privilege.

As noted in the examples where appropriate, some of the statements will fail if the server's SQL mode has been set to enable certain restrictions. In particular, strict mode (STRICT_TRANS_TABLES, STRICT_ALL_TABLES) and NO_AUTO_CREATE_USER will prevent the server from accepting some of the statements. Workarounds are indicated for these cases. For more information about SQL modes and their effect on grant table manipulation, see Section 5.1.6, “Server SQL Modes”, and Section 12.7.1.3, “GRANT Синтаксис”.

First, use the mysql program to connect to the server as the MySQL root user:

shell> mysql --user=root mysql

If you have assigned a password to the root account, you will also need to supply a --password or -p option, both for this mysql command and for those later in this section.

After connecting to the server as root, you can add new accounts. The following statements use GRANT to set up four new accounts:

mysql> CREATE USER 'monty'@'localhost' IDENTIFIED BY 'some_pass';
mysql> GRANT ALL PRIVILEGES ON *.* TO 'monty'@'localhost'
    ->     WITH GRANT OPTION;
mysql> CREATE USER 'monty'@'%' IDENTIFIED BY 'some_pass';
mysql> GRANT ALL PRIVILEGES ON *.* TO 'monty'@'%'
    ->     WITH GRANT OPTION;
mysql> CREATE USER 'admin'@'localhost';
mysql> GRANT RELOAD,PROCESS ON *.* TO 'admin'@'localhost';
mysql> CREATE USER 'dummy'@'localhost';

The accounts created by these statements have the following properties:

  • Two of the accounts have a user name of monty and a password of some_pass. Both accounts are superuser accounts with full privileges to do anything. The 'monty'@'localhost' account can be used only when connecting from the local host. The 'monty'@'%' account uses the '%' wildcard for the host part, so it can be used to connect from any host.

    It is necessary to have both accounts for monty to be able to connect from anywhere as monty. Without the localhost account, the anonymous-user account for localhost that is created by mysql_install_db would take precedence when monty connects from the local host. As a result, monty would be treated as an anonymous user. The reason for this is that the anonymous-user account has a more specific Host column value than the 'monty'@'%' account and thus comes earlier in the user table sort order. (user table sorting is discussed in Section 5.4.4, “Access Control, Stage 1: Connection Verification”.)

  • The 'admin'@'localhost' account has no password. This account can be used only by admin to connect from the local host. It is granted the RELOAD and PROCESS administrative privileges. These privileges enable the admin user to execute the mysqladmin reload, mysqladmin refresh, and mysqladmin flush-xxx commands, as well as mysqladmin processlist . No privileges are granted for accessing any databases. You could add such privileges later by issuing other GRANT statements.

  • The 'dummy'@'localhost' account has no password. This account can be used only to connect from the local host. No privileges are granted. It is assumed that you will grant specific privileges to the account later.

The statements that create accounts with no password will fail if the NO_AUTO_CREATE_USER SQL mode is enabled. To deal with this, use an IDENTIFIED BY clause that specifies a nonempty password.

To check the privileges for an account, use SHOW GRANTS:

mysql> SHOW GRANTS FOR 'admin'@'localhost';
+-----------------------------------------------------+
| Grants for admin@localhost                          |
+-----------------------------------------------------+
| GRANT RELOAD, PROCESS ON *.* TO 'admin'@'localhost' |
+-----------------------------------------------------+

As an alternative to CREATE USER and GRANT, you can create the same accounts directly by issuing INSERT statements and then telling the server to reload the grant tables using FLUSH PRIVILEGES:

shell> mysql --user=root mysql
mysql> INSERT INTO user
    ->     VALUES('localhost','monty',PASSWORD('some_pass'),
    ->     'Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y');
mysql> INSERT INTO user
    ->     VALUES('%','monty',PASSWORD('some_pass'),
    ->     'Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y',
    ->     'Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y',
    ->     '','','','',0,0,0,0);
mysql> INSERT INTO user SET Host='localhost',User='admin',
    ->     Reload_priv='Y', Process_priv='Y';
mysql> INSERT INTO user (Host,User,Password)
    ->     VALUES('localhost','dummy','');
mysql> FLUSH PRIVILEGES;

When you create accounts with INSERT, it is necessary to use FLUSH PRIVILEGES to tell the server to reload the grant tables. Otherwise, the changes go unnoticed until you restart the server. With CREATE USER, FLUSH PRIVILEGES is unnecessary.

The reason for using the PASSWORD() function with INSERT is to encrypt the password. The CREATE USER statement encrypts the password for you, so PASSWORD() is unnecessary.

The 'Y' values enable privileges for the accounts. Depending on your MySQL version, you may have to use a different number of 'Y' values in the first two INSERT statements. The INSERT statement for the admin account employs the more readable extended INSERT syntax using SET.

In the INSERT statement for the dummy account, only the Host, User, and Password columns in the user table row are assigned values. None of the privilege columns are set explicitly, so MySQL assigns them all the default value of 'N'. This is equivalent to what CREATE USER does.

If strict SQL mode is enabled, all columns that have no default value must have a value specified. In this case, INSERT statements must explicitly specify values for the ssl_cipher, x509_issuer, and x509_subject columns.

To set up a superuser account, it is necessary only to insert a user table row with all privilege columns set to 'Y'. The user table privileges are global, so no entries in any of the other grant tables are needed.

The next examples create three accounts and give them access to specific databases. Each of them has a user name of custom and password of obscure.

To create the accounts with CREATE USER and GRANT, use the following statements:

shell> mysql --user=root mysql
mysql> CREATE USER 'custom'@'localhost' IDENTIFIED BY 'obscure';
mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP
    ->     ON bankaccount.*
    ->     TO 'custom'@'localhost';
mysql> CREATE USER 'custom'@'host47.example.com' IDENTIFIED BY 'obscure';
mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP
    ->     ON expenses.*
    ->     TO 'custom'@'host47.example.com';
mysql> CREATE USER 'custom'@'server.domain' IDENTIFIED BY 'obscure';
mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP
    ->     ON customer.*
    ->     TO 'custom'@'server.domain';

The three accounts can be used as follows:

  • The first account can access the bankaccount database, but only from the local host.

  • The second account can access the expenses database, but only from the host host47.example.com.

  • The third account can access the customer database, but only from the host server.domain.

To set up the custom accounts without GRANT, use INSERT statements as follows to modify the grant tables directly:

shell> mysql --user=root mysql
mysql> INSERT INTO user (Host,User,Password)
    ->     VALUES('localhost','custom',PASSWORD('obscure'));
mysql> INSERT INTO user (Host,User,Password)
    ->     VALUES('host47.example.com','custom',PASSWORD('obscure'));
mysql> INSERT INTO user (Host,User,Password)
    ->     VALUES('server.domain','custom',PASSWORD('obscure'));
mysql> INSERT INTO db
    ->     (Host,Db,User,Select_priv,Insert_priv,
    ->     Update_priv,Delete_priv,Create_priv,Drop_priv)
    ->     VALUES('localhost','bankaccount','custom',
    ->     'Y','Y','Y','Y','Y','Y');
mysql> INSERT INTO db
    ->     (Host,Db,User,Select_priv,Insert_priv,
    ->     Update_priv,Delete_priv,Create_priv,Drop_priv)
    ->     VALUES('host47.example.com','expenses','custom',
    ->     'Y','Y','Y','Y','Y','Y');
mysql> INSERT INTO db
    ->     (Host,Db,User,Select_priv,Insert_priv,
    ->     Update_priv,Delete_priv,Create_priv,Drop_priv)
    ->     VALUES('server.domain','customer','custom',
    ->     'Y','Y','Y','Y','Y','Y');
mysql> FLUSH PRIVILEGES;

The first three INSERT statements add user table entries that permit the user custom to connect from the various hosts with the given password, but grant no global privileges (all privileges are set to the default value of 'N'). The next three INSERT statements add db table entries that grant privileges to custom for the bankaccount, expenses, and customer databases, but only when accessed from the proper hosts. As usual when you modify the grant tables directly, you must tell the server to reload them with FLUSH PRIVILEGES so that the privilege changes take effect.

To create a user who has access from all machines in a given domain (for example, mydomain.com), you can use the “%” wildcard character in the host part of the account name:

mysql> CREATE USER 'myname'@'%.mydomain.com' IDENTIFIED BY 'mypass';

To do the same thing by modifying the grant tables directly, do this:

mysql> INSERT INTO user (Host,User,Password,...)
    ->     VALUES('%.mydomain.com','myname',PASSWORD('mypass'),...);
mysql> FLUSH PRIVILEGES;

5.5.3. Removing User Accounts

To remove an account, use the DROP USER statement, which is described in Section 12.7.1.2, “DROP USER Синтаксис”.

5.5.4. Setting Account Resource Limits

One means of limiting use of MySQL server resources is to set the global max_user_connections system variable to a nonzero value. This limits the number of simultaneous connections that can be made by any given account, but places no limits on what a client can do once connected. In addition, setting max_user_connections does not enable management of individual accounts. Both types of control are of interest to many MySQL administrators, particularly those working for Internet Service Providers.

In MySQL 5.5, you can limit use of the following server resources for individual accounts:

  • The number of queries that an account can issue per hour

  • The number of updates that an account can issue per hour

  • The number of times an account can connect to the server per hour

  • The number of simultaneous connections to the server by an account

Any statement that a client can issue counts against the query limit (unless its results are served from the query cache). Only statements that modify databases or tables count against the update limit.

An “account” in this context corresponds to a row in the mysql.user table. That is, a connection is assessed against the User and Host values in the user table row that applies to the connection. For example, an account 'usera'@'%.example.com' corresponds to a row in the user table that has User and Host values of usera and %.example.com, to permit usera to connect from any host in the example.com domain. In this case, the server applies resource limits in this row collectively to all connections by usera from any host in the example.com domain because all such connections use the same account.

Before MySQL 5.0.3, an “account” was assessed against the actual host from which a user connects. This older method accounting may be selected by starting the server with the --old-style-user-limits option. In this case, if usera connects simultaneously from host1.example.com and host2.example.com, the server applies the account resource limits separately to each connection. If usera connects again from host1.example.com, the server applies the limits for that connection together with the existing connection from that host.

To set resource limits for an account, use the GRANT statement (see Section 12.7.1.3, “GRANT Синтаксис”). Provide a WITH clause that names each resource to be limited. The default value for each limit is zero (no limit). For example, to create a new account that can access the customer database, but only in a limited fashion, issue these statements:

mysql> CREATE USER 'francis'@'localhost' IDENTIFIED BY 'frank';
mysql> GRANT ALL ON customer.* TO 'francis'@'localhost'
    ->     WITH MAX_QUERIES_PER_HOUR 20
    ->          MAX_UPDATES_PER_HOUR 10
    ->          MAX_CONNECTIONS_PER_HOUR 5
    ->          MAX_USER_CONNECTIONS 2;

The limit types need not all be named in the WITH clause, but those named can be present in any order. The value for each per-hour limit should be an integer representing a count per hour. For MAX_USER_CONNECTIONS, the limit is an integer representing the maximum number of simultaneous connections by the account. If this limit is set to zero, the global max_user_connections system variable value determines the number of simultaneous connections. If max_user_connections is also zero, there is no limit for the account.

To modify existing limits for an account, use a GRANT USAGE statement at the global level (ON *.*). The following statement changes the query limit for francis to 100:

mysql> GRANT USAGE ON *.* TO 'francis'@'localhost'
    ->     WITH MAX_QUERIES_PER_HOUR 100;

The statement modifies only the limit value specified and leaves the account otherwise unchanged.

To remove a limit, set its value to zero. For example, to remove the limit on how many times per hour francis can connect, use this statement:

mysql> GRANT USAGE ON *.* TO 'francis'@'localhost'
    ->     WITH MAX_CONNECTIONS_PER_HOUR 0;

As mentioned previously, the simultaneous-connection limit for an account is determined from the MAX_USER_CONNECTIONS limit and the max_user_connections system variable. Suppose that the global max_user_connections value is 10 and three accounts have resource limits specified with GRANT:

GRANT ... TO 'user1'@'localhost' WITH MAX_USER_CONNECTIONS 0;
GRANT ... TO 'user2'@'localhost' WITH MAX_USER_CONNECTIONS 5;
GRANT ... TO 'user3'@'localhost' WITH MAX_USER_CONNECTIONS 20;

user1 has a connection limit of 10 (the global max_user_connections value) because it has a zero MAX_USER_CONNECTIONS limit). user2 and user3 have connection limits of 5 and 20, respectively, because they have nonzero MAX_USER_CONNECTIONS limits.

The server stores resource limits for an account in the user table row corresponding to the account. The max_questions, max_updates, and max_connections columns store the per-hour limits, and the max_user_connections column stores the MAX_USER_CONNECTIONS limit. (See Section 5.4.2, “Privilege System Grant Tables”.)

Resource-use counting takes place when any account has a nonzero limit placed on its use of any of the resources.

As the server runs, it counts the number of times each account uses resources. If an account reaches its limit on number of connections within the last hour, further connections for the account are rejected until that hour is up. Similarly, if the account reaches its limit on the number of queries or updates, further queries or updates are rejected until the hour is up. In all such cases, an appropriate error message is issued.

Resource counting is done per account, not per client. For example, if your account has a query limit of 50, you cannot increase your limit to 100 by making two simultaneous client connections to the server. Queries issued on both connections are counted together.

The current per-hour resource-use counts can be reset globally for all accounts, or individually for a given account:

  • To reset the current counts to zero for all accounts, issue a FLUSH USER_RESOURCES statement. The counts also can be reset by reloading the grant tables (for example, with a FLUSH PRIVILEGES statement or a mysqladmin reload command).

  • The counts for an individual account can be set to zero by re-granting it any of its limits. To do this, use GRANT USAGE as described earlier and specify a limit value equal to the value that the account currently has.

Counter resets do not affect the MAX_USER_CONNECTIONS limit.

All counts begin at zero when the server starts; counts are not carried over through a restart.

For the MAX_USER_CONNECTIONS limit, an edge case can occur if the account currently has open the maximum number of connections permitted to it: A disconnect followed quickly by a connect can result in an error (ER_TOO_MANY_USER_CONNECTIONS or ER_USER_LIMIT_REACHED) if the server has not fully processed the disconnect by the time the connect occurs. When the server finishes disconnect processing, another connection will once more be permitted.

5.5.5. Assigning Account Passwords

Required credentials for clients that connect to the MySQL server can include a password. This section describes how to assign passwords for MySQL accounts. In MySQL 5.5, it is also possible for clients to authenticate using plugins. For information, see Section 5.5.6, “Pluggable Authentication”.

To assign a password when you create a new account with CREATE USER, include an IDENTIFIED BY clause:

mysql> CREATE USER 'jeffrey'@'localhost'
    -> IDENTIFIED BY 'mypass';

To assign or change a password for an existing account, one way is to issue a SET PASSWORD statement:

mysql> SET PASSWORD FOR
    -> 'jeffrey'@'localhost' = PASSWORD('mypass');

MySQL stores passwords in the user table in the mysql database. Only users such as root that have update access to the mysql database can change the password for other users. If you are not connected as an anonymous user, you can change your own password by omitting the FOR clause:

mysql> SET PASSWORD = PASSWORD('mypass');

You can also use a GRANT USAGE statement at the global level (ON *.*) to assign a password to an account without affecting the account's current privileges:

mysql> GRANT USAGE ON *.* TO 'jeffrey'@'localhost'
    -> IDENTIFIED BY 'mypass';

To assign a password from the command line, use the mysqladmin command:

shell> mysqladmin -u user_name -h host_name password "newpwd"

The account for which this command sets the password is the one with a user table row that matches user_name in the User column and the client host from which you connect in the Host column.

It is preferable to assign passwords using one of the preceding methods, but it is also possible to modify the user table directly. In this case, you must also use FLUSH PRIVILEGES to cause the server to reread the grant tables. Otherwise, the change remains unnoticed by the server until you restart it.

  • To establish a password for a new account, provide a value for the Password column:

    mysql> INSERT INTO mysql.user (Host,User,Password)
        -> VALUES('localhost','jeffrey',PASSWORD('mypass'));
    mysql> FLUSH PRIVILEGES;
    
  • To change the password for an existing account, use UPDATE to set the Password column value:

    mysql> UPDATE mysql.user SET Password = PASSWORD('bagel')
        -> WHERE Host = 'localhost' AND User = 'francis';
    mysql> FLUSH PRIVILEGES;
    

During authentication when a client connects to the server, MySQL treats the password in the user table as an encrypted hash value (the value that PASSWORD() would return for the password). When assigning a password to an account, it is important to store an encrypted value, not the plaintext password. Use the following guidelines:

  • When you assign a password using CREATE USER, GRANT with an IDENTIFIED BY clause, or the mysqladmin password command, they encrypt the password for you. Specify the literal plaintext password:

    mysql> CREATE USER 'jeffrey'@'localhost'
        -> IDENTIFIED BY 'mypass';
    
  • For CREATE USER or GRANT, you can avoid sending the plaintext password if you know the hash value that PASSWORD() would return for the password. Specify the hash value preceded by the keyword PASSWORD:

    mysql> CREATE USER 'jeffrey'@'localhost'
        -> IDENTIFIED BY PASSWORD '*90E462C37378CED12064BB3388827D2BA3A9B689';
    
  • When you assign an account a nonempty password using SET PASSWORD, INSERT, or UPDATE, you must use the PASSWORD() function to encrypt the password, otherwise the password is stored as plaintext. Suppose that you assign a password like this:

    mysql> SET PASSWORD FOR
        -> 'jeffrey'@'localhost' = 'mypass';
    

    The result is that the literal value 'mypass' is stored as the password in the user table, not the encrypted value. When jeffrey attempts to connect to the server using this password, the value is encrypted and compared to the value stored in the user table. However, the stored value is the literal string 'mypass', so the comparison fails and the server rejects the connection with an Access denied error.

In MySQL 5.5, enabling the read_only system variable prevents the use of the SET PASSWORD statement by any user not having the SUPER privilege.

Замечание

PASSWORD() encryption differs from Unix password encryption. See Section 5.5.1, “User Names and Passwords”.

5.5.6. Pluggable Authentication

When a client connects to the MySQL server, the server uses the user name provided by the client and the client host to select the appropriate account row from the mysql.user table. It then uses this row to authenticate the client.

Before MySQL 5.5.7, the server authenticates the password provided by the client against the Password column of the account row.

