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 Configuration Defaults
5.1.3 Server Command Options
5.1.4 Server System Variables
5.1.5 Using System Variables
5.1.6 Server Status Variables
5.1.7 Server SQL Modes
5.1.8 Server Plugins
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 The DDL Log
5.2.7 Server Log Maintenance
5.3 Running Multiple MySQL Instances on One Machine
5.3.1 Setting Up Multiple Data Directories
5.3.2 Running Multiple MySQL Instances on Windows
5.3.3 Running Multiple MySQL Instances on Unix
5.3.4 Using Client Programs in a Multiple-Server Environment

End of Product Lifecycle. Active development for MySQL Database Server version 5.1 has ended. Oracle offers various support offerings which may be of interest. For details and more information, see the MySQL section of the Lifetime Support Policy for Oracle Technology Products (http://www.oracle.com/us/support/lifetime-support/index.html). Please consider upgrading to a recent version.

MySQL Server (mysqld) is the main program that does most of the work in a MySQL installation. This chapter provides an overview of MySQL Server and covers general server administration:

For additional information on administrative topics, see also:

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. You can specify these options on the command line, through configuration files, or both.

  • Server system variables. These variables reflect the current state and values of the startup options, some of which can be modified while the server is running.

  • Server status variables. These variables contain counters and statistics about runtime operation.

  • How to set the server SQL mode. This setting modifies certain aspects of SQL syntax and semantics, for example for compatibility with code from other database systems, or to control the error handling for particular situations.

  • The server shutdown process. There are performance and reliability considerations depending on the type of table (transactional or nontransactional) and whether you use replication.

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 13.7.5.17, “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.

For a version of this table that is specific to MySQL Cluster, see Section 17.3.4.1, “MySQL Cluster mysqld Option and Variable Reference”.

