Chapter 5. MySQL Server Administration

Table of Contents

5.1. The MySQL Server
5.1.1. Server Option and Variable Reference
5.1.2. Server Command Options
5.1.3. Server Options for Loading Plugins
5.1.4. Server System Variables
5.1.5. Session System Variables
5.1.6. Using System Variables
5.1.7. Server Status Variables
5.1.8. Server SQL Modes
5.1.9. Server-Side Help
5.1.10. Server Response to Signals
5.1.11. 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. Making MySQL Secure Against Attackers
5.3.3. Security-Related mysqld Options
5.3.4. Security Issues with LOAD DATA LOCAL
5.3.5. 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 Errors
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. Limiting Account Resources
5.5.5. Assigning Account Passwords
5.5.6. Password Security in MySQL
5.5.7. Using SSL for Secure Connections
5.5.8. Connecting to MySQL Remotely from Windows with SSH
5.5.9. Auditing MySQL Account Activity
5.6. Running Multiple MySQL Servers on the Same Machine
5.6.1. Running Multiple Servers on Windows
5.6.2. Running Multiple Servers on Unix
5.6.3. 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:

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

Note

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 12.5.6.17, “SHOW ENGINES Syntax”.

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.

Table 5.1. mysqld Option/Variable Summary

NameCmd-LineOption fileSystem VarStatus VarVar ScopeDynamic
abort-slave-event-countYesYes    
Aborted_clients   YesGlobalNo
Aborted_connects   YesGlobalNo
allow-suspicious-udfsYesYes    
ansiYesYes    
auto_increment_incrementYesYesYes BothYes
auto_increment_offsetYesYesYes BothYes
autocommit  Yes SessionYes
automatic_sp_privileges  Yes GlobalYes
back_logYesYesYes GlobalNo
backup_history_logYesYesYes GlobalYes
backup_history_log_fileYesYesYes GlobalYes
backup_progress_logYesYesYes GlobalYes
backup_progress_log_fileYesYesYes GlobalYes
backup_wait_timeout  Yes SessionYes
backupdirYesYesYes GlobalYes
basedirYesYesYes GlobalNo
big-tablesYesYes  SessionYes
- Variable: big_tables  Yes SessionYes
bind-addressYesYes    
Binlog_cache_disk_use   YesGlobalNo
binlog_cache_sizeYesYesYes GlobalYes
Binlog_cache_use   YesGlobalNo
binlog-do-dbYesYes    
binlog-formatYesYes  BothYes
- Variable: binlog_format  Yes BothYes
binlog-ignore-dbYesYes    
binlog-row-event-max-sizeYesYes    
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_event   YesBothNo
Com_alter_table   YesBothNo
Com_analyze   YesBothNo
Com_backup   YesBothNo
Com_backup_table   YesBothNo
Com_begin   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_table   YesBothNo
Com_create_user   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_table   YesBothNo
Com_drop_user   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_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_rename_table   YesBothNo
Com_repair   YesBothNo
Com_replace   YesBothNo
Com_replace_select   YesBothNo
Com_reset   YesBothNo
Com_restore   YesBothNo
Com_restore_table   YesBothNo
Com_revoke   YesBothNo
Com_revoke_all   YesBothNo
Com_rollback   YesBothNo
Com_savepoint   YesBothNo
Com_select   YesBothNo
Com_set_option   YesBothNo
Com_show_binlog_events   YesBothNo
Com_show_binlogs   YesBothNo
Com_show_charsets   YesBothNo
Com_show_collations   YesBothNo
Com_show_column_types   YesBothNo
Com_show_create_db   YesBothNo
Com_show_create_event   YesBothNo
Com_show_create_table   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_grants   YesBothNo
Com_show_innodb_status   YesBothNo
Com_show_keys   YesBothNo
Com_show_logs   YesBothNo
Com_show_master_status   YesBothNo
Com_show_ndb_status   YesBothNo
Com_show_new_master   YesBothNo
Com_show_open_tables   YesBothNo
Com_show_plugins   YesBothNo
Com_show_privileges   YesBothNo
Com_show_processlist   YesBothNo
Com_show_profile   YesBothNo
Com_show_profiles   YesBothNo
Com_show_slave_hosts   YesBothNo
Com_show_slave_status   YesBothNo
Com_show_status   YesBothNo
Com_show_storage_engines   YesBothNo
Com_show_tables   YesBothNo
Com_show_triggers   YesBothNo
Com_show_variables   YesBothNo
Com_show_warnings   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_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 BothYes
datetime_formatYesYesYes BothYes
debugYesYesYes BothYes
debug_sync  Yes BothYes
debug-sync-timeoutYesYes    
default-storage-engineYesYes    
default-table-typeYesYes    
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    
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      
falconYesYes    
falcon_checkpoint_scheduleYesYesYes GlobalYes
falcon_checksumsYesYesYes GlobalYes
falcon_consistent_readYesYesYes BothYes
falcon_debug_maskYesYesYes GlobalYes
falcon_debug_serverYesYesYes GlobalNo
falcon_disable_fsyncYesYesYes GlobalYes
falcon_gopher_threadsYesYesYes GlobalNo
falcon_index_chill_thresholdYesYesYes GlobalYes
falcon_initial_allocationYesYesYes GlobalYes
falcon_io_threadsYesYesYes GlobalYes
falcon_large_blob_thresholdYesYesYes GlobalNo
falcon_lock_wait_timeoutYesYesYes GlobalYes
falcon_max_transaction_backlogYesYesYes GlobalYes
falcon_page_cache_sizeYesYesYes GlobalNo
falcon_page_sizeYesYesYes GlobalNo
falcon_record_chill_thresholdYesYesYes GlobalYes
falcon_record_memory_maxYesYesYes GlobalYes
falcon_record_scavenge_floorYesYesYes GlobalYes
falcon_record_scavenge_thresholdYesYesYes GlobalYes
falcon_scavenge_scheduleYesYesYes GlobalNo
falcon_serial_log_buffersYesYesYes GlobalNo
falcon_serial_log_dirYesYesYes GlobalNo
falcon_serial_log_priorityYesYesYes GlobalYes
falcon_support_xaYesYesYes GlobalNo
falcon_use_deferred_index_hashYesYesYes GlobalNo
falcon_use_sectorcacheYesYesYes GlobalNo
falcon_use_supernodesYesYesYes GlobalNo
flushYesYesYes GlobalYes
Flush_commands   YesGlobalNo
flush_timeYesYesYes GlobalYes
foreign_key_checks  Yes SessionYes
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_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_query_cache  Yes GlobalNo
have_rtree_keys  Yes GlobalNo
have_ssl  Yes GlobalNo
have_symlink  Yes GlobalNo
helpYesYes    
hostname  Yes GlobalNo
identity  Yes SessionYes
init_connectYesYesYes GlobalYes
init-fileYesYes  GlobalNo
- Variable: init_file  Yes GlobalNo
init_slaveYesYesYes GlobalYes
innodbYesYes    
innodb_adaptive_hash_indexYesYesYes GlobalNo
innodb_additional_mem_pool_sizeYesYesYes GlobalNo
innodb_autoextend_incrementYesYesYes GlobalYes
innodb_autoinc_lock_modeYesYesYes 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_rnd   YesGlobalNo
Innodb_buffer_pool_read_ahead_seq   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_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_io_threadsYesYesYes GlobalNo
innodb_file_per_tableYesYesYes GlobalNo
innodb_flush_log_at_trx_commitYesYesYes GlobalYes
innodb_flush_methodYesYesYes GlobalNo
innodb_force_recoveryYesYesYes GlobalNo
innodb_lock_wait_timeoutYesYesYes GlobalNo
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_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_rollback_on_timeoutYesYesYes GlobalNo
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_stats_on_metadataYesYesYes GlobalYes
innodb_status_fileYesYes    
innodb_support_xaYesYesYes BothYes
innodb_sync_spin_loopsYesYesYes GlobalYes
innodb_table_locksYesYesYes BothYes
innodb_thread_concurrencyYesYesYes GlobalYes
innodb_thread_sleep_delayYesYesYes GlobalYes
insert_id  Yes SessionYes
interactive_timeoutYesYesYes BothYes
join_buffer_sizeYesYesYes BothYes
join_cache_levelYesYesYes 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_page_size  Yes GlobalNo
large-pagesYesYes  GlobalNo
- Variable: large_pages  Yes GlobalNo
last_insert_id  Yes SessionYes
Last_query_cost   YesSessionNo
lc_time_names  Yes BothYes
license  Yes GlobalNo
local_infile  Yes GlobalYes
local-infileYesYes    
- Variable: local_infile      
locked_in_memory  Yes GlobalNo
logYesYesYes GlobalYes
log-backup-outputYesYes  GlobalYes
- Variable: log_backup_output  Yes 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-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
mariaYesYes    
maria-block-sizeYesYes   No
- Variable: maria_block_size  Yes  No
maria-checkpoint-intervalYesYesYes GlobalYes
maria-force-start-after-recovery-failuresYesYes    
maria-log-dir-pathYesYes    
maria-log-file-sizeYesYes  GlobalYes
- Variable: maria_log_file_size  Yes GlobalYes
maria-log-purge-typeYesYes  GlobalYes
- Variable: maria_log_purge_type  Yes GlobalYes
maria-max-sort-file-sizeYesYesYes GlobalYes
maria-page-checksumYesYes  GlobalYes
- Variable: maria_page_checksum  Yes GlobalYes
maria-pagecache-age-thresholdYesYes  GlobalYes
- Variable: maria_pagecache_age_threshold  Yes GlobalYes
maria-pagecache-buffer-sizeYesYes  GlobalNo
- Variable: maria_pagecache_buffer_size  Yes GlobalNo
maria-pagecache-division-limitYesYes  GlobalYes
- Variable: maria_pagecache_division_limit  Yes GlobalYes
maria-recoverYesYes  GlobalYes
- Variable: maria_recover  Yes GlobalYes
maria-repair-threadsYesYes  BothYes
- Variable: maria_repair_threads  Yes BothYes
maria-sort-buffer-sizeYesYes  BothYes
- Variable: maria_sort_buffer_size  Yes BothYes
maria-stats-methodYesYes  BothYes
- Variable: maria_stats_method  Yes BothYes
maria-sync-log-dirYesYes  GlobalYes
- Variable: maria_sync_log_dir  Yes GlobalYes
master-bindYesYesYes  No
master-info-fileYesYes    
master-retry-countYesYes    
max_allowed_packetYesYesYes BothYes
max_binlog_cache_sizeYesYesYes GlobalYes
max-binlog-dump-eventsYesYes    
max_binlog_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_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
min-examined-row-limitYesYesYes BothYes
myisam-block-sizeYesYes    
myisam_data_pointer_sizeYesYesYes GlobalYes
myisam_max_sort_file_sizeYesYesYes GlobalYes
myisam-recoverYesYes    
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_autoincrement_prefetch_szYesYesYes BothYes
Ndb_cluster_node_id   YesBothNo
Ndb_config_from_host   YesBothNo
Ndb_config_from_port   YesBothNo
Ndb_conflict_fn_max   YesGlobalNo
Ndb_conflict_fn_old   YesGlobalNo
ndb_index_stat_cache_entriesYesYes    
ndb_index_stat_enableYesYes    
ndb_index_stat_update_freqYesYes    
Ndb_number_of_data_nodes   YesGlobalNo
ndb_report_thresh_binlog_epoch_slipYesYes    
ndb_report_thresh_binlog_mem_usageYesYes    
ndb_use_transactionsYesYesYes BothYes
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
optimizer_use_mrr  Yes BothYes
pid-fileYesYes  GlobalNo
- Variable: pid_file  Yes GlobalNo
plugin_dirYesYesYes GlobalNo
plugin-loadYesYes    
portYesYesYes GlobalNo
port-open-timeoutYesYes    
preload_buffer_sizeYesYesYes BothYes
Prepared_stmt_count   YesGlobalNo
print-defaultsYes     
profiling  Yes SessionYes
profiling_history_size  Yes BothYes
protocol_version  Yes GlobalNo
pseudo_thread_id  Yes BothYes
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    
- Variable: relay_log_index      
relay-log-info-fileYesYes    
- Variable: relay_log_info_file      
relay_log_purgeYesYesYes GlobalYes
relay_log_recoveryYesYesYes GlobalYes
relay_log_space_limitYesYesYes GlobalNo
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_reply_log_file_pos  Yes GlobalYes
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_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-backup-file-privYesYes  GlobalNo
- Variable: secure_backup_file_priv  Yes GlobalNo
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
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-external-lockingYesYes  GlobalNo
- Variable: skip_external_locking  Yes GlobalNo
skip-falconYesYes    
skip-grant-tablesYesYes    
skip-host-cacheYesYes    
skip-innodbYesYes    
skip-innodb-checksumsYesYes    
skip-lockingYesYes    
skip-log-warningsYes     
skip-name-resolveYesYes    
skip-ndbclusterYesYes    
skip-networkingYesYes  GlobalNo
- Variable: skip_networking  Yes GlobalNo
skip-newYesYes    
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_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
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
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 SessionYes
sql_big_selects  Yes SessionYes
sql_big_tables  Yes SessionYes
sql_buffer_result  Yes SessionYes
sql_log_bin  Yes SessionYes
sql_log_off  Yes SessionYes
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 SessionYes
sql_quote_show_create  Yes SessionYes
sql_safe_updates  Yes SessionYes
sql_select_limit  Yes BothYes
sql_slave_skip_counter  Yes GlobalYes
sql_warnings  Yes SessionYes
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-binlogYesYes  GlobalYes
- Variable: sync_binlog  Yes GlobalYes
sync-frmYesYes  GlobalYes
- Variable: sync_frm  Yes 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
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_sizeYesYesYes GlobalNo
thread_stackYesYesYes GlobalNo
Threads_cached   YesGlobalNo
Threads_connected   YesGlobalNo
Threads_created   YesGlobalNo
Threads_running   YesGlobalNo
time_formatYesYesYes BothYes
time_zoneYesYesYes BothYes
timed_mutexesYesYesYes GlobalYes
timestamp  Yes SessionYes
tmp_table_sizeYesYesYes BothYes
tmpdirYesYesYes GlobalNo
transaction_alloc_block_sizeYesYesYes BothYes
transaction-isolationYesYes    
transaction_prealloc_sizeYesYesYes BothYes
tx_isolation  Yes BothYes
unique_checks  Yes SessionYes
updatable_views_with_limitYesYesYes BothYes
Uptime   YesGlobalNo
Uptime_since_flush_status   YesGlobalNo
use-symbolic-linksYesYes    
userYesYes    
verboseYesYes    
versionYesYesYes 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”.