As of MySQL 5.5.7, the server authenticates clients using plugins. Selection of the proper account row from the mysql.user table is based on the user name and client host, as before, but the server authenticates the client credentials as follows:

  • The server determines from the account row which authentication plugin applies for the client:

    • If the account row specifies no plugin name, the server uses native authentication; that is, authentication against the password stored in the Password column of the account row. This is the same authentication method provided by MySQL servers older than 5.5.7, before pluggable authentication was implemented, but now is implemented using two plugins that are built in and cannot be disabled.

    • If the account row specifies a plugin, the server invokes it to authenticate the user. If the server cannot find the plugin, an error occurs.

  • The plugin returns a status to the server indicating whether the user is permitted to connect.

Pluggable authentication enables two important capabilities:

  • External authentication: Pluggable authentication makes it possible for clients to connect to the MySQL server with credentials that are appropriate for authentication methods other than native authentication based on passwords stored in the mysql.user table. For example, plugins can be created to use external authentication methods such as PAM, Windows login IDs, LDAP, or Kerberos.

  • Proxy users: If a user is permitted to connect, an authentication plugin can return to the server a user name different from the name of the connecting user, to indicate that the connecting user is a proxy for another user. While the connection lasts, the proxy user is treated, for purposes of access control, as having the privileges of a different user. In effect, one user impersonates another. For more information, see Section 5.5.7, “Proxy Users”.

Several authentication plugins are available in MySQL. The following sections provide details about specific plugins.

Замечание

For information about current restrictions on the use of pluggable authentication, including which connectors support which plugins, see Section E.9, “Restrictions on Pluggable Authentication”.

Third-party connector developers should read that section to determine the extent to which a connector can take advantage of pluggable authentication capabilities and what steps to take to become more compliant.

If you are interested in writing your own authentication plugins, see Section 22.2.4.9, “Writing Authentication Plugins”.

In general, pluggable authentication uses corresponding plugins on the server and client sides, so you use a given authentication method like this:

  • On the server host, install the appropriate library containing the server plugin, if necessary, so that the server can use it to authenticate client connections. Similarly, on each client host, install the appropriate library containing the client plugin for use by client programs.

  • Create MySQL accounts that specify use of the plugin for authentication.

  • When a client connects, the server plugin tells the client program which client plugin to use for authentication.

The remainder of this section provides general instructions for installing and using authentication plugins. The instructions use an an example authentication plugin included in MySQL distributions (see Section 5.5.6.6, “The Test Authentication Plugin”). The procedure is similar for other authentication plugins; substitute the appropriate plugin and file names.

The example authentication plugin has these characteristics:

  • The server-side plugin name is test_plugin_server.

  • The client-side plugin name is auth_test_plugin.

  • Both plugins are located in the shared library object file named auth_test_plugin.so in the plugin directory (the directory named by the plugin_dir system variable). The file name suffix might differ on your system.

Install and use the example authentication plugin as follows:

  1. Make sure that the plugin library is installed on the server and client hosts.

  2. Install the server-side test plugin at server startup or at runtime:

    • To install the plugin at startup, use the --plugin-load option. For example, use these lines in a my.cnf option file:

      [mysqld]
      plugin-load=test_plugin_server=auth_test_plugin.so

      With this plugin-loading method, the option must be given each time you start the server. The plugin is not installed if you omit the option.

    • To install the plugin at runtime, use the INSTALL PLUGIN statement:

      mysql> INSTALL PLUGIN test_plugin_server SONAME 'auth_test_plugin.so';
      

      This installs the plugin permanently and need be done only once.

  3. Verify that the plugin is installed. For example, use SHOW PLUGINS:

    mysql> SHOW PLUGINS\G
    ...
    *************************** 21. row ***************************
       Name: test_plugin_server
     Status: ACTIVE
       Type: AUTHENTICATION
    Library: auth_test_plugin.so
    License: GPL
    

    For other ways to check the plugin, see Section 5.1.7.2, “Obtaining Server Plugin Information”.

  4. To specify that a MySQL user must be authenticated using the plugin, name it in the IDENTIFIED WITH clause of the CREATE USER statement that creates the user:

    CREATE USER 'testuser'@'localhost' IDENTIFIED WITH test_plugin_server;
  5. Connect to the server using a client program. The test plugin authenticates the same way as native MySQL authentication, so provide the usual --user and --password options that you normally use to connect to the server. For example:

    shell> mysql --user=your_name --password=your_pass
    

    For connections by testuser, the server sees that the account must be authenticated using the server-side plugin named test_plugin_server and communicates to the client program which client-side plugin it must use—in this case, auth_test_plugin.

    In the case that the account uses the authentication method that is the default for both the server and the client program, the server need not communicate to the client which plugin to use, and a round trip in client/server negotiation can be avoided. Currently this is true for accounts that use native MySQL authentication (mysql_native_password).

    The --default-auth=plugin_name option can be specified on the mysql command line to make explicit which client-side plugin the program can expect to use, although the server will override this if the user account requires a different plugin.

    If mysql does not find the plugin, specify a --plugin-dir=dir_name option to indicate where the plugin is located.

Замечание

If you start the server with the --skip-grant-tables option, authentication plugins are not used even if loaded because the server performs no client authentication and permits any client to connect. Because this is insecure, you might want to use --skip-grant-tables in conjunction with --skip-networking to prevent remote clients from connecting.

5.5.6.1. The Native Authentication Plugins

MySQL includes two plugins that implement the same kind of native authentication that older servers provide; that is, authentication against passwords stored in the Password column of the mysql.user table:

  • The mysql_native_password authentication plugin implements the same default authentication against the mysql.user table as used prior to the implementation of pluggable authentication.

  • The mysql_old_password plugin Implements authentication as used before MySQL 4.1.1 that is based on shorter password hash values. For information about this authentication method, see Section 5.3.2.3, “Password Hashing in MySQL”.

The native authentication plugins are backward compatible. Clients older than MySQL 5.5.7 do not support authentication plugins but use native authentication, so they can connect to servers from 5.5.7 and up.

The following tables show the plugin names. Both are considered to implement native authentication even though only one has “native” in the name.

Table 5.12. MySQL Native Password Authentication Plugin

Server-side plugin namemysql_native_password
Client-side plugin namemysql_native_password
Library object file nameNone (built in)

Table 5.13. MySQL Native Old-Password Authentication Plugin

Server-side plugin namemysql_old_password
Client-side plugin namemysql_old_password
Library object file nameNone (built in)

Each plugin exists in both client and server form. MySQL client programs use mysql_native_password by default. The --default-auth option can be used to specify either plugin explicitly:

shell> mysql --default-auth=mysql_native_password ...
shell> mysql --default-auth=mysql_old_password ...

The server-side plugins are built into the server and cannot be disabled by unloading them. The client-side plugins are built into the libmysql client library as of MySQL 5.5.7 and available to any program linked against libmysql from that version or newer.

For general information about pluggable authentication in MySQL, see Section 5.5.6, “Pluggable Authentication”.

5.5.6.2. The PAM Authentication Plugin

PAM (Pluggable Authentication Modules) enables a system to access various kinds of authentication methods through a standard interface. As of MySQL 5.5.16, commercial distributions of MySQL include a PAM authentication plugin that enables MySQL Server to use PAM to authenticate MySQL users.

The PAM plugin uses the information passed to it by the MySQL server (such as user name, host name, password, and authentication string), plus whatever is available for PAM lookup (such as Unix passwords or an LDAP directory). The plugin checks the user credentials against PAM and returns 'Authentication succeeded, Username is user_name' or 'Authentication failed'.

The PAM authentication plugin provides these capabilities:

  • External authentication: The plugin enables MySQL Server to accept connections from users defined outside the MySQL grant tables.

  • Proxy user support: The plugin can return to MySQL a user name different from the login user, based on the groups the external user is in and the authentication string provided. This means that the plugin can return the MySQL user that defines the privileges the external PAM-authenticated user should have. For example, a PAM user named joe can connect and have the privileges of the MySQL user named developer.

The following table shows the plugin and library file names. The file name suffix might be different on your system. The file location must be the directory named by the plugin_dir system variable. For installation information, see Section 5.5.6.2.1, “Installing the PAM Authentication Plugin”.

Table 5.14. MySQL PAM Authentication Plugin

Server-side plugin nameauthentication_pam
Client-side plugin namemysql_clear_password
Library object file nameauthentication_pam.so

The library file includes only the server-side plugin. As of MySQL 5.5.10, the client-side plugin is built into the libmysql client library. See Section 5.5.6.4, “The Clear-Text Client-Side Authentication Plugin”.

The server-side PAM authentication plugin is included only in commercial distributions. It is not included in MySQL community distributions. The client-side clear-text plugin that communicates with the server-side plugin is built into the MySQL client library and is included in all distributions, including community distributions. This permits clients from any 5.5.10 or newer distribution to connect to a server that has the server-side plugin loaded.

The PAM authentication plugin has been tested on Linux and Mac OS X. It requires MySQL Server 5.5.16 or newer.

For general information about pluggable authentication in MySQL, see Section 5.5.6, “Pluggable Authentication”. For proxy user information, see Section 5.5.7, “Proxy Users”.

5.5.6.2.1. Installing the PAM Authentication Plugin

The PAM authentication plugin must be installed in the MySQL plugin directory (the directory named by the plugin_dir system variable). To enable the plugin, start the server with the --plugin-load option. For example, put the following lines in your my.cnf file. If object files have a suffix different from .so on your system, substitute the correct suffix.

[mysqld]
plugin-load=authentication_pam.so

Use the plugin name authentication_pam in the IDENTIFIED WITH clause of CREATE USER or GRANT statements for MySQL accounts that should be authenticated with this plugin.

You can also use a --plugin-dir=path_name option if it is necessary to tell the server the location of the plugin directory.

To verify plugin installation, examine the INFORMATION_SCHEMA.PLUGINS table or use the SHOW PLUGINS statement. See Section 5.1.7.2, “Obtaining Server Plugin Information”.

5.5.6.2.2. Using the PAM Authentication Plugin

This section describes how to use the PAM authentication plugin to connect from MySQL client programs to the server. It is assumed that the server-side plugin is enabled and that client programs are recent enough to include the client-side plugin.

Замечание

The client-side plugin with which the PAM plugin communicates simply sends the password to the server in clear text so it can be passed to PAM. This may be a security problem in some configurations, but is necessary to use the server-side PAM library. To avoid problems if there is any possibility that the password would be intercepted, clients should connect to MySQL Server using SSL. See Section 5.5.6.4, “The Clear-Text Client-Side Authentication Plugin”.

To refer to the PAM authentication plugin in the IDENTIFIED WITH clause of a CREATE USER or GRANT statement, use the name authentication_pam. For example:

CREATE USER user
  IDENTIFIED WITH authentication_pam
  AS 'authentication_string';

The authentication string specifies the following types of information:

  • PAM supports the notion of “service name,” which is a name that the system administrator can use to configure the authentication method for a particular application. There can be several such “applications” associated with a single database server instance, so the choice of service name is left to the SQL application developer. When you define an account that should authenticate using PAM, specify the service name in the authentication string.

  • PAM provides a way for a PAM module to return to the server a MySQL user name other than the login name supplied at login time. Use the authentication string to control the mapping between login name and MySQL user name. If you want to take advantage of proxy user capabilities, the authentication string must include this kind of mapping.

For example, if the service name is mysql and users in the root and users PAM groups should be mapped to the developer and data_entry users, respectively, use a statement like this:

CREATE USER user
  IDENTIFIED WITH authentication_pam
  AS 'mysql, root=developer, users=data_entry';

Authentication string syntax for the PAM authentication plugin follows these rules:

  • The string consists of a PAM service name, optionally followed by a group mapping list consisting of one or more keyword/value pairs each specifying a group name and a SQL user name:

    pam_service_name[,group_name=sql_user_name]...
    
  • Each group_name=sql_user_name pair must be preceded by a comma.

  • Leading and trailing spaces not inside double quotation marks are ignored.

  • Unquoted pam_service_name, group_name, and sql_user_name values can contain anything except equal sign, comma, or space.

  • If a pam_service_name, group_name, or sql_user_name value is quoted with double quotation marks, everything between the quotation marks is part of the value. This is necessary, for example, if the value contains space characters. All characters are legal except double quotation mark and backslash ('\'). To include either character, escape it with a backslash.

The plugin parses the authentication string on each login check. To minimize overhead, keep the string as short as possible.

If the plugin successfully authenticates a login name, it looks for a group mapping list in the authentication string and uses it to return a different user name to the MySQL server based on the groups the external user is a member of:

  • If the authentication string contains no group mapping list, the plugin returns the login name.

  • If the authentication string does contain a group mapping list, the plugin examines each group_name=sql_user_name pair in the list from left to right and tries to find a match for the group_name value in a non-MySQL directory of the groups assigned to the authenticated user and returns sql_user_name for the first match it finds. If the plugin finds no match for any group, it returns the login name. If the plugin is not capable of looking up a group in a directory, it ignores the group mapping list and returns the login name.

The following sections describe how to set up several authentication scenarios that use the PAM authentication plugin:

  • No proxy users. This uses PAM only to check login names and passwords. Every external user permitted to connect to MySQL Server should have a matching MySQL account that is defined to use external PAM authentication. Authentication can be performed by various PAM-supported methods. The discussion shows how to use traditional Unix passwords and LDAP.

    PAM authentication, when not done through proxy users or groups, requires the MySQL account to have the same user name as the Unix account. Because MySQL user names are limited to 16 characters (see Section 5.4.2, “Privilege System Grant Tables”), this limits PAM nonproxy authentication to Unix accounts with names of at most 16 characters.

  • Proxy login only and group mapping. For this scenario, create a few MySQL accounts that define different sets of privileges. (Ideally, nobody should log in through these directly.) Then define a default user authenticating through PAM that uses some mapping scheme (usually by the external groups the users are in) to map all the external logins to the few MySQL accounts holding the privilege sets. Any user that logs in is mapped to one of the MySQL accounts and uses its privileges. The discussion shows how to set this up using Unix passwords, but other PAM methods such as LDAP could be used instead.

Variations on these scenarios are possible. For example, you can permit some users to log in directly but require others to connect through proxy users.

The examples make the following assumptions. You might need to make some adjustments if your system is set up differently.

  • The PAM configuration directory is /etc/pam.d.

  • The PAM service name is mysql, which means that you must set up a PAM file named mysql in the PAM configuration directory (creating the file if it does not exist). If you use a different service name, the file name will be different and you must use a different name in the AS clause of CREATE USER and GRANT statements.

  • The examples use a login name of antonio and password of verysecret. Change these to correspond to the users you want to authenticate.

The PAM authentication plugin checks at initialization time whether the AUTHENTICATION_PAM_LOG environment value is set. If so, the plugin enables logging of diagnostic messages to the standard output. These messages may be helpful for debugging PAM-related problems that occur when the plugin performs authentication. For more information, see Section 5.5.6.2.3, “PAM Authentication Plugin Debugging”.

5.5.6.2.2.1. Unix Password Authentication without Proxy Users

This authentication scenario uses PAM only to check Unix user login names and passwords. Every external user permitted to connect to MySQL Server should have a matching MySQL account that is defined to use external PAM authentication.

  1. Verify that Unix authentication in PAM permits you to log in as antonio with password verysecret.

  2. Set up PAM to authenticate the mysql service. Put the following in /etc/pam.d/mysql:

    #%PAM-1.0
    auth            include         password-auth
    account         include         password-auth
  3. Create a MySQL account with the same user name as the Unix login name and define it to authenticate using the PAM plugin:

    CREATE USER 'antonio'@'localhost'
      IDENTIFIED WITH authentication_pam AS 'mysql';
    GRANT ALL PRIVILEGES ON mydb.* TO 'antonio'@'localhost';
  4. Try to connect to the MySQL server using the mysql command-line client. For example:

    mysql --user=antonio --password=verysecret mydb

    The server should permit the connection and the following query should return output as shown:

    mysql> SELECT USER(), CURRENT_USER(), @@proxy_user;
    +-------------------+-------------------+--------------+
    | USER()            | CURRENT_USER()    | @@proxy_user |
    +-------------------+-------------------+--------------+
    | antonio@localhost | antonio@localhost | NULL         |
    +-------------------+-------------------+--------------+
    

    This shows that antonio uses the privileges granted to the antonio MySQL account, and that no proxying has occurred.

5.5.6.2.2.2. LDAP Authentication without Proxy Users

This authentication scenario uses PAM only to check LDAP user login names and passwords. Every external user permitted to connect to MySQL Server should have a matching MySQL account that is defined to use external PAM authentication.

  1. Verify that LDAP authentication in PAM permits you to log in as antonio with password verysecret.

  2. Set up PAM to authenticate the mysql service through LDAP. Put the following in /etc/pam.d/mysql:

    #%PAM-1.0
    auth        required    pam_ldap.so
    account     required    pam_ldap.so

    If PAM object files have a suffix different from .so on your system, substitute the correct suffix.

  3. MySQL account creation and connecting to the server is the same as previously described in Section 5.5.6.2.2.1, “Unix Password Authentication without Proxy Users”.

5.5.6.2.2.3. Unix Password Authentication with Proxy Users and Group Mapping

This authentication scheme uses proxying and group mapping to map users who connect to the MySQL server through PAM onto a few MySQL accounts that define different sets of privileges. Users do not connect directly through the accounts that define the privileges. Instead, they connect through a default proxy user authenticating through PAM that uses a mapping scheme to map all the external logins to the few MySQL accounts holding the privileges. Any user who connects is mapped to one of the MySQL accounts and uses its privileges.

The procedure shown here uses Unix password authentication. To use LDAP instead, see the early steps of Section 5.5.6.2.2.2, “LDAP Authentication without Proxy Users”.

  1. Verify that Unix authentication in PAM permits you to log in as antonio with password verysecret and that antonio is a member of the root or users group.

  2. Set up PAM to authenticate the mysql service. Put the following in /etc/pam.d/mysql:

    #%PAM-1.0
    auth            include         password-auth
    account         include         password-auth
  3. Create the default proxy user that maps the external PAM users to the proxied accounts. It maps external users from the root PAM group to the developer MySQL account and the external users from the users PAM group to the data_entry MySQL account:

    CREATE USER ''@''
      IDENTIFIED WITH authentication_pam
      AS 'mysql, root=developer, users=data_entry';

    The mapping list following the service name is required when you set up proxy users. Otherwise, the plugin cannot tell how to map the name of PAM groups to the proper proxied user name.