Table 5.1 Option/Variable Summary

NameCmd-LineOption FileSystem VarStatus VarVar ScopeDynamic
abort-slave-event-countYesYes    
Aborted_clients   YesGlobalNo
Aborted_connects   YesGlobalNo
allow-suspicious-udfsYesYes    
ansiYesYes    
auto_increment_increment  Yes BothYes
auto_increment_offset  Yes BothYes
autocommitYesYesYes SessionYes
automatic_sp_privileges  Yes GlobalYes
back_log  Yes GlobalNo
basedirYesYesYes GlobalNo
big-tablesYesYes  SessionYes
- Variable: big_tables  Yes SessionYes
bind-addressYesYesYes GlobalNo
Binlog_cache_disk_use   YesGlobalNo
binlog_cache_sizeYesYesYes GlobalYes
Binlog_cache_use   YesGlobalNo
binlog_direct_non_transactional_updatesYesYesYes BothYes
binlog-do-dbYesYes    
binlog-formatYesYes  BothYes
- Variable: binlog_format  Yes BothYes
binlog-ignore-dbYesYes    
binlog-row-event-max-sizeYesYes    
bootstrapYesYes    
bulk_insert_buffer_sizeYesYesYes BothYes
Bytes_received   YesBothNo
Bytes_sent   YesBothNo
character_set_client  Yes BothYes
character-set-client-handshakeYesYes    
character_set_connection  Yes BothYes
character_set_database[a]  Yes BothYes
character-set-filesystemYesYes  BothYes
- Variable: character_set_filesystem  Yes BothYes
character_set_results  Yes BothYes
character-set-serverYesYes  BothYes
- Variable: character_set_server  Yes BothYes
character_set_system  Yes GlobalNo
character-sets-dirYesYes  GlobalNo
- Variable: character_sets_dir  Yes GlobalNo
chrootYesYes    
collation_connection  Yes BothYes
collation_database[b]  Yes BothYes
collation-serverYesYes  BothYes
- Variable: collation_server  Yes BothYes
Com_admin_commands   YesBothNo
Com_alter_db   YesBothNo
Com_alter_db_upgrade   YesBothNo
Com_alter_event   YesBothNo
Com_alter_function   YesBothNo
Com_alter_procedure   YesBothNo
Com_alter_server   YesBothNo
Com_alter_table   YesBothNo
Com_alter_tablespace   YesBothNo
Com_analyze   YesBothNo
Com_assign_to_keycache   YesBothNo
Com_backup_table   YesBothNo
Com_begin   YesBothNo
Com_binlog   YesBothNo
Com_call_procedure   YesBothNo
Com_change_db   YesBothNo
Com_change_master   YesBothNo
Com_check   YesBothNo
Com_checksum   YesBothNo
Com_commit   YesBothNo
Com_create_db   YesBothNo
Com_create_event   YesBothNo
Com_create_function   YesBothNo
Com_create_index   YesBothNo
Com_create_procedure   YesBothNo
Com_create_server   YesBothNo
Com_create_table   YesBothNo
Com_create_trigger   YesBothNo
Com_create_udf   YesBothNo
Com_create_user   YesBothNo
Com_create_view   YesBothNo
Com_dealloc_sql   YesBothNo
Com_delete   YesBothNo
Com_delete_multi   YesBothNo
Com_do   YesBothNo
Com_drop_db   YesBothNo
Com_drop_event   YesBothNo
Com_drop_function   YesBothNo
Com_drop_index   YesBothNo
Com_drop_procedure   YesBothNo
Com_drop_server   YesBothNo
Com_drop_table   YesBothNo
Com_drop_trigger   YesBothNo
Com_drop_user   YesBothNo
Com_drop_view   YesBothNo
Com_empty_query   YesBothNo
Com_execute_sql   YesBothNo
Com_flush   YesBothNo
Com_grant   YesBothNo
Com_ha_close   YesBothNo
Com_ha_open   YesBothNo
Com_ha_read   YesBothNo
Com_help   YesBothNo
Com_insert   YesBothNo
Com_insert_select   YesBothNo
Com_install_plugin   YesBothNo
Com_kill   YesBothNo
Com_load   YesBothNo
Com_lock_tables   YesBothNo
Com_optimize   YesBothNo
Com_preload_keys   YesBothNo
Com_prepare_sql   YesBothNo
Com_purge   YesBothNo
Com_purge_before_date   YesBothNo
Com_release_savepoint   YesBothNo
Com_rename_table   YesBothNo
Com_rename_user   YesBothNo
Com_repair   YesBothNo
Com_replace   YesBothNo
Com_replace_select   YesBothNo
Com_reset   YesBothNo
Com_restore_table   YesBothNo
Com_revoke   YesBothNo
Com_revoke_all   YesBothNo
Com_rollback   YesBothNo
Com_rollback_to_savepoint   YesBothNo
Com_savepoint   YesBothNo
Com_select   YesBothNo
Com_set_option   YesBothNo
Com_show_authors   YesBothNo
Com_show_binlog_events   YesBothNo
Com_show_binlogs   YesBothNo
Com_show_charsets   YesBothNo
Com_show_collations   YesBothNo
Com_show_column_types   YesBothNo
Com_show_contributors   YesBothNo
Com_show_create_db   YesBothNo
Com_show_create_event   YesBothNo
Com_show_create_func   YesBothNo
Com_show_create_proc   YesBothNo
Com_show_create_table   YesBothNo
Com_show_create_trigger   YesBothNo
Com_show_databases   YesBothNo
Com_show_engine_logs   YesBothNo
Com_show_engine_mutex   YesBothNo
Com_show_engine_status   YesBothNo
Com_show_errors   YesBothNo
Com_show_events   YesBothNo
Com_show_fields   YesBothNo
Com_show_function_code   YesBothNo
Com_show_function_status   YesBothNo
Com_show_grants   YesBothNo
Com_show_keys   YesBothNo
Com_show_logs   YesBothNo
Com_show_master_status   YesBothNo
Com_show_ndb_status   YesBothNo
Com_show_new_master   YesBothNo
Com_show_open_tables   YesBothNo
Com_show_plugins   YesBothNo
Com_show_privileges   YesBothNo
Com_show_procedure_code   YesBothNo
Com_show_procedure_status   YesBothNo
Com_show_processlist   YesBothNo
Com_show_profile   YesBothNo
Com_show_profiles   YesBothNo
Com_show_slave_hosts   YesBothNo
Com_show_slave_status   YesBothNo
Com_show_status   YesBothNo
Com_show_storage_engines   YesBothNo
Com_show_table_status   YesBothNo
Com_show_tables   YesBothNo
Com_show_triggers   YesBothNo
Com_show_variables   YesBothNo
Com_show_warnings   YesBothNo
Com_slave_start   YesBothNo
Com_slave_stop   YesBothNo
Com_stmt_close   YesBothNo
Com_stmt_execute   YesBothNo
Com_stmt_fetch   YesBothNo
Com_stmt_prepare   YesBothNo
Com_stmt_reprepare   YesBothNo
Com_stmt_reset   YesBothNo
Com_stmt_send_long_data   YesBothNo
Com_truncate   YesBothNo
Com_uninstall_plugin   YesBothNo
Com_unlock_tables   YesBothNo
Com_update   YesBothNo
Com_update_multi   YesBothNo
Com_xa_commit   YesBothNo
Com_xa_end   YesBothNo
Com_xa_prepare   YesBothNo
Com_xa_recover   YesBothNo
Com_xa_rollback   YesBothNo
Com_xa_start   YesBothNo
completion_typeYesYesYes BothYes
Compression   YesSessionNo
concurrent_insertYesYesYes GlobalYes
connect_timeoutYesYesYes GlobalYes
Connections   YesGlobalNo
consoleYesYes    
core-fileYesYes    
Created_tmp_disk_tables   YesBothNo
Created_tmp_files   YesGlobalNo
Created_tmp_tables   YesBothNo
datadirYesYesYes GlobalNo
date_format  Yes BothNo
datetime_format  Yes BothNo
debugYesYesYes BothYes
debug_sync  Yes BothYes
debug-sync-timeoutYesYes    
default-character-setYesYes    
default-storage-engineYesYesYes BothYes
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    
- Variable: named_pipe      
enable-pstackYesYes    
engine-condition-pushdownYesYes  BothYes
- Variable: engine_condition_pushdown  Yes BothYes
error_count  Yes SessionNo
event-schedulerYesYes  GlobalYes
- Variable: event_scheduler  Yes GlobalYes
exit-infoYesYes    
expire_logs_daysYesYesYes GlobalYes
external-lockingYesYes    
- Variable: skip_external_locking      
federatedYesYes    
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_archive  Yes GlobalNo
have_blackhole_engine  Yes GlobalNo
have_community_features  Yes GlobalNo
have_compress  Yes GlobalNo
have_crypt  Yes GlobalNo
have_csv  Yes GlobalNo
have_dynamic_loading  Yes GlobalNo
have_example_engine  Yes GlobalNo
have_federated_engine  Yes GlobalNo
have_geometry  Yes GlobalNo
have_innodb  Yes GlobalNo
have_isam  Yes GlobalNo
have_merge_engine  Yes GlobalNo
have_ndbcluster  Yes GlobalNo
have_openssl  Yes GlobalNo
have_partition_engine  Yes GlobalNo
have_partitioning  Yes GlobalNo
have_query_cache  Yes GlobalNo
have_raid  Yes GlobalNo
have_row_based_replication  Yes GlobalNo
have_rtree_keys  Yes GlobalNo
have_ssl  Yes GlobalNo
have_symlink  Yes GlobalNo
helpYesYes    
hostname  Yes GlobalNo
identity  Yes SessionYes
ignore-builtin-innodbYesYes  GlobalNo
- Variable: ignore_builtin_innodb  Yes GlobalNo
init_connectYesYesYes GlobalYes
init-fileYesYes  GlobalNo
- Variable: init_file  Yes GlobalNo
init-rpl-roleYesYes    
init_slaveYesYesYes GlobalYes
innodbYesYes    
innodb_adaptive_flushingYesYesYes GlobalYes
innodb_adaptive_hash_indexYesYesYes GlobalNo
innodb_additional_mem_pool_sizeYesYesYes GlobalNo
innodb_autoextend_incrementYesYesYes GlobalYes
innodb_autoinc_lock_modeYesYesYes GlobalNo
innodb_buffer_pool_awe_mem_mbYesYesYes GlobalNo
Innodb_buffer_pool_pages_data   YesGlobalNo
Innodb_buffer_pool_pages_dirty   YesGlobalNo
Innodb_buffer_pool_pages_flushed   YesGlobalNo
Innodb_buffer_pool_pages_free   YesGlobalNo
Innodb_buffer_pool_pages_latched   YesGlobalNo
Innodb_buffer_pool_pages_misc   YesGlobalNo
Innodb_buffer_pool_pages_total   YesGlobalNo
Innodb_buffer_pool_read_ahead   YesGlobalNo
Innodb_buffer_pool_read_ahead_evicted   YesGlobalNo
Innodb_buffer_pool_read_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_change_bufferingYesYesYes GlobalYes
innodb_checksumsYesYesYes GlobalNo
innodb_commit_concurrencyYesYesYes GlobalYes
innodb_concurrency_ticketsYesYesYes GlobalYes
innodb_data_file_pathYesYesYes GlobalNo
Innodb_data_fsyncs   YesGlobalNo
innodb_data_home_dirYesYesYes GlobalNo
Innodb_data_pending_fsyncs   YesGlobalNo
Innodb_data_pending_reads   YesGlobalNo
Innodb_data_pending_writes   YesGlobalNo
Innodb_data_read   YesGlobalNo
Innodb_data_reads   YesGlobalNo
Innodb_data_writes   YesGlobalNo
Innodb_data_written   YesGlobalNo
Innodb_dblwr_pages_written   YesGlobalNo
Innodb_dblwr_writes   YesGlobalNo