MySQL Enterprise For expert advice on setting command options, subscribe to the MySQL Enterprise Monitor. For more information, see http://www.mysql.com/products/enterprise/advisors.html.

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.

  • --help, -?

    Command Line Format-?
    Config 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
    Config File Formatallow-suspicious-udfs
    Value Set
    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 21.3.2.6, “User-Defined Function Security Precautions”.

  • --ansi

    Command Line Format--ansi
    Config 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 1.7.3, “Running MySQL in ANSI Mode”, and Section 5.1.8, “Server SQL Modes”.

  • --basedir=path, -b path

    Command Line Format--basedir=name
    Config File Formatbasedir
    Option Sets VariableYes, basedir
    Variable Namebasedir
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

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

  • --big-tables

    Command Line Format--big-tables
    Config File Formatbig-tables
    Option Sets VariableYes, big_tables
    Variable Namebig-tables
    Variable ScopeSession
    Dynamic VariableYes
    Value Set
    Typeboolean

    Allow 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
    Config File Formatbind-address
    Value Set
    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
    Config File Formatbinlog-format
    Option Sets VariableYes, binlog_format
    Variable Namebinlog_format
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeenumeration
    DefaultSTATEMENT
    Valid ValuesROW, STATEMENT, MIXED

    Specify whether to use row-based, statement-based, or mixed replication (mixed is the default in MySQL 6.0). See Section 16.1.2, “Replication Formats”.

    Important

    Setting the binary logging format without enabling binary logging prevents the MySQL server from starting. This is a known issue in MySQL 6.0 which is fixed in MySQL 5.4. (Bug#42928)

  • --bootstrap

    Command Line Format--bootstrap
    Config 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 option. See Section 2.9.2, “Typical configure Options”.

  • --character-sets-dir=path

    Command Line Format--character-sets-dir=name
    Config File Formatcharacter-sets-dir
    Option Sets VariableYes, character_sets_dir
    Variable Namecharacter-sets-dir
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    The directory where character sets are installed. See Section 9.2, “The Character Set Used for Data and Sorting”.

  • --character-set-client-handshake

    Command Line Format--character-set-client-handshake
    Config File Formatcharacter-set-client-handshake
    Value Set
    Typeboolean
    DefaultTRUE

    Don't 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
    Config File Formatcharacter-set-filesystem
    Option Sets VariableYes, character_set_filesystem
    Variable Namecharacter_set_filesystem
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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
    Config File Formatcharacter-set-server
    Option Sets VariableYes, character_set_server
    Variable Namecharacter_set_server
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typestring

    Use charset_name as the default server character set. See Section 9.2, “The Character Set Used for Data and Sorting”. 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
    Config File Formatchroot
    Value Set
    Typefilename

    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
    Config File Formatcollation-server
    Option Sets VariableYes, collation_server
    Variable Namecollation_server
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typestring

    Use collation_name as the default server collation. See Section 9.2, “The Character Set Used for Data and Sorting”.

  • --console

    Command Line Format--console
    Config 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
    Config File Formatcore-file
    Value Set
    Typeboolean
    DefaultTRUE

    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=name
    Config File Formatdatadir
    Option Sets VariableYes, datadir
    Variable Namedatadir
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    The path to the data directory.

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

    Command Line Format--debug[=debug_options]
    Config File Formatdebug
    Variable Namedebug
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typestring
    Default'd:t:o,/tmp/mysqld.trace

    If MySQL is configured with --with-debug, 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 --with-debug 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]

    Version Introduced6.0.6
    Command Line Format--debug-sync-timeout[=#]
    Config File Formatdebug-sync-timeout
    Value Set
    Typenumeric

    Controls whether the Debug Sync facility for testing and debugging is enabled. Use of Debug Sync requires that MySQL be configured with the --enable-debug-sync option (see Section 2.9.2, “Typical configure 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.

    This option was added in MySQL 6.0.6.

  • --default-character-set=charset_name (DEPRECATED)

    Command Line Format--default-character-set=name
    Config File Formatdefault-character-set
    Deprecated5.0
    Value Set
    Typestring

    Use charset_name as the default character set. This option is deprecated in favor of --character-set-server. See Section 9.2, “The Character Set Used for Data and Sorting”.

  • --default-collation=collation_name

    Command Line Format--default-collation=name
    Variable Namedefault-collation
    Variable Scope 
    Dynamic VariableNo
    Deprecated4.1.3
    Value Set
    Typestring

    Use collation_name as the default collation. This option is deprecated in favor of --collation-server. See Section 9.2, “The Character Set Used for Data and Sorting”.

  • --default-storage-engine=type

    Command Line Format--default-storage-engine=name
    Config File Formatdefault-storage-engine

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

  • --default-table-type=type

    Version Removed6.0.8
    Command Line Format--default-table-type=name
    Config File Formatdefault-table-type
    Deprecated5.0, by default-storage-engine
    Value Set
    Typestring

    This option is a deprecated synonym for --default-storage-engine. It has been removed as of MySQL 6.0.8.

  • --default-time-zone=timezone

    Command Line Format--default-time-zone=name
    Config File Formatdefault-time-zone
    Value Set
    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]
    Config File Formatdelay-key-write
    Option Sets VariableYes, delay_key_write
    Variable Namedelay-key-write
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typeenumeration
    DefaultON
    Valid ValuesON, 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 7.5.3, “Tuning Server Parameters”, and Section 13.5.1, “MyISAM Startup Options”.

    Note

    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=name
    Config File Formatdes-key-file

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

  • --enable-named-pipe

    Enable support for named pipes. This option applies only on Windows NT, 2000, XP, and 2003 systems.

  • --enable-pstack

    Command Line Format--enable-pstack
    Config File Formatenable-pstack
    Value Set
    Typeboolean
    DefaultFALSE

    Print a symbolic stack trace on failure.

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

    Command Line Format--engine-condition-pushdown
    Config File Formatengine-condition-pushdown
    Option Sets VariableYes, engine_condition_pushdown
    Variable Nameengine_condition_pushdown
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeboolean
    DefaultON

    Sets the engine_condition_pushdown system variable. For more information, see Section 7.2.7, “Condition Pushdown Optimization”.

  • --event-scheduler[=value]

    Command Line Format--event-scheduler[=value]
    Config File Formatevent-scheduler
    Option Sets VariableYes, event_scheduler
    Variable Nameevent_scheduler
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typeenumeration
    DefaultOFF
    Valid ValuesON, 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]
    Config File Formatexit-info
    Value Set
    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
    Config File Formatexternal-locking
    Option Sets VariableYes, skip_external_locking
    Disabled byskip-external-locking
    Value Set
    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. This option previously was named --enable-locking.

    For more information about external locking, including conditions under which it can and cannot be used, see Section 7.3.5, “External Locking”.

  • --flush

    Command Line Format--flush
    Config File Formatflush
    Variable Nameflush
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    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 B.1.4.2, “What to Do If MySQL Keeps Crashing”.

  • --gdb

    Command Line Format--gdb
    Config File Formatgdb
    Value Set
    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
    Config File Formatgeneral-log
    Option Sets VariableYes, general_log
    Variable Namegeneral_log
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    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=name
    Config File Formatinit-file
    Option Sets VariableYes, init_file
    Variable Nameinit_file
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    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 option. See Section 2.9.2, “Typical configure Options”.

  • --innodb-xxx

    The InnoDB options are listed in Section 13.7.3, “InnoDB Startup Options and System Variables”.

  • --language=lang_name, -L lang_name

    Command Line Format--language=name
    Config File Formatlanguage
    Option Sets VariableYes, language
    Variable Namelanguage
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename
    Default/usr/local/mysql/share/mysql/english/

    Return client error messages in the given language. 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 9.3, “Setting the Error Message Language”.

  • --large-pages

    Command Line Format--large-pages
    Config File Formatlarge-pages
    Option Sets VariableYes, large_pages
    Variable Namelarge_pages
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform Specificlinux
    Value Set
    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.

    Currently, MySQL supports only the Linux implementation of large page support (which is called HugeTLB in Linux). See Section 7.5.9, “Enabling Large Page Support”.

    --large-pages is disabled by default.

  • --log[=file_name], -l [file_name]

    Command Line Format--log[=name]
    Config File Formatlog
    Option Sets VariableYes, log
    Variable Namelog
    Variable ScopeGlobal
    Dynamic VariableYes
    Deprecated5.1.29, by general-log
    Value Set
    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. See Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”, and Section 5.2.3, “The General Query Log”.

    As of MySQL 6.0.8, the --log option is deprecated and will be removed (along with the log system variable) in MySQL 7.0. 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-backup-output[=value,...]

    Version Introduced6.0.8
    Command Line Format--log-backup-output[=name]
    Config File Formatlog-backup-output
    Option Sets VariableYes, log_backup_output
    Variable Namelog_backup_output
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typeenumeration
    DefaultTABLE
    Valid ValuesTABLE, FILE, NONE

    This option determines the destination for MySQL Backup history and progress 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 TABLE. TABLE selects logging to the backup_history and backup_progress 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 --backup_history_log and --backup_progress_log options. For FILE logging, the default log files are backup_history.log and backup_progress.log in the data directory. To change the names, set the global backup_history_log_file and backup_progress_log_file system variables. For more information, see Section 6.3.3.1, “MySQL Backup Log Control”.

    This option was added in MySQL 6.0.8.

  • --log-error[=file_name]

    Command Line Format--log-error[=name]
    Config File Formatlog-error
    Option Sets VariableYes, log_error
    Variable Namelog_error
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    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]
    Config File Formatlog-isam
    Value Set
    Typefilename

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

  • --log-long-format (DEPRECATED)

    Command Line Format--log-long-format
    Config 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-output[=value,...]

    Command Line Format--log-output[=name]
    Config File Formatlog-output
    Option Sets VariableYes, log_output
    Variable Namelog_output
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typeenumeration
    DefaultFILE
    Valid ValuesTABLE, 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 selects 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. (Before MySQL 6.0.8, enable the logs with the --log and --log-slow-queries options. The options take an optional file name argument to specify the log file name.) 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
    Config File Formatlog-queries-not-using-indexes
    Option Sets VariableYes, log_queries_not_using_indexes
    Variable Namelog_queries_not_using_indexes
    Variable ScopeGlobal
    Dynamic VariableYes
    Deprecated5.1.29, by slow-query-log
    Value Set
    Typeboolean

    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
    Config File Formatlog-short-format
    Value Set
    Typeboolean
    DefaultFALSE

    Originally intended to log less information to the binary log and slow query log, if they have been activated. However, this option is not operational.

  • --log-slow-admin-statements

    Command Line Format--log-slow-admin-statements
    Config File Formatlog-slow-admin-statements
    Value Set
    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]
    Config File Formatlog-slow-queries
    Option Sets VariableYes, log_slow_queries
    Variable Namelog_slow_queries
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    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”.

    As of MySQL 6.0.8, the --log-slow-queries option is deprecated and will be removed (along with the log_slow_queries system variable) in MySQL 7.0. 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
    Config File Formatlog-tc
    Value Set
    Typefilename
    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=#
    Config File Formatlog-tc-size
    Value Set
    Platform Bit Size32
    Typenumeric
    Default24576
    Max Value4294967295
    Value Set
    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[=#]
    Config File Formatlog-warnings
    Option Sets VariableYes, log_warnings
    Variable Namelog_warnings
    Variable ScopeBoth
    Dynamic VariableYes
    Disabled byskip-log-warnings
    Value Set
    Platform Bit Size32
    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 B.1.2.11, “Communication Errors 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.

  • --low-priority-updates

    Command Line Format--low-priority-updates
    Config File Formatlow-priority-updates
    Option Sets VariableYes, low_priority_updates
    Variable Namelow_priority_updates
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeboolean
    DefaultFALSE

    Give table-modifying operations (INSERT, REPLACE, DELETE, UPDATE) lower priority than selects. This can also be done via {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 7.3.2, “Table Locking Issues”.

  • --min-examined-row-limit=number

    Version Introduced6.0.4
    Command Line Format--min-examined-row-limit=#
    Config File Formatmin-examined-row-limit
    Variable Namemin_examined_row_limit
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Platform Bit Size32
    Typenumeric
    Default0
    Range0-4294967295
    Value Set
    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.

    This option was introduced in MySQL 6.0.4.