  4. Create the proxied accounts that will be used to access the databases:

    CREATE USER 'developer'@'localhost' IDENTIFIED BY 'very secret password';
    GRANT ALL PRIVILEGES ON mydevdb.* TO 'developer'@'localhost';
    CREATE USER 'data_entry'@'localhost' IDENTIFIED BY 'very secret password';
    GRANT ALL PRIVILEGES ON mydb.* TO 'data_entry'@'localhost'; 
    

    If you do not let anyone know the passwords for these accounts, other users cannot use them to connect directly to the MySQL server. Instead, it is expected that users will authenticate using PAM and that they will use the developer or data_entry account by proxy based on their PAM group.

  5. Grant the PROXY privilege to the proxy account for the proxied accounts:

    GRANT PROXY ON 'developer'@'localhost' TO ''@'';
    GRANT PROXY ON 'data_entry'@'localhost' TO ''@'';
  6. Try to connect to the MySQL server using the mysql command-line client. For example:

    mysql --user=antonio --password=verysecret mydb

    The server authenticates the connection using the ''@'' account. The privileges antonio will have depends on what PAM groups he is a member of. If antonio is a member of the root PAM group, the PAM plugin maps root to the developer MySQL user name and returns that name to the server. The server verifies that ''@'' has the PROXY privilege for developer and permits the connection. the following query should return output as shown:

    mysql> SELECT USER(), CURRENT_USER(), @@proxy_user;
    +-------------------+---------------------+--------------+
    | USER()            | CURRENT_USER()      | @@proxy_user |
    +-------------------+---------------------+--------------+
    | antonio@localhost | developer@localhost | ''@''        |
    +-------------------+---------------------+--------------+
    

    This shows that antonio uses the privileges granted to the developer MySQL account, and that proxying occurred through the default proxy user account.

    If antonio is not a member of the root PAM group but is a member of the users group, a similar process occurs, but the plugin maps user group membership to the data_entry MySQL user name and returns that name to the server. In this case, antonio uses the privileges of the data_entry MySQL account:

    mysql> SELECT USER(), CURRENT_USER(), @@proxy_user;
    +-------------------+----------------------+--------------+
    | USER()            | CURRENT_USER()       | @@proxy_user |
    +-------------------+----------------------+--------------+
    | antonio@localhost | data_entry@localhost | ''@''        |
    +-------------------+----------------------+--------------+
    
5.5.6.2.3. PAM Authentication Plugin Debugging

The PAM authentication plugin checks at initialization time whether the AUTHENTICATION_PAM_LOG environment value is set (the value does not matter). If so, the plugin enables logging of diagnostic messages to the standard output. These messages may be helpful for debugging PAM-related problems that occur when the plugin performs authentication.

Some messages include reference to PAM plugin source files and line numbers, which enables plugin actions to be tied more closely to the location in the code where they occur.

The following transcript demonstrates the kind of information produced by enabling logging. It resulted from a successful proxy authentication attempt.

entering auth_pam_server
entering auth_pam_next_token
auth_pam_next_token:reading at [cups,admin=writer,everyone=reader], sep=[,]
auth_pam_next_token:state=PRESPACE, ptr=[cups,admin=writer,everyone=reader],
out=[]
auth_pam_next_token:state=IDENT, ptr=[cups,admin=writer,everyone=reader],
out=[]
auth_pam_next_token:state=AFTERSPACE, ptr=[,admin=writer,everyone=reader],
out=[cups]
auth_pam_next_token:state=DELIMITER, ptr=[,admin=writer,everyone=reader],
out=[cups]
auth_pam_next_token:state=DONE, ptr=[,admin=writer,everyone=reader],
out=[cups]
leaving auth_pam_next_token on
/Users/gkodinov/mysql/work/x-5.5.16-release-basket/release/plugin/pam-authentication-plugin/src/parser.c:191
auth_pam_server:password 12345qq received
auth_pam_server:pam_start rc=0
auth_pam_server:pam_set_item(PAM_RUSER,gkodinov) rc=0
auth_pam_server:pam_set_item(PAM_RHOST,localhost) rc=0
entering auth_pam_server_conv
auth_pam_server_conv:PAM_PROMPT_ECHO_OFF [Password:] received
leaving auth_pam_server_conv on
/Users/gkodinov/mysql/work/x-5.5.16-release-basket/release/plugin/pam-authentication-plugin/src/authentication_pam.c:257
auth_pam_server:pam_authenticate rc=0
auth_pam_server:pam_acct_mgmt rc=0
auth_pam_server:pam_setcred(PAM_ESTABLISH_CRED) rc=0
auth_pam_server:pam_get_item rc=0
auth_pam_server:pam_setcred(PAM_DELETE_CRED) rc=0
entering auth_pam_map_groups
entering auth_pam_walk_namevalue_list
auth_pam_walk_namevalue_list:reading at: [admin=writer,everyone=reader]
entering auth_pam_next_token
auth_pam_next_token:reading at [admin=writer,everyone=reader], sep=[=]
auth_pam_next_token:state=PRESPACE, ptr=[admin=writer,everyone=reader], out=[]
auth_pam_next_token:state=IDENT, ptr=[admin=writer,everyone=reader], out=[]
auth_pam_next_token:state=AFTERSPACE, ptr=[=writer,everyone=reader],
out=[admin]
auth_pam_next_token:state=DELIMITER, ptr=[=writer,everyone=reader],
out=[admin]
auth_pam_next_token:state=DONE, ptr=[=writer,everyone=reader], out=[admin]
leaving auth_pam_next_token on
/Users/gkodinov/mysql/work/x-5.5.16-release-basket/release/plugin/pam-authentication-plugin/src/parser.c:191
auth_pam_walk_namevalue_list:name=[admin]
entering auth_pam_next_token
auth_pam_next_token:reading at [writer,everyone=reader], sep=[,]
auth_pam_next_token:state=PRESPACE, ptr=[writer,everyone=reader], out=[]
auth_pam_next_token:state=IDENT, ptr=[writer,everyone=reader], out=[]
auth_pam_next_token:state=AFTERSPACE, ptr=[,everyone=reader], out=[writer]
auth_pam_next_token:state=DELIMITER, ptr=[,everyone=reader], out=[writer]
auth_pam_next_token:state=DONE, ptr=[,everyone=reader], out=[writer]
leaving auth_pam_next_token on
/Users/gkodinov/mysql/work/x-5.5.16-release-basket/release/plugin/pam-authentication-plugin/src/parser.c:191
walk, &error_namevalue_list:value=[writer]
entering auth_pam_map_group_to_user
auth_pam_map_group_to_user:pam_user=gkodinov, name=admin, value=writer
examining member root
examining member gkodinov
substitution was made to mysql user writer
leaving auth_pam_map_group_to_user on
/Users/gkodinov/mysql/work/x-5.5.16-release-basket/release/plugin/pam-authentication-plugin/src/authentication_pam.c:118
auth_pam_walk_namevalue_list:found mapping
leaving auth_pam_walk_namevalue_list on
/Users/gkodinov/mysql/work/x-5.5.16-release-basket/release/plugin/pam-authentication-plugin/src/parser.c:270
auth_pam_walk_namevalue_list returned 0
leaving auth_pam_map_groups on
/Users/gkodinov/mysql/work/x-5.5.16-release-basket/release/plugin/pam-authentication-plugin/src/authentication_pam.c:171
auth_pam_server:authenticated_as=writer
auth_pam_server: rc=0
leaving auth_pam_server on
/Users/gkodinov/mysql/work/x-5.5.16-release-basket/release/plugin/pam-authentication-plugin/src/authentication_pam.c:429

5.5.6.3. The Windows Native Authentication Plugin

As of MySQL 5.5.16, commercial distributions of MySQL for Windows include an authentication plugin that performs external authentication on Windows, enabling MySQL Server to use native Windows services to authenticate client connections. Users who have logged in to Windows can connect from MySQL client programs to the server based on the information in their environment without specifying an additional password.

The client and server exchange data packets in the authentication handshake. As a result of this exchange, the server creates a security context object that represents the identity of the client in the Windows OS. This identity includes the name of the client account. The Windows authentication plugin uses the identity of the client to check whether it is a given account or a member of a group. By default, negotiation uses Kerberos to authenticate, then NTLM if Kerberos is unavailable.

The Windows authentication plugin provides these capabilities:

  • External authentication: The plugin enables MySQL Server to accept connections from users defined outside the MySQL grant tables.

  • Proxy user support: The plugin can return to MySQL a user name different from the client user. This means that the plugin can return the MySQL user that defines the privileges the external Windows-authenticated user should have. For example, a Windows user named joe can connect and have the privileges of the MySQL user named developer.

The following table shows the plugin and library file names. The file location must be the directory named by the plugin_dir system variable. For installation information, see Section 5.5.6.3.1, “Installing the Windows Authentication Plugin”.

Table 5.15. MySQL Windows Authentication Plugin

Server-side plugin nameauthentication_windows
Client-side plugin nameauthentication_windows_client
Library object file nameauthentication_windows.dll

The library file includes only the server-side plugin. As of MySQL 5.5.13, the client-side plugin is built into the libmysql client library.

The server-side Windows authentication plugin is included only in commercial distributions. It is not included in MySQL community distributions. The client-side plugin is included in all distributions, including community distributions. This permits clients from any 5.5.13 or newer distribution to connect to a server that has the server-side plugin loaded.

The Windows authentication plugin should work on Windows 2000 Professional and up. It requires MySQL Server 5.5.16 or newer.

For general information about pluggable authentication in MySQL, see Section 5.5.6, “Pluggable Authentication”. For proxy user information, see Section 5.5.7, “Proxy Users”.

5.5.6.3.1. Installing the Windows Authentication Plugin

The Windows authentication plugin must be installed in the MySQL plugin directory (the directory named by the plugin_dir system variable). To enable the plugin, start the server with the --plugin-load option. For example, put these lines in your my.ini file:

[mysqld]
plugin-load=authentication_windows.dll

Use the plugin name authentication_windows in the IDENTIFIED WITH clause of CREATE USER or GRANT statements for MySQL accounts that should be authenticated with this plugin.

You can also use a --plugin-dir=path_name option if it is necessary to tell the server the location of the plugin directory.

To verify plugin installation, examine the INFORMATION_SCHEMA.PLUGINS table or use the SHOW PLUGINS statement. See Section 5.1.7.2, “Obtaining Server Plugin Information”.

5.5.6.3.2. Using the Windows Authentication Plugin

The Windows authentication plugin supports the use of MySQL accounts such that users who have logged in to Windows can connect to the MySQL server without having to specify an additional password. It is assumed that the server-side plugin is enabled and that client programs are recent enough to include the client-side plugin built into libmysql (MySQL 5.5.13 or higher). Once the DBA has enabled the server-side plugin and set up accounts to use it, clients can connect using those accounts with no other setup required on their part.

To refer to the Windows authentication plugin in the IDENTIFIED WITH clause of a CREATE USER or GRANT statement, use the name authentication_windows. Suppose that the Windows users Rafal and Tasha should be permitted to connect to MySQL, as well as any users in the Administrators or Power Users group. To set this up, create a MySQL account named sql_admin that uses the Windows plugin for authentication:

CREATE USER sql_admin
  IDENTIFIED WITH authentication_windows
  AS 'Rafal, Tasha, Administrators, "Power Users"';

The plugin name is authentication_windows. The string following the AS keyword is the authentication string. It specifies that the Windows users named Rafal or Tasha are permitted to authenticate to the server as the MySQL user sql_admin, as are any Windows users in the Administrators or Power Users group. The latter group name contains a space, so it must be quoted with double quote characters.

After you create the sql_admin account, a user who has logged in to Windows can attempt to connect to the server using that account:

C:\> mysql --user=sql_admin

No password is required here. The authentication_windows plugin uses the Windows security API to check which Windows user is connecting. If that user is named Rafal or Tasha, or is in the Administrators or Power Users group, the server grants access and the client is authenticated as sql_admin and has whatever privileges are granted to the sql_admin account. Otherwise, the server denies access.

Authentication string syntax for the Windows authentication plugin follows these rules:

  • The string consists of one or more user mappings separated by commas.

  • Each user mapping associates a Windows user or group name with a MySQL user name:

    win_user_or_group_name=sql_user_name
    win_user_or_group_name
    

    For the latter syntax, with no sql_user_name value given, the implicit value is the MySQL user created by the CREATE USER statement. Thus, these statements are equivalent:

    CREATE USER sql_admin
      IDENTIFIED WITH authentication_windows
      AS 'Rafal, Tasha, Administrators, "Power Users"';
    
    CREATE USER sql_admin
      IDENTIFIED WITH authentication_windows
      AS 'Rafal=sql_admin, Tasha=sql_admin, Administrators=sql_admin,
          "Power Users"=sql_admin';
  • Each backslash ('\') in a value must be doubled because backslash is the escape character in MySQL strings.

  • Leading and trailing spaces not inside double quotation marks are ignored.

  • Unquoted win_user_or_group_name and sql_user_name values can contain anything except equal sign, comma, or space.

  • If a win_user_or_group_name and or sql_user_name value is quoted with double quotation marks, everything between the quotation marks is part of the value. This is necessary, for example, if the name contains space characters. All characters within double quotes are legal except double quotation mark and backslash. To include either character, escape it with a backslash.

  • win_user_or_group_name values use conventional syntax for Windows principals, either local or in a domain. Examples (note the doubling of backslashes):

    domain\\user
    .\\user
    domain\\group
    .\\group
    BUILTIN\\WellKnownGroup

When invoked by the server to authenticate a client, the plugin scans the authentication string left to right for a user or group match to the Windows user. If there is a match, the plugin returns the corresponding sql_user_name to the MySQL server. If there is no match, authentication fails.

A user name match takes preference over a group name match. Suppose that the Windows user named win_user is a member of win_group and the authentication string looks like this:

'win_group = sql_user1, win_user = sql_user2'

When win_user connects to the MySQL server, there is a match both to win_group and to win_user. The plugin authenticates the user as sql_user2 because the more-specific user match takes precedence over the group match, even though the group is listed first in the authentication string.

Windows authentication always works for connections from the same computer on which the server is running. For cross-computer connections, both computers must be registered with Windows Active Directory. If they are in the same Windows domain, it is unnecessary to specify a domain name. It is also possible to permit connections from a different domain, as in this example:

CREATE USER sql_accounting
  IDENTIFIED WITH authentication_windows
  AS 'SomeDomain\\Accounting';

Here SomeDomain is the name of the other domain. The backslash character is doubled because it is the MySQL escape character within strings.

MySQL supports the concept of proxy users whereby a client can connect and authenticate to the MySQL server using one account but while connected has the privileges of another account (see Section 5.5.7, “Proxy Users”). Suppose that you want Windows users to connect using a single user name but be mapped based on their Windows user and group names onto specific MySQL accounts as follows:

  • The local_user and MyDomain\domain_user local and domain Windows users should map to the local_wlad MySQL account.

  • Users in the MyDomain\Developers domain group should map to the local_dev MySQL account.

  • Local machine administrators should map to the local_admin MySQL account.

To set this up, create a proxy account for Windows users to connect to, and configure this account so that users and groups map to the appropriate MySQL accounts (local_wlad, local_dev, local_admin). In addtion, grant the MySQL accounts the privileges appropriate to the operations they need to perform. The following instructions use win_proxy as the proxy account, and local_wlad, local_dev, and local_admin as the proxied accounts.

  1. Create the proxy MySQL account:

    CREATE USER win_proxy
      IDENTIFIED WITH  authentication_windows
      AS 'local_user = local_wlad,
          MyDomain\\domain_user = local_wlad,
          MyDomain\\Developers = local_dev,
          BUILTIN\\Administrators = local_admin';
  2. For proxying to work, the proxied accounts must exist, so create them:

    CREATE USER local_wlad IDENTIFIED BY 'wlad_pass';
    CREATE USER local_dev IDENTIFIED BY 'dev_pass';
    CREATE USER local_admin IDENTIFIED BY  'admin_pass';

    If you do not let anyone know the passwords for these accounts, other users cannot use them to connect directly to the MySQL server.

    You should also issue GRANT statements (not shown) that grant each proxied account the privileges it needs.

  3. The proxy account must have the PROXY privilege for each of the proxied accounts:

    GRANT PROXY ON local_wlad TO win_proxy;
    GRANT PROXY ON local_dev TO win_proxy;
    GRANT PROXY ON local_admin TO win_proxy;

Now the Windows users local_user and MyDomain\domain_user can connect to the MySQL server as win_proxy and when authenticated have the privileges of the account given in the authentication string—in this case, local_wlad. A user in the MyDomain\Developers group who connects as win_proxy has the privileges of the local_dev account. A user in the BUILTIN\Administrators group has the privileges of the local_admin account.

To configure authentication so that all Windows users who do not have their own MySQL account go through a proxy account, substitute the default proxy user (''@'') for win_proxy in the preceding instructions. For information about the default proxy user, see Section 5.5.7, “Proxy Users”.

Additional control over the Windows authentication plugin is provided by the authentication_windows_use_principal_name and authentication_windows_log_level system variables. See Section 5.1.3, “Server System Variables”.

5.5.6.4. The Clear-Text Client-Side Authentication Plugin

As of MySQL 5.5.10, a client-side authentication plugin is available that sends the password to the server without hashing or encryption. This plugin is built into the MySQL client library.

The following table shows the plugin name.

Table 5.16. MySQL Clear Text Authentication Plugin

Server-side plugin nameNone, see discussion
Client-side plugin namemysql_clear_password
Library object file nameNone (built in)

With native MySQL authentication, the client performs one-way hashing on the password before sending it to the server. This enables the client to avoid sending the password in clear text. See Section 5.3.2.3, “Password Hashing in MySQL”. However, because the hash algorithm is one way, the original password cannot be recovered on the server side.

One-way hashing cannot be done for authentication schemes that require the server to receive the password as entered on the client side. In such cases, the mysql_clear_password client-side plugin can be used to send the password to the server in clear text. There is no corresponding server-side plugin. Rather, the client-side plugin can be used by any server-side plugin that needs a clear text password.

For general information about pluggable authentication in MySQL, see Section 5.5.6, “Pluggable Authentication”.

Замечание

Sending passwords in clear text may be a security problem in some configurations. To avoid problems if there is any possibility that the password would be intercepted, clients should connect to MySQL Server using a method that protects the password. Possibilities include SSL (see Section 5.5.8, “Using SSL for Secure Connections”), IPsec, or a private network.