innodb_doublewriteYesYesYes GlobalNo
innodb_fast_shutdownYesYesYes GlobalYes
innodb_file_formatYesYesYes GlobalYes
innodb_file_format_checkYesYesYes 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_have_atomic_builtins   YesGlobalNo
innodb_io_capacityYesYesYes GlobalNo
innodb_lock_wait_timeoutYesYesYes BothNo
innodb_locks_unsafe_for_binlogYesYesYes GlobalNo
innodb_log_arch_dirYesYesYes GlobalNo
innodb_log_archiveYesYesYes GlobalNo
innodb_log_buffer_sizeYesYesYes GlobalNo
innodb_log_file_sizeYesYesYes GlobalNo
innodb_log_files_in_groupYesYesYes GlobalNo
innodb_log_group_home_dirYesYesYes GlobalNo
Innodb_log_waits   YesGlobalNo
Innodb_log_write_requests   YesGlobalNo
Innodb_log_writes   YesGlobalNo
innodb_max_dirty_pages_pctYesYesYes GlobalYes
innodb_max_purge_lagYesYesYes GlobalYes
innodb_mirrored_log_groupsYesYesYes GlobalNo
innodb_old_blocks_pctYesYesYes GlobalYes
innodb_old_blocks_timeYesYesYes GlobalYes
innodb_open_filesYesYesYes GlobalNo
Innodb_os_log_fsyncs   YesGlobalNo
Innodb_os_log_pending_fsyncs   YesGlobalNo
Innodb_os_log_pending_writes   YesGlobalNo
Innodb_os_log_written   YesGlobalNo
Innodb_page_size   YesGlobalNo
Innodb_pages_created   YesGlobalNo
Innodb_pages_read   YesGlobalNo
Innodb_pages_written   YesGlobalNo
innodb_random_read_aheadYesYesYes GlobalYes
innodb_read_ahead_thresholdYesYesYes GlobalYes
innodb_read_io_threadsYesYesYes GlobalNo
innodb_replication_delayYesYesYes GlobalYes
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_spin_wait_delayYesYesYes GlobalYes
innodb_stats_methodYesYesYes GlobalYes
innodb_stats_on_metadataYesYesYes GlobalYes
innodb_stats_sample_pagesYesYesYes GlobalYes
innodb-status-fileYesYes    
innodb_strict_modeYesYesYes BothYes
innodb_support_xaYesYesYes BothYes
innodb_sync_spin_loopsYesYesYes GlobalYes
innodb_table_locksYesYesYes BothYes
innodb_thread_concurrencyYesYesYes GlobalYes
innodb_thread_sleep_delayYesYesYes GlobalYes
innodb_use_legacy_cardinality_algorithmYesYesYes GlobalYes
innodb_use_sys_mallocYesYesYes GlobalNo
innodb_version  Yes GlobalNo
innodb_write_io_threadsYesYesYes GlobalNo
insert_id  Yes SessionYes
installYes     
install-manualYes     
interactive_timeoutYesYesYes BothYes
join_buffer_sizeYesYesYes BothYes
keep_files_on_createYesYesYes BothYes
Key_blocks_not_flushed   YesGlobalNo
Key_blocks_unused   YesGlobalNo
Key_blocks_used   YesGlobalNo
key_buffer_sizeYesYesYes GlobalYes
key_cache_age_thresholdYesYesYes GlobalYes
key_cache_block_sizeYesYesYes GlobalYes
key_cache_division_limitYesYesYes GlobalYes
Key_read_requests   YesGlobalNo
Key_reads   YesGlobalNo
Key_write_requests   YesGlobalNo
Key_writes   YesGlobalNo
languageYesYesYes GlobalNo
large_files_support  Yes GlobalNo
large_page_size  Yes GlobalNo
large-pagesYesYes  GlobalNo
- Variable: large_pages  Yes GlobalNo
last_insert_id  Yes SessionYes
Last_query_cost   YesSessionNo
lc_time_names  Yes BothYes
license  Yes GlobalNo
local_infile  Yes GlobalYes
local-serviceYes     
locked_in_memory  Yes GlobalNo
logYesYesYes GlobalYes
log_bin  Yes GlobalNo
log-binYesYesYes GlobalNo
log-bin-indexYesYes    
log-bin-trust-function-creatorsYesYes  GlobalYes
- Variable: log_bin_trust_function_creators  Yes GlobalYes
log-bin-trust-routine-creatorsYesYes  GlobalYes
- Variable: log_bin_trust_routine_creators  Yes GlobalYes
log_bin_use_v1_row_eventsYesYesYes GlobalNo
log-bin-use-v1-row-eventsYesYes  GlobalNo
- Variable: log_bin_use_v1_row_events  Yes GlobalNo
log-errorYesYes  GlobalNo
- Variable: log_error  Yes GlobalNo
log-isamYesYes    
log-outputYesYes  GlobalYes
- Variable: log_output  Yes GlobalYes
log-queries-not-using-indexesYesYes  GlobalYes
- Variable: log_queries_not_using_indexes  Yes GlobalYes
log-short-formatYesYes    
log-slave-updatesYesYes  GlobalNo
- Variable: log_slave_updates  Yes GlobalNo
log_slave_updatesYesYesYes 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_system  Yes GlobalNo
lower_case_table_namesYesYesYes GlobalNo
master-connect-retryYesYes    
master-hostYesYes    
master-info-fileYesYes    
master-passwordYesYes    
master-portYesYes    
master-retry-countYesYes    
master-sslYesYes    
master-ssl-caYesYes    
master-ssl-capathYesYes    
master-ssl-certYesYes    
master-ssl-cipherYesYes    
master-ssl-keyYesYes    
master-userYesYes    
max_allowed_packetYesYesYes GlobalYes
max_binlog_cache_sizeYesYesYes GlobalYes
max-binlog-dump-eventsYesYes    
max_binlog_sizeYesYesYes GlobalYes
max_connect_errorsYesYesYes GlobalYes
max_connectionsYesYesYes GlobalYes
max_delayed_threadsYesYesYes BothYes
max_error_countYesYesYes BothYes
max_heap_table_sizeYesYesYes BothYes
max_insert_delayed_threads  Yes BothYes
max_join_sizeYesYesYes BothYes
max_length_for_sort_dataYesYesYes BothYes
max_long_data_sizeYesYesYes GlobalNo
max_prepared_stmt_countYesYesYes GlobalYes
max_relay_log_sizeYesYesYes GlobalYes
max_seeks_for_keyYesYesYes BothYes
max_sort_lengthYesYesYes BothYes
max_sp_recursion_depthYesYesYes BothYes
Max_used_connections   YesGlobalNo
max_user_connectionsYesYesYes BothYes
max_write_lock_countYesYesYes GlobalYes
memlockYesYesYes GlobalNo
mergeYesYes    
min-examined-row-limitYesYesYes BothYes
multi_range_countYesYesYes BothYes
myisam-block-sizeYesYes    
myisam_data_pointer_sizeYesYesYes GlobalYes
myisam_max_sort_file_sizeYesYesYes GlobalYes
myisam_mmap_sizeYesYesYes GlobalNo
myisam-recoverYesYes    
- Variable: myisam_recover_options      
myisam_recover_options  Yes GlobalNo
myisam_repair_threadsYesYesYes BothYes
myisam_sort_buffer_sizeYesYesYes BothYes
myisam_stats_methodYesYesYes BothYes
myisam_use_mmapYesYesYes GlobalYes
named_pipe  Yes GlobalNo
Ndb_api_bytes_received_count   YesGlobalNo
Ndb_api_bytes_received_count_session   YesSessionNo
Ndb_api_bytes_received_count_slave   YesGlobalNo
Ndb_api_bytes_sent_count   YesGlobalNo
Ndb_api_bytes_sent_count_session   YesSessionNo
Ndb_api_bytes_sent_count_slave   YesGlobalNo
Ndb_api_event_bytes_count   YesGlobalNo
Ndb_api_event_bytes_count_injector   YesGlobalNo
Ndb_api_event_data_count   YesGlobalNo
Ndb_api_event_data_count_injector   YesGlobalNo
Ndb_api_event_nondata_count   YesGlobalNo
Ndb_api_event_nondata_count_injector   YesGlobalNo
Ndb_api_pk_op_count   YesGlobalNo
Ndb_api_pk_op_count_session   YesSessionNo
Ndb_api_pk_op_count_slave   YesGlobalNo
Ndb_api_pruned_scan_count   YesGlobalNo
Ndb_api_pruned_scan_count_session   YesSessionNo
Ndb_api_pruned_scan_count_slave   YesGlobalNo
Ndb_api_range_scan_count   YesGlobalNo
Ndb_api_range_scan_count_session   YesSessionNo
Ndb_api_range_scan_count_slave   YesGlobalNo
Ndb_api_read_row_count   YesGlobalNo
Ndb_api_read_row_count_session   YesSessionNo
Ndb_api_read_row_count_slave   YesGlobalNo
Ndb_api_scan_batch_count   YesGlobalNo
Ndb_api_scan_batch_count_session   YesSessionNo
Ndb_api_scan_batch_count_slave   YesGlobalNo
Ndb_api_table_scan_count   YesGlobalNo
Ndb_api_table_scan_count_session   YesSessionNo
Ndb_api_table_scan_count_slave   YesGlobalNo
Ndb_api_trans_abort_count   YesGlobalNo
Ndb_api_trans_abort_count_session   YesSessionNo
Ndb_api_trans_abort_count_slave   YesGlobalNo
Ndb_api_trans_close_count   YesGlobalNo
Ndb_api_trans_close_count_session   YesSessionNo
Ndb_api_trans_close_count_slave   YesGlobalNo
Ndb_api_trans_commit_count   YesGlobalNo
Ndb_api_trans_commit_count_session   YesSessionNo
Ndb_api_trans_commit_count_slave   YesGlobalNo
Ndb_api_trans_local_read_row_count   YesGlobalNo
Ndb_api_trans_local_read_row_count_session   YesSessionNo
Ndb_api_trans_local_read_row_count_slave   YesGlobalNo
Ndb_api_trans_start_count   YesGlobalNo
Ndb_api_trans_start_count_session   YesSessionNo
Ndb_api_trans_start_count_slave   YesGlobalNo
Ndb_api_uk_op_count   YesGlobalNo
Ndb_api_uk_op_count_session   YesSessionNo
Ndb_api_uk_op_count_slave   YesGlobalNo
Ndb_api_wait_exec_complete_count   YesGlobalNo
Ndb_api_wait_exec_complete_count_session   YesSessionNo
Ndb_api_wait_exec_complete_count_slave   YesGlobalNo
Ndb_api_wait_meta_request_count   YesGlobalNo
Ndb_api_wait_meta_request_count_session   YesSessionNo
Ndb_api_wait_meta_request_count_slave   YesGlobalNo
Ndb_api_wait_nanos_count   YesGlobalNo
Ndb_api_wait_nanos_count_session   YesSessionNo
Ndb_api_wait_nanos_count_slave   YesGlobalNo
Ndb_api_wait_scan_result_count   YesGlobalNo
Ndb_api_wait_scan_result_count_session   YesSessionNo
Ndb_api_wait_scan_result_count_slave   YesGlobalNo
ndb_autoincrement_prefetch_szYesYesYes BothYes
ndb-batch-sizeYesYesYes GlobalNo
ndb-blob-read-batch-bytesYesYesYes BothYes
ndb-blob-write-batch-bytesYesYesYes BothYes
ndb_cache_check_timeYesYesYes GlobalYes
ndb-cluster-connection-poolYesYesYesYesGlobalNo
Ndb_cluster_node_id   YesBothNo
Ndb_config_from_host   YesBothNo
Ndb_config_from_port   YesBothNo
Ndb_conflict_fn_epoch   YesGlobalNo
Ndb_conflict_fn_epoch_trans   YesGlobalNo
Ndb_conflict_fn_max   YesGlobalNo
Ndb_conflict_fn_old   YesGlobalNo
Ndb_conflict_trans_conflict_commit_count   YesGlobalNo
Ndb_conflict_trans_detect_iter_count   YesGlobalNo
Ndb_conflict_trans_reject_count   YesGlobalNo
Ndb_conflict_trans_row_conflict_count   YesGlobalNo
Ndb_conflict_trans_row_reject_count   YesGlobalNo
ndb-connectstringYesYes    
ndb-deferred-constraintsYesYes  BothYes