  • --memlock

    Command Line Format--memlock
    Config File Formatmemlock
    Variable Namelocked_in_memory
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    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 5.3.5, “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=#
    Config File Formatmyisam-block-size
    Value Set
    Typenumeric
    Default1024
    Range1024-16384

    The block size to be used for MyISAM index pages.

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

    Command Line Format--myisam-recover[=name]
    Config File Formatmyisam-recover
    Value Set
    Typeenumeration
    DefaultOFF
    Valid ValuesDEFAULT, BACKUP, FORCE, QUICK

    Set the MyISAM storage engine recovery mode. The option value is any combination of the values of DEFAULT, 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 wasn't 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.

    OptionDescription
    DEFAULTRecovery 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.
    QUICKDon't check the rows in the table if there aren't 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.

    See Section 13.5.1, “MyISAM Startup Options”.

  • --old-alter-table

    Command Line Format--old-alter-table
    Config File Formatold-alter-table
    Option Sets VariableYes, old_alter_table
    Variable Nameold-alter-table
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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 12.1.6, “ALTER TABLE Syntax”.

  • --old-passwords

    Command Line Format--old_passwords
    Config File Formatold-passwords
    Option Sets VariableYes, old_passwords
    Variable Nameold_passwords
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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 5.5.6.3, “Password Hashing in MySQL”.

  • --old-style-user-limits

    Command Line Format--old-style-user-limits
    Config File Formatold-style-user-limits
    Value Set
    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, “Limiting Account Resources”.

  • --one-thread

    Command Line Format--one-thread
    Config 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; use --thread_handling=no-threads instead.

  • --open-files-limit=count

    Command Line Format--open-files-limit=#
    Config File Formatopen-files-limit
    Option Sets VariableYes, open_files_limit
    Variable Nameopen_files_limit
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    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.

  • --pid-file=path

    Command Line Format--pid-file=name
    Config File Formatpid-file
    Option Sets VariableYes, pid_file
    Variable Namepid_file
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    The path name of the process ID file. This file is used by other programs such as mysqld_safe to determine the server's process ID.

  • --plugin-load=plugin_list

    Command Line Format--plugin-load=plugin_list
    Config File Formatplugin-load
    Value Set
    Typestring

    Under normal startup, the server determines which plugins to load by reading the mysql.plugins system table. This option enables plugins to be loaded even when --skip-grant-tables is given (which tells the server not to read system tables). This option also enables plugins to be loaded at startup under configurations when plugins cannot be loaded at runtime.

    The option value is a colon-separated list of name=plugin_library values. 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.

    The plugins are loaded for a single invocation of mysqld only. After a restart, the plugins are 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.

  • --port=port_num, -P port_num

    Command Line Format--port=#
    Config File Formatport
    Option Sets VariableYes, port
    Variable Nameport
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    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=#
    Config File Formatport-open-timeout
    Value Set
    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.

  • --safe-mode

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

    Skip some optimization stages.

  • --safe-show-database (DEPRECATED)

    Command Line Format--safe-show-database
    Config File Formatsafe-show-database
    Variable Namesafe_show_database
    Variable ScopeGlobal
    Dynamic VariableYes
    Deprecated4.0.2
    Value Set
    Typeboolean

    See Section 5.4.1, “Privileges Provided by MySQL”.

  • --safe-user-create

    Command Line Format--safe-user-create
    Config File Formatsafe-user-create
    Value Set
    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
    Config File Formatsecure-auth
    Option Sets VariableYes, secure_auth
    Variable Namesecure_auth
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typeboolean
    DefaultFALSE

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

  • --secure-backup-file-priv=path

    Command Line Format--secure-backup-file-priv
    Config File Formatsecure-backup-file-priv
    Option Sets VariableYes, secure_backup_file_priv
    Variable Namesecure_backup_file_priv
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typestring

    This option limits the effect of the BACKUP DATABASE and RESTORE statements to work only with files in the specified directory. This option was added in MySQL 6.0.11; in older releases, use --secure-file-priv instead.

  • --secure-file-priv=path

    Command Line Format--secure-file-priv
    Config File Formatsecure-file-priv
    Option Sets VariableYes, secure_file_priv
    Variable Namesecure_file_priv
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    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. Before MySQL 6.0.11, it also applies to the BACKUP DATABASE and RESTORE statements; as of 6.0.11, --secure-backup-file-priv applies to those statements.

  • --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 7.3.3, “Concurrent Inserts”.

  • --skip-external-locking

    Do not use external locking (system locking). For more information about external locking, including conditions under which it can and cannot be used, see Section 7.3.5, “External Locking”.

    External locking has been disabled by default since MySQL 4.0.

  • --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, 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 option. See Section 2.9.2, “Typical configure 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 7.5.11, “How MySQL Uses DNS”.

  • --skip-innodb

    Disable the InnoDB storage engine. This saves memory and disk space and might speed up some operations. Do not use this option if you require InnoDB tables.

  • --skip-name-resolve

    Do not resolve host names when checking client connections. Use only IP numbers. If you use this option, all Host column values in the grant tables must be IP numbers or localhost. See Section 7.5.11, “How MySQL Uses DNS”.

  • --skip-networking

    Don't listen for TCP/IP connections at all. All interaction with mysqld must be made via 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 allowed. See Section 7.5.11, “How MySQL Uses DNS”.

  • --ssl*

    Options that begin with --ssl specify whether to allow clients to connect via SSL and indicate where to find SSL keys and certificates. See Section 5.5.7.3, “SSL Command Options”.

  • --standalone

    Command Line Format--standalone
    Config File Formatstandalone
    Platform Specificwindows

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

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

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

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

  • --skip-safemalloc

    Command Line Format--skip-safe-malloc
    Config File Formatskip-safemalloc

    If MySQL is configured with --with-debug=full, 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 don't need it by using the --skip-safemalloc option.

  • --skip-show-database

    Command Line Format--skip-show-database
    Config 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 allowed only to users who have the SHOW DATABASES privilege, and the statement displays all database names. Without this option, SHOW DATABASES is allowed 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
    Config File Formatskip-stack-trace

    Don't 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

    Version Removed6.0.8
    Command Line Format--skip-thread-priority
    Config File Formatskip-thread-priority
    Deprecated5.1.29

    Disable using thread priorities for faster response time. This option was removed in MySQL 6.0.8

  • --slow-query-log[={0|1}]

    Command Line Format--slow-query-log
    Config File Formatslow-query-log
    Option Sets VariableYes, slow_query_log
    Variable Nameslow_query_log
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    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.

  • --socket=path

    Command Line Format--socket=name
    Config File Formatsocket
    Option Sets VariableYes, socket
    Variable Namesocket
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename
    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. 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
    Config File Formatsql-mode
    Option Sets VariableYes, sql_mode
    Variable Namesql_mode
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeset
    Default''
    Valid ValuesALLOW_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 5.1.8, “Server SQL Modes”.

  • --sysdate-is-now

    Command Line Format--sysdate-is-now
    Config File Formatsysdate-is-now
    Value Set
    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 11.6, “Date and Time Functions” and for SET TIMESTAMP in Section 5.1.5, “Session System Variables”.

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

    Command Line Format--tc-heuristic-recover=name
    Config File Formattc-heuristic-recover
    Value Set
    Typeenumeration
    Valid ValuesCOMMIT, RECOVER

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

  • --temp-pool

    Command Line Format--temp-pool
    Config File Formattemp-pool
    Value Set
    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. As of MySQL 6.0.10, this option is ignored except on Linux.

  • --transaction-isolation=level

    Command Line Format--transaction-isolation=name
    Config File Formattransaction-isolation
    Value Set
    Typeenumeration
    Valid ValuesREAD-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 12.4.6, “SET TRANSACTION Syntax”.

  • --tmpdir=path, -t path

    Command Line Format--tmpdir=name
    Config File Formattmpdir
    Option Sets VariableYes, tmpdir
    Variable Nametmpdir
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    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, NetWare, and OS/2. 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 B.1.4.4, “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
    Config File Formatuser
    Value Set
    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 allowable value if only certain values are allowed.

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 12.5.5, “SET Syntax”.

Section 5.1.4, “Server System Variables”, provides a full description for all variables, and additional information for setting them at server startup and runtime. Section 7.5.3, “Tuning Server Parameters”, includes information on optimizing the server by tuning system variables.

5.1.3. Server Options for Loading Plugins

The server can load plugins under the control of startup options. For example, many storage engines can be built in pluggable form and loaded when the server starts. In the following descriptions, plugin_name stands for a plugin name such as innodb.

Options to load plugins are boolean options and are handled like other 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

Suppose that CSV, InnoDB, and ARCHIVE are built as pluggable storage engines and that you want the server to load CSV and InnoDB but not ARCHIVE at startup. To accomplish that, use these lines in an option file:

[mysqld]
csv
innodb
skip-archive

Plugins can also be loaded at runtime, via the INSTALL PLUGIN statement (see Section 12.5.4.3, “INSTALL PLUGIN Syntax”).

5.1.4. 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 6.0 releases. For historical information concerning their implementation, please see http://dev.mysql.com/doc/refman/5.1/en/, 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. mysqld System Variable Summary