5.5.6.5. The Socket Peer-Credential Authentication Plugin

As of MySQL 5.5.10, a server-side authentication plugin is available that authenticates clients that connect from the local host through the Unix socket file. This plugin works only on Linux systems.

The source code for this plugin can be examined as a relatively simple example demonstrating how to write a loadable authentication plugin.

The following table shows the plugin and library file names. The file name suffix might differ on your system. The file location is the directory named by the plugin_dir system variable. For installation information, see Section 5.5.6, “Pluggable Authentication”.

Table 5.17. MySQL Socket Peer-Credential Authentication Plugin

Server-side plugin nameauth_socket
Client-side plugin nameNone, see discussion
Library object file nameauth_socket.so

The auth_socket authentication plugin authenticates clients that connect from the local host through the Unix socket file. The plugin uses the SO_PEERCRED socket option to obtain information about the user running the client program. The plugin checks whether the user name matches the MySQL user name specified by the client program to the server, and permits the connection only if the names match. The plugin can be built only on systems that support the SO_PEERCRED option, such as Linux.

Suppose that a MySQL account is created for a user named valerie who is to be authenticated by the auth_socket plugin for connections from the local host through the socket file:

CREATE USER 'valerie'@'localhost' IDENTIFIED WITH auth_socket;

If a user on the local host with a login name of stefanie invokes mysql with the option --user=valerie to connect through the socket file, the server uses auth_socket to authenticate the client. The plugin determines that the --user option value (valerie) differs from the client user's name (stephanie) and refuses the connection. If a user named valerie tries the same thing, the plugin finds that the user name and the MySQL user name are both valerie and permits the connection. However, the plugin refuses the connection even for valerie if the connection is made using a different protocol, such as TCP/IP.

For general information about pluggable authentication in MySQL, see Section 5.5.6, “Pluggable Authentication”.

5.5.6.6. The Test Authentication Plugin

MySQL includes a test plugin that authenticates using MySQL native authentication, but is a loadable plugin (not built in) and must be installed prior to use. It can authenticate against either normal or older (shorter) password hash values.

This plugin is intended for testing and development purposes, and not for use in production environments. The test plugin source code is separate from the server source, unlike the built-in native plugin, so it can be examined as a relatively simple example demonstrating how to write a loadable authentication plugin.

The following table shows the plugin and library file names. The file name suffix might differ on your system. The file location is the directory named by the plugin_dir system variable. For installation information, see Section 5.5.6, “Pluggable Authentication”.

Table 5.18. MySQL Test Authentication Plugin

Server-side plugin nametest_plugin_server
Client-side plugin nameauth_test_plugin
Library object file nameauth_test_plugin.so

Because the test plugin authenticates the same way as native MySQL authentication, provide the usual --user and --password options that you normally use for accounts that use native authentication when you connect to the server. For example:

shell> mysql --user=your_name --password=your_pass

For general information about pluggable authentication in MySQL, see Section 5.5.6, “Pluggable Authentication”.

5.5.7. Proxy Users

When authentication to the MySQL server occurs through an authentication plugin, the plugin may request that the connecting (external) user be treated as a different user for privilege-checking purposes. This enables the external user to be a proxy for the second user; that is, to have the privileges of the second user. In other words, the external user is a “proxy user” (a user who can impersonate or become known as another user) and the second user is a “proxied user” (a user whose identity can be taken on by a proxy user).

This section describes how the proxy user capability works. For general information about authentication plugins, see Section 5.5.6, “Pluggable Authentication”. If you are interested in writing your own authentication plugins that support proxy users, see Section 22.2.4.9.4, “Implementing Proxy User Support in Authentication Plugins”.

For proxying to occur, these conditions must be satisfied:

  • When a connecting client should be treated as a proxy user, the plugin must return a different name, to indicate the proxied user name.

  • Proxy user accounts must be set up to be authenticated by the plugin. Use the CREATE USER or GRANT statement to associate accounts with plugins.

  • Proxy user accounts must have the PROXY privilege for the proxied accounts. Use the GRANT statement for this.

Consider the following definitions:

CREATE USER 'empl_external'@'localhost'
  IDENTIFIED WITH auth_plugin AS 'auth_string';
CREATE USER 'employee'@'localhost'
  IDENTIFIED BY 'employee_pass';
GRANT PROXY
  ON 'employee'@'localhost'
  TO 'empl_external'@'localhost';

When a client connects as empl_external from the local host, MySQL uses auth_plugin to perform authentication. If auth_plugin returns the employee user name to the server (based on the content of 'auth_string' and perhaps by consulting some external authentication system), that serves as a request to the server to treat this client, for purposes of privilege checking, as the employee local user.

In this case, empl_external is the proxy user and employee is the proxied user.

The server verifies that proxy authentication for employee is possible for the empl_external user by checking whether empl_external has the PROXY privilege for employee. (If this privilege had not been granted, an error would occur.)

When proxying occurs, the USER() and CURRENT_USER() functions can be used to see the difference between the connecting user and the account whose privileges apply during the current session. For the example just described, those functions return these values:

mysql> SELECT USER(), CURRENT_USER();
+-------------------------+--------------------+
| USER()                  | CURRENT_USER()     |
+-------------------------+--------------------+
| empl_external@localhost | employee@localhost |
+-------------------------+--------------------+

The IDENTIFIED WITH clause that names the authentication plugin may be followed by an AS clause specifying a string that the server passes to the plugin when the user connects. It is up to each plugin whether the AS clause is required. If it is required, the format of the authentication string depends on how the plugin intends to use it. Consult the documentation for a given plugin for information about the authentication string values it accepts.

Granting the Proxy Privilege

A special PROXY privilege is needed to enable an external user to connect as and have the privileges of another user. To grant this privilege, use the GRANT statement. For example:

GRANT PROXY ON 'proxied_user' TO 'proxy_user';

proxy_user must represent a valid externally authenticated MySQL user at connection time or connection attempts fail. proxied_user must represent a valid locally authenticated user at connection time or connection attempts fail.

The corresponding REVOKE syntax is:

REVOKE PROXY ON 'proxied_user' FROM 'proxy_user';

MySQL GRANT and REVOKE syntax extensions work as usual. For example:

GRANT PROXY ON 'a' TO 'b', 'c', 'd';
GRANT PROXY ON ''@'' TO 'd';
GRANT PROXY ON 'a' TO 'd' IDENTIFIED BY ...;
GRANT PROXY ON 'a' TO 'd' WITH GRANT OPTION;
REVOKE PROXY ON 'a' FROM 'b', 'c', 'd';

In the preceding example, ''@'' is the default proxy user and means “any user.” The default proxy user is discussed later in this section.

The PROXY privilege can be granted in these cases:

  • By proxied_user for itself: The value of USER() must exactly match CURRENT_USER() and proxied_user, for both the user name and host name parts of the account name.

  • By a user that has GRANT PROXY ... WITH GRANT OPTION for proxied_user.

The root account created by default during MySQL installation has the PROXY ... WITH GRANT OPTION privilege for ''@'', that is, for all users. This enables root to set up proxy users, as well as to delegate to other accounts the authority to set up proxy users. For example, root can do this:

CREATE USER 'admin'@'localhost' IDENTIFIED BY 'test';
GRANT PROXY ON ''@'' TO 'admin'@'localhost' WITH GRANT OPTION;

Now the admin user can manage all the specific GRANT PROXY mappings. For example, admin can do this:

GRANT PROXY ON sally TO joe;

Default Proxy Users

To specify that some or all users should connect using a given external plugin, create a “blank” MySQL user, set it up to use that plugin for authentication, and let the plugin return the real authenticated user name (if different from the blank user). For example, suppose that there exists a hypothetical plugin named ldap_auth that implements LDAP authentication:

CREATE USER ''@'' IDENTIFIED WITH ldap_auth AS 'O=Oracle, OU=MySQL';
CREATE USER 'developer'@'localhost' IDENTIFIED BY 'developer_pass';
CREATE USER 'manager'@'localhost' IDENTIFIED BY 'manager_pass';
GRANT PROXY ON 'manager'@'localhost' TO ''@'';
GRANT PROXY ON 'developer'@'localhost' TO ''@'';

Now assume that a client tries to connect as follows:

mysql --user=myuser --password='myuser_pass' ...

The server will not find myuser defined as a MySQL user. But because there is a blank user account (''@''), that matches the client user name and host name, the server authenticates the client against that account: The server invokes ldap_auth, passing it myuser and myuser_pass as the user name and password.

If the ldap_auth plugin finds in the LDAP directory that myuser_pass is not the correct password for myuser, authentication fails and the server rejects the connection.

If the password is correct and ldap_auth finds that myuser is a developer, it returns the user name developer to the MySQL server, rather than myuser. The server verifies that ''@'' can authenticate as developer (because it has the PROXY privilege to do so) and accepts the connection. The session proceeds with myuser having the privileges of developer. (These privileges should be set up by the DBA using GRANT statements, not shown.) The USER() and CURRENT_USER() functions return these values:

mysql> SELECT USER(), CURRENT_USER();
+------------------+---------------------+
| USER()           | CURRENT_USER()      |
+------------------+---------------------+
| myuser@localhost | developer@localhost |
+------------------+---------------------+

If the plugin instead finds in the LDAP directory that myuser is a manager, it returns manager as the user name and the session proceeds with myuser having the privileges of manager.

mysql> SELECT USER(), CURRENT_USER();
+------------------+-------------------+
| USER()           | CURRENT_USER()    |
+------------------+-------------------+
| myuser@localhost | manager@localhost |
+------------------+-------------------+

For simplicity, external authentication cannot be multilevel: Neither the credentials for developer nor those for manager are taken into account in the preceding example. However, they are still used if a client tries to authenticate directly against the developer or manager account, which is why those accounts should be assigned passwords.

The default proxy account uses '' in the host part, which matches any host. If you set up a default proxy user, take care to also check for accounts with '%' in the host part, because that also matches any host, but has precedence over '' by the rules that the server uses to sort account rows interally (see Section 5.4.4, “Access Control, Stage 1: Connection Verification”).

Suppose that a MySQL installation includes these two accounts:

CREATE USER ''@'' IDENTIFIED WITH some_plugin;
CREATE USER ''@'%' IDENTIFIED BY 'some_password';

The intent of the first account is to serve as the default proxy user, to be used to authenticate connections for users who do not otherwise match a more-specific account. The second account might have been created, for example, to enable users without their own account as the anonymous user.

However, in this configuration, the first account will never be used because the matching rules sort ''@'%' ahead of ''@''. For accounts that do not match any more-specific account, the server will attempt to authenticate them against ''@'%' rather than ''@''.

If you intend to create a default proxy user, check for other existing “match any user” accounts that will take precedence over the default proxy user and thus prevent that user from working as intended. It may be necessary to remove any such accounts.

Proxy User System Variables

Two system variables help trace the proxy login process:

  • proxy_user: This value is NULL if proxying is not used. Otherwise, it indicates the proxy user account. For example, if a client authenticates through the default proxy account, this variable will be set as follows:

    mysql> SELECT @@proxy_user;
    +--------------+
    | @@proxy_user |
    +--------------+
    | ''@''        |
    +--------------+
    
  • external_user: Sometimes the authentication plugin may use an external user to authenticate to the MySQL server. For example, when using Windows native authentication, a plugin that authenticates using the windows API does not need the login ID passed to it. However, it still uses an Windows user ID to authenticate. The plugin may return this external user ID (or the first 512 UTF-8 bytes of it) to the server using the external_user read-only session variable. If the plugin does not set this variable, its value is NULL.

5.5.8. Using SSL for Secure Connections

MySQL supports secure (encrypted) connections between MySQL clients and the server using the Secure Sockets Layer (SSL) protocol. This section discusses how to use SSL connections. For information on how to require users to use SSL connections, see the discussion of the REQUIRE clause of the GRANT statement in Section 12.7.1.3, “GRANT Синтаксис”.

The standard configuration of MySQL is intended to be as fast as possible, so encrypted connections are not used by default. For applications that require the security provided by encrypted connections, the extra computation to encrypt the data is worthwhile.

MySQL enables encryption on a per-connection basis. You can choose a normal unencrypted connection or a secure encrypted SSL connection according the requirements of individual applications.

Secure connections are based on the OpenSSL API and are available through the MySQL C API. Replication uses the C API, so secure connections can be used between master and slave servers.

Another way to connect securely is from within an SSH connection to the MySQL server host. For an example, see Section 5.5.9, “Connecting to MySQL Remotely from Windows with SSH”.

5.5.8.1. Basic SSL Concepts

To understand how MySQL uses SSL, it is necessary to explain some basic SSL and X509 concepts. People who are familiar with these can skip this part of the discussion.

By default, MySQL uses unencrypted connections between the client and the server. This means that someone with access to the network could watch all your traffic and look at the data being sent or received. They could even change the data while it is in transit between client and server. To improve security a little, you can compress client/server traffic by using the --compress option when invoking client programs. However, this does not foil a determined attacker.

When you need to move information over a network in a secure fashion, an unencrypted connection is unacceptable. Encryption is the way to make any kind of data unreadable. In fact, today's practice requires many additional security elements from encryption algorithms. They should resist many kind of known attacks such as changing the order of encrypted messages or replaying data twice.

SSL is a protocol that uses different encryption algorithms to ensure that data received over a public network can be trusted. It has mechanisms to detect any data change, loss, or replay. SSL also incorporates algorithms that provide identity verification using the X509 standard.

X509 makes it possible to identify someone on the Internet. It is most commonly used in e-commerce applications. In basic terms, there should be some company called a “Certificate Authority” (or CA) that assigns electronic certificates to anyone who needs them. Certificates rely on asymmetric encryption algorithms that have two encryption keys (a public key and a secret key). A certificate owner can show the certificate to another party as proof of identity. A certificate consists of its owner's public key. Any data encrypted with this public key can be decrypted only using the corresponding secret key, which is held by the owner of the certificate.

If you need more information about SSL, X509, or encryption, use your favorite Internet search engine to search for the keywords in which you are interested.

5.5.8.2. Using SSL Connections

To use SSL connections between the MySQL server and client programs, your system must support either OpenSSL or yaSSL and your version of MySQL must be built with SSL support.

To make it easier to use secure connections, MySQL is bundled with yaSSL. (MySQL and yaSSL employ the same licensing model, whereas OpenSSL uses an Apache-style license.) yaSSL support initially was available only for a few platforms, but now it is available on all MySQL platforms supported by Oracle Corporation.

To get secure connections to work with MySQL and SSL, you must do the following:

  1. If you are not using a binary (precompiled) version of MySQL that has been built with SSL support, and you are going to use OpenSSL rather than the bundled yaSSL library, install OpenSSL if it has not already been installed. We have tested MySQL with OpenSSL 0.9.6. To obtain OpenSSL, visit http://www.openssl.org.

    Building MySQL using OpenSSL requires a shared OpenSSL library, otherwise linker errors occur. Alternatively, build MySQL using yaSSL.

  2. If you are not using a binary (precompiled) version of MySQL that has been built with SSL support, configure a MySQL source distribution to use SSL. When you configure MySQL, invoke CMake like this:

    shell> cmake . -DWITH_SSL=bundled
    

    That configures the distribution to use the bundled yaSSL library. To use the system SSL library instead, specify the option as -DWITH_SSL=system instead. See Section 2.9.4, “MySQL Source-Configuration Options”.

    Note that yaSSL support on Unix platforms requires that either /dev/urandom or /dev/random be available to retrieve true random numbers. For additional information (especially regarding yaSSL on Solaris versions prior to 2.8 and HP-UX), see Bug #13164.

  3. Make sure that the user in the mysql database includes the SSL-related columns (beginning with ssl_ and x509_). If your user table does not have these columns, it must be upgraded; see Section 4.4.7, “mysql_upgrade — Check Tables for MySQL Upgrade”.

  4. To check whether a server binary is compiled with SSL support, invoke it with the --ssl option. An error will occur if the server does not support SSL:

    shell> mysqld --ssl --help
    060525 14:18:52 [ERROR] mysqld: unknown option '--ssl'
    

    To check whether a running mysqld server supports SSL, examine the value of the have_ssl system variable (if you have no have_ssl variable, check for have_openssl):

    mysql> SHOW VARIABLES LIKE 'have_ssl';
    +---------------+-------+
    | Variable_name | Value |
    +---------------+-------+
    | have_ssl      | YES   |
    +---------------+-------+
    

    If the value is YES, the server supports SSL connections. If the value is DISABLED, the server supports SSL connections but was not started with the appropriate --ssl-xxx options (described later in this section).

To enable SSL connections, the proper SSL-related options must be used (see Section 5.5.8.3, “SSL Command Options”).

To start the MySQL server so that it permits clients to connect using SSL, use the options that identify the key and certificate files the server needs when establishing a secure connection:

shell> mysqld --ssl-ca=ca-cert.pem \
       --ssl-cert=server-cert.pem \
       --ssl-key=server-key.pem
  • --ssl-ca identifies the Certificate Authority (CA) certificate.

  • --ssl-cert identifies the server public key. This can be sent to the client and authenticated against the CA certificate that it has.

  • --ssl-key identifies the server private key.

To establish a secure connection to a MySQL server with SSL support, the options that a client must specify depend on the SSL requirements of the user account that the client uses. (See the discussion of the REQUIRE clause in Section 12.7.1.3, “GRANT Синтаксис”.)

If the account has no special SSL requirements or was created using a GRANT statement that includes the REQUIRE SSL option, a client can connect securely by using just the --ssl-ca option:

shell> mysql --ssl-ca=ca-cert.pem

To require that a client certificate also be specified, create the account using the REQUIRE X509 option. Then the client must also specify the proper client key and certificate files or the server will reject the connection:

shell> mysql --ssl-ca=ca-cert.pem \
       --ssl-cert=client-cert.pem \
       --ssl-key=client-key.pem

In other words, the options are similar to those used for the server. Note that the Certificate Authority certificate has to be the same.

A client can determine whether the current connection with the server uses SSL by checking the value of the Ssl_cipher status variable. The value of Ssl_cipher is nonempty if SSL is used, and empty otherwise. For example:

mysql> SHOW STATUS LIKE 'Ssl_cipher';
+---------------+--------------------+
| Variable_name | Value              |
+---------------+--------------------+
| Ssl_cipher    | DHE-RSA-AES256-SHA |
+---------------+--------------------+

For the mysql client, you can use the STATUS or \s command and check the SSL line:

mysql> \s
...
SSL:                    Not in use
...