- Variable: ndb_deferred_constraints  Yes BothYes
ndb_deferred_constraintsYesYesYes BothYes
ndb_distributionYesYesYes GlobalYes
ndb-distributionYesYes  GlobalYes
- Variable: ndb_distribution  Yes GlobalYes
ndb_eventbuffer_max_allocYesYesYes GlobalYes
ndb_execute_count   YesGlobalNo
ndb_extra_loggingYesYesYes GlobalYes
ndb_force_sendYesYesYes BothYes
ndb_index_stat_cache_entriesYesYesYes BothYes
ndb_index_stat_enableYesYesYes BothYes
ndb_index_stat_optionYesYesYes BothYes
ndb_index_stat_update_freqYesYesYes BothYes
ndb_join_pushdown  Yes BothYes
ndb-log-apply-statusYesYes  GlobalNo
- Variable: ndb_log_apply_status  Yes GlobalNo
ndb_log_apply_statusYesYesYes GlobalNo
ndb_log_binYes Yes BothYes
ndb_log_binlog_indexYes Yes GlobalYes
ndb_log_empty_epochsYesYesYes GlobalYes
ndb-log-empty-epochsYesYesYes GlobalYes
ndb-log-origYesYes  GlobalNo
- Variable: ndb_log_orig  Yes GlobalNo
ndb_log_origYesYesYes GlobalNo
ndb-log-transaction-idYesYes  GlobalNo
- Variable: ndb_log_transaction_id  Yes GlobalNo
ndb_log_transaction_id  Yes GlobalNo
ndb-log-update-as-writeYesYesYes GlobalYes
ndb_log_updated_onlyYesYesYes GlobalYes
ndb-mgmd-hostYesYes    
ndb-nodeidYesYes YesGlobalNo
Ndb_number_of_data_nodes   YesGlobalNo
ndb_optimization_delay  Yes GlobalYes
ndb_optimized_node_selectionYesYesYes GlobalNo
ndb_pruned_scan_count   YesGlobalNo
Ndb_pushed_queries_defined   YesGlobalNo
Ndb_pushed_queries_dropped   YesGlobalNo
Ndb_pushed_queries_executed   YesGlobalNo
Ndb_pushed_reads   YesGlobalNo
ndb_report_thresh_binlog_epoch_slipYesYes    
ndb_report_thresh_binlog_mem_usageYesYes    
ndb_scan_count   YesGlobalNo
ndb_table_no_logging  Yes SessionYes
ndb_table_temporary  Yes SessionYes
ndb-transid-mysql-connection-mapYes     
ndb_use_copying_alter_table  Yes BothNo
ndb_use_exact_count  Yes BothYes
ndb_use_transactionsYesYesYes BothYes
ndb_version  Yes GlobalNo
ndb_version_string  Yes GlobalNo
ndb-wait-connectedYesYesYes GlobalNo
ndb-wait-setupYesYesYes GlobalNo
ndbclusterYesYes    
- Variable: have_ndbcluster      
ndbinfo_database  Yes GlobalNo
ndbinfo_max_bytesYes Yes BothYes
ndbinfo_max_rowsYes Yes BothYes
ndbinfo_offline  Yes GlobalYes
ndbinfo_show_hiddenYes Yes BothYes
ndbinfo_table_prefixYes Yes BothYes
ndbinfo_version  Yes GlobalNo
net_buffer_lengthYesYesYes BothYes
net_read_timeoutYesYesYes BothYes
net_retry_countYesYesYes BothYes
net_write_timeoutYesYesYes BothYes
newYesYesYes BothYes
no-defaultsYes     
Not_flushed_delayed_rows   YesGlobalNo
oldYesYesYes GlobalNo
old-alter-tableYesYes  BothYes
- Variable: old_alter_table  Yes BothYes
old_passwords  Yes BothYes
old-style-user-limitsYesYes    
one-threadYesYes    
Open_files   YesGlobalNo
open-files-limitYesYes  GlobalNo
- Variable: open_files_limit  Yes GlobalNo
Open_streams   YesGlobalNo
Open_table_definitions   YesGlobalNo
Open_tables   YesBothNo
Opened_files   YesGlobalNo
Opened_table_definitions   YesBothNo
Opened_tables   YesBothNo
optimizer_prune_levelYesYesYes BothYes
optimizer_search_depthYesYesYes BothYes
optimizer_switchYesYesYes BothYes
partitionYesYes    
- Variable: have_partitioning      
pid-fileYesYes  GlobalNo
- Variable: pid_file  Yes GlobalNo
pluginYesYes    
plugin_dirYesYesYes GlobalNo
plugin-loadYesYes    
portYesYesYes GlobalNo
port-open-timeoutYesYes    
preload_buffer_sizeYesYesYes BothYes
prepared_stmt_count  Yes GlobalNo
Prepared_stmt_count   YesGlobalNo
print-defaultsYes     
profiling  Yes SessionYes
profiling_history_sizeYesYesYes BothYes
protocol_version  Yes GlobalNo
pseudo_thread_id  Yes SessionYes
Qcache_free_blocks   YesGlobalNo
Qcache_free_memory   YesGlobalNo
Qcache_hits   YesGlobalNo
Qcache_inserts   YesGlobalNo
Qcache_lowmem_prunes   YesGlobalNo
Qcache_not_cached   YesGlobalNo
Qcache_queries_in_cache   YesGlobalNo
Qcache_total_blocks   YesGlobalNo
Queries   YesBothNo
query_alloc_block_sizeYesYesYes BothYes
query_cache_limitYesYesYes GlobalYes
query_cache_min_res_unitYesYesYes GlobalYes
query_cache_sizeYesYesYes GlobalYes
query_cache_typeYesYesYes BothYes
query_cache_wlock_invalidateYesYesYes BothYes
query_prealloc_sizeYesYesYes BothYes
Questions   YesBothNo
rand_seed1  Yes SessionYes
rand_seed2  Yes SessionYes
range_alloc_block_sizeYesYesYes BothYes
read_buffer_sizeYesYesYes BothYes
read_onlyYesYesYes GlobalYes
read_rnd_buffer_sizeYesYesYes BothYes
relay-logYesYes  GlobalNo
- Variable: relay_log  Yes GlobalNo
relay-log-indexYesYes  GlobalNo
- Variable: relay_log_index  Yes GlobalNo
relay_log_indexYesYesYes GlobalNo
relay-log-info-fileYesYes    
- Variable: relay_log_info_file      
relay_log_info_fileYesYesYes GlobalNo
relay_log_purgeYesYesYes GlobalYes
relay_log_space_limitYesYesYes GlobalNo
removeYes     
replicate-do-dbYesYes    
replicate-do-tableYesYes    
replicate-ignore-dbYesYes    
replicate-ignore-tableYesYes    
replicate-rewrite-dbYesYes    
replicate-same-server-idYesYes    
replicate-wild-do-tableYesYes    
replicate-wild-ignore-tableYesYes    
report-hostYesYes  GlobalNo
- Variable: report_host  Yes GlobalNo
report-passwordYesYes  GlobalNo
- Variable: report_password  Yes GlobalNo
report-portYesYes  GlobalNo
- Variable: report_port  Yes GlobalNo
report-userYesYes  GlobalNo
- Variable: report_user  Yes GlobalNo
rpl_recovery_rank  Yes GlobalYes
Rpl_status   YesGlobalNo
safe-modeYesYes    
safe-show-databaseYesYesYes GlobalYes
safe-user-createYesYes    
safemalloc-mem-limitYesYes    
secure-authYesYes  GlobalYes
- Variable: secure_auth  Yes GlobalYes
secure-file-privYesYes  GlobalNo
- Variable: secure_file_priv  Yes GlobalNo
Select_full_join   YesBothNo
Select_full_range_join   YesBothNo
Select_range   YesBothNo
Select_range_check   YesBothNo
Select_scan   YesBothNo
server-idYesYes  GlobalYes
- Variable: server_id  Yes GlobalYes
server_id_bitsYesYesYes GlobalNo
server-id-bitsYesYes  GlobalNo
- Variable: server_id_bits  Yes GlobalNo
shared_memoryYesYesYes GlobalNo
shared_memory_base_name  Yes GlobalNo
show-slave-auth-infoYesYes    
skip-character-set-client-handshakeYesYes    
skip-concurrent-insertYesYes    
- Variable: concurrent_insert      
skip-event-schedulerYesYes    
skip_external_lockingYesYesYes GlobalNo
skip-grant-tablesYesYes    
skip-host-cacheYesYes    
skip-lockingYesYes    
skip-mergeYesYes    
skip-name-resolveYesYes  GlobalNo
- Variable: skip_name_resolve  Yes GlobalNo
skip-ndbclusterYesYes    
skip-networkingYesYes  GlobalNo
- Variable: skip_networking  Yes GlobalNo
skip-newYesYes    
skip-partitionYesYes    
skip-safemallocYesYes    
skip-show-databaseYesYes  GlobalNo
- Variable: skip_show_database  Yes GlobalNo
skip-slave-startYesYes    
skip-sslYesYes    
skip-stack-traceYesYes    
skip-symbolic-linksYes     
skip-symlinkYesYes    
skip-thread-priorityYesYes    
slave_allow_batchingYesYesYes GlobalYes
slave_compressed_protocolYesYesYes GlobalYes
slave_exec_modeYesYesYes GlobalYes
Slave_heartbeat_period   YesGlobalNo
slave-load-tmpdirYesYes  GlobalNo
- Variable: slave_load_tmpdir  Yes GlobalNo
slave_max_allowed_packet  Yes GlobalYes
slave-max-allowed-packetYesYes    
- Variable: slave_max_allowed_packet      
slave-net-timeoutYesYes  GlobalYes
- Variable: slave_net_timeout  Yes GlobalYes
Slave_open_temp_tables   YesGlobalNo
Slave_received_heartbeats   YesGlobalNo
Slave_retried_transactions   YesGlobalNo
Slave_running   YesGlobalNo
slave-skip-errorsYesYes  GlobalNo
- Variable: slave_skip_errors  Yes GlobalNo
slave_transaction_retriesYesYesYes GlobalYes
slave_type_conversionsYesYesYes GlobalNo
Slow_launch_threads   YesBothNo
slow_launch_timeYesYesYes GlobalYes
Slow_queries   YesBothNo
slow-query-logYesYes  GlobalYes
- Variable: slow_query_log  Yes GlobalYes
slow_query_log_fileYesYesYes GlobalYes
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_version   YesBothNo
standaloneYesYes    
storage_engine  Yes BothYes
symbolic-linksYesYes    
sync_binlogYesYesYes GlobalYes
sync_frmYesYesYes GlobalYes
sysdate-is-nowYesYes    
system_time_zone  Yes GlobalNo
table_cacheYesYesYes GlobalYes
table_definition_cache  Yes GlobalYes
table_lock_wait_timeoutYesYesYes GlobalYes
Table_locks_immediate   YesGlobalNo
Table_locks_waited   YesGlobalNo
table_open_cache  Yes GlobalYes
table_type  Yes BothYes
tc-heuristic-recoverYesYes    
Tc_log_max_pages_used   YesGlobalNo
Tc_log_page_size   YesGlobalNo
Tc_log_page_waits   YesGlobalNo
temp-poolYesYes    
thread_cache_sizeYesYesYes GlobalYes
thread_concurrencyYesYesYes GlobalNo
thread_handlingYesYesYes GlobalNo
thread_stackYesYesYes GlobalNo
Threads_cached   YesGlobalNo
Threads_connected   YesGlobalNo
Threads_created   YesGlobalNo
Threads_running   YesGlobalNo
time_format  Yes BothNo
time_zone  Yes BothYes
timed_mutexesYesYesYes GlobalYes
timestamp  Yes SessionYes
tmp_table_sizeYesYesYes BothYes
tmpdirYesYesYes GlobalNo
transaction_alloc_block_sizeYesYesYes BothYes
transaction_allow_batching  Yes SessionYes
transaction-isolationYesYes    
- Variable: tx_isolation      
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    
version  Yes GlobalNo
version_comment  Yes GlobalNo
version_compile_machine  Yes GlobalNo
version_compile_os  Yes GlobalNo
wait_timeoutYesYesYes BothYes
warning_count  Yes SessionNo