NameCmd-LineOption fileSystem VarVar ScopeDynamic
auto_increment_incrementYesYesYesBothYes
auto_increment_offsetYesYesYesBothYes
autocommit  YesSessionYes
automatic_sp_privileges  YesGlobalYes
back_logYesYesYesGlobalNo
backup_history_logYesYesYesGlobalYes
backup_history_log_fileYesYesYesGlobalYes
backup_progress_logYesYesYesGlobalYes
backup_progress_log_fileYesYesYesGlobalYes
backup_wait_timeout  YesSessionYes
backupdirYesYesYesGlobalYes
basedirYesYesYesGlobalNo
big-tablesYesYes  Yes
- Variable: big_tables  YesSessionYes
binlog_cache_sizeYesYesYesGlobalYes
binlog-formatYesYes  Yes
- Variable: binlog_format  YesBothYes
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  YesBothYes
datetime_formatYesYesYesBothYes
debugYesYesYesBothYes
debug_sync  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
falcon_checkpoint_scheduleYesYesYesGlobalYes
falcon_checksumsYesYesYesGlobalYes
falcon_consistent_readYesYesYesBothYes
falcon_debug_maskYesYesYesGlobalYes
falcon_debug_serverYesYesYesGlobalNo
falcon_disable_fsyncYesYesYesGlobalYes
falcon_gopher_threadsYesYesYesGlobalNo
falcon_index_chill_thresholdYesYesYesGlobalYes
falcon_initial_allocationYesYesYesGlobalYes
falcon_io_threadsYesYesYesGlobalYes
falcon_large_blob_thresholdYesYesYesGlobalNo
falcon_lock_wait_timeoutYesYesYesGlobalYes
falcon_max_transaction_backlogYesYesYesGlobalYes
falcon_page_cache_sizeYesYesYesGlobalNo
falcon_page_sizeYesYesYesGlobalNo
falcon_record_chill_thresholdYesYesYesGlobalYes
falcon_record_memory_maxYesYesYesGlobalYes
falcon_record_scavenge_floorYesYesYesGlobalYes
falcon_record_scavenge_thresholdYesYesYesGlobalYes
falcon_scavenge_scheduleYesYesYesGlobalNo
falcon_serial_log_buffersYesYesYesGlobalNo
falcon_serial_log_dirYesYesYesGlobalNo
falcon_serial_log_priorityYesYesYesGlobalYes
falcon_support_xaYesYesYesGlobalNo
falcon_use_deferred_index_hashYesYesYesGlobalNo
falcon_use_sectorcacheYesYesYesGlobalNo
falcon_use_supernodesYesYesYesGlobalNo
flushYesYesYesGlobalYes
flush_timeYesYesYesGlobalYes
foreign_key_checks  YesSessionYes
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_query_cache  YesGlobalNo
have_rtree_keys  YesGlobalNo
have_ssl  YesGlobalNo
have_symlink  YesGlobalNo
hostname  YesGlobalNo
identity  YesSessionYes
init_connectYesYesYesGlobalYes
init-fileYesYes  No
- Variable: init_file  YesGlobalNo
init_slaveYesYesYesGlobalYes
innodb_adaptive_hash_indexYesYesYesGlobalNo
innodb_additional_mem_pool_sizeYesYesYesGlobalNo
innodb_autoextend_incrementYesYesYesGlobalYes
innodb_autoinc_lock_modeYesYesYesGlobalNo
innodb_buffer_pool_sizeYesYesYesGlobalNo
innodb_checksumsYesYesYesGlobalNo
innodb_commit_concurrencyYesYesYesGlobalYes
innodb_concurrency_ticketsYesYesYesGlobalYes
innodb_data_file_pathYesYesYesGlobalNo
innodb_data_home_dirYesYesYesGlobalNo
innodb_doublewriteYesYesYesGlobalNo
innodb_fast_shutdownYesYesYesGlobalYes
innodb_file_io_threadsYesYesYesGlobalNo
innodb_file_per_tableYesYesYesGlobalNo
innodb_flush_log_at_trx_commitYesYesYesGlobalYes
innodb_flush_methodYesYesYesGlobalNo
innodb_force_recoveryYesYesYesGlobalNo
innodb_lock_wait_timeoutYesYesYesGlobalNo
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_open_filesYesYesYesGlobalNo
innodb_rollback_on_timeoutYesYesYesGlobalNo
innodb_stats_on_metadataYesYesYesGlobalYes
innodb_support_xaYesYesYesBothYes
innodb_sync_spin_loopsYesYesYesGlobalYes
innodb_table_locksYesYesYesBothYes
innodb_thread_concurrencyYesYesYesGlobalYes
innodb_thread_sleep_delayYesYesYesGlobalYes
insert_id  YesSessionYes
interactive_timeoutYesYesYesBothYes
join_buffer_sizeYesYesYesBothYes
join_cache_levelYesYesYesBothYes
keep_files_on_createYesYesYesBothYes
key_buffer_sizeYesYesYesGlobalYes
key_cache_age_thresholdYesYesYesGlobalYes
key_cache_block_sizeYesYesYesGlobalYes
key_cache_division_limitYesYesYesGlobalYes
languageYesYesYesGlobalNo
large_page_size  YesGlobalNo
large-pagesYesYes  No
- Variable: large_pages  YesGlobalNo
last_insert_id  YesSessionYes
lc_time_names  YesBothYes
license  YesGlobalNo
local_infile  YesGlobalYes
locked_in_memory  YesGlobalNo
logYesYesYesGlobalYes
log-backup-outputYesYes  Yes
- Variable: log_backup_output  YesGlobalYes
log_bin  YesGlobalNo
log-binYesYesYesGlobalNo
log-bin-trust-function-creatorsYesYes  Yes
- Variable: log_bin_trust_function_creators  YesGlobalYes
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
maria-block-sizeYesYes  No
- Variable: maria_block_size  Yes No
maria-checkpoint-intervalYesYesYesGlobalYes
maria-log-file-sizeYesYes  Yes
- Variable: maria_log_file_size  YesGlobalYes
maria-log-purge-typeYesYes  Yes
- Variable: maria_log_purge_type  YesGlobalYes
maria-max-sort-file-sizeYesYesYesGlobalYes
maria-page-checksumYesYes  Yes
- Variable: maria_page_checksum  YesGlobalYes
maria-pagecache-age-thresholdYesYes  Yes
- Variable: maria_pagecache_age_threshold  YesGlobalYes
maria-pagecache-buffer-sizeYesYes  No
- Variable: maria_pagecache_buffer_size  YesGlobalNo
maria-pagecache-division-limitYesYes  Yes
- Variable: maria_pagecache_division_limit  YesGlobalYes
maria-recoverYesYes  Yes
- Variable: maria_recover  YesGlobalYes
maria-repair-threadsYesYes  Yes
- Variable: maria_repair_threads  YesBothYes
maria-sort-buffer-sizeYesYes  Yes
- Variable: maria_sort_buffer_size  YesBothYes
maria-stats-methodYesYes  Yes
- Variable: maria_stats_method  YesBothYes
maria-sync-log-dirYesYes  Yes
- Variable: maria_sync_log_dir  YesGlobalYes
master-bindYesYesYes No
max_allowed_packetYesYesYesBothYes
max_binlog_cache_sizeYesYesYesGlobalYes
max_binlog_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_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
min-examined-row-limitYesYesYesBothYes
myisam_data_pointer_sizeYesYesYesGlobalYes
myisam_max_sort_file_sizeYesYesYesGlobalYes
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_use_transactionsYesYesYesBothYes
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
optimizer_use_mrr  YesBothYes
pid-fileYesYes  No
- Variable: pid_file  YesGlobalNo
plugin_dirYesYesYesGlobalNo
portYesYesYesGlobalNo
preload_buffer_sizeYesYesYesBothYes
profiling  YesSessionYes
profiling_history_size  YesBothYes
protocol_version  YesGlobalNo
pseudo_thread_id  YesBothYes
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_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_reply_log_file_pos  YesGlobalYes
rpl_semi_sync_master_timeout  YesGlobalYes
rpl_semi_sync_master_trace_level  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-backup-file-privYesYes  No
- Variable: secure_backup_file_priv  YesGlobalNo
secure-file-privYesYes  No
- Variable: secure_file_priv  YesGlobalNo
server-idYesYes  Yes
- Variable: server_id  YesGlobalYes
shared_memory  YesGlobalNo
shared_memory_base_name  YesGlobalNo
skip-external-lockingYesYes  No
- Variable: skip_external_locking  YesGlobalNo
skip-networkingYesYes  No
- Variable: skip_networking  YesGlobalNo
skip-show-databaseYesYes  No
- Variable: skip_show_database  YesGlobalNo
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
slow_launch_timeYesYesYesGlobalYes
slow-query-logYesYes  Yes
- Variable: slow_query_log  YesGlobalYes
slow_query_log_fileYesYesYesGlobalYes
socketYesYesYesGlobalNo
sort_buffer_sizeYesYesYesBothYes
sql_auto_is_null  YesSessionYes
sql_big_selects  YesSessionYes
sql_big_tables  YesSessionYes
sql_buffer_result  YesSessionYes
sql_log_bin  YesSessionYes
sql_log_off  YesSessionYes
sql_log_update  YesSessionYes
sql_low_priority_updates  YesBothYes
sql_max_join_size  YesBothYes
sql-modeYesYes  Yes
- Variable: sql_mode  YesBothYes
sql_notes  YesSessionYes
sql_quote_show_create  YesSessionYes
sql_safe_updates  YesSessionYes
sql_select_limit  YesBothYes
sql_slave_skip_counter  YesGlobalYes
sql_warnings  YesSessionYes
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-binlogYesYes  Yes
- Variable: sync_binlog  YesGlobalYes
sync-frmYesYes  Yes
- Variable: sync_frm  YesGlobalYes
sync-master-infoYesYesYesGlobalYes
sync-relay-logYesYesYesGlobalYes
sync-relay-log-infoYesYesYesGlobalYes
system_time_zone  YesGlobalNo
table_definition_cacheYesYesYesGlobalYes
table_lock_wait_timeoutYesYesYesGlobalYes
table_open_cacheYesYesYesGlobalYes
thread_cache_sizeYesYesYesGlobalYes
thread_concurrencyYesYesYesGlobalNo
thread_handlingYesYesYesGlobalNo
thread_pool_sizeYesYesYesGlobalNo
thread_stackYesYesYesGlobalNo
time_formatYesYesYesBothYes
time_zoneYesYesYesBothYes
timed_mutexesYesYesYesGlobalYes
timestamp  YesSessionYes
tmp_table_sizeYesYesYesBothYes
tmpdirYesYesYesGlobalNo
transaction_alloc_block_sizeYesYesYesBothYes
transaction_prealloc_sizeYesYesYesBothYes
tx_isolation  YesBothYes
unique_checks  YesSessionYes
updatable_views_with_limitYesYesYesBothYes
versionYesYesYesGlobalNo
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:

Note

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, 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.

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

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.

  • automatic_sp_privileges

    Variable Nameautomatic_sp_privileges
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    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 when the creator drops the routine. If automatic_sp_privileges is 0, the server does not automatically add or drop these privileges.

  • backup_history_log

    Version Introduced6.0.8
    Command Line Format--backup_history_log
    Config File Formatbackup_history_log
    Option Sets VariableYes, backup_history_log
    Variable Namebackup_history_log
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typeboolean
    DefaultON

    Whether the MySQL Backup history log is enabled. The value can be 0 (or OFF) to disable the log or 1 (or ON) to enable the log. The destination for log output is controlled by the log_backup_output system variable; if that value is NONE, no log entries are written even if the log is enabled. This variable was added in MySQL 6.0.8.

  • backup_history_log_file

    Version Introduced6.0.8
    Command Line Format--backup_history_log_file
    Config File Formatbackup_history_log_file
    Option Sets VariableYes, backup_history_log_file
    Variable Namebackup_history_log_file
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typefilename
    Defaultbackup_history.log

    The name of the MySQL Backup history log file. The default value is backup_history.log. This variable was added in MySQL 6.0.8.

  • backup_progress_log

    Version Introduced6.0.8
    Command Line Format--backup_progress_log
    Config File Formatbackup_progress_log
    Option Sets VariableYes, backup_progress_log
    Variable Namebackup_progress_log
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typeboolean
    DefaultON

    Whether the MySQL Backup progress log is enabled. The value can be 0 (or OFF) to disable the log or 1 (or ON) to enable the log. The destination for log output is controlled by the log_backup_output system variable; if that value is NONE, no log entries are written even if the log is enabled. This variable was added in MySQL 6.0.8.

  • backup_progress_log_file

    Version Introduced6.0.8
    Command Line Format--backup_progress_log_file
    Config File Formatbackup_progress_log_file
    Option Sets VariableYes, backup_progress_log_file
    Variable Namebackup_progress_log_file
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typefilename
    Defaultbackup_progress.log

    The name of the MySQL Backup progress log file. The default value is backup_progress.log. This variable was added in MySQL 6.0.8.

  • back_log

    Command Line Format--back_log=#
    Config File Formatback_log
    Option Sets VariableYes, back_log
    Variable Nameback_log
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    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.

  • backupdir

    Version Introduced6.0.7
    Command Line Format--backupdir=name
    Config File Formatbackupdir
    Option Sets VariableYes, backupdir
    Variable Namebackupdir
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typefilename

    The path to the default image file directory for BACKUP DATABASE and RESTORE operations. If an image file is named as a relative path name, it is interpreted relative to the value of backupdir. If the value of backupdir is itself a relative path name, its value is interpreted relative to the data directory. The default value is the data directory.

    If backupdir is set to a nonexistent path, BACKUP DATABASE and RESTORE cannot be executed. The same is true if backupdir references a symbolic link that points at a nonexistent path. Specifying the backup image file name as an absolute path name does not help.

    If backupdir is set to an existing plain file or pipe, BACKUP DATABASE and RESTORE fail if the value is a relative path, unless it starts with a leading ../ component or unless the backup image file name is given as an absolute path. The same is true if backupdir references a symbolic link that points at an existent plain file or pipe.

    This variable was added in MySQL 6.0.7.

  • basedir

    Command Line Format--basedir=name
    Config File Formatbasedir
    Option Sets VariableYes, basedir
    Variable Namebasedir
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    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.

  • bulk_insert_buffer_size

    Command Line Format--bulk_insert_buffer_size=#
    Config File Formatbulk_insert_buffer_size
    Option Sets VariableYes, bulk_insert_buffer_size
    Variable Namebulk_insert_buffer_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Platform Bit Size32
    Typenumeric
    Default8388608
    Range0-4294967295
    Value Set
    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 ScopeBoth
    Dynamic VariableYes
    Value Set
    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.

  • character_set_connection

    Variable Namecharacter_set_connection
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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 ScopeBoth
    Dynamic VariableYes
    FootnoteThis option is dynamic, but only the server should set this information. You should not set the value of this variable manually.
    Value Set
    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
    Config File Formatcharacter-set-filesystem
    Option Sets VariableYes, character_set_filesystem
    Variable Namecharacter_set_filesystem
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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 allowed, 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 ScopeBoth
    Dynamic VariableYes
    Value Set
    Typestring

    The character set used for returning query results to the client.

  • character_set_server

    Command Line Format--character-set-server
    Config File Formatcharacter-set-server
    Option Sets VariableYes, character_set_server
    Variable Namecharacter_set_server
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typestring

    The server's default character set.

  • character_set_system

    Variable Namecharacter_set_system
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    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=name
    Config File Formatcharacter-sets-dir
    Option Sets VariableYes, character_sets_dir
    Variable Namecharacter-sets-dir
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    The directory where character sets are installed.

  • collation_connection

    Variable Namecollation_connection
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typestring

    The collation of the connection character set.

  • collation_database

    Variable Namecollation_database
    Variable ScopeBoth
    Dynamic VariableYes
    FootnoteThis option is dynamic, but only the server should set this information. You should not set the value of this variable manually.
    Value Set
    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
    Config File Formatcollation-server
    Option Sets VariableYes, collation_server
    Variable Namecollation_server
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typestring

    The server's default collation.

  • completion_type

    Command Line Format--completion_type=#
    Config File Formatcompletion_type
    Option Sets VariableYes, completion_type
    Variable Namecompetion_type
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default0
    Valid Values0, 1, 2

    The transaction completion type:

    • If the value is 0 (the default), COMMIT and ROLLBACK are unaffected.

    • If the value is 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.)

    • If the value is 2, COMMIT and ROLLBACK are equivalent to COMMIT RELEASE and ROLLBACK RELEASE, respectively. (The server disconnects after terminating the transaction.)

  • concurrent_insert

    Command Line Format--concurrent_insert[=#]
    Config File Formatconcurrent_insert
    Option Sets VariableYes, concurrent_insert
    Variable Nameconcurrent_insert
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default1
    Valid Values0, 1, 2

    If 1 (the default), MySQL allows INSERT and SELECT statements to run concurrently for MyISAM tables that have no free blocks in the middle of the data file. You can turn this option off by starting mysqld with --safe-mode or --skip-new.

    This variable can take three integer values.

    ValueDescription
    0Off
    1(Default) Enables concurrent insert for MyISAM tables that don't have holes
    2Enables 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 7.3.3, “Concurrent Inserts”.

  • connect_timeout

    Command Line Format--connect_timeout=#
    Config File Formatconnect_timeout
    Option Sets VariableYes, connect_timeout
    Variable Nameconnect_timeout
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    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=name
    Config File Formatdatadir
    Option Sets VariableYes, datadir
    Variable Namedatadir
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    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]
    Config File Formatdebug
    Variable Namedebug
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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

    Version Introduced6.0.6
    Variable Namedebug_sync
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typestring

    This variable is the user interface to the Debug Sync facility. Use of Debug Sync requires that MySQL be configured with the --enable-debug-sync option (see Section 2.9.2, “Typical configure 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.

    This variable was added in MySQL 6.0.6.