Or:

mysql> \s
...
SSL:                    Cipher in use is DHE-RSA-AES256-SHA
...

To establish a secure connection from within an application program, use the mysql_ssl_set() C API function to set the appropriate certificate options before calling mysql_real_connect(). See Section 21.9.3.67, “mysql_ssl_set(). After the connection is established, you can use mysql_get_ssl_cipher() to determine whether SSL is in use. A non-NULL return value indicates a secure connection and names the SSL cipher used for encryption. A NULL return value indicates that SSL is not being used. See Section 21.9.3.33, “mysql_get_ssl_cipher().

5.5.8.3. SSL Command Options

The following list describes options that are used for specifying the use of SSL, certificate files, and key files. They can be given on the command line or in an option file. These options are not available unless MySQL has been built with SSL support. See Section 5.5.8.2, “Using SSL Connections”.

Table 5.19. SSL Option/Variable Summary

NameCmd-LineOption fileSystem VarStatus VarVar ScopeDynamic
have_openssl  Yes GlobalNo
have_ssl  Yes GlobalNo
skip-sslYesYes    
sslYesYes    
ssl-caYesYes  GlobalNo
- Variable: ssl_ca  Yes GlobalNo
ssl-capathYesYes  GlobalNo
- Variable: ssl_capath  Yes GlobalNo
ssl-certYesYes  GlobalNo
- Variable: ssl_cert  Yes GlobalNo
ssl-cipherYesYes  GlobalNo
- Variable: ssl_cipher  Yes GlobalNo
ssl-keyYesYes  GlobalNo
- Variable: ssl_key  Yes GlobalNo
ssl-verify-server-certYesYes    
  • --ssl

    For the server, this option specifies that the server permits SSL connections. For a client program, it permits the client to connect to the server using SSL. This option is not sufficient in itself to cause an SSL connection to be used. You must also specify the --ssl-ca option, and possibly the --ssl-cert and --ssl-key options.

    This option is more often used in its opposite form to override any other SSL options and indicate that SSL should not be used. To do this, specify the option as --skip-ssl or --ssl=0.

    Note that use of --ssl does not require an SSL connection. For example, if the server or client is compiled without SSL support, a normal unencrypted connection is used.

    The secure way to require use of an SSL connection is to create an account on the server that includes a REQUIRE SSL clause in the GRANT statement. Then use that account to connect to the server, where both the server and the client have SSL support enabled.

    The REQUIRE clause permits other SSL-related restrictions as well. The description of REQUIRE in Section 12.7.1.3, “GRANT Синтаксис”, provides additional detail about which SSL command options may or must be specified by clients that connect using accounts that are created using the various REQUIRE options.

  • --ssl-ca=file_name

    The path to a file that contains a list of trusted SSL CAs.

  • --ssl-capath=directory_name

    The path to a directory that contains trusted SSL CA certificates in PEM format.

  • --ssl-cert=file_name

    The name of the SSL certificate file to use for establishing a secure connection.

  • --ssl-cipher=cipher_list

    A list of permissible ciphers to use for SSL encryption. For greatest portability, cipher_list should be a list of one or more cipher names, separated by colons. Examples:

    --ssl-cipher=AES128-SHA
    --ssl-cipher=DHE-RSA-AES256-SHA:AES128-SHA

    This format is understood both by OpenSSL and yaSSL. OpenSSL supports a more flexible syntax for specifying ciphers, as described in the OpenSSL documentation at http://www.openssl.org/docs/apps/ciphers.html. However, this extended syntax will fail if used with a MySQL installation compiled against yaSSL.

    If no cipher in the list is supported, SSL connections will not work.

  • --ssl-key=file_name

    The name of the SSL key file to use for establishing a secure connection.

    If the key file is protected by a passphrase, and the MySQL distribution was built using OpenSSL, the program will prompt the user for the passphrase. The password must be given interactively; it cannot be stored in a file. If the passphrase is incorrect, the program continues as if it could not read the key. An error occurs if the key file is protected by a passphrase for distributions built using yaSSL.

  • --ssl-verify-server-cert

    This option is available for client programs only, not the server. It causes the server's Common Name value in the certificate that the server sends to the client to be verified against the host name that the client uses for connecting to the server, and the connection is rejected if there is a mismatch. This feature can be used to prevent man-in-the-middle attacks. Verification is disabled by default.

If you use SSL when establishing a client connection, you can tell the client not to authenticate the server certificate by specifying neither --ssl-ca nor --ssl-capath. The server still verifies the client according to any applicable requirements established using GRANT statements for the client, and it still uses any --ssl-ca/--ssl-capath values that were passed to server at startup time.

5.5.8.4. Setting Up SSL Certificates for MySQL

This section demonstrates how to set up SSL certificate and key files for use by MySQL servers and clients. The first example shows a simplified procedure such as you might use from the command line. The second shows a script that contains more detail. The first two examples are intended for use on Unix and both use the openssl command that is part of OpenSSL. The third example describes how to set up SSL files on Windows.

Following the third example, instructions are given for using the files to test SSL connections. You can also use the files as described in Section 5.5.8.2, “Using SSL Connections”.

Пример 1: Creating SSL Files from the Command Line on Unix

The following example shows a set of commands to create MySQL server and client certificate and key files. You will need to respond to several prompts by the openssl commands. To generate test files, you can press Enter to all prompts. To generate files for production use, you should provide nonempty responses.

# Create clean environment
shell> rm -rf newcerts
shell> mkdir newcerts && cd newcerts

# Create CA certificate
shell> openssl genrsa 2048 > ca-key.pem
shell> openssl req -new -x509 -nodes -days 1000 \
         -key ca-key.pem -out ca-cert.pem

# Create server certificate, remove passphrase, and sign it
shell> openssl req -newkey rsa:2048 -days 1000 \
         -nodes -keyout server-key.pem -out server-req.pem
shell> openssl rsa -in server-key.pem -out server-key.pem
shell> openssl x509 -req -in server-req.pem -days 1000 \
         -CA ca-cert.pem -CAkey ca-key.pem -set_serial 01 -out server-cert.pem

# Create client certificate, remove passphrase, and sign it
shell> openssl req -newkey rsa:2048 -days 1000 \
         -nodes -keyout client-key.pem -out client-req.pem
shell> openssl rsa -in client-key.pem -out client-key.pem
shell> openssl x509 -req -in client-req.pem -days 1000 \
         -CA ca-cert.pem -CAkey ca-key.pem -set_serial 01 -out client-cert.pem

After generating the certificates, verify them:

mysql> openssl verify -CAfile ca-cert.pem server-cert.pem client-cert.pem
Пример 2: Creating SSL Files Using a Script on Unix

Here is an example script that shows how to set up SSL certificates for MySQL:

DIR=`pwd`/openssl
PRIV=$DIR/private

mkdir $DIR $PRIV $DIR/newcerts
cp /usr/share/ssl/openssl.cnf $DIR
replace ./demoCA $DIR -- $DIR/openssl.cnf

# Create necessary files: $database, $serial and $new_certs_dir
# directory (optional)

touch $DIR/index.txt
echo "01" > $DIR/serial

#
# Generation of Certificate Authority(CA)
#

openssl req -new -x509 -keyout $PRIV/cakey.pem -out $DIR/ca-cert.pem \
    -days 3600 -config $DIR/openssl.cnf

# Sample output:
# Using configuration from /home/monty/openssl/openssl.cnf
# Generating a 1024 bit RSA private key
# ................++++++
# .........++++++
# writing new private key to '/home/monty/openssl/private/cakey.pem'
# Enter PEM pass phrase:
# Verifying password - Enter PEM pass phrase:
# -----
# You are about to be asked to enter information that will be
# incorporated into your certificate request.
# What you are about to enter is what is called a Distinguished Name
# or a DN.
# There are quite a few fields but you can leave some blank
# For some fields there will be a default value,
# If you enter '.', the field will be left blank.
# -----
# Country Name (2 letter code) [AU]:FI
# State or Province Name (full name) [Some-State]:.
# Locality Name (eg, city) []:
# Organization Name (eg, company) [Internet Widgits Pty Ltd]:MySQL AB
# Organizational Unit Name (eg, section) []:
# Common Name (eg, YOUR name) []:MySQL admin
# Email Address []:

#
# Create server request and key
#
openssl req -new -keyout $DIR/server-key.pem -out \
    $DIR/server-req.pem -days 3600 -config $DIR/openssl.cnf

# Sample output:
# Using configuration from /home/monty/openssl/openssl.cnf
# Generating a 1024 bit RSA private key
# ..++++++
# ..........++++++
# writing new private key to '/home/monty/openssl/server-key.pem'
# Enter PEM pass phrase:
# Verifying password - Enter PEM pass phrase:
# -----
# You are about to be asked to enter information that will be
# incorporated into your certificate request.
# What you are about to enter is what is called a Distinguished Name
# or a DN.
# There are quite a few fields but you can leave some blank
# For some fields there will be a default value,
# If you enter '.', the field will be left blank.
# -----
# Country Name (2 letter code) [AU]:FI
# State or Province Name (full name) [Some-State]:.
# Locality Name (eg, city) []:
# Organization Name (eg, company) [Internet Widgits Pty Ltd]:MySQL AB
# Organizational Unit Name (eg, section) []:
# Common Name (eg, YOUR name) []:MySQL server
# Email Address []:
#
# Please enter the following 'extra' attributes
# to be sent with your certificate request
# A challenge password []:
# An optional company name []:

#
# Remove the passphrase from the key
#
openssl rsa -in $DIR/server-key.pem -out $DIR/server-key.pem

#
# Sign server cert
#
openssl ca  -policy policy_anything -out $DIR/server-cert.pem \
    -config $DIR/openssl.cnf -infiles $DIR/server-req.pem

# Sample output:
# Using configuration from /home/monty/openssl/openssl.cnf
# Enter PEM pass phrase:
# Check that the request matches the signature
# Signature ok
# The Subjects Distinguished Name is as follows
# countryName           :PRINTABLE:'FI'
# organizationName      :PRINTABLE:'MySQL AB'
# commonName            :PRINTABLE:'MySQL admin'
# Certificate is to be certified until Sep 13 14:22:46 2003 GMT
# (365 days)
# Sign the certificate? [y/n]:y
#
#
# 1 out of 1 certificate requests certified, commit? [y/n]y
# Write out database with 1 new entries
# Data Base Updated

#
# Create client request and key
#
openssl req -new -keyout $DIR/client-key.pem -out \
    $DIR/client-req.pem -days 3600 -config $DIR/openssl.cnf

# Sample output:
# Using configuration from /home/monty/openssl/openssl.cnf
# Generating a 1024 bit RSA private key
# .....................................++++++
# .............................................++++++
# writing new private key to '/home/monty/openssl/client-key.pem'
# Enter PEM pass phrase:
# Verifying password - Enter PEM pass phrase:
# -----
# You are about to be asked to enter information that will be
# incorporated into your certificate request.
# What you are about to enter is what is called a Distinguished Name
# or a DN.
# There are quite a few fields but you can leave some blank
# For some fields there will be a default value,
# If you enter '.', the field will be left blank.
# -----
# Country Name (2 letter code) [AU]:FI
# State or Province Name (full name) [Some-State]:.
# Locality Name (eg, city) []:
# Organization Name (eg, company) [Internet Widgits Pty Ltd]:MySQL AB
# Organizational Unit Name (eg, section) []:
# Common Name (eg, YOUR name) []:MySQL user
# Email Address []:
#
# Please enter the following 'extra' attributes
# to be sent with your certificate request
# A challenge password []:
# An optional company name []:

#
# Remove the passphrase from the key
#
openssl rsa -in $DIR/client-key.pem -out $DIR/client-key.pem

#
# Sign client cert
#

openssl ca  -policy policy_anything -out $DIR/client-cert.pem \
    -config $DIR/openssl.cnf -infiles $DIR/client-req.pem

# Sample output:
# Using configuration from /home/monty/openssl/openssl.cnf
# Enter PEM pass phrase:
# Check that the request matches the signature
# Signature ok
# The Subjects Distinguished Name is as follows
# countryName           :PRINTABLE:'FI'
# organizationName      :PRINTABLE:'MySQL AB'
# commonName            :PRINTABLE:'MySQL user'
# Certificate is to be certified until Sep 13 16:45:17 2003 GMT
# (365 days)
# Sign the certificate? [y/n]:y
#
#
# 1 out of 1 certificate requests certified, commit? [y/n]y
# Write out database with 1 new entries
# Data Base Updated

#
# Create a my.cnf file that you can use to test the certificates
#

cnf=""
cnf="$cnf [client]"
cnf="$cnf ssl-ca=$DIR/ca-cert.pem"
cnf="$cnf ssl-cert=$DIR/client-cert.pem"
cnf="$cnf ssl-key=$DIR/client-key.pem"
cnf="$cnf [mysqld]"
cnf="$cnf ssl-ca=$DIR/ca-cert.pem"
cnf="$cnf ssl-cert=$DIR/server-cert.pem"
cnf="$cnf ssl-key=$DIR/server-key.pem"
echo $cnf | replace " " '
' > $DIR/my.cnf
Пример 3: Creating SSL Files on Windows

Download OpenSSL for Windows. An overview of available packages can be seen here: http://www.slproweb.com/products/Win32OpenSSL.html Choose the Win32 OpenSSL Light or Win64 OpenSSL Light package, depending on your architecture (32-bit or 64-bit). The default installation location will be C:\OpenSSL-Win32 or C:\OpenSSL-Win64, depending on which package you downloaded. The following instructions assume a default location of C:\OpenSSL-Win32. Modify this as necessary if you are using the 64-bit package.

if a message occurs during setup indicating '...critical component is missing: Microsoft Visual C++ 2008 Redistributables', cancel the setup and download one of the following packages as well, again depending on your architecture (32-bit or 64-bit):

After installing the additional package, restart the OpenSSL setup.

During installation, leave the default C:\OpenSSL-Win32 as the install path, and also leave the default option 'Copy OpenSSL DLL files to the Windows system directory' selected.

When the installation has finished, add C:\OpenSSL-Win32\bin to the Windows System Path variable of your server:

  1. On the Windows desktop, right-click the My Computer icon, and select Properties.

  2. Select the Advanced tab from the System Properties menu that appears, and click the Environment Variables button.

  3. Under System Variables, select Path, then click the Edit button. The Edit System Variable dialogue should appear.

  4. Add ';C:\OpenSSL-Win32\bin' to the end (notice the semicolon).

  5. Press OK 3 times.

  6. Check that OpenSSL was correctly integrated into the Path variable by opening a new command console (Start>Run>cmd.exe) and verifying that OpenSSL is available:

    Microsoft Windows [Version ...]
    Copyright (c) 2006 Microsoft Corporation. All rights reserved.
    
    C:\Windows\system32>cd \
    
    C:\>openssl
    OpenSSL> exit <<< If you see the OpenSSL prompt, installation was successful.
    
    C:\>
    

Depending on your version of Windows, the preceding instructions might be slightly different.

After OpenSSL has been installed, use instructions similar to those from from Пример 1 (shown earlier in this section), with the following changes:

  • Change the following Unix commands:

    # Create clean environment
    shell> rm -rf newcerts
    shell> mkdir newcerts && cd newcerts
    

    On Windows, use these commands instead:

    # Create clean environment
    shell> md c:\newcerts
    shell> cd c:\newcerts
    
  • When a '\' character is shown at the end of a command line, this '\' character must be removed and the command lines entered all on a single line.

Testing SSL Connections

To test SSL connections, start the server as follows, where $DIR is the path name to the directory where the sample my.cnf option file (or my.ini on Windows) is located:

shell> mysqld --defaults-file=$DIR/my.cnf &

Then invoke a client program using the same option file:

shell> mysql --defaults-file=$DIR/my.cnf

If you have a MySQL source distribution, you can also test your setup by modifying the preceding my.cnf file to refer to the demonstration certificate and key files in the mysql-test/std_data directory of the distribution.

5.5.9. Connecting to MySQL Remotely from Windows with SSH

This section describes how to get a secure connection to a remote MySQL server with SSH. The information was provided by David Carlson .

  1. Install an SSH client on your Windows machine. As a user, the best nonfree one I have found is from SecureCRT from http://www.vandyke.com/. Another option is f-secure from http://www.f-secure.com/. You can also find some free ones on Google at http://directory.google.com/Top/Computers/Internet/Protocols/SSH/Clients/Windows/.

  2. Start your Windows SSH client. Set Host_Name = yourmysqlserver_URL_or_IP. Set userid=your_userid to log in to your server. This userid value might not be the same as the user name of your MySQL account.

  3. Set up port forwarding. Either do a remote forward (Set local_port: 3306, remote_host: yourmysqlservername_or_ip, remote_port: 3306 ) or a local forward (Set port: 3306, host: localhost, remote port: 3306).

  4. Save everything, otherwise you will have to redo it the next time.

  5. Log in to your server with the SSH session you just created.

  6. On your Windows machine, start some ODBC application (such as Access).

  7. Create a new file in Windows and link to MySQL using the ODBC driver the same way you normally do, except type in localhost for the MySQL host server, not yourmysqlservername.

At this point, you should have an ODBC connection to MySQL, encrypted using SSH.

5.5.10. Auditing MySQL Account Activity

Applications can use the following guidelines to perform auditing that ties database activity to MySQL accounts.

MySQL accounts correspond to rows in the mysql.user table. When a client connects successfully, the server authenticates the client to a particular row in this table. The User and Host column values in this row uniquely identify the account and correspond to the 'user_name'@'host_name' format in which account names are written in SQL statements.

The account used to authenticate a client determines which privileges the client has. Normally, the CURRENT_USER() function can be invoked to determine which account this is for the client user. Its value is constructed from the User and Host columns of the user table row for the account.

However, there are circumstances under which the CURRENT_USER() value corresponds not to the client user but to a different account. This occurs in contexts when privilege checking is not based the client's account:

  • Stored routines (procedures and functions) defined with the SQL SECURITY DEFINER characteristic

  • Views defined with the SQL SECURITY DEFINER characteristic

  • Triggers and events

In those contexts, privilege checking is done against the DEFINER account and CURRENT_USER() refers to that account, not to the account for the client who invoked the stored routine or view or who caused the trigger to activate. To determine the invoking user, you can call the USER() function, which returns a value indicating the actual user name provided by the client and the host from which the client connected. However, this value does not necessarily correspond directly to an account in the user table, because the USER() value never contains wildcards, whereas account values (as returned by CURRENT_USER()) may contain user name and host name wildcards.