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

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


5.1.2 Server Configuration Defaults

The MySQL server has many operating parameters, which you can change at server startup using command-line options or configuration files (option files). It is also possible to change many parameters at runtime. For general instructions on setting parameters at startup or runtime, see Section 5.1.3, “Server Command Options”, and Section 5.1.4, “Server System Variables”.

MySQL provides a number of preconfigured option files that can be used as a basis for tuning the MySQL server. Look for files named my-small.cnf, my-medium.cnf, my-large.cnf, and my-huge.cnf, which are sample option files for small, medium, large, and very large systems. On Windows, the extension is .ini rather than .cnf.

Note

On Windows, the .ini or .cnf option file extension might not be displayed.

For a binary distribution, look for the sample files in or under your installation directory. If you have a source distribution, look in the support-files directory. To use a sample file as a base configuration file, rename a copy of it and place the copy in the appropriate location. Regarding names and appropriate location, see the general information provided in Section 4.2.6, “Using Option Files”. That section also describes option file format and syntax.

5.1.3 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 4.2.6, “Using Option Files”.

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

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

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

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

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

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

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

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

  • --help, -?

    Command-Line Format-?
     --help

    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
     Permitted Values
    Typeboolean
    DefaultFALSE

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

  • --ansi

    Command-Line Format--ansi
     -a

    Use standard (ANSI) SQL syntax instead of MySQL syntax. For more precise control over the server SQL mode, use the --sql-mode option instead. See Section 1.8, “MySQL Standards Compliance”, and Section 5.1.7, “Server SQL Modes”.

  • --basedir=path, -b path

    Command-Line Format--basedir=path
     -b
    System Variable Namebasedir
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typedirectory name

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

  • --big-tables

    Command-Line Format--big-tables
    System Variable Namebig_tables
    Variable ScopeSession
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

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

  • --bind-address=addr

    Command-Line Format--bind-address=addr
    System Variable Namebind_address
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring
    Default0.0.0.0

    The MySQL server listens on a single network socket for TCP/IP connections. This socket is bound to a single address, but it is possible for an address to map onto multiple network interfaces. The default address is 0.0.0.0. To specify an address explicitly, use the --bind-address=addr option at server startup, where addr is an IPv4 address or a host name. If addr is a host name, the server resolves the name to an IPv4 address and binds to that address.

    The server treats different types of addresses as follows:

    • If the address is 0.0.0.0, the server accepts TCP/IP connections on all server host IPv4 interfaces.

    • If the address is a regular IPv4 address (such as 127.0.0.1), the server accepts TCP/IP connections only for that particular IPv4 address.

    If you intend to bind the server to a specific address, be sure that the mysql.user grant table contains an account with administrative privileges that you can use connect to that address. Otherwise, you will not be able to shut down the server. For example, if you bind to 0.0.0.0, you can connect to the server using all existing accounts. But if you bind to 127.0.0.1, the server accepts connections only on that address. In this case, first make sure that the 'root'@'127.0.0.1' account is present in the mysql.user table so that you can still connect to the server to shut it down.