  • default_week_format

    Command Line Format--default_week_format=#
    Config File Formatdefault_week_format
    Option Sets VariableYes, default_week_format
    Variable Namedefault_week_format
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default0
    Range0-7

    The default mode value to use for the WEEK() function. See Section 11.6, “Date and Time Functions”.

  • delay_key_write

    Command Line Format--delay-key-write[=name]
    Config File Formatdelay-key-write
    Option Sets VariableYes, delay_key_write
    Variable Namedelay-key-write
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typeenumeration
    DefaultON
    Valid ValuesON, 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.

    OptionDescription
    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 option (for example, --myisam-recover=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=#
    Config File Formatdelayed_insert_limit
    Option Sets VariableYes, delayed_insert_limit
    Variable Namedelayed_insert_limit
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Platform Bit Size32
    Typenumeric
    Default100
    Range1-4294967295
    Value Set
    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 allows them to execute before continuing to insert delayed rows.

  • delayed_insert_timeout

    Command Line Format--delayed_insert_timeout=#
    Config File Formatdelayed_insert_timeout
    Option Sets VariableYes, delayed_insert_timeout
    Variable Namedelayed_insert_timeout
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    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=#
    Config File Formatdelayed_queue_size
    Option Sets VariableYes, delayed_queue_size
    Variable Namedelayed_queue_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Platform Bit Size32
    Typenumeric
    Default1000
    Range1-4294967295
    Value Set
    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=#
    Config File Formatdiv_precision_increment
    Option Sets VariableYes, div_precision_increment
    Variable Namediv_precision_increment
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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

    Command Line Format--engine-condition-pushdown
    Config File Formatengine-condition-pushdown
    Option Sets VariableYes, engine_condition_pushdown
    Variable Nameengine_condition_pushdown
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeboolean
    DefaultON

    When the value of this variable is 0 (OFF), a query such as SELECT * FROM t WHERE mycol = 42, where mycol is a nonindexed column, is executed as a full table scan. The storage engine sends every row to the MySQL server, which applies the WHERE condition. If engine_condition_pushdown is set to 1 (ON), the condition is “pushed down” to the storage engine, which uses the condition to perform the scan, and sends back to the MySQL server only those rows that match the condition. By default, this variable is OFF.

    In MySQL 6.0, this variable can be used only with the MyISAM storage engine. It may be implemented for additional storage engines in future MySQL releases.

    For more information, see Section 7.2.7, “Condition Pushdown Optimization”.

  • event_scheduler

    Command Line Format--event-scheduler[=value]
    Config File Formatevent-scheduler
    Option Sets VariableYes, event_scheduler
    Variable Nameevent_scheduler
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typeenumeration
    DefaultOFF
    Valid ValuesON, 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=#
    Config File Formatexpire_logs_days
    Option Sets VariableYes, expire_logs_days
    Variable Nameexpire_logs_days
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default0
    Range0-99

    The number of days for automatic binary log removal. The default is 0, which means “no automatic removal.” Possible removals happen at startup and at binary log rotation.

  • flush

    Command Line Format--flush
    Config File Formatflush
    Variable Nameflush
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    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 B.1.4.2, “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=#
    Config File Formatflush_time
    Option Sets VariableYes, flush_time
    Variable Nameflush_time
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default0
    Min Value0
    Value Set
    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.

  • ft_boolean_syntax

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

    The list of operators supported by boolean full-text searches performed using IN BOOLEAN MODE. See Section 11.8.2, “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 allowed 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=#
    Config File Formatft_max_word_len
    Option Sets VariableYes, ft_max_word_len
    Variable Nameft_max_word_len
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typenumeric
    Min Value10

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

    Note

    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=#
    Config File Formatft_min_word_len
    Option Sets VariableYes, ft_min_word_len
    Variable Nameft_min_word_len
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typenumeric
    Default4
    Min Value1

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

    Note

    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=#
    Config File Formatft_query_expansion_limit
    Option Sets VariableYes, ft_query_expansion_limit
    Variable Nameft_query_expansion_limit
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    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=name
    Config File Formatft_stopword_file
    Option Sets VariableYes, ft_stopword_file
    Variable Nameft_stopword_file
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    The file from which to read the list of stopwords for full-text searches. 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.

    Note

    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
    Config File Formatgeneral-log
    Option Sets VariableYes, general_log
    Variable Namegeneral_log
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    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 (--log before MySQL 6.0.8). 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
    Config File Formatgeneral_log_file
    Option Sets VariableYes, general_log_file
    Variable Namegeneral_log_file
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typefilename
    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 (--log before MySQL 6.0.8).

  • group_concat_max_len

    Command Line Format--group_concat_max_len=#
    Config File Formatgroup_concat_max_len
    Option Sets VariableYes, group_concat_max_len
    Variable Namegroup_concat_max_len
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Platform Bit Size32
    Typenumeric
    Default1024
    Range4-4294967295
    Value Set
    Platform Bit Size64
    Typenumeric
    Default1024
    Range4-18446744073709547520

    The maximum allowed 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 ARCHIVE tables, NO if not.

  • 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.

  • have_openssl

    This variable is an alias for have_ssl.

  • have_partitioning

    YES if mysqld supports partitioning.

  • have_query_cache

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

  • 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.

  • 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
    Value Set
    Typestring

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

  • init_connect

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

    A string to be executed by the server for each client that connects. The string consists of one or more SQL statements. To specify multiple statements, separate them by semicolon characters. For example, each client begins by default with autocommit mode enabled. There is no global system variable to specify that autocommit should be disabled by default, but init_connect can be used to achieve the same effect:

    SET GLOBAL init_connect='SET autocommit=0';
    

    This 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'
    

    Note that 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=name
    Config File Formatinit-file
    Option Sets VariableYes, init_file
    Variable Nameinit_file
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    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.

    Note that the --init-file option is unavailable if MySQL was configured with the --disable-grant-options option. See Section 2.9.2, “Typical configure Options”.

  • innodb_xxx

    InnoDB system variables are listed in Section 13.7.3, “InnoDB Startup Options and System Variables”.

  • interactive_timeout

    Command Line Format--interactive_timeout=#
    Config File Formatinteractive_timeout
    Option Sets VariableYes, interactive_timeout
    Variable Nameinteractive_timeout
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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=#
    Config File Formatjoin_buffer_size
    Option Sets VariableYes, join_buffer_size
    Variable Namejoin_buffer_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set (<= 6.0.8)
    Platform Bit Size64
    Typenumeric
    Default131072
    Range8200-18446744073709547520
    Value Set (>= 6.0.9)
    Platform Bit Size64
    Typenumeric
    Default131072
    Range128-18446744073709547520

    The 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.

    The maximum allowable setting for join_buffer_size is 4GB. As of MySQL 5.2.6, values larger than 4GB are allowed for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB with a warning).

  • join_cache_level

    Version Introduced6.0.9
    Command Line Format--join_cache_level=#
    Config File Formatjoin_cache_level
    Option Sets VariableYes, join_cache_level
    Variable Namejoin_cache_level
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default1
    Range0-8

    This variable is used for join buffer managment. It controls for which join operations of which types join buffers are supposed to be used. See Section 7.2.15, “Block Nested-Loop and Batched Key Access Joins”. The allowable join_cache_level values are shown in the following table.

    OptionDescription
    0No join buffer is used for any join operation. This setting can be useful for assessing baseline join performance in comparison to performance with nonzero values that enable use of join buffering.
    1This is the default value. Join buffers are employed exactly in the same cases as in versions of MySQL prior to 6.0.9: They are used only for inner joins that are executed by the original Block Nested-Loop (BNL) join algorithm. When this algorithm is applied, rows of the inner table are accessed through a table scan, a plain index scan, or a range index scan.
    2The server employs an incremental join buffer for a join operation if its first operand is produced by a join operation that uses a join buffer itself.
    3The BNL algorithm is used for an outer join and semi-join operation with one inner table, and for inner joins.
    4The BNL algorithm uses incremental buffers for inner tables. In this case, the BNL algorithm can be used for nested outer joins and semi-joins (outer joins and semi-joins with several inner tables). Such an operation can be executed only if incremental join buffers are used to join all inner tables but the first one.
    5The BKA algorithm uses regular buffers for any join operation with index access to the joined table.
    6The BKA algorithm uses incremental buffers for any join operation with index access to the joined table.
    7The BKA algorithm uses regular join buffers with a hash table.
    8The BKA algorithm uses incremental join buffers with a hash table.

    This variable was added in MySQL 6.0.9.

  • keep_files_on_create

    Command Line Format--keep_files_on_create=#
    Config File Formatkeep_files_on_create
    Option Sets VariableYes, keep_files_on_create
    Variable Namekeep_files_on_create
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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=#
    Config File Formatkey_buffer_size
    Option Sets VariableYes, key_buffer_size
    Variable Namekey_buffer_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    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 allowable setting for key_buffer_size is 4GB on 32-bit platforms. Values larger than 4GB are allowed 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.

    Increase the value to get better index handling (for all reads and multiple writes) to as much as you can afford. Using a value that is 25% of total memory on a machine that mainly runs MySQL is quite common. However, if you make the value too large (for example, more than 50% of your total memory) your system might start to page and become extremely slow. 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. Consider also the memory requirements of other storage engines.

    For even more speed when writing many rows at the same time, use LOCK TABLES. See Section 7.2.25, “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 12.5.6, “SHOW Syntax”.) 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 may be allocated internally for administrative structures.

    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 7.4.5, “The MyISAM Key Cache”.

  • key_cache_age_threshold

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

    This value controls the demotion of buffers from the hot sub-chain of a key cache to the warm sub-chain. Lower values cause demotion to happen more quickly. The minimum value is 100. The default value is 300. See Section 7.4.5, “The MyISAM Key Cache”.

  • key_cache_block_size

    Command Line Format--key_cache_block_size=#
    Config File Formatkey_cache_block_size
    Option Sets VariableYes, key_cache_block_size
    Variable Namekey_cache_block_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default1024
    Range512-16384

    The size in bytes of blocks in the key cache. The default value is 1024. See Section 7.4.5, “The MyISAM Key Cache”.

  • key_cache_division_limit

    Command Line Format--key_cache_division_limit=#
    Config File Formatkey_cache_division_limit
    Option Sets VariableYes, key_cache_division_limit
    Variable Namekey_cache_division_limit
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default100
    Range1-100

    The division point between the hot and warm sub-chains of the key cache buffer chain. The value is the percentage of the buffer chain to use for the warm sub-chain. Allowable values range from 1 to 100. The default value is 100. See Section 7.4.5, “The MyISAM Key Cache”.

  • language

    Command Line Format--language=name
    Config File Formatlanguage
    Option Sets VariableYes, language
    Variable Namelanguage
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename
    Default/usr/local/mysql/share/mysql/english/

    The language used for error messages.

  • 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
    Config File Formatlarge-pages
    Option Sets VariableYes, large_pages
    Variable Namelarge_pages
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform Specificlinux
    Value Set
    Type (linux)boolean
    DefaultFALSE

    Whether large page support is enabled (via the --large-pages option). See Section 7.5.9, “Enabling Large Page Support”.

  • large_page_size

    Variable Namelarge_page_size
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    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 7.5.9, “Enabling Large Page Support”.

  • lc_time_names

    Variable Namelc_time_names
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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 9.8, “MySQL Server Locale Support”.

  • license

    Variable Namelicense
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typestring
    DefaultGPL

    The type of license the server has.

  • local_infile

    Variable Namelocal_infile
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Type

    Whether LOCAL is supported for LOAD DATA INFILE statements. See Section 5.3.4, “Security Issues with LOAD DATA LOCAL.

  • 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 as of MySQL 6.0.8; use general_log instead.

  • log_backup_output

    Version Introduced6.0.8
    Command Line Format--log-backup-output[=name]
    Config File Formatlog-backup-output
    Option Sets VariableYes, log_backup_output
    Variable Namelog_backup_output
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typeenumeration
    DefaultTABLE
    Valid ValuesTABLE, FILE, NONE

    The destination for MySQL Backup history and progress 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_backup_output is not NONE. For more information, see Section 6.3.3.1, “MySQL Backup Log Control”.

    This variable was added in MySQL 6.0.8.

  • log_bin

    Variable Namelog_bin
    Variable ScopeGlobal
    Dynamic VariableNo

    Whether the binary log is enabled. See Section 5.2.4, “The Binary Log”.

  • log_bin_trust_function_creators

    Command Line Format--log-bin-trust-function-creators
    Config File Formatlog-bin-trust-function-creators
    Option Sets VariableYes, log_bin_trust_function_creators
    Variable Namelog_bin_trust_function_creators
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    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 allowed 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 18.6, “Binary Logging of Stored Programs”.

  • log_error

    Command Line Format--log-error[=name]
    Config File Formatlog-error
    Option Sets VariableYes, log_error
    Variable Namelog_error
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    The location of the error log.

  • log_output

    Command Line Format--log-output[=name]
    Config File Formatlog-output
    Option Sets VariableYes, log_output
    Variable Namelog_output
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typeenumeration
    DefaultFILE
    Valid ValuesTABLE, 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
    Config File Formatlog-queries-not-using-indexes
    Option Sets VariableYes, log_queries_not_using_indexes
    Variable Namelog_queries_not_using_indexes
    Variable ScopeGlobal
    Dynamic VariableYes
    Deprecated5.1.29, by slow-query-log
    Value Set
    Typeboolean

    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 16.1.3, “Replication and Binary Logging Options and Variables”.