For example, a blank user name matches any user, so an account of ''@'localhost' enables clients to connect as an anonymous user from the local host with any user name. If this case, if a client connects as user1 from the local host, USER() and CURRENT_USER() return different values:

mysql> SELECT USER(), CURRENT_USER();
+-----------------+----------------+
| USER()          | CURRENT_USER() |
+-----------------+----------------+
| user1@localhost | @localhost     |
+-----------------+----------------+

The host name part of an account can contain wildcards, too. If the host name contains a '%' or '_' pattern character or uses netmask notation, the account can be used for clients connecting from multiple hosts and the CURRENT_USER() value will not indicate which one. For example, the account 'user2'@'%.example.com' can be used by user2 to connect from any host in the example.com domain. If user2 connects from remote.example.com, USER() and CURRENT_USER() return different values:

mysql> SELECT USER(), CURRENT_USER();
+--------------------------+---------------------+
| USER()                   | CURRENT_USER()      |
+--------------------------+---------------------+
| user2@remote.example.com | user2@%.example.com |
+--------------------------+---------------------+

If an application must invoke USER() for user auditing (for example, if it does auditing from within triggers) but must also be able to associate the USER() value with an account in the user table, it is necessary to avoid accounts that contain wildcards in the User or Host column. Specifically, do not permit User to be empty (which creates an anonymous-user account), and do not permit pattern characters or netmask notation in Host values. All accounts must have a nonempty User value and literal Host value.

With respect to the previous examples, the ''@'localhost' and 'user2'@'%.example.com' accounts should be changed not to use wildcards:

RENAME USER ''@'localhost' TO 'user1'@'localhost';
RENAME USER 'user2'@'%.example.com' TO 'user2'@'remote.example.com';

If user2 must be able to connect from several hosts in the example.com domain, there should be a separate account for each host.

To extract the user name or host name part from a CURRENT_USER() or USER() value, use the SUBSTRING() function:

mysql> SELECT SUBSTRING_INDEX(CURRENT_USER(),'@',1);
+---------------------------------------+
| SUBSTRING_INDEX(CURRENT_USER(),'@',1) |
+---------------------------------------+
| user1                                 |
+---------------------------------------+

mysql> SELECT SUBSTRING_INDEX(CURRENT_USER(),'@',-1);
+----------------------------------------+
| SUBSTRING_INDEX(CURRENT_USER(),'@',-1) |
+----------------------------------------+
| localhost                              |
+----------------------------------------+

5.6. Running Multiple MySQL Instances on One Machine

In some cases, you might want to run multiple instances of MySQL on a single machine. You might want to test a new MySQL release while leaving an existing production setup undisturbed. Or you might want to give different users access to different mysqld servers that they manage themselves. (For example, you might be an Internet Service Provider that wants to provide independent MySQL installations for different customers.)

It is possible to use a different MySQL server binary per instance, or use the same binary for multiple instances, or any combination of the two approaches. For example, you might run a server from MySQL 5.1 and one from MySQL 5.5, to see how different versions handle a given workload. Or you might run multiple instances of the current production version, each managing a different set of databases.

Whether or not you use distinct server binaries, each instance that you run must be configured with unique values for several operating parameters. This eliminates the potential for conflict between instances. Parameters can be set on the command line, in option files, or by setting environment variables. See Section 4.2.3, “Specifying Program Options”. To see the values used by a given instance, connect to it and execute a SHOW VARIABLES statement.

The primary resource managed by a MySQL instance is the data directory. Each instance should use a different data directory, the location of which is specified using the --datadir=path option. For methods of configuring each instance with its own data directory, and warnings about the dangers of failing to do so, see Section 5.6.1, “Setting Up Multiple Data Directories”.

In addition to using different data directories, several other options must have different values for each server instance:

  • --port=port_num

    --port controls the port number for TCP/IP connections. Alternatively, if the host has multiple network addresses, you can use --bind-address to cause each server to listen to a different address.

  • --socket=path

    --socket controls the Unix socket file path on Unix or the named pipe name on Windows. On Windows, it is necessary to specify distinct pipe names only for those servers configured to permit named-pipe connections.

  • --shared-memory-base-name=name

    This option is used only on Windows. It designates the shared-memory name used by a Windows server to permit clients to connect using shared memory. It is necessary to specify distinct shared-memory names only for those servers configured to permit shared-memory connections.

  • --pid-file=file_name

    This option indicates the path name of the file in which the server writes its process ID.

If you use the following log file options, their values must differ for each server:

For further discussion of log file options, see Section 5.2, “MySQL Server Logs”.

To achieve better performance, you can specify the following option differently for each server, to spread the load between several physical disks:

Having different temporary directories also makes it easier to determine which MySQL server created any given temporary file.

If you have multiple MySQL installations in different locations, you can specify the base directory for each installation with the --basedir=path option. This causes each instance to automatically use a different data directory, log files, and PID file because the default for each of those parameters is relative to the base directory. In that case, the only other options you need to specify are the --socket and --port options. Suppose that you install different versions of MySQL using tar file binary distributions. These install in different locations, so you can start the server for each installation using the command bin/mysqld_safe under its corresponding base directory. mysqld_safe determines the proper --basedir option to pass to mysqld, and you need specify only the --socket and --port options to mysqld_safe.

As discussed in the following sections, it is possible to start additional servers by specifying appropriate command options or by setting environment variables. However, if you need to run multiple servers on a more permanent basis, it is more convenient to use option files to specify for each server those option values that must be unique to it. The --defaults-file option is useful for this purpose.

5.6.1. Setting Up Multiple Data Directories

Each MySQL Instance on a machine should have its own data directory. The location is specified using the --datadir=path option.

There are different methods of setting up a data directory for a new instance:

  • Create a new data directory

  • Copy an existing data directory

The following discussion provides more detail about each method.

Warning

Normally, you should never have two servers that update data in the same databases. This may lead to unpleasant surprises if your operating system does not support fault-free system locking. If (despite this warning) you run multiple servers using the same data directory and they have logging enabled, you must use the appropriate options to specify log file names that are unique to each server. Otherwise, the servers try to log to the same files.

Even when the preceding precautions are observed, this kind of setup works only with MyISAM and MERGE tables, and not with any of the other storage engines. Also, this warning against sharing a data directory among servers always applies in an NFS environment. Permitting multiple MySQL servers to access a common data directory over NFS is a very bad idea. The primary problem is that NFS is the speed bottleneck. It is not meant for such use. Another risk with NFS is that you must devise a way to ensure that two or more servers do not interfere with each other. Usually NFS file locking is handled by the lockd daemon, but at the moment there is no platform that performs locking 100% reliably in every situation.

Create a New Data Directory

With this method, the data directory will be in the same state as when you first install MySQL. It will have the default set of MySQL accounts and no user data.

On Unix, initialize the data directory by running mysql_install_db. See Section 2.10.1, “Unix Postinstallation Procedures”.

On Windows, the data directory is included in the MySQL distribution:

  • MySQL Zip archive distributions for Windows contain an unmodified data directory. You can unpack such a distribution into a temporary location, then copy it data directory to where you are setting up the new instance.

  • As of MySQL 5.5.5, Windows MSI package installers create and set up the data directory that the installed server will use, but also create a pristine “template” data directory named data under the installation directory. After an installation has been performed using an MSI package, the template data directory can be copied to set up additional MySQL instances.

Copy an Existing Data Directory

With this method, any MySQL accounts or user data present in the data directory are carried over to the new data directory.

  1. Stop the existing MySQL instance using the data directory. This must be a clean shutdown so that the instance flushes any pending changes to disk.

  2. Copy the data directory to the location where the new data directory should be.

  3. Copy the my.cnf or my.ini option file used by the existing instance. This serves as a basis for the new instance.

  4. Modify the new option file so that any pathnames referring to the original data directory refer to the new data directory. Also, modify any other options that must be unique per instance, such as the TCP/IP port number and the log files. For a list of parameters that must be unique per instance, see Section 5.6, “Running Multiple MySQL Instances on One Machine”.

  5. Start the new instance, telling it to use the new option file.

5.6.2. Running Multiple MySQL Instances on Windows

You can run multiple servers on Windows by starting them manually from the command line, each with appropriate operating parameters, or by installing several servers as Windows services and running them that way. General instructions for running MySQL from the command line or as a service are given in Section 2.3, “Installing MySQL on Microsoft Windows”. The following sections describe how to start each server with different values for those options that must be unique per server, such as the data directory. These options are listed in Section 5.6, “Running Multiple MySQL Instances on One Machine”.

5.6.2.1. Starting Multiple MySQL Instances at the Windows Command Line

The procedure for starting a single MySQL server manually from the command line is described in Section 2.3.6.5, “Starting MySQL from the Windows Command Line”. To start multiple servers this way, you can specify the appropriate options on the command line or in an option file. It is more convenient to place the options in an option file, but it is necessary to make sure that each server gets its own set of options. To do this, create an option file for each server and tell the server the file name with a --defaults-file option when you run it.

Suppose that you want to run mysqld on port 3307 with a data directory of C:\mydata1, and mysqld-debug on port 3308 with a data directory of C:\mydata2. Use this procedure:

  1. Make sure that each data directory exists, including its own copy of the mysql database that contains the grant tables.

  2. Create two option files. For example, create one file named C:\my-opts1.cnf that looks like this:

    [mysqld]
    datadir = C:/mydata1
    port = 3307

    Create a second file named C:\my-opts2.cnf that looks like this:

    [mysqld]
    datadir = C:/mydata2
    port = 3308
  3. Use the --defaults-file option to start each server with its own option file:

    C:\> C:\mysql\bin\mysqld --defaults-file=C:\my-opts1.cnf
    C:\> C:\mysql\bin\mysqld-debug --defaults-file=C:\my-opts2.cnf
    

    Each server starts in the foreground (no new prompt appears until the server exits later), so you will need to issue those two commands in separate console windows.

To shut down the servers, connect to each using the appropriate port number:

C:\> C:\mysql\bin\mysqladmin --port=3307 shutdown
C:\> C:\mysql\bin\mysqladmin --port=3308 shutdown

Servers configured as just described permit clients to connect over TCP/IP. If your version of Windows supports named pipes and you also want to permit named-pipe connections, use the mysqld or mysqld-debug server and specify options that enable the named pipe and specify its name. Each server that supports named-pipe connections must use a unique pipe name. For example, the C:\my-opts1.cnf file might be written like this:

[mysqld]
datadir = C:/mydata1
port = 3307
enable-named-pipe
socket = mypipe1

Modify C:\my-opts2.cnf similarly for use by the second server. Then start the servers as described previously.

A similar procedure applies for servers that you want to permit shared-memory connections. Enable such connections with the --shared-memory option and specify a unique shared-memory name for each server with the --shared-memory-base-name option.

5.6.2.2. Starting Multiple MySQL Instances as Windows Services

On Windows, a MySQL server can run as a Windows service. The procedures for installing, controlling, and removing a single MySQL service are described in Section 2.3.6.7, “Starting MySQL as a Windows Service”.

To set up multiple MySQL services, you must make sure that each instance uses a different service name in addition to the other parameters that must be unique per instance.

For the following instructions, suppose that you want to run the mysqld server from two different versions of MySQL that are installed at C:\mysql-5.1.55 and C:\mysql-5.5.22, respectively. (This might be the case if you are running 5.1.55 as your production server, but also want to conduct tests using 5.5.22.)

To install MySQL as a Windows service, use the --install or --install-manual option. For information about these options, see Section 2.3.6.7, “Starting MySQL as a Windows Service”.

Based on the preceding information, you have several ways to set up multiple services. The following instructions describe some examples. Before trying any of them, shut down and remove any existing MySQL services.

  • Approach 1: Specify the options for all services in one of the standard option files. To do this, use a different service name for each server. Suppose that you want to run the 5.1.55 mysqld using the service name of mysqld1 and the 5.5.22 mysqld using the service name mysqld2. In this case, you can use the [mysqld1] group for 5.1.55 and the [mysqld2] group for 5.5.22. For example, you can set up C:\my.cnf like this:

    # options for mysqld1 service
    [mysqld1]
    basedir = C:/mysql-5.1.55
    port = 3307
    enable-named-pipe
    socket = mypipe1
    
    # options for mysqld2 service
    [mysqld2]
    basedir = C:/mysql-5.5.22
    port = 3308
    enable-named-pipe
    socket = mypipe2

    Install the services as follows, using the full server path names to ensure that Windows registers the correct executable program for each service:

    C:\> C:\mysql-5.1.55\bin\mysqld --install mysqld1
    C:\> C:\mysql-5.5.22\bin\mysqld --install mysqld2
    

    To start the services, use the services manager, or use NET START with the appropriate service names:

    C:\> NET START mysqld1
    C:\> NET START mysqld2
    

    To stop the services, use the services manager, or use NET STOP with the appropriate service names:

    C:\> NET STOP mysqld1
    C:\> NET STOP mysqld2
    
  • Approach 2: Specify options for each server in separate files and use --defaults-file when you install the services to tell each server what file to use. In this case, each file should list options using a [mysqld] group.

    With this approach, to specify options for the 5.1.55 mysqld, create a file C:\my-opts1.cnf that looks like this:

    [mysqld]
    basedir = C:/mysql-5.1.55
    port = 3307
    enable-named-pipe
    socket = mypipe1

    For the 5.5.22 mysqld, create a file C:\my-opts2.cnf that looks like this:

    [mysqld]
    basedir = C:/mysql-5.5.22
    port = 3308
    enable-named-pipe
    socket = mypipe2

    Install the services as follows (enter each command on a single line):

    C:\> C:\mysql-5.1.55\bin\mysqld --install mysqld1
               --defaults-file=C:\my-opts1.cnf
    C:\> C:\mysql-5.5.22\bin\mysqld --install mysqld2
               --defaults-file=C:\my-opts2.cnf
    

    When you install a MySQL server as a service and use a --defaults-file option, the service name must precede the option.

    After installing the services, start and stop them the same way as in the preceding example.

To remove multiple services, use mysqld --remove for each one, specifying a service name following the --remove option. If the service name is the default (MySQL), you can omit it.

5.6.3. Running Multiple MySQL Instances on Unix

One way is to run multiple MySQL instances on Unix is to compile different servers with different default TCP/IP ports and Unix socket files so that each one listens on different network interfaces. Compiling in different base directories for each installation also results automatically in a separate, compiled-in data directory, log file, and PID file location for each server.

Assume that an existing 5.1 server is configured for the default TCP/IP port number (3306) and Unix socket file (/tmp/mysql.sock). To configure a new 5.5.22 server to have different operating parameters, use a CMake command something like this:

shell> cmake . -DMYSQL_TCP_PORT=port_number \
             -DMYSQL_UNIX_ADDR=file_name \
             -DCMAKE_INSTALL_PREFIX=/usr/local/mysql-5.5.22

Here, port_number and file_name must be different from the default TCP/IP port number and Unix socket file path name, and the CMAKE_INSTALL_PREFIX value should specify an installation directory different from the one under which the existing MySQL installation is located.

If you have a MySQL server listening on a given port number, you can use the following command to find out what operating parameters it is using for several important configurable variables, including the base directory and Unix socket file name:

shell> mysqladmin --host=host_name --port=port_number variables

With the information displayed by that command, you can tell what option values not to use when configuring an additional server.

If you specify localhost as the host name, mysqladmin defaults to using a Unix socket file connection rather than TCP/IP. To explicitly specify the connection protocol, use the --protocol={TCP|SOCKET|PIPE|MEMORY} option.

You need not compile a new MySQL server just to start with a different Unix socket file and TCP/IP port number. It is also possible to use the same server binary and start each invocation of it with different parameter values at runtime. One way to do so is by using command-line options:

shell> mysqld_safe --socket=file_name --port=port_number

To start a second server, provide different --socket and --port option values, and pass a --datadir=path option to mysqld_safe so that the server uses a different data directory.

Alternatively, put the options for each server in a different option file, then start each server using a --defaults-file option that specifies the path to the appropriate option file. For example, if the option files for two server instances are named /usr/local/mysql/my.cnf and /usr/local/mysql/my.cnf2, start the servers like this: command:

shell> mysqld_safe --defaults-file=/usr/local/mysql/my.cnf
shell> mysqld_safe --defaults-file=/usr/local/mysql/my.cnf2

Another way to achieve a similar effect is to use environment variables to set the Unix socket file name and TCP/IP port number:

shell> MYSQL_UNIX_PORT=/tmp/mysqld-new.sock
shell> MYSQL_TCP_PORT=3307
shell> export MYSQL_UNIX_PORT MYSQL_TCP_PORT
shell> mysql_install_db --user=mysql
shell> mysqld_safe --datadir=/path/to/datadir &

This is a quick way of starting a second server to use for testing. The nice thing about this method is that the environment variable settings apply to any client programs that you invoke from the same shell. Thus, connections for those clients are automatically directed to the second server.

Section 2.12, “Environment Variables”, includes a list of other environment variables you can use to affect MySQL programs.

On Unix, the mysqld_multi script provides another way to start multiple servers. See Section 4.3.4, “mysqld_multi — Manage Multiple MySQL Servers”.

5.6.4. Using Client Programs in a Multiple-Server Environment

To connect with a client program to a MySQL server that is listening to different network interfaces from those compiled into your client, you can use one of the following methods:

  • Start the client with --host=host_name --port=port_number to connect using TCP/IP to a remote server, with --host=127.0.0.1 --port=port_number to connect using TCP/IP to a local server, or with --host=localhost --socket=file_name to connect to a local server using a Unix socket file or a Windows named pipe.

  • Start the client with --protocol=TCP to connect using TCP/IP, --protocol=SOCKET to connect using a Unix socket file, --protocol=PIPE to connect using a named pipe, or --protocol=MEMORY to connect using shared memory. For TCP/IP connections, you may also need to specify --host and --port options. For the other types of connections, you may need to specify a --socket option to specify a Unix socket file or Windows named-pipe name, or a --shared-memory-base-name option to specify the shared-memory name. Shared-memory connections are supported only on Windows.

  • On Unix, set the MYSQL_UNIX_PORT and MYSQL_TCP_PORT environment variables to point to the Unix socket file and TCP/IP port number before you start your clients. If you normally use a specific socket file or port number, you can place commands to set these environment variables in your .login file so that they apply each time you log in. See Section 2.12, “Environment Variables”.