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

    Introduced5.1.5
    Command-Line Format--binlog-format=format
    System Variable Namebinlog_format
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values (>= 5.1.5, <= 5.1.7)
    Typeenumeration
    DefaultSTATEMENT
    Valid ValuesROW
    STATEMENT
     Permitted Values (>= 5.1.8, <= 5.1.11)
    Typeenumeration
    DefaultSTATEMENT
    Valid ValuesROW
    STATEMENT
    MIXED
     Permitted Values (>= 5.1.12, <= 5.1.28)
    Typeenumeration
    DefaultMIXED
    Valid ValuesROW
    STATEMENT
    MIXED
     Permitted Values (>= 5.1.29)
    Typeenumeration
    DefaultSTATEMENT
    Valid ValuesROW
    STATEMENT
    MIXED

    Specify whether to use row-based, statement-based, or mixed replication (statement-based was the default prior to MySQL 5.1.12; in 5.1.12, the default was changed to mixed replication; in 5.1.29, the default was changed back to statement-based). See Section 16.1.2, “Replication Formats”. This option was added in MySQL 5.1.5.

    Under some conditions, changing this variable at runtime is not possible, or causes replication to fail. See Section 5.2.4.2, “Setting The Binary Log Format”, for more information.

    Important

    Setting the binary logging format without enabling binary logging prevents the MySQL server from starting. This is a known issue in MySQL 5.1 which is fixed in MySQL 5.5. (Bug #42928)

    MySQL Cluster.  The default value for this option in all MySQL Cluster NDB 6.1 through 7.1 releases is MIXED. See Section 17.6.2, “General Requirements for MySQL Cluster Replication”, for more information.

  • --bootstrap

    Command-Line Format--bootstrap

    This option is used by the mysql_install_db program 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 2.11.4, “MySQL Source-Configuration Options”.

  • --character-sets-dir=path

    Command-Line Format--character-sets-dir=path
    System Variable Namecharacter_sets_dir
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typedirectory name

    The directory where character sets are installed. See Section 10.5, “Character Set Configuration”.

  • --character-set-client-handshake

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

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

  • --character-set-filesystem=charset_name

    Introduced5.1.6
    Command-Line Format--character-set-filesystem=name
    System Variable Namecharacter_set_filesystem
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring
    Defaultbinary

    The file system character set. This option sets the character_set_filesystem system variable. It was added in MySQL 5.1.6.

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

    Command-Line Format--character-set-server
    System Variable Namecharacter_set_server
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring
    Defaultlatin1

    Use charset_name as the default server character set. See Section 10.5, “Character Set Configuration”. If you use this option to specify a nondefault character set, you should also use --collation-server to specify the collation.

  • --chroot=path, -r path

    Command-Line Format--chroot=dir_name
     -r name
     Permitted Values
    Typedirectory name

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

  • --collation-server=collation_name

    Command-Line Format--collation-server
    System Variable Namecollation_server
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring
    Defaultlatin1_swedish_ci

    Use collation_name as the default server collation. See Section 10.5, “Character Set Configuration”.

  • --console

    Command-Line Format--console
    Platform SpecificWindows

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

    If both --log-error and --console are specified, whichever option is given last takes precedence.

  • --core-file

    Command-Line Format--core-file
     Permitted Values
    Typeboolean
    DefaultOFF

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

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

  • --datadir=path, -h path

    Command-Line Format--datadir=path
     -h
    System Variable Namedatadir
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typedirectory name

    The path to the data directory.

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

    Command-Line Format--debug[=debug_options]
    System Variable Namedebug
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Type (Unix)string
    Defaultd:t:i:o,/tmp/mysqld.trace
     Permitted Values
    Type (Windows)string
    Defaultd:t:i:O,\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,/tmp/mysqld.trace on Unix and d:t:i:O,\mysqld.trace on Windows.

    As of MySQL 5.1.12, 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.

    For more information, see Section 22.4.3, “The DBUG Package”.

  • --debug-sync-timeout[=N]

    Introduced5.1.41
    Command-Line Format--debug-sync-timeout[=#]
     Permitted Values
    Typenumeric

    Controls whether the Debug Sync facility for testing and debugging is enabled. Use of Debug Sync requires that MySQL be configured with the --enable-debug-sync option (see Section 2.11.4, “MySQL Source-Configuration Options”). If Debug Sync is not compiled in, this option is not available. The option value is a timeout in seconds. The default value is 0, which disables Debug Sync. To enable it, specify a value greater than 0; this value also becomes the default timeout for individual synchronization points. If the option is given without a value, the timeout is set to 300 seconds.

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

    This option was added in MySQL 5.1.41.

  • --default-character-set=charset_name

    Deprecated5.0.0
    Command-Line Format--default-character-set=name
     -C name
     Permitted Values
    Typestring

    Use charset_name as the default character set. This option is deprecated in favor of --character-set-server. See Section 10.5, “Character Set Configuration”. --default-character-set is removed in MySQL 5.5.

  • --default-collation=collation_name

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

    Use collation_name as the default collation. This option is deprecated in favor of --collation-server. See Section 10.5, “Character Set Configuration”. --default-collation is removed in MySQL 5.5.

  • --default-storage-engine=type

    Command-Line Format--default-storage-engine=name
    System Variable Namestorage_engine
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeenumeration
    DefaultMyISAM

    Set the default storage engine (table type) for tables. See Chapter 14, Storage Engines.

  • --default-table-type=type

    Deprecated5.0.0, by default-storage-engine
    Command-Line Format--default-table-type=name
     Permitted Values
    Typestring

    This option is a synonym for --default-storage-engine. It is deprecated and removed in MySQL 5.5.

  • --default-time-zone=timezone

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

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

  • --defaults-extra-file=file_name

    Read this option file after the global option file but (on Unix) before the user option file. If the file does not exist or is otherwise inaccessible, an error occurs. file_name is the full path name to the file.

  • --defaults-file=file_name

    Use only the given option file. If the file does not exist or is otherwise inaccessible, an error occurs. file_name is the full path name to the file.

  • --defaults-group-suffix=str

    Read not only the usual option groups, but also groups with the usual names and a suffix of str. For example, mysqld normally reads the [mysqld] group. If the --defaults-group-suffix=_other option is given, mysqld also reads the [mysqld_other] group.

  • --delay-key-write[={OFF|ON|ALL}]

    Command-Line Format--delay-key-write[=name]
    System Variable Namedelay_key_write
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    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 8.9.2, “Tuning Server Parameters”, and Section 14.5.1, “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=file_name

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

  • --enable-locking

    This option is deprecated. Use --external-locking instead.

  • --enable-named-pipe

    Command-Line Format--enable-named-pipe
    Platform SpecificWindows

    Enable support for named pipes. This option applies only on Windows. For MySQL 5.1.20 and earlier, this option is available only when using the mysqld-nt and mysqld-debug servers that support named-pipe connections. For MySQL 5.1.21 and later, mysqld-nt is not available, but support is included in the standard mysqld and mysqld-debug servers.

  • --enable-pstack

    Deprecated5.1.54
    Command-Line Format--enable-pstack
     Permitted Values
    Typeboolean
    DefaultFALSE

    This option is nonfunctional. It is deprecated as of MySQL 5.1.54 and removed in MySQL 5.5.

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

    Command-Line Format--engine-condition-pushdown
    System Variable Nameengine_condition_pushdown
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultON

    Sets the engine_condition_pushdown system variable. For more information, see Section 8.3.1.5, “Engine Condition Pushdown Optimization”.

  • --event-scheduler[=value]

    Introduced5.1.6
    Command-Line Format--event-scheduler[=value]
    System Variable Nameevent_scheduler
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeenumeration
    DefaultOFF
    Valid ValuesON
    OFF
    DISABLED

    Enable or disable, and start or stop, the event scheduler. This option was added in MySQL 5.1.6. Note that its permitted values and behavior changed in MySQL 5.1.11, and again in MySQL 5.1.12.

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

  • --exit-info[=flags], -T [flags]

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

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

  • --external-locking

    Command-Line Format--external-locking
     Permitted Values
    Typeboolean
    DefaultFALSE

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

    To disable external locking explicitly, use --skip-external-locking.