  • log_slow_queries

    Command Line Format--log-slow-queries[=name]
    Config File Formatlog-slow-queries
    Option Sets VariableYes, log_slow_queries
    Variable Namelog_slow_queries
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    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 as of MySQL 6.0.8; use slow_query_log instead.

  • log_warnings

    Command Line Format--log-warnings[=#]
    Config File Formatlog-warnings
    Option Sets VariableYes, log_warnings
    Variable Namelog_warnings
    Variable ScopeBoth
    Dynamic VariableYes
    Disabled byskip-log-warnings
    Value Set
    Platform Bit Size32
    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.

  • long_query_time

    Command Line Format--long_query_time=#
    Config File Formatlong_query_time
    Option Sets VariableYes, long_query_time
    Variable Namelong_query_time
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set (<= 6.0.3)
    Typenumeric
    Default10
    Min Value1
    Value Set (>= 6.0.4)
    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. Prior to MySQL 6.0.4, the minimum value is 1, and the value for this variable must be an integer. Beginning with MySQL 6.0.4, the minimum is 0, and a resolution of microseconds is supported when logging to a file. However, the microseconds part is ignored and only integer values are written when logging to tables. The default value is 10. See Section 5.2.5, “The Slow Query Log”.

  • low_priority_updates

    Command Line Format--low-priority-updates
    Config File Formatlow-priority-updates
    Option Sets VariableYes, low_priority_updates
    Variable Namelow_priority_updates
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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 (MyISAM, MEMORY, MERGE). This variable previously was named sql_low_priority_updates.

  • lower_case_file_system

    Command Line Format--lower_case_file_system[=#]
    Config File Formatlower_case_file_system
    Option Sets VariableYes, lower_case_file_system
    Variable Namelower_case_file_system
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    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.

  • lower_case_table_names

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

    If set to 1, table names are stored in lowercase on disk and table name 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. See Section 8.2.2, “Identifier Case Sensitivity”.

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

    You should not set this variable to 0 if you are running MySQL on a system that does not have case-sensitive file names (such as Windows or Mac OS X). If this variable is not set at startup and the file system on which the data directory is located does not have case-sensitive file names, MySQL automatically sets lower_case_table_names to 2.

  • max_allowed_packet

    Command Line Format--max_allowed_packet=#
    Config File Formatmax_allowed_packet
    Option Sets VariableYes, max_allowed_packet
    Variable Namemax_allowed_packet
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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 allows 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.

    As of MySQL 6.0.9, the session value of this variable is read only. Before 6.0.9, setting the session value is allowed but has no effect.

  • max_connect_errors

    Command Line Format--max_connect_errors=#
    Config File Formatmax_connect_errors
    Option Sets VariableYes, max_connect_errors
    Variable Namemax_connect_errors
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Platform Bit Size32
    Typenumeric
    Default10
    Range1-4294967295
    Value Set
    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.

  • max_connections

    Command Line Format--max_connections=#
    Config File Formatmax_connections
    Option Sets VariableYes, max_connections
    Variable Namemax_connections
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default151
    Range1-100000

    The number of simultaneous client connections allowed. By default, this is 151. See Section B.1.2.7, “Too many connections, for more information.

    MySQL Enterprise For notification that the maximum number of connections is getting dangerously high and for advice on setting the optimum value for max_connections subscribe to the MySQL Enterprise Monitor. For more information, see http://www.mysql.com/products/enterprise/advisors.html.

    Increasing this value increases the number of file descriptors that mysqld requires. See Section 7.4.7, “How MySQL Opens and Closes Tables”, for comments on file descriptor limits.

  • max_delayed_threads

    Command Line Format--max_delayed_threads=#
    Config File Formatmax_delayed_threads
    Option Sets VariableYes, max_delayed_threads
    Variable Namemax_delayed_threads
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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 wasn't 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=#
    Config File Formatmax_error_count
    Option Sets VariableYes, max_error_count
    Variable Namemax_error_count
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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=#
    Config File Formatmax_heap_table_size
    Option Sets VariableYes, max_heap_table_size
    Variable Namemax_heap_table_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default16777216
    Range16384-4294967295

    This variable sets the maximum size to which MEMORY tables are allowed 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.

    Note

    On 64-bit platforms, the maximum value for this variable is 1844674407370954752.

    MySQL Enterprise Subscribers to the MySQL Enterprise Monitor receive recommendations for the optimum setting for max_heap_table_size. For more information, see http://www.mysql.com/products/enterprise/advisors.html.

  • max_insert_delayed_threads

    Variable Namemax_insert_delayed_threads
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric

    This variable is a synonym for max_delayed_threads.

  • max_join_size

    Command Line Format--max_join_size=#
    Config File Formatmax_join_size
    Option Sets VariableYes, max_join_size
    Variable Namemax_join_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default4294967295
    Range1-4294967295

    Do not allow 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=#
    Config File Formatmax_length_for_sort_data
    Option Sets VariableYes, max_length_for_sort_data
    Variable Namemax_length_for_sort_data
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default1024
    Range4-8388608

    The cutoff on the size of index values that determines which filesort algorithm to use. See Section 7.2.17, “ORDER BY Optimization”.

  • max_prepared_stmt_count

    Command Line Format--max_prepared_stmt_count=#
    Config File Formatmax_prepared_stmt_count
    Option Sets VariableYes, max_prepared_stmt_count
    Variable Namemax_prepared_stmt_count
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    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 allowable 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=#
    Config File Formatmax_relay_log_size
    Option Sets VariableYes, max_relay_log_size
    Variable Namemax_relay_log_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    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 16.4.1, “Replication Implementation Details”.

  • max_seeks_for_key

    Command Line Format--max_seeks_for_key=#
    Config File Formatmax_seeks_for_key
    Option Sets VariableYes, max_seeks_for_key
    Variable Namemax_seeks_for_key
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Platform Bit Size32
    Typenumeric
    Default4294967295
    Range1-4294967295
    Value Set
    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 12.5.6.23, “SHOW INDEX Syntax”). 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=#
    Config File Formatmax_sort_length
    Option Sets VariableYes, max_sort_length
    Variable Namemax_sort_length
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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[=#]
    Config File Formatmax_sp_recursion_depth
    Option Sets VariableYes, max_sp_recursion_depth
    Variable Namemax_sp_recursion_depth
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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 disallows 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=#
    Config File Formatmax_tmp_tables
    Option Sets VariableYes, max_tmp_tables
    Variable Namemax_tmp_tables
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Platform Bit Size32
    Typenumeric
    Default32
    Range1-4294967295
    Value Set
    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=#
    Config File Formatmax_user_connections
    Option Sets VariableYes, max_user_connections
    Variable Namemax_user_connections
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Range1-4294967295

    The maximum number of simultaneous connections allowed to any given MySQL account. A value of 0 means “no limit.

    This variable has both a global scope and a (read-only) session scope. The session variable has the same value as the global variable unless the current account has a nonzero MAX_USER_CONNECTIONS resource limit. In that case, the session value reflects the account limit.

  • max_write_lock_count

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

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

  • min_examined_row_limit

    Version Introduced6.0.4
    Command Line Format--min-examined-row-limit=#
    Config File Formatmin-examined-row-limit
    Variable Namemin_examined_row_limit
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Platform Bit Size32
    Typenumeric
    Default0
    Range0-4294967295
    Value Set
    Platform Bit Size64
    Typenumeric
    Default0
    Range0-18446744073709547520

    Queries that examine fewer than this number of rows are not logged to the slow query log. This variable was added in MySQL 6.0.4.

  • myisam_data_pointer_size

    Command Line Format--myisam_data_pointer_size=#
    Config File Formatmyisam_data_pointer_size
    Option Sets VariableYes, myisam_data_pointer_size
    Variable Namemyisam_data_pointer_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    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 B.1.2.12, “The table is full.

  • myisam_max_sort_file_size

    Command Line Format--myisam_max_sort_file_size=#
    Config File Formatmyisam_max_sort_file_size
    Option Sets VariableYes, myisam_max_sort_file_size
    Variable Namemyisam_max_sort_file_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default2147483648

    The maximum size of the temporary file that MySQL is allowed 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.

  • myisam_recover_options

    Variable Namemyisam_recover_options
    Variable ScopeGlobal
    Dynamic VariableNo

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

  • myisam_repair_threads

    Command Line Format--myisam_repair_threads=#
    Config File Formatmyisam_repair_threads
    Option Sets VariableYes, myisam_repair_threads
    Variable Namemyisam_repair_threads
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Platform Bit Size32
    Typenumeric
    Default1
    Range1-4294967295
    Value Set
    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.

    Note

    Multi-threaded repair is still beta-quality code.

  • myisam_sort_buffer_size

    Command Line Format--myisam_sort_buffer_size=#
    Config File Formatmyisam_sort_buffer_size
    Option Sets VariableYes, myisam_sort_buffer_size
    Variable Namemyisam_sort_buffer_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Platform Bit Size32
    Typenumeric
    Default8388608
    Range4-4294967295
    Value Set
    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 allowable setting for myisam_sort_buffer_size is 4GB. Values larger than 4GB are allowed 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
    Config File Formatmyisam_stats_method
    Option Sets VariableYes, myisam_stats_method
    Variable Namemyisam_stats_method
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeenumeration
    Valid Valuesnulls_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 7.4.6, “MyISAM Index Statistics Collection”.

    Any unique prefix of a valid value may be used to set the value of this variable.

  • myisam_use_mmap

    Command Line Format--myisam_use_mmap
    Config File Formatmyisam_use_mmap
    Option Sets VariableYes, myisam_use_mmap
    Variable Namemyisam_use_mmap
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typeboolean
    DefaultFALSE

    Use memory mapping for reading and writing MyISAM tables.

  • named_pipe

    Variable Namenamed_pipe
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform Specificwindows

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

  • net_buffer_length

    Command Line Format--net_buffer_length=#
    Config File Formatnet_buffer_length
    Option Sets VariableYes, net_buffer_length
    Variable Namenet_buffer_length
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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.

    As of MySQL 6.0.9, the session value of this variable is read only. Before 6.0.9, setting the session value is allowed but has no effect.

  • net_read_timeout

    Command Line Format--net_read_timeout=#
    Config File Formatnet_read_timeout
    Option Sets VariableYes, net_read_timeout
    Variable Namenet_read_timeout
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default30
    Min Value1

    The number of seconds to wait for more data from a connection before aborting the read. This timeout applies only to TCP/IP connections, not to connections made via Unix socket files, named pipes, or shared memory. 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=#
    Config File Formatnet_retry_count
    Option Sets VariableYes, net_retry_count
    Variable Namenet_retry_count
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Platform Bit Size32
    Typenumeric
    Default10
    Range1-4294967295
    Value Set
    Platform Bit Size64
    Typenumeric
    Default10
    Range1-18446744073709547520

    If a read 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=#
    Config File Formatnet_write_timeout
    Option Sets VariableYes, net_write_timeout
    Variable Namenet_write_timeout
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default60
    Min Value1

    The number of seconds to wait for a block to be written to a connection before aborting the write. This timeout applies only to TCP/IP connections, not to connections made via Unix socket files, named pipes, or shared memory. See also net_read_timeout.

  • new

    Command Line Format--new
    Config File Formatnew
    Option Sets VariableYes, new
    Variable Namenew
    Variable ScopeBoth
    Dynamic VariableYes
    Disabled byskip-new
    Value Set
    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 6.0, its value is always OFF.

  • old

    Command Line Formatold
    Config 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 12.2.9.2, “Index Hint Syntax”.) 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
    Config File Formatold-alter-table
    Option Sets VariableYes, old_alter_table
    Variable Nameold-alter-table
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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 12.1.6, “ALTER TABLE Syntax”.

  • old_passwords

    Command Line Format--old_passwords
    Config File Formatold-passwords
    Option Sets VariableYes, old_passwords
    Variable Nameold_passwords
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeboolean
    DefaultFALSE

    Whether the server should use pre-4.1-style passwords for MySQL user accounts. See Section B.1.2.4, “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 12.5.5, “SET Syntax”.

  • open_files_limit

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

    The number of files that the operating system allows mysqld to open. This is the real value allowed 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 can't change the number of open files.

  • optimizer_prune_level

    Command Line Format--optimizer_prune_level[=#]
    Config File Formatoptimizer_prune_level
    Option Sets VariableYes, optimizer_prune_level
    Variable Nameoptimizer_prune_level
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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[=#]
    Config File Formatoptimizer_search_depth
    Option Sets VariableYes, optimizer_search_depth
    Variable Nameoptimizer_search_depth
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default62

    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 the maximum number of tables used in a query plus 2, the optimizer switches to the algorithm used in MySQL 5.0.0 (and previous versions) for performing searches.

  • optimizer_switch

    Command Line Format--optimizer_switch=value
    Config File Formatoptimizer_switch
    Option Sets VariableYes, optimizer_switch
    Variable Nameoptimizer_switch
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set (>= 6.0.0, <= 6.0.10)
    Typeset
    Default''
    Valid Valuesno_semijoin, no_materialization, no_loosescan, no_firstmatch
    Value Set (>= 6.0.11)
    Typeset
    Valid Valuesindex_merge={on|off}, index_merge_intersection={on|off}, index_merge_union={on|off}, semijoin={on|off}, materialization={on|off}, loosescan={on|off}, firstmatch={on|off}

    The optimizer_switch system variable enables control over optimizer behavior. As of MySQL 6.0.11, 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 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: firstmatch=on,index_merge=on,index_merge_union=on,
                        index_merge_sort_union=on,index_merge_intersection=on,
                        loosescan=on,materialization=on,semijoin=on
    

    For more information about the syntax of this variable and the optimizer behaviors that it controls, see Section 7.2.22, “Using optimizer_switch to Control the Optimizer”.