  • Specify the default Unix socket file and TCP/IP port number in the [client] group of an option file. For example, you can use C:\my.cnf on Windows, or the .my.cnf file in your home directory on Unix. See Section 4.2.3.3, “Using Option Files”.

  • In a C program, you can specify the socket file or port number arguments in the mysql_real_connect() call. You can also have the program read option files by calling mysql_options(). See Section 21.9.3, “C API Function Описаниеs”.

  • If you are using the Perl DBD::mysql module, you can read options from MySQL option files. For example:

    $dsn = "DBI:mysql:test;mysql_read_default_group=client;"
            . "mysql_read_default_file=/usr/local/mysql/data/my.cnf";
    $dbh = DBI->connect($dsn, $user, $password);

    See Section 21.11, “MySQL Perl API”.

    Other programming interfaces may provide similar capabilities for reading option files.

5.7. Tracing mysqld Using DTrace

The DTrace probes in the MySQL server are designed to provide information about the execution of queries within MySQL and the different areas of the system being utilized during that process. The organization and triggering of the probes means that the execution of an entire query can be monitored with one level of probes (query-start and query-done) but by monitoring other probes you can get successively more detailed information about the execution of the query in terms of the locks used, sort methods and even row-by-row and storage-engine level execution information.

The DTrace probes are organized so that you can follow the entire query process, from the point of connection from a client, through the query execution, row-level operations, and back out again. You can think of the probes as being fired within a specific sequence during a typical client connect/execute/disconnect sequence, as shown in the following figure.

Figure 5.1. The MySQL Architecture Using Pluggable Storage Engines

DTrace Probe Structure in
        mysqld

Global information is provided in the arguments to the DTrace probes at various levels. Global information, that is, the connection ID and user/host and where relevant the query string, is provided at key levels (connection-start, command-start, query-start, and query-exec-start). As you go deeper into the probes, it is assumed either you are only interested in the individual executions (row-level probes provide information on the database and table name only), or that you will combine the row-level probes with the notional parent probes to provide the information about a specific query. Examples of this will be given as the format and arguments of each probe are provided.

For more information on DTrace and writing DTrace scripts, read the DTrace User Guide.

MySQL 5.5 includes support for DTrace probes on Solaris 10 Update 5 (Solaris 5/08) on SPARC, x86 and x86_64 platforms. Probes are also supported on Mac OS X 10.4 and higher. Enabling the probes should be automatic on these platforms. To explicitly enable or disable the probes during building, use the -DENABLE_DTRACE=1 or -DENABLE_DTRACE=0 option to CMake.

5.7.1. mysqld DTrace Probe Reference

MySQL supports the following static probes, organized into groups of functionality.

Table 5.20. MySQL DTrace Probes

GroupProbesIntroduced
Connectionconnection-start, connection-done5.4.0
Commandcommand-start, command-done5.4.0
Queryquery-start, query-done5.4.0
Query Parsingquery-parse-start, query-parse-done5.4.0
Query Cachequery-cache-hit, query-cache-miss5.4.0
Query Executionquery-exec-start, query-exec-done5.4.0
Row Levelinsert-row-start, insert-row-done5.4.0
 update-row-start, update-row-done5.4.0
 delete-row-start, delete-row-done5.4.0
Row Readsread-row-start, read-row-done5.4.0
Index Readsindex-read-row-start, index-read-row-done5.4.0
Lockhandler-rdlock-start, handler-rdlock-done5.4.0
 handler-wrlock-start, handler-wrlock-done5.4.0
 handler-unlock-start, handler-unlock-done5.4.0
Filesortfilesort-start, filesort-done5.4.0
Statementselect-start, select-done5.4.0
 insert-start, insert-done5.4.0
 insert-select-start, insert-select-done5.4.0
 update-start, update-done5.4.0
 multi-update-start, multi-update-done5.4.0
 delete-start, delete-done5.4.0
 multi-delete-start, multi-delete-done5.4.0
Networknet-read-start, net-read-done, net-write-start, net-write-done5.4.0
Keycachekeycache-read-start, keycache-read-block, keycache-read-done, keycache-read-hit, keycache-read-miss, keycache-write-start, keycache-write-block, keycache-write-done5.4.0
Замечание

When extracting the argument data from the probes, each argument is available as argN, starting with arg0. To identify each argument within the definitions they are provided with a descriptive name, but you must access the information using the corresponding argN parameter.

5.7.1.1. Connection Probes

The connection-start and connection-done probes enclose a connection from a client, regardless of whether the connection is through a socket or network connection.

connection-start(connectionid, user, host)
connection-done(status, connectionid)
  • connection-start: Triggered after a connection and successful login/authentication have been completed by a client. The arguments contain the connection information:

    • connectionid: An unsigned long containing the connection ID. This is the same as the process ID shown as the Id value in the output from SHOW PROCESSLIST.

    • user: The username used when authenticating. The value will be blank for the anonymous user.

    • host: The host of the client connection. For a connection made using UNIX sockets, the value will be blank.

  • connection-done: Triggered just as the connection to the client has been closed. The arguments are:

    • status: The status of the connection when it was closed. A logout operation will have a value of 0; any other termination of the connection has a nonzero value.

    • connectionid: The connection ID of the connection that was closed.

The following D script will quantify and summarize the average duration of individual connections, and provide a count, dumping the information every 60 seconds:

#!/usr/sbin/dtrace -s

mysql*:::connection-start
{
  self->start = timestamp;
}

mysql*:::connection-done
/self->start/
{
  @ = quantize(((timestamp - self->start)/1000000));
  self->start = 0;
}

tick-60s
{
  printa(@);
}

When executed on a server with a large number of clients you might see output similar to this:

  1  57413                        :tick-60s

           value  ------------- Distribution ------------- count
              -1 |                                         0
               0 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 30011
               1 |                                         59
               2 |                                         5
               4 |                                         20
               8 |                                         29
              16 |                                         18
              32 |                                         27
              64 |                                         30
             128 |                                         11
             256 |                                         10
             512 |                                         1
            1024 |                                         6
            2048 |                                         8
            4096 |                                         9
            8192 |                                         8
           16384 |                                         2
           32768 |                                         1
           65536 |                                         1
          131072 |                                         0
          262144 |                                         1
          524288 |                                         0        

5.7.1.2. Command Probes

The command probes are executed before and after a client command is executed, including any SQL statement that might be executed during that period. Commands include operations such as the initialization of the DB, use of the COM_CHANGE_USER operation (supported by the MySQL protocol), and manipulation of prepared statements. Many of these commands are used only by the MySQL client API from various connectors such as PHP and Java.

command-start(connectionid, command, user, host)
command-done(status)
  • command-start: Triggered when a command is submitted to the server.

    • connectionid: The connection ID of the client executing the command.

    • command: An integer representing the command that was executed. Possible values are shown in the following table.

      ValueNameОписание
      00COM_SLEEPInternal thread state
      01COM_QUITClose connection
      02COM_INIT_DBSelect database (USE ...)
      03COM_QUERYExecute a query
      04COM_FIELD_LISTGet a list of fields
      05COM_CREATE_DBCreate a database (deprecated)
      06COM_DROP_DBDrop a database (deprecated)
      07COM_REFRESHRefresh connection
      08COM_SHUTDOWNShutdown server
      09COM_STATISTICSGet statistics
      10COM_PROCESS_INFOGet processes (SHOW PROCESSLIST)
      11COM_CONNECTInitialize connection
      12COM_PROCESS_KILLKill process
      13COM_DEBUGGet debug information
      14COM_PINGPing
      15COM_TIMEInternal thread state
      16COM_DELAYED_INSERTInternal thread state
      17COM_CHANGE_USERChange user
      18COM_BINLOG_DUMPUsed by a replication slave or mysqlbinlog to initiate a binary log read
      19COM_TABLE_DUMPUsed by a replication slave to get the master table information
      20COM_CONNECT_OUTUsed by a replication slave to log a connection to the server
      21COM_REGISTER_SLAVEUsed by a replication slave during registration
      22COM_STMT_PREPAREPrepare a statement
      23COM_STMT_EXECUTEExecute a statement
      24COM_STMT_SEND_LONG_DATAUsed by a client when requesting extended data
      25COM_STMT_CLOSEClose a prepared statement
      26COM_STMT_RESETReset a prepared statement
      27COM_SET_OPTIONSet a server option
      28COM_STMT_FETCHFetch a prepared statement
    • user: The user executing the command.

    • host: The client host.

  • command-done: Triggered when the command execution completes. The status argument contains 0 if the command executed successfully, or 1 if the statement was terminated before normal completion.

The command-start and command-done probes are best used when combined with the statement probes to get an idea of overall execution time.

5.7.1.3. Query Probes

The query-start and query-done probes are triggered when a specific query is received by the server and when the query has been completed and the information has been successfully sent to the client.

query-start(query, connectionid, database, user, host)
query-done(status)
  • query-start: Triggered after the query string has been received from the client. The arguments are:

    • query: The full text of the submitted query.

    • connectionid: The connection ID of the client that submitted the query. The connection ID equals the connection ID returned when the client first connects and the Id value in the output from SHOW PROCESSLIST.

    • database: The database name on which the query is being executed.

    • user: The username used to connect to the server.

    • host: The hostname of the client.

  • query-done: Triggered once the query has been executed and the information has been returned to the client. The probe includes a single argument, status, which returns 0 when the query is successfully executed and 1 if there was an error.

You can get a simple report of the execution time for each query using the following D script:

#!/usr/sbin/dtrace -s

#pragma D option quiet

dtrace:::BEGIN
{
   printf("%-20s %-20s %-40s %-9s\n", "Who", "Database", "Query", "Time(ms)");
}

mysql*:::query-start
{
   self->query = copyinstr(arg0);
   self->connid = arg1;
   self->db    = copyinstr(arg2);
   self->who   = strjoin(copyinstr(arg3),strjoin("@",copyinstr(arg4)));
   self->querystart = timestamp;
}

mysql*:::query-done
{
   printf("%-20s %-20s %-40s %-9d\n",self->who,self->db,self->query,
          (timestamp - self->querystart) / 1000000);
}

When executing the above script you should get a basic idea of the execution time of your queries:

shell> ./query.d
Who                  Database             Query                                    Time(ms)
root@localhost       test                 select * from t1 order by i limit 10     0
root@localhost       test                 set global query_cache_size=0            0
root@localhost       test                 select * from t1 order by i limit 10     776
root@localhost       test                 select * from t1 order by i limit 10     773
root@localhost       test                 select * from t1 order by i desc limit 10 795 

5.7.1.4. Query Parsing Probes

The query parsing probes are triggered before the original SQL statement is parsed and when the parsing of the statement and determination of the execution model required to process the statement has been completed:

query-parse-start(query)
query-parse-done(status)
  • query-parse-start: Triggered just before the statement is parsed by the MySQL query parser. The single argument, query, is a string containing the full text of the original query.

  • query-parse-done: Triggered when the parsing of the original statement has been completed. The status is an integer describing the status of the operation. A 0 indicates that the query was successfully parsed. A 1 indicates that the parsing of the query failed.

For example, you could monitor the execution time for parsing a given query using the following D script:

#!/usr/sbin/dtrace -s

#pragma D option quiet

mysql*:::query-parse-start
{
   self->parsestart = timestamp;
   self->parsequery = copyinstr(arg0);
}

mysql*:::query-parse-done
/arg0 == 0/
{
   printf("Parsing %s: %d microseconds\n", self->parsequery,((timestamp - self->parsestart)/1000));
}

mysql*:::query-parse-done
/arg0 != 0/
{
   printf("Error parsing %s: %d microseconds\n", self->parsequery,((timestamp - self->parsestart)/1000));
}

In the above script a predicate is used on query-parse-done so that different output is generated based on the status value of the probe.

When running the script and monitoring the execution:

shell> ./query-parsing.d
Error parsing select from t1 join (t2) on (t1.i = t2.i) order by t1.s,t1.i limit 10: 36 ms
Parsing select * from t1 join (t2) on (t1.i = t2.i) order by t1.s,t1.i limit 10: 176 ms

5.7.1.5. Query Cache Probes

The query cache probes are fired when executing any query. The query-cache-hit query is triggered when a query exists in the query cache and can be used to return the query cache information. The arguments contain the original query text and the number of rows returned from the query cache for the query. If the query is not within the query cache, or the query cache is not enabled, then the query-cache-miss probe is triggered instead.

query-cache-hit(query, rows)
query-cache-miss(query)
  • query-cache-hit: Triggered when the query has been found within the query cache. The first argument, query, contains the original text of the query. The second argument, rows, is an integer containing the number of rows in the cached query.

  • query-cache-miss: Triggered when the query is not found within the query cache. The first argument, query, contains the original text of the query.

The query cache probes are best combined with a probe on the main query so that you can determine the differences in times between using or not using the query cache for specified queries. For example, in the following D script, the query and query cache information are combined into the information output during monitoring:

#!/usr/sbin/dtrace -s

#pragma D option quiet

dtrace:::BEGIN
{
   printf("%-20s %-20s %-40s %2s %-9s\n", "Who", "Database", "Query", "QC", "Time(ms)");
}

mysql*:::query-start
{
   self->query = copyinstr(arg0);
   self->connid = arg1;
   self->db    = copyinstr(arg2);
   self->who   = strjoin(copyinstr(arg3),strjoin("@",copyinstr(arg4)));
   self->querystart = timestamp;
   self->qc = 0;
}

mysql*:::query-cache-hit
{
   self->qc = 1;
}

mysql*:::query-cache-miss
{
   self->qc = 0;
}

mysql*:::query-done
{
   printf("%-20s %-20s %-40s %-2s %-9d\n",self->who,self->db,self->query,(self->qc ? "Y" : "N"),
          (timestamp - self->querystart) / 1000000);
}

When executing the script you can see the effects of the query cache. Initially the query cache is disabled. If you set the query cache size and then execute the query multiple times you should see that the query cache is being used to return the query data:

shell> ./query-cache.d
root@localhost       test                 select * from t1 order by i limit 10     N  1072
root@localhost                            set global query_cache_size=262144       N  0
root@localhost       test                 select * from t1 order by i limit 10     N  781
root@localhost       test                 select * from t1 order by i limit 10     Y  0 

5.7.1.6. Query Execution Probes

The query execution probe is triggered when the actual execution of the query starts, after the parsing and checking the query cache but before any privilege checks or optimization. By comparing the difference between the start and done probes you can monitor the time actually spent servicing the query (instead of just handling the parsing and other elements of the query).

query-exec-start(query, connectionid, database, user, host, exec_type)
query-exec-done(status)
Замечание

The information provided in the arguments for query-start and query-exec-start are almost identical and designed so that you can choose to monitor either the entire query process (using query-start) or only the execution (using query-exec-start) while exposing the core information about the user, client, and query being executed.

  • query-exec-start: Triggered when the execution of a individual query is started. The arguments are:

    • query: The full text of the submitted query.

    • connectionid: The connection ID of the client that submitted the query. The connection ID equals the connection ID returned when the client first connects and the Id value in the output from SHOW PROCESSLIST.

    • database: The database name on which the query is being executed.

    • user: The username used to connect to the server.

    • host: The hostname of the client.

    • exec_type: The type of execution. Execution types are determined based on the contents of the query and where it was submitted. The values for each type are shown in the following table.

      ValueОписание
      0Executed query from sql_parse, top-level query.
      1Executed prepared statement
      2Executed cursor statement
      3Executed query in stored procedure
  • query-exec-done: Triggered when the execution of the query has completed. The probe includes a single argument, status, which returns 0 when the query is successfully executed and 1 if there was an error.

5.7.1.7. Row-Level Probes

The *row-{start,done} probes are triggered each time a row operation is pushed down to a storage engine. For example, if you execute an INSERT statement with 100 rows of data, then the insert-row-start and insert-row-done probes will be triggered 100 times each, for each row insert.

insert-row-start(database, table)
insert-row-done(status)

update-row-start(database, table)
update-row-done(status)

delete-row-start(database, table)
delete-row-done(status)
  • insert-row-start: Triggered before a row is inserted into a table.

  • insert-row-done: Triggered after a row is inserted into a table.

  • update-row-start: Triggered before a row is updated in a table.

  • update-row-done: Triggered before a row is updated in a table.

  • delete-row-start: Triggered before a row is deleted from a table.

  • delete-row-done: Triggered before a row is deleted from a table.

The arguments supported by the probes are consistent for the corresponding start and done probes in each case:

  • database: The database name.

  • table: The table name.

  • status: The status; 0 for success or 1 for failure.

Because the row-level probes are triggered for each individual row access, these probes can be triggered many thousands of times each second, which may have a detrimental effect on both the monitoring script and MySQL. The DTrace environment should limit the triggering on these probes to prevent the performance being adversely affected. Either use the probes sparingly, or use counter or aggregation functions to report on these probes and then provide a summary when the script terminates or as part of a query-done or query-exec-done probes.

The following example script summarizes the duration of each row operation within a larger query:

#!/usr/sbin/dtrace -s

#pragma D option quiet

dtrace:::BEGIN
{
   printf("%-2s %-10s %-10s %9s %9s %-s \n",
          "St", "Who", "DB", "ConnID", "Dur ms", "Query");
}

mysql*:::query-start
{
   self->query = copyinstr(arg0);
   self->who   = strjoin(copyinstr(arg3),strjoin("@",copyinstr(arg4)));
   self->db    = copyinstr(arg2);
   self->connid = arg1;
   self->querystart = timestamp;
   self->rowdur = 0;
}

mysql*:::query-done
{
   this->elapsed = (timestamp - self->querystart) /1000000;
   printf("%2d %-10s %-10s %9d %9d %s\n",
          arg0, self->who, self->db,
          self->connid, this->elapsed, self->query);
}

mysql*:::query-done
/ self->rowdur /
{
   printf("%34s %9d %s\n", "", (self->rowdur/1000000), "-> Row ops");
}

mysql*:::insert-row-start
{
   self->rowstart = timestamp;
}

mysql*:::delete-row-start
{
   self->rowstart = timestamp;
}

mysql*:::update-row-start
{
   self->rowstart = timestamp;
}

mysql*:::insert-row-done
{
   self->rowdur += (timestamp-self->rowstart);
}

mysql*:::delete-row-done
{
   self->rowdur += (timestamp-self->rowstart);
}

mysql*:::update-row-done
{
   self->rowdur += (timestamp-self->rowstart);
}

Running the above script with a query that inserts data into a table, you can monitor the exact time spent performing the raw row insertion:

St Who        DB            ConnID    Dur ms Query
 0 @localhost test              13     20767 insert into t1(select * from t2)
                                        4827 -> Row ops

5.7.1.8. Read Row Probes

The read row probes are triggered at a storage engine level each time a row read operation occurs. These probes are specified within each storage engine (as opposed to the *row-start probes which are in the storage engine interface). These probes can therefore be used to monitor individual storage engine row-level operations and performance. Because these probes are triggered around the storage engine row read interface, they may be hit a significant number of times during a basic query.

read-row-start(database, table, scan_flag)
read-row-done(status)
  • read-row-start: Triggered when a row is read by the storage engine from the specified database and table. The scan_flag is set to 1 (true) when the read is part of a table scan (that is, a sequential read), or 0 (false) when the read is of a specific record.