    External locking affects only MyISAM table access. For more information, including conditions under which it can and cannot be used, see Section 8.7.4, “External Locking”.

  • --flush

    Command-Line Format--flush
    System Variable Nameflush
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

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

  • --gdb

    Command-Line Format--gdb
     Permitted Values
    Typeboolean
    DefaultFALSE

    Install an interrupt handler for SIGINT (needed to stop mysqld with ^C to set breakpoints) and disable stack tracing and core file handling. See Section 22.4, “Debugging and Porting MySQL”.

  • --general-log[={0|1}]

    Introduced5.1.12
    Command-Line Format--general-log
    System Variable Namegeneral_log
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    Specify the initial general query log state. With no argument or an argument of 1, the --general-log option enables the log. If omitted or given with an argument of 0, the option disables the log. This option was added in MySQL 5.1.12.

  • --init-file=file_name

    Command-Line Format--init-file=file_name
    System Variable Nameinit_file
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

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

    This option is unavailable if MySQL was configured with the --disable-grant-options option. See Section 2.11.4, “MySQL Source-Configuration Options”.

  • --innodb-xxx

    Set an option for the InnoDB storage engine. The InnoDB options are listed in Section 14.6.7, “InnoDB Startup Options and System Variables”.

  • --install [service_name]

    Command-Line Format--install [service_name]

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

    Note

    If the server is started with the --defaults-file and --install options, --install must be first.

  • --install-manual [service_name]

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

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

    Note

    If the server is started with the --defaults-file and --install-manual options, --install-manual must be first.

  • --language=lang_name, -L lang_name

    Command-Line Format--language=name
     -L
    System Variable Namelanguage
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typedirectory name
    Default/usr/local/mysql/share/mysql/english/

    The language to use for error messages. lang_name can be given as the language name or as the full path name to the directory where the language files are installed. See Section 10.2, “Setting the Error Message Language”.

  • --large-pages

    Command-Line Format--large-pages
    System Variable Namelarge_pages
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform SpecificLinux
     Permitted Values
    Type (Linux)boolean
    DefaultFALSE

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

    Currently, MySQL supports only the Linux implementation of large page support (which is called HugeTLB in Linux). See Section 8.9.7, “Enabling Large Page Support”.

    --large-pages is disabled by default.

  • --local-service

    Command-Line Format--local-service

    (Windows only) A --local-service option following the service name causes the server to run using the LocalService Windows account that has limited system privileges. This account is available only for Windows XP or newer. If both --defaults-file and --local-service are given following the service name, they can be in any order. See Section 2.3.6.7, “Starting MySQL Server as a Microsoft Windows Service”.

  • --log[=file_name], -l [file_name]

    Deprecated5.1.29, by general-log
    Command-Line Format--log[=file_name]
     -l
    System Variable Namelog
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typefile name

    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 as of MySQL 5.1.6. Before 5.1.6, logging occurs to the general query log file. If you omit the file name, MySQL uses host_name.log as the file name. See Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”, and Section 5.2.3, “The General Query Log”.

    As of MySQL 5.1.29, the --log option is deprecated and is removed (along with the log system variable) in MySQL 5.6. Instead, use the --general_log option to enable the general query log and the --general_log_file=file_name option to set the general query log file name.

  • --log-error[=file_name]

    Command-Line Format--log-error[=file_name]
    System Variable Namelog_error
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

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

  • --log-isam[=file_name]

    Command-Line Format--log-isam[=file_name]
     Permitted Values
    Typefile name

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

  • --log-long-format

    Deprecated4.1.0
    Command-Line Format--log-long-format
     -0

    Log extra information to the binary log and slow query log, if they have been activated. For example, the user name and timestamp are logged for all queries. This option is deprecated, as it now represents the default logging behavior. (See the description for --log-short-format.) The --log-queries-not-using-indexes option is available for the purpose of logging queries that do not use indexes to the slow query log. --log-long-format is removed in MySQL 5.5.

  • --log-output[=value,...]

    Introduced5.1.6
    Command-Line Format--log-output=name
    System Variable Namelog_output
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeset
    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. (For MySQL 5.1.6 through 5.1.20, the default is TABLE.) TABLE select logging to the general_log and slow_log tables in the mysql database as a destination. FILE selects logging to log files as a destination. NONE disables logging. If NONE is present in the option value, it takes precedence over any other words that are present. TABLE and FILE can both be given to select to both log output destinations.

    This option selects log output destinations, but does not enable log output. To do that, use the --general_log and --slow_query_log options. For FILE logging, the --general_log_file and -slow_query_log_file options determine the log file location. (Before MySQL 5.1.29, 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”.

    The --log-output option was added in MySQL 5.1.6.

  • --log-queries-not-using-indexes

    Command-Line Format--log-queries-not-using-indexes
    System Variable Namelog_queries_not_using_indexes
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

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

  • --log-short-format

    Command-Line Format--log-short-format
     Permitted Values
    Typeboolean
    DefaultFALSE

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

  • --log-slow-admin-statements

    Command-Line Format--log-slow-admin-statements
     Permitted Values
    Typeboolean
    DefaultOFF

    Include slow administrative statements in the statements written to the slow query log. Administrative statements include ALTER TABLE, ANALYZE TABLE, CHECK TABLE, CREATE INDEX, DROP INDEX, OPTIMIZE TABLE, and REPAIR TABLE.

  • --log-slow-queries[=file_name]

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

    This option enables logging to the slow query log, which contains entries for all queries that have taken more than long_query_time seconds to execute. See the descriptions of the --log-long-format and --log-short-format options for details.

    The log output destination can be selected with the --log-output option as of MySQL 5.1.6. Before 5.1.6, logging occurs to the slow query log file. 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 5.1.29, the --log-slow-queries option is deprecated and is removed (along with the log_slow_queries system variable) in MySQL 5.6. Instead, use the --slow_query_log option to enable the slow query log and the --slow_query_log_file=file_name option to set the slow query log file name.

  • --log-tc=file_name

    Command-Line Format--log-tc=file_name
     Permitted Values
    Typefile name
    Defaulttc.log

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

  • --log-tc-size=size

    Command-Line Format--log-tc-size=#
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default24576
    Max Value18446744073709547520

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

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

    Command-Line Format--log-warnings[=#]
     -W [#]
    System Variable Namelog_warnings
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default1
    Min Value0
    Max Value18446744073709547520

    Print out warnings such as Aborted connection... to the error log. This option is enabled (1) by default. To disable it, use --log-warnings=0. Specifying the option without a level value increments the current value by 1. Enabling this option by setting it greater than 0 is recommended, for example, if you use replication (you get more information about what is happening, such as messages about network failures and reconnections). If the value is greater than 1, aborted connections are written to the error log. See Section B.5.2.11, “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. As of MySQL 5.1.38, the server logs messages about statements that are unsafe for statement-based logging if --log-warnings is greater than 0.

  • --low-priority-updates

    Command-Line Format--low-priority-updates
    System Variable Namelow_priority_updates
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultFALSE

    Give table-modifying operations (INSERT, REPLACE, DELETE, UPDATE) lower priority than selects. This can also be done using {INSERT | REPLACE | DELETE | UPDATE} LOW_PRIORITY ... to lower the priority of only one query, or by SET LOW_PRIORITY_UPDATES=1 to change the priority in one thread. This affects only storage engines that use only table-level locking (MyISAM, MEMORY, MERGE). See Section 8.7.2, “Table Locking Issues”.

  • --min-examined-row-limit=number

    Introduced5.1.21
    Command-Line Format--min-examined-row-limit=#
    System Variable Namemin_examined_row_limit
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default0
    Min Value0
    Max Value4294967295

    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 5.1.21.

  • --memlock

    Command-Line Format--memlock
    System Variable Namelocked_in_memory
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typeboolean
    DefaultFALSE

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

    --memlock works on systems that support the mlockall() system call; this includes Solaris, most Linux distributions that use a 2.4 or newer kernel, and perhaps other Unix systems. 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

    Use of this option may require you to run the server as root, which, for reasons of security, is normally not a good idea. See Section 6.1.5, “How to Run MySQL as a Normal User”.

    On Linux and perhaps other systems, you can avoid the need to run the server as root by changing the limits.conf file. See the notes regarding the memlock limit in Section 8.9.7, “Enabling Large Page Support”.