    Prior to MySQL 6.0.11, the syntax of optimizer_switch is like that of a SET column or the sql_mode system variable. The value can be set to a comma-separated list of flags to disable specific optimizer behaviors, chosen from no_semijoin (disable semi-join), no_materialization (disable materialization), no_loosescan (disable LooseScan, available as of MySQL 6.0.7), and no_firstmatch (disable FirstMatch, available as of MySQL 6.0.10). For example:

    SET @optimizer_switch='no_semijoin,no_materialization';
    

    Presence or absence of a no_opt_name keyword means that the behavior is disabled or enabled, respectively. The default value is the empty string (no optimizations disabled).

  • optimizer_use_mrr

    Variable Nameoptimizer_use_mrr
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeenumeration
    Defaultforce
    Valid Valuesauto, disable, force

    Controls whether the optimizer uses the Multi-Range Read (MRR) access method for which a number of ranges are sent to a storage engine at once during range selects. Sending multiple ranges to a handler at once can improve the performance of certain selects dramatically.

    The value can be 'force' (use MRR when possible; this is the default), 'disable' (do not use MRR), or 'auto'. (attempt to make a cost-based choice between using and not using MRR).

    Any unique prefix of a valid value may be used to set the value of this variable.

    The optimizer interface provided by this variable is tentative. (For example, at the moment, the cost formula is such that a setting of 'force' or 'disable' is better than 'auto'.) Currently, this variable enables use of MRR to be turned on or off, but the syntax might change to allow control over additional capabilities.

    The optimizer_use_mrr system variable replaces the multi_range_count variable from older versions of MySQL.

  • pid_file

    Command Line Format--pid-file=name
    Config File Formatpid-file
    Option Sets VariableYes, pid_file
    Variable Namepid_file
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    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=name
    Config File Formatplugin_dir
    Option Sets VariableYes, plugin_dir
    Variable Nameplugin_dir
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename
    Default/usr/local/mysql/lib/mysql

    The path name of the plugin directory.

  • port

    Command Line Format--port=#
    Config File Formatport
    Option Sets VariableYes, port
    Variable Nameport
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    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=#
    Config File Formatpreload_buffer_size
    Option Sets VariableYes, preload_buffer_size
    Variable Namepreload_buffer_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default32768
    Range1024-1073741824

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

  • protocol_version

    Variable Nameprotocol_version
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typenumeric

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

  • pseudo_thread_id

    Variable Namepseudo_thread_id
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric

    This variable is for internal server use.

  • query_alloc_block_size

    Command Line Format--query_alloc_block_size=#
    Config File Formatquery_alloc_block_size
    Option Sets VariableYes, query_alloc_block_size
    Variable Namequery_alloc_block_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Platform Bit Size32
    Typenumeric
    Default8192
    Range1024-4294967295
    Value Set
    Platform Bit Size64
    Typenumeric
    Default8192
    Range1024-18446744073709547520

    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 a bit.

  • query_cache_limit

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

    Don't 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=#
    Config File Formatquery_cache_min_res_unit
    Option Sets VariableYes, query_cache_min_res_unit
    Variable Namequery_cache_min_res_unit
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Platform Bit Size32
    Typenumeric
    Default4096
    Range512-4294967295
    Value Set
    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 7.5.5.3, “Query Cache Configuration”.

  • query_cache_size

    Command Line Format--query_cache_size=#
    Config File Formatquery_cache_size
    Option Sets VariableYes, query_cache_size
    Variable Namequery_cache_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Platform Bit Size32
    Typenumeric
    Default0
    Range0-4294967295
    Value Set
    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. The allowable 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 7.5.5.3, “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, you'll get a warning, as described in Section 7.5.5.3, “Query Cache Configuration”.

  • query_cache_type

    Command Line Format--query_cache_type=#
    Config File Formatquery_cache_type
    Option Sets VariableYes, query_cache_type
    Variable Namequery_cache_type
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeenumeration
    Default1
    Valid Values0, 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.

    OptionDescription
    0 or OFFDon't 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.

    Any unique prefix of a valid value may be used to set the value of this variable.

  • query_cache_wlock_invalidate

    Command Line Format--query_cache_wlock_invalidate
    Config File Formatquery_cache_wlock_invalidate
    Option Sets VariableYes, query_cache_wlock_invalidate
    Variable Namequery_cache_wlock_invalidate
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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=#
    Config File Formatquery_prealloc_size
    Option Sets VariableYes, query_prealloc_size
    Variable Namequery_prealloc_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Platform Bit Size32
    Typenumeric
    Default8192
    Range8192-4294967295
    Value Set
    Platform Bit Size64
    Typenumeric
    Default8192
    Range8192-18446744073709547520

    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.

  • range_alloc_block_size

    Command Line Format--range_alloc_block_size=#
    Config File Formatrange_alloc_block_size
    Option Sets VariableYes, range_alloc_block_size
    Variable Namerange_alloc_block_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Platform Bit Size64
    Typenumeric
    Default4096
    Range4096-18446744073709547520

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

  • read_buffer_size

    Command Line Format--read_buffer_size=#
    Config File Formatread_buffer_size
    Option Sets VariableYes, read_buffer_size
    Variable Nameread_buffer_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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 allowable 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 7.5.8, “How MySQL Uses Memory”, for example.

  • read_only

    Command Line Format--read_only
    Config File Formatread_only
    Option Sets VariableYes, read_only
    Variable Nameread_only
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default0

    This variable is off by default. When it is enabled, the server allows no updates except from users that have the SUPER privilege or (on a slave server) from updates performed by slave threads. On a slave server, this can be useful to ensure that the slave accepts updates only from its master server and not from clients. This variable 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”).

    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.

    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 6.0.11, 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=#
    Config File Formatread_rnd_buffer_size
    Option Sets VariableYes, read_rnd_buffer_size
    Variable Nameread_rnd_buffer_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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 7.2.17, “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 allowable 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 7.5.8, “How MySQL Uses Memory”, for example.

  • relay_log_purge

    Command Line Format--relay_log_purge
    Config File Formatrelay_log_purge
    Option Sets VariableYes, relay_log_purge
    Variable Namerelay_log_purge
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    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=#
    Config File Formatrelay_log_space_limit
    Option Sets VariableYes, relay_log_space_limit
    Variable Namerelay_log_space_limit
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Platform Bit Size32
    Typenumeric
    Default0
    Range0-4294967295
    Value Set
    Platform Bit Size64
    Typenumeric
    Default0
    Range0-18446744073709547520

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

  • report_host

    The value of the --report-host option. This variable was added in MySQL 6.0.5.

  • report_password

    The value of the --report-password option. This variable was added in MySQL 6.0.5.

  • report_port

    The value of the --report-port option. This variable was added in MySQL 6.0.5.

  • report_user

    The value of the --report-user option. This variable was added in MySQL 6.0.5.

  • rpl_semi_sync_master_enabled

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

    This variable is was added in MySQL 6.0.8. It is available only if the master-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_master_reply_log_file_pos

    For internal use.

    This variable is was added in MySQL 6.0.8. It is available only if the master-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_master_timeout

    A value in seconds 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 10 seconds.

    This variable is was added in MySQL 6.0.8. It is available only if the master-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_master_trace_level

    For internal use.

    This variable is was added in MySQL 6.0.8. It is available only if the master-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_slave_enabled

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

    This variable is was added in MySQL 6.0.8. It is available only if the slave-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_slave_trace_level

    For internal use.

    This variable is was added in MySQL 6.0.8. It is available only if the slave-side semisynchronous replication plugin is installed.

  • secure_auth

    Command Line Format--secure-auth
    Config File Formatsecure-auth
    Option Sets VariableYes, secure_auth
    Variable Namesecure_auth
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    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 B.1.2.4, “Client does not support authentication protocol.

  • secure_backup_file_priv

    By default, this variable is empty. If set to the name of a directory, it limits the effect of the BACKUP DATABASE and RESTORE statements to work only with files in that directory. This variable was added in MySQL 6.0.11; in older releases, use secure_backup_file_priv instead.

  • secure_file_priv

    Command Line Format--secure-file-priv
    Config File Formatsecure-file-priv
    Option Sets VariableYes, secure_file_priv
    Variable Namesecure_file_priv
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    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. Before MySQL 6.0.11, it also applies to the BACKUP DATABASE and RESTORE statements; as of 6.0.11, secure_backup_file_priv applies to those statements.

  • server_id

    Command Line Format--server-id=#
    Config File Formatserver-id
    Option Sets VariableYes, server_id
    Variable Nameserver_id
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    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 allows 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.

  • skip_networking

    This is ON if the server allows 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. On NetWare, only TCP/IP connections are supported, so do not set this variable to ON. 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 allowed only to users who have the SHOW DATABASES privilege, and the statement displays all database names. If the value is OFF, SHOW DATABASES is allowed 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=#
    Config File Formatslow_launch_time
    Option Sets VariableYes, slow_launch_time
    Variable Nameslow_launch_time
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default2

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

  • slow_query_log

    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 (--log-slow-queries before MySQL 6.0.8). 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_query_log_file

    Command Line Format--slow-query-log-file=file_name
    Config File Formatslow_query_log_file
    Option Sets VariableYes, slow_query_log_file
    Variable Nameslow_query_log_file
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typefilename

    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 (--log-slow-queries before MySQL 6.0.8).

  • socket

    Command Line Format--socket=name
    Config File Formatsocket
    Option Sets VariableYes, socket
    Variable Namesocket
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename
    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=#
    Config File Formatsort_buffer_size
    Option Sets VariableYes, sort_buffer_size
    Variable Namesort_buffer_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Platform Bit Size32
    Typenumeric
    Default2097144
    Max Value4294967295
    Value Set
    Platform Bit Size64
    Typenumeric
    Default2097144
    Max Value18446744073709547520

    Each thread that needs to do a sort allocates a buffer of this size. Increase this value for faster ORDER BY or GROUP BY operations. See Section B.1.4.4, “Where MySQL Stores Temporary Files”.

    The maximum allowable setting for sort_buffer_size is 4GB. As of MySQL 5.2.6, values larger than 4GB are allowed for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB with a warning).

  • sql_mode

    Command Line Format--sql-mode=name
    Config File Formatsql-mode
    Option Sets VariableYes, sql_mode
    Variable Namesql_mode
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeset
    Default''
    Valid ValuesALLOW_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 5.1.8, “Server SQL Modes”.

  • sql_select_limit

    Variable Namesql_select_limit
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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 allows per table, which depends on the server configuration and may be affected if the server build was configured with --with-big-tables. 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.

  • ssl_ca

    Command Line Format--ssl-ca=name
    Config File Formatssl-ca
    Option Sets VariableYes, ssl_ca
    Variable Namessl_ca
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

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

  • ssl_capath

    Command Line Format--ssl-capath=name
    Config File Formatssl-capath
    Option Sets VariableYes, ssl_capath
    Variable Namessl_capath
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

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

  • ssl_cert

    Command Line Format--ssl-cert=name
    Config File Formatssl-cert
    Option Sets VariableYes, ssl_cert
    Variable Namessl_cert
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

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

  • ssl_cipher

    Command Line Format--ssl-cipher=name
    Config File Formatssl-cipher
    Option Sets VariableYes, ssl_cipher
    Variable Namessl_cipher
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    A list of allowable ciphers to use for SSL encryption.

  • ssl_key

    Command Line Format--ssl-key=name
    Config File Formatssl-key
    Option Sets VariableYes, ssl_key
    Variable Namessl_key
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typestring

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

  • storage_engine

    Variable Namestorage_engine
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeenumeration

    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”.

  • sync_frm

    Command Line Format--sync-frm
    Config File Formatsync-frm
    Option Sets VariableYes, sync_frm
    Variable Namesync_frm
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    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
    Value Set
    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 9.7, “MySQL Server Time Zone Support”.

  • table_definition_cache

    Command Line Format--table_definition_cache=#
    Config File Formattable_definition_cache
    Option Sets VariableYes, table_definition_cache
    Variable Nametable_definition_cache
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set (<= 6.0.5)
    Typenumeric
    Default128
    Range1-524288
    Value Set (>= 6.0.6)
    Typenumeric
    Default256
    Range256-524288

    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 1 and 128 before MySQL 6.0.6. The minimum and default are both 256 as of MySQL 6.0.6.

  • table_lock_wait_timeout

    Command Line Format--table_lock_wait_timeout=#
    Config File Formattable_lock_wait_timeout
    Option Sets VariableYes, table_lock_wait_timeout
    Variable Nametable_lock_wait_timeout
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default50
    Range1-1073741824

    This variable currently is unused.

  • table_open_cache

    Command Line Format--table-open-cache=#
    Config File Formattable_open_cache
    Variable Nametable_open_cache
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default64
    Range1-524288

    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 5.1.7, “Server Status Variables”. If the value of Opened_tables is large and you don't do 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 7.4.7, “How MySQL Opens and Closes Tables”.

  • thread_cache_size

    Command Line Format--thread_cache_size=#
    Config File Formatthread_cache_size
    Option Sets VariableYes, thread_cache_size
    Variable Namethread_cache_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    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 doesn't provide a notable performance improvement if you have a good thread implementation.) 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 5.1.7, “Server Status Variables”.