  • read-row-done: Triggered when a row read operation within a storage engine completes. The status returns 0 on success, or a positive value on failure.

5.7.1.9. Index Probes

The index probes are triggered each time a a row is read using one of the indexes for the specified table. The probe is triggered within the corresponding storage engine for the table.

index-read-row-start(database, table)
index-read-row-done(status)
  • index-read-row-start: Triggered when a row is read by the storage engine from the specified database and table.

  • index-read-row-done: Triggered when an indexed row read operation within a storage engine completes. The status returns 0 on success, or a positive value on failure.

5.7.1.10. Lock Probes

The lock probes are called whenever an external lock is requested by MySQL for a table using the corresponding lock mechanism on the table as defined by the table's engine type. There are three different types of lock, the read lock, write lock, and unlock operations. Using the probes you can determine the duration of the external locking routine (that is, the time taken by the storage engine to implement the lock, including any time waiting for another lock to become free) and the total duration of the lock/unlock process.

handler-rdlock-start(database, table)
handler-rdlock-done(status)

handler-wrlock-start(database, table)
handler-wrlock-done(status)

handler-unlock-start(database, table)
handler-unlock-done(status)
  • handler-rdlock-start: Triggered when a read lock is requested on the specified database and table.

  • handler-wrlock-start: Triggered when a write lock is requested on the specified database and table.

  • handler-unlock-start: Triggered when an unlock request is made on the specified database and table.

  • handler-rdlock-done: Triggered when a read lock request completes. The status is 0 if the lock operation succeeded, or >0 on failure.

  • handler-wrlock-done: Triggered when a write lock request completes. The status is 0 if the lock operation succeeded, or >0 on failure.

  • handler-unlock-done: Triggered when an unlock request completes. The status is 0 if the unlock operation succeeded, or >0 on failure.

You can use arrays to monitor the locking and unlocking of individual tables and then calculate the duration of the entire table lock using the following script:

#!/usr/sbin/dtrace -s

#pragma D option quiet

mysql*:::handler-rdlock-start
{
   self->rdlockstart = timestamp;
   this->lockref = strjoin(copyinstr(arg0),strjoin("@",copyinstr(arg1)));
   self->lockmap[this->lockref] = self->rdlockstart;
   printf("Start: Lock->Read   %s.%s\n",copyinstr(arg0),copyinstr(arg1));
}

mysql*:::handler-wrlock-start
{
   self->wrlockstart = timestamp;
   this->lockref = strjoin(copyinstr(arg0),strjoin("@",copyinstr(arg1)));
   self->lockmap[this->lockref] = self->rdlockstart;
   printf("Start: Lock->Write  %s.%s\n",copyinstr(arg0),copyinstr(arg1));
}

mysql*:::handler-unlock-start
{
   self->unlockstart = timestamp;
   this->lockref = strjoin(copyinstr(arg0),strjoin("@",copyinstr(arg1)));
   printf("Start: Lock->Unlock %s.%s (%d ms lock duration)\n",
          copyinstr(arg0),copyinstr(arg1),
          (timestamp - self->lockmap[this->lockref])/1000000);
}

mysql*:::handler-rdlock-done
{
   printf("End:   Lock->Read   %d ms\n",
          (timestamp - self->rdlockstart)/1000000);
}

mysql*:::handler-wrlock-done
{
   printf("End:   Lock->Write  %d ms\n",
          (timestamp - self->wrlockstart)/1000000);
}

mysql*:::handler-unlock-done
{
   printf("End:   Lock->Unlock %d ms\n",
          (timestamp - self->unlockstart)/1000000);
}

When executed, you should get information both about the duration of the locking process itself, and of the locks on a specific table:

Start: Lock->Read   test.t2
End:   Lock->Read   0 ms
Start: Lock->Unlock test.t2 (25743 ms lock duration)
End:   Lock->Unlock 0 ms
Start: Lock->Read   test.t2
End:   Lock->Read   0 ms
Start: Lock->Unlock test.t2 (1 ms lock duration)
End:   Lock->Unlock 0 ms
Start: Lock->Read   test.t2
End:   Lock->Read   0 ms
Start: Lock->Unlock test.t2 (1 ms lock duration)
End:   Lock->Unlock 0 ms
Start: Lock->Read   test.t2
End:   Lock->Read   0 ms

5.7.1.11. Filesort Probes

The filesort probes are triggered whenever a filesort operation is applied to a table. For more information on filesort and the conditions under which it occurs, see Section 7.13.9, “ORDER BY Optimization”.

filesort-start(database, table)
filesort-done(status, rows)
  • filesort-start: Triggered when the filesort operation starts on a table. The two arguments to the probe, database and table, will identify the table being sorted.

  • filesort-done: Triggered when the filesort operation completes. Two arguments are supplied, the status (0 for success, 1 for failure), and the number of rows sorted during the filesort process.

An example of this is in the following script, which tracks the duration of the filesort process in addition to the duration of the main query:

#!/usr/sbin/dtrace -s

#pragma D option quiet

dtrace:::BEGIN
{
   printf("%-2s %-10s %-10s %9s %18s %-s \n",
          "St", "Who", "DB", "ConnID", "Dur microsec", "Query");
}

mysql*:::query-start
{
   self->query = copyinstr(arg0);
   self->who   = strjoin(copyinstr(arg3),strjoin("@",copyinstr(arg4)));
   self->db    = copyinstr(arg2);
   self->connid = arg1;
   self->querystart = timestamp;
   self->filesort = 0;
   self->fsdb = "";
   self->fstable = "";
}

mysql*:::filesort-start
{
  self->filesort = timestamp;
  self->fsdb = copyinstr(arg0);
  self->fstable = copyinstr(arg1);
}

mysql*:::filesort-done
{
   this->elapsed = (timestamp - self->filesort) /1000;
   printf("%2d %-10s %-10s %9d %18d Filesort on %s\n",
          arg0, self->who, self->fsdb,
          self->connid, this->elapsed, self->fstable);
}

mysql*:::query-done
{
   this->elapsed = (timestamp - self->querystart) /1000;
   printf("%2d %-10s %-10s %9d %18d %s\n",
          arg0, self->who, self->db,
          self->connid, this->elapsed, self->query);
}

Executing a query on a large table with an ORDER BY clause that triggers a filesort, and then creating an index on the table and then repeating the same query, you can see the difference in execution speed:

St Who        DB            ConnID       Dur microsec Query
 0 @localhost test              14           11335469 Filesort on t1
 0 @localhost test              14           11335787 select * from t1 order by i limit 100
 0 @localhost test              14          466734378 create index t1a on t1 (i)
 0 @localhost test              14              26472 select * from t1 order by i limit 100

5.7.1.12. Statement Probes

The individual statement probes are provided to give specific information about different statement types. For the start probes the string of the query is provided as a the only argument. Depending on the statement type, the information provided by the corresponding done probe will differ. For all done probes the status of the operation (0 for success, >0 for failure) is provided. For SELECT, INSERT, INSERT ... (SELECT FROM ...), DELETE, and DELETE FROM t1,t2 operations the number of rows affected is returned.

For UPDATE and UPDATE t1,t2 ... statements the number of rows matched and the number of rows actually changed is provided. This is because the number of rows actually matched by the corresponding WHERE clause, and the number of rows changed can differ. MySQL does not update the value of a row if the value already matches the new setting.

select-start(query)
select-done(status,rows)

insert-start(query)
insert-done(status,rows)

insert-select-start(query)
insert-select-done(status,rows)

update-start(query)
update-done(status,rowsmatched,rowschanged)

multi-update-start(query)
multi-update-done(status,rowsmatched,rowschanged)

delete-start(query)
delete-done(status,rows)

multi-delete-start(query)
multi-delete-done(status,rows)
  • select-start: Triggered before a SELECT statement.

  • select-done: Triggered at the end of a SELECT statement.

  • insert-start: Triggered before a INSERT statement.

  • insert-done: Triggered at the end of an INSERT statement.

  • insert-select-start: Triggered before an INSERT ... SELECT statement.

  • insert-select-done: Triggered at the end of an INSERT ... SELECT statement.

  • update-start: Triggered before an UPDATE statement.

  • update-done: Triggered at the end of an UPDATE statement.

  • multi-update-start: Triggered before an UPDATE statement involving multiple tables.

  • multi-update-done: Triggered at the end of an UPDATE statement involving multiple tables.

  • delete-start: Triggered before a DELETE statement.

  • delete-done: Triggered at the end of a DELETE statement.

  • multi-delete-start: Triggered before a DELETE statement involving multiple tables.

  • multi-delete-done: Triggered at the end of a DELETE statement involving multiple tables.

The arguments for the statement probes are:

  • query: The query string.

  • status: The status of the query. 0 for success, and >0 for failure.

  • rows: The number of rows affected by the statement. This returns the number rows found for SELECT, the number of rows deleted for DELETE, and the number of rows successfully inserted for INSERT.

  • rowsmatched: The number of rows matched by the WHERE clause of an UPDATE operation.

  • rowschanged: The number of rows actually changed during an UPDATE operation.

You use these probes to monitor the execution of these statement types without having to monitor the user or client executing the statements. A simple example of this is to track the execution times:

#!/usr/sbin/dtrace -s

#pragma D option quiet

dtrace:::BEGIN
{
   printf("%-60s %-8s %-8s %-8s\n", "Query", "RowsU", "RowsM", "Dur (ms)");
}

mysql*:::update-start, mysql*:::insert-start,
mysql*:::delete-start, mysql*:::multi-delete-start,
mysql*:::multi-delete-done, mysql*:::select-start,
mysql*:::insert-select-start, mysql*:::multi-update-start
{
    self->query = copyinstr(arg0);
    self->querystart = timestamp;
}

mysql*:::insert-done, mysql*:::select-done,
mysql*:::delete-done, mysql*:::multi-delete-done, mysql*:::insert-select-done
/ self->querystart /
{
    this->elapsed = ((timestamp - self->querystart)/1000000);
    printf("%-60s %-8d %-8d %d\n",
           self->query,
           0,
           arg1,
           this->elapsed);
    self->querystart = 0;
}

mysql*:::update-done, mysql*:::multi-update-done
/ self->querystart /
{
    this->elapsed = ((timestamp - self->querystart)/1000000);
    printf("%-60s %-8d %-8d %d\n",
           self->query,
           arg1,
           arg2,
           this->elapsed);
    self->querystart = 0;
}

When executed you can see the basic execution times and rows matches:

Query                                                        RowsU    RowsM    Dur (ms)
select * from t2                                             0        275      0
insert into t2 (select * from t2)                            0        275      9
update t2 set i=5 where i > 75                               110      110      8
update t2 set i=5 where i < 25                               254      134      12
delete from t2 where i < 5                                   0        0        0

Another alternative is to use the aggregation functions in DTrace to aggregate the execution time of individual statements together:

#!/usr/sbin/dtrace -s

#pragma D option quiet

mysql*:::update-start, mysql*:::insert-start,
mysql*:::delete-start, mysql*:::multi-delete-start,
mysql*:::multi-delete-done, mysql*:::select-start,
mysql*:::insert-select-start, mysql*:::multi-update-start
{
    self->querystart = timestamp;
}

mysql*:::select-done
{
        @statements["select"] = sum(((timestamp - self->querystart)/1000000));
}

mysql*:::insert-done, mysql*:::insert-select-done
{
        @statements["insert"] = sum(((timestamp - self->querystart)/1000000));
}

mysql*:::update-done, mysql*:::multi-update-done
{
        @statements["update"] = sum(((timestamp - self->querystart)/1000000));
}

mysql*:::delete-done, mysql*:::multi-delete-done
{
        @statements["delete"] = sum(((timestamp - self->querystart)/1000000));
}

tick-30s
{
        printa(@statements);
}

The script just shown aggregates the times spent doing each operation, which could be used to help benchmark a standard suite of tests.

 delete                                                            0
  update                                                            0
  insert                                                           23
  select                                                         2484

  delete                                                            0
  update                                                            0
  insert                                                           39
  select                                                        10744

  delete                                                            0
  update                                                           26
  insert                                                           56
  select                                                        10944

  delete                                                            0
  update                                                           26
  insert                                                         2287
  select                                                        15985

5.7.1.13. Network Probes

The network probes monitor the transfer of information from the MySQL server and clients of all types over the network. The probes are defined as follows:

net-read-start()
net-read-done(status, bytes)
net-write-start(bytes)
net-write-done(status)
  • net-read-start: Triggered when a network read operation is started.

  • net-read-done: Triggered when the network read operation completes. The status is an integer representing the return status for the operation, 0 for success and 1 for failure. The bytes argument is an integer specifying the number of bytes read during the process.

  • net-start-bytes: Triggered when data is written to a network socket. The single argument, bytes, specifies the number of bytes written to the network socket.

  • net-write-done: Triggered when the network write operation has completed. The single argument, status, is an integer representing the return status for the operation, 0 for success and 1 for failure.

You can use the network probes to monitor the time spent reading from and writing to network clients during execution. The following D script provides an example of this. Both the cumlative time for the read or write is calculated, and the number of bytes. Note that the dynamic variable size has been increased (using the dynvarsize option) to cope with the rapid firing of the individual probes for the network reads/writes.

#!/usr/sbin/dtrace -s

#pragma D option quiet
#pragma D option dynvarsize=4m

dtrace:::BEGIN
{
   printf("%-2s %-30s %-10s %9s %18s %-s \n",
          "St", "Who", "DB", "ConnID", "Dur microsec", "Query");
}

mysql*:::query-start
{
   self->query = copyinstr(arg0);
   self->who   = strjoin(copyinstr(arg3),strjoin("@",copyinstr(arg4)));
   self->db    = copyinstr(arg2);
   self->connid = arg1;
   self->querystart = timestamp;
   self->netwrite = 0;
   self->netwritecum = 0;
   self->netwritebase = 0;
   self->netread = 0;
   self->netreadcum = 0;
   self->netreadbase = 0;
}

mysql*:::net-write-start
{
   self->netwrite += arg0;
   self->netwritebase = timestamp;
}

mysql*:::net-write-done
{
   self->netwritecum += (timestamp - self->netwritebase);
   self->netwritebase = 0;
}

mysql*:::net-read-start
{
   self->netreadbase = timestamp;
}

mysql*:::net-read-done
{
   self->netread += arg1;
   self->netreadcum += (timestamp - self->netreadbase);
   self->netreadbase = 0;
}

mysql*:::query-done
{
   this->elapsed = (timestamp - self->querystart) /1000000;
   printf("%2d %-30s %-10s %9d %18d %s\n",
          arg0, self->who, self->db,
          self->connid, this->elapsed, self->query);
   printf("Net read: %d bytes (%d ms) write: %d bytes (%d ms)\n",
               self->netread, (self->netreadcum/1000000),
               self->netwrite, (self->netwritecum/1000000));
}

When executing the above script on a machine with a remote client, you can see that approximately a third of the time spent executing the query is related to writing the query results back to the client.

St Who                            DB            ConnID       Dur microsec Query
 0 root@::ffff:192.168.0.108      test              31               3495 select * from t1 limit 1000000
Net read: 0 bytes (0 ms) write: 10000075 bytes (1220 ms)

5.7.1.14. Keycache Probes

The keycache probes are triggered when using the index key cache used with the MyISAM storage engine. Probes exist to monitor when data is read into the keycache, cached key data is written from the cache into a cached file, or when accessing the keycache.

Keycache usage indicates when data is read or written from the index files into the cache, and can be used to monitor how efficient the memory allocated to the keycache is being used. A high number of keycache reads across a range of queries may indicate that the keycache is too small for size of data being accessed.

keycache-read-start(filepath, bytes, mem_used, mem_free)
keycache-read-block(bytes)
keycache-read-hit()
keycache-read-miss()
keycache-read-done(mem_used, mem_free)
keycache-write-start(filepath, bytes, mem_used, mem_free)
keycache-write-block(bytes)
keycache-write-done(mem_used, mem_free)

When reading data from the index files into the keycache, the process first initializes the read operation (indicated by keycache-read-start), then loads blocks of data (keycache-read-block), and then the read block is either matches the data being identified (keycache-read-hit) or more data needs to be read (keycache-read-miss). Once the read operation has completed, reading stops with the keycache-read-done.

Data will be read from the index file into the keycache only when the specified key is not already within the keycache.

  • keycache-read-start: Triggered when the keycache read operation is started. Data is read from the specified filepath, reading the specified number of bytes. The mem_used and mem_avail indicate memory currently used by the keycache and the amount of memory available within the keycache.

  • keycache-read-block: Triggered when the keycache reads a block of data, of the specified number of bytes, from the index file into the keycache.

  • keycache-read-hit: Triggered when the block of data read from the index file matches the key data requested.

  • keycache-read-miss: Triggered when the block of data read from the index file does not match the key data needed.

  • keycache-read-done: Triggered when the keycache read operation has completed. The mem_used and mem_avail indicate memory currently used by the keycache and the amount of memory available within the keycache.

Keycache writes occur when the index information is updated during an INSERT, UPDATE, or DELETE operation, and the cached key information is flushed back to the index file.

  • keycache-write-start: Triggered when the keycache write operation is started. Data is written to the specified filepath, reading the specified number of bytes. The mem_used and mem_avail indicate memory currently used by the keycache and the amount of memory available within the keycache.

  • keycache-write-block: Triggered when the keycache writes a block of data, of the specified number of bytes, to the index file from the keycache.

  • keycache-write-done: Triggered when the keycache write operation has completed. The mem_used and mem_avail indicate memory currently used by the keycache and the amount of memory available within the keycache.

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