  • thread_concurrency

    Command Line Format--thread_concurrency=#
    Config File Formatthread_concurrency
    Option Sets VariableYes, thread_concurrency
    Variable Namethread_concurrency
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    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
    Config File Formatthread_handling
    Option Sets VariableYes, thread_handling
    Variable Namethread_handling
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set (<= 6.0.3)
    Typeenumeration
    Valid Valuesno-threads, one-thread-per-connection
    Value Set (>= 6.0.4)
    Typeenumeration
    Valid Valuesno-threads, one-thread-per-connection, pool-of-threads

    The thread-handling model. The allowable values are no-threads (the server uses one thread), one-thread-per-connection (the server uses one thread to handle each client connection), pool-of-threads (the server does not create a thread per client connection, but uses a pool of threads for processing statements). no-threads is useful for debugging under Linux; see MySQL Internals: Porting. pool-of-threads is available as of MySQL 6.0.4. To use thread pooling, MySQL must be configured with the --with-libevent option when you run configure.

    For information about choosing one thread model over the other and tuning the parameters that control thread resources, see Section 7.5.7, “How MySQL Uses Threads for Client Connections”.

  • thread_pool_size

    Version Introduced6.0.4
    Command Line Format--thread_pool_size=#
    Config File Formatthread_pool_size
    Option Sets VariableYes, thread_pool_size
    Variable Namethread_pool_size
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typenumeric
    Default20
    Range1-16384

    The size of the thread pool that is use if thread_handling is set to pool-of-threads. The default pool size is 20, and the range of values is 1 to 16,384. This variable was added in MySQL 6.0.4.

  • thread_stack

    Command Line Format--thread_stack=#
    Config File Formatthread_stack
    Option Sets VariableYes, thread_stack
    Variable Namethread_stack
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Platform Bit Size32
    Typenumeric
    Default196608
    Range131072-4294967295
    Value Set
    Platform Bit Size64
    Typenumeric
    Default196608
    Range131072-18446744073709547520

    The stack size for each thread. Many of the limits detected by the crash-me test are dependent on this value. See Section 7.1.4, “The MySQL Benchmark Suite”. The default (192KB) 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
    Config File Formatdefault_time_zone
    Variable Nametime_zone
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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 9.7, “MySQL Server Time Zone Support”.

  • timed_mutexes

    Command Line Format--timed_mutexes
    Config File Formattimed_mutexes
    Option Sets VariableYes, timed_mutexes
    Variable Nametimed_mutexes
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    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.

  • tmp_table_size

    Command Line Format--tmp_table_size=#
    Config File Formattmp_table_size
    Option Sets VariableYes, tmp_table_size
    Variable Nametmp_table_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Defaultsystem dependent
    Range1024-4294967295

    The maximum size of internal in-memory temporary tables. (The actual limit is determined as the smaller of max_heap_table_size and tmp_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.

  • tmpdir

    Command Line Format--tmpdir=name
    Config File Formattmpdir
    Option Sets VariableYes, tmpdir
    Variable Nametmpdir
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    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, NetWare, and OS/2.

    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. However, if you are using MySQL 4.0.0 or later, you can set the slave's temporary directory using the slave_load_tmpdir variable. In that case, the slave won't 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=#
    Config File Formattransaction_alloc_block_size
    Option Sets VariableYes, transaction_alloc_block_size
    Variable Nametransaction_alloc_block_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Platform Bit Size32
    Typenumeric
    Default8192
    Range1024-4294967295

    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=#
    Config File Formattransaction_prealloc_size
    Option Sets VariableYes, transaction_prealloc_size
    Variable Nametransaction_prealloc_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Platform Bit Size32
    Typenumeric
    Default4096
    Range1024-4294967295
    Value Set
    Platform Bit Size64
    Typenumeric
    Default4096
    Range1024-18446744073709547520

    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 ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeenumeration
    DefaultREPEATABLE-READ
    Valid ValuesREAD-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 12.4.6, “SET TRANSACTION Syntax”. If you set tx_isolation directly to an isolation level name that contains a space, the name should be enclosed within quotes, with the space replaced by a dash. For example:

    SET tx_isolation = 'READ-COMMITTED';
    
  • updatable_views_with_limit

    Command Line Format--updatable_views_with_limit=#
    Config File Formatupdatable_views_with_limit
    Option Sets VariableYes, updatable_views_with_limit
    Variable Nameupdatable_views_with_limit
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    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

    Command Line Format--version
    Config File Formatversion
    Variable Nameversion
    Variable ScopeGlobal
    Dynamic VariableNo

    The version number for the server.

  • version_comment

    The configure script has a --with-comment option that allows a comment to be specified when building MySQL. This variable contains the value of that comment.

  • version_compile_machine

    The type of machine or architecture on which MySQL was built.

  • version_compile_os

    Variable Nameversion_compile_os
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typestring

    The type of operating system on which MySQL was built.

  • wait_timeout

    Command Line Format--wait_timeout=#
    Config File Formatwait_timeout
    Option Sets VariableYes, wait_timeout
    Variable Namewait_timeout
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default28800
    Range1-31536000
    Value Set
    Type (windows)numeric
    Default28800
    Range1-2147483

    The number of seconds the server waits for activity on a noninteractive connection before closing it. This timeout applies only to TCP/IP and Unix socket file connections, not to connections made via named pipes, or shared memory.

    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.

MySQL Enterprise Expert use of server system variables is part of the service offered by the MySQL Enterprise Monitor. To subscribe, see http://www.mysql.com/products/enterprise/advisors.html.

5.1.5. Session System Variables

Several system variables exist only as session variables. These cannot be set at server startup but can be assigned values at runtime using the SET statement (except for those that are read only). Most of them are not displayed by SHOW VARIABLES, but you can obtain their values using SELECT. This section describes the session system variables. For information about setting or displaying their values, see Section 5.1.6, “Using System Variables”. For example:

mysql> SELECT @@autocommit;
+--------------+
| @@autocommit |
+--------------+
|            1 |
+--------------+

The lettercase of these variables does not matter.

The following table lists the system variables that have only session scope:

Table 5.3. mysqld Session System Variable Summary

NameCmd-LineOption fileSystem VarDynamic
autocommit  YesYes
backup_wait_timeout  YesYes
big-tablesYesYes  
- Variable: big_tables  YesYes
error_count  YesNo
foreign_key_checks  YesYes
identity  YesYes
insert_id  YesYes
last_insert_id  YesYes
profiling  YesYes
rand_seed1  YesYes
rand_seed2  YesYes
sql_auto_is_null  YesYes
sql_big_selects  YesYes
sql_big_tables  YesYes
sql_buffer_result  YesYes
sql_log_bin  YesYes
sql_log_off  YesYes
sql_log_update  YesYes
sql_notes  YesYes
sql_quote_show_create  YesYes
sql_safe_updates  YesYes
sql_warnings  YesYes
timestamp  YesYes
unique_checks  YesYes
warning_count  YesNo
  • autocommit

    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. By default, client connections begin with autocommit set to 1. If you change autocommit mode from 0 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 12.4.1, “START TRANSACTION, COMMIT, and ROLLBACK Syntax”.

  • backup_wait_timeout

    The number of seconds DDL statements wait for a BACKUP DATABASE or RESTORE operation before aborting with an error. The default value is 50. A value of 0 means “immediate timeout.” This variable was added in MySQL 6.0.7.

  • 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.

    Note

    This variable was formerly named sql_big_tables.

  • error_count

    The number of errors that resulted from the last statement that generated messages. This variable is read only. See Section 12.5.6.18, “SHOW ERRORS Syntax”.

  • 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 13.7.4.4, “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.

    Note

    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.

  • 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.

  • 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.

  • 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.

  • 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 12.5.6.32, “SHOW PROFILES Syntax”. This variable was added in MySQL 6.0.5.

  • 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 12.5.6.32, “SHOW PROFILES Syntax”. This variable was added in MySQL 6.0.5.

  • rand_seed1

    The rand_seed1 and rand_seed2 variables exist as session variables only, and can be set but not read. Beginning with MySQL 6.0.5, 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.

  • sql_auto_is_null

    If set to 1 (the default), you can find the last inserted row for a table that contains an AUTO_INCREMENT column by using the following construct:

    WHERE auto_increment_column IS NULL
    

    This behavior is used by some ODBC programs, such as Access.

  • sql_big_selects

    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 allows 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

    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

    If set to 0, no logging is done to the binary log for the client. The client must have the SUPER privilege to set this option. The default value is 1.

  • sql_log_off

    If set to 1, no logging is done to the general query log for this client. The client must have the SUPER privilege to set this option. The default value is 0.

  • sql_log_update

    This variable is deprecated, and is mapped to sql_log_bin.

  • sql_notes

    If set to 1 (the default), warnings of Note level are recorded. If set to 0, Note warnings are suppressed. 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 12.5.6.12, “SHOW CREATE TABLE Syntax”, and Section 12.5.6.8, “SHOW CREATE DATABASE Syntax”.

  • 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_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.

  • 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.

  • unique_checks

    If set to 1 (the default), uniqueness checks for secondary indexes in InnoDB tables are performed. If set to 0, storage engines are allowed 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 allowed to check for them and issue duplicate-key errors if it detects them.

  • 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 12.5.6.40, “SHOW WARNINGS Syntax”.

5.1.6. Using System Variables

The MySQL server maintains many system variables that indicate how it is configured. Section 5.1.4, “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 5.1.6.2, “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 sesson 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.)

Note

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;

Note

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.

5.1.6.1. 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 6.0 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 7.4.5, “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.

5.1.6.2. 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 5.1.6, “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 5.1.5, “Session 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.

Variable NameVariable TypeVariable Scope
auto_increment_incrementnumericGLOBAL | SESSION
auto_increment_offsetnumericGLOBAL | SESSION
autocommitbooleanSESSION
automatic_sp_privilegesbooleanGLOBAL
backup_history_logbooleanGLOBAL
backup_history_log_filefilenameGLOBAL
backup_progress_logbooleanGLOBAL
backup_progress_log_filefilenameGLOBAL
backup_wait_timeoutnumericSESSION
backupdirfilenameGLOBAL
big_tablesbooleanSESSION
binlog_cache_sizenumericGLOBAL
binlog_formatenumerationGLOBAL | SESSION
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
date_formatstringGLOBAL | SESSION
datetime_formatstringGLOBAL | SESSION
debugstringGLOBAL | SESSION
debug_syncstringGLOBAL | 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
falcon_checkpoint_schedulestringGLOBAL
falcon_checksumsbooleanGLOBAL
falcon_consistent_readbooleanGLOBAL | SESSION
falcon_debug_maskbitmapGLOBAL
falcon_disable_fsyncbooleanGLOBAL
falcon_index_chill_thresholdnumericGLOBAL
falcon_initial_allocationnumericGLOBAL
falcon_io_threadsnumericGLOBAL
falcon_lock_wait_timeoutnumericGLOBAL
falcon_max_transaction_backlognumericGLOBAL
falcon_record_chill_thresholdnumericGLOBAL
falcon_record_memory_maxnumericGLOBAL
falcon_record_scavenge_floornumericGLOBAL
falcon_record_scavenge_thresholdnumericGLOBAL
falcon_serial_log_prioritybooleanGLOBAL
flushbooleanGLOBAL
flush_timenumericGLOBAL
foreign_key_checksbooleanSESSION
ft_boolean_syntaxstringGLOBAL
general_logbooleanGLOBAL
general_log_filefilenameGLOBAL
group_concat_max_lennumericGLOBAL | SESSION
identitynumericSESSION
init_connectstringGLOBAL
init_slavestringGLOBAL
innodb_autoextend_incrementnumericGLOBAL
innodb_commit_concurrencynumericGLOBAL
innodb_concurrency_ticketsnumericGLOBAL
innodb_fast_shutdownbooleanGLOBAL
innodb_flush_log_at_trx_commitnumericGLOBAL
innodb_max_dirty_pages_pctnumericGLOBAL
innodb_max_purge_lagnumericGLOBAL
innodb_stats_on_metadatabooleanGLOBAL
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
join_cache_levelnumericGLOBAL | 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_time_namesstringGLOBAL | SESSION
local_infile GLOBAL
logstringGLOBAL
log_backup_outputenumerationGLOBAL
log_bin_trust_function_creatorsbooleanGLOBAL
log_outputenumerationGLOBAL
log_queries_not_using_indexesbooleanGLOBAL
log_slow_queriesbooleanGLOBAL
log_warningsnumericGLOBAL | SESSION
long_query_timenumericGLOBAL | SESSION
low_priority_updatesbooleanGLOBAL | SESSION
maria-checkpoint-interval GLOBAL
maria_log_file_sizenumericGLOBAL
maria_log_purge_typeenumerationGLOBAL
maria_max_sort_file_size GLOBAL
maria_page_checksumenumerationGLOBAL
maria_pagecache_age_thresholdnumericGLOBAL
maria_pagecache_division_limitnumericGLOBAL
maria_recoverbooleanGLOBAL
maria_repair_threadsnumericGLOBAL | SESSION
maria_sort_buffer_sizenumericGLOBAL | SESSION
maria_stats_methodenumerationGLOBAL | SESSION
maria_sync_log_direnumerationGLOBAL
max_allowed_packetnumericGLOBAL | SESSION
max_binlog_cache_sizenumericGLOBAL
max_binlog_sizenumericGLOBAL
max_connect_errorsnumericGLOBAL
max_connectionsnumericGLOBAL
max_delayed_threadsnumericGLOBAL | SESSION
max_error_countnumericGLOBAL | SESSION
max_heap_table_sizenumericGLOBAL | SESSION
max_insert_delayed_threadsnumericGLOBAL | SESSION