    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=#
     Permitted Values
    Typenumeric
    Default1024
    Min Value1024
    Max Value16384

    The block size to be used for MyISAM index pages.

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

    Command-Line Format--myisam-recover[=name]
     Permitted Values
    Typeenumeration
    DefaultOFF
    Valid ValuesOFF
    DEFAULT
    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 was not closed properly. (The last option works only if you are running with external locking disabled.) If this is the case, mysqld runs a check on the table. If the table was corrupted, mysqld attempts to repair it.

    The following options affect how the repair works.

    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.
    QUICKDo not check the rows in the table if there are not any delete blocks.

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

    See Section 14.5.1, “MyISAM Startup Options”.

  • --no-defaults

    Do not read any option files. If program startup fails due to reading unknown options from an option file, --no-defaults can be used to prevent them from being read.

  • --old-alter-table

    Command-Line Format--old-alter-table
    System Variable Nameold_alter_table
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    When this option is given, the server does not use the optimized method of processing an ALTER TABLE operation. It reverts to using a temporary table, copying over the data, and then renaming the temporary table to the original, as used by MySQL 5.0 and earlier. For more information on the operation of ALTER TABLE, see Section 13.1.7, “ALTER TABLE Syntax”.

  • --old-style-user-limits

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

    Enable old-style user limits. (Before MySQL 5.0.3, account resource limits were counted separately for each host from which a user connected rather than per account row in the user table.) See Section 6.3.4, “Setting Account Resource Limits”.

  • --one-thread

    Command-Line Format--one-thread

    Only use one thread (for debugging under Linux). This option is available only if the server is built with debugging enabled. See Section 22.4, “Debugging and Porting MySQL”.

    As of MySQL 5.1.17, this option is deprecated and is removed in MySQL 5.6. Use --thread_handling=no-threads instead.

  • --open-files-limit=count

    Command-Line Format--open-files-limit=#
    System Variable Nameopen_files_limit
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default0
    Min Value0
    Max Valueplatform dependent

    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(). Internally, the maximum value for this option is the maximum unsigned integer value, but the actual maximum is platform dependent. 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.

    On Unix, the value cannot be set less than ulimit -n.

  • --partition[=value]

    Command-Line Format--partition
    Disabled byskip-partition
     Permitted Values
    Typeboolean
    DefaultON

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

  • --pid-file=path

    Command-Line Format--pid-file=file_name
    System Variable Namepid_file
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

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

  • --plugin-xxx

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

    For boolean options that can be enabled or disabled, the --skip prefix and other alternative formats are supported as well (see Section 4.2.5, “Program Option Modifiers”). For example, --skip-plugin-innodb_file_per_table disables innodb_file_per_table.

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

  • --plugin-load=plugin_list

    Introduced5.1.18
    Command-Line Format--plugin-load=plugin_list
     Permitted Values
    Typestring

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

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

    Quotes are used around the argument value here because semicolon (;) is interpreted as a special character by some command interpreters. (Unix shells treat it as a command terminator, for example.)

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

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

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

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

    For additional information about plugin loading, see Section 5.1.8.1, “Installing and Uninstalling Plugins”.

    This option was added in MySQL 5.1.18.

  • --port=port_num, -P port_num

    Command-Line Format--port=#
     -P
    System Variable Nameport
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default3306
    Min Value0
    Max Value65535

    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

    Introduced5.1.5
    Command-Line Format--port-open-timeout=#
     Permitted Values
    Typenumeric
    Default0

    On some systems, when the server is stopped, the TCP/IP port might not become available immediately. If the server is restarted quickly afterward, its attempt to reopen the port can fail. This option indicates how many seconds the server should wait for the TCP/IP port to become free if it cannot be opened. The default is not to wait. This option was added in MySQL 5.1.5.

  • --print-defaults

    Print the program name and all options that it gets from option files.

  • --remove [service_name]

    Command-Line Format--remove [service_name]

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

  • --safe-mode

    Command-Line Format--safe-mode

    Skip some optimization stages. This option is deprecated and is removed in MySQL 5.6.

  • --safe-show-database

    Deprecated4.0.2
    Command-Line Format--safe-show-database
    System Variable Namesafe_show_database
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean

    This option is deprecated and does not do anything because there is a SHOW DATABASES privilege that can be used to control access to database names on a per-account basis. See Section 6.2.1, “Privileges Provided by MySQL”. --safe-show-database is removed in MySQL 5.5.

  • --safe-user-create

    Command-Line Format--safe-user-create
     Permitted Values
    Typeboolean
    DefaultFALSE

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

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

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

  • --secure-auth

    Command-Line Format--secure-auth
    System Variable Namesecure_auth
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    This option causes the server to block connections by clients that attempt to use accounts that have passwords stored in the old (pre-4.1) format. Use it 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.5.2.4, “Client does not support authentication protocol”.

    The mysql client also has a --secure-auth option, which prevents connections to a server if the server requires a password in old format for the client account.

  • --secure-file-priv=path

    Introduced5.1.17
    Command-Line Format--secure-file-priv=path
    System Variable Namesecure_file_priv
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring

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

    This option was added in MySQL 5.1.17.

  • --shared-memory

    Command-Line Format--shared-memory-base-name=name
    System Variable Nameshared_memory
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform SpecificWindows

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

  • --shared-memory-base-name=name

    System Variable Nameshared_memory_base_name
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform SpecificWindows

    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 8.7.3, “Concurrent Inserts”.

  • --skip-event-scheduler

    Command-Line Format--skip-event-scheduler
     --disable-event-scheduler

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

  • --skip-grant-tables

    This option causes the server to start without using the privilege system at all, which gives anyone with access to the server unrestricted access to all databases. You can cause a running server to start using the grant tables again by executing mysqladmin flush-privileges or mysqladmin reload command from a system shell, or by issuing a MySQL FLUSH PRIVILEGES statement after connecting to the server. This option also suppresses loading of plugins that were installed with the INSTALL PLUGIN statement, user-defined functions (UDFs), and, beginning with MySQL 5.1.17, scheduled events. To cause plugins to be loaded anyway, use the --plugin-load option.

    Note that FLUSH PRIVILEGES might be executed implicitly by other actions performed after startup. For example, mysql_upgrade flushes the privileges during the upgrade procedure.

    --skip-grant-tables is unavailable if MySQL was configured with the --disable-grant-options option. See Section 2.11.4, “MySQL Source-Configuration Options”.

  • --skip-host-cache

    Disable use of the internal host cache for faster name-to-IP resolution. In this case, the server performs a DNS lookup every time a client connects. See Section 8.9.8, “DNS Lookup Optimization and the Host Cache”.

  • --skip-innodb

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

  • --skip-merge

    Disable the MERGE storage engine. This option was added in MySQL 5.1.12 and removed in 5.1.14.

  • --skip-name-resolve

    Do not resolve host names when checking client connections. Use only IP addresses. If you use this option, all Host column values in the grant tables must be IP addresses or localhost. See Section 8.9.8, “DNS Lookup Optimization and the Host Cache”.

    Depending on the network configuration of your system and the Host values for your accounts, clients may need to connect using an explicit --host option, such as --host=localhost or --host=127.0.0.1.

  • --skip-networking

    Do not listen for TCP/IP connections at all. All interaction with mysqld must be made using named pipes or shared memory (on Windows) or Unix socket files (on Unix). This option is highly recommended for systems where only local clients are permitted. See Section 8.9.8, “DNS Lookup Optimization and the Host Cache”.

  • --skip-partition

    Command-Line Format--skip-partition
     --disable-partition

    Disables user-defined partitioning. Partitioned tables can be seen using SHOW TABLES or by querying the INFORMATION_SCHEMA.TABLES table, but cannot be created or modified, nor can data in such tables be accessed. All partition-specific columns in the INFORMATION_SCHEMA.PARTITIONS table display NULL.

    Since DROP TABLE removes table definition (.frm) files, this statement works on partitioned tables even when partitioning is disabled using the option. The statement, however, does not remove .par files associated with partitioned tables in such cases. For this reason, you should avoid dropping partitioned tables with partitioning disabled, or take action to remove the orphaned .par files manually.

  • --ssl*

    Options that begin with --ssl specify whether to permit clients to connect using SSL and indicate where to find SSL keys and certificates. See Section 6.3.6.4, “SSL Command Options”.

  • --standalone

    Command-Line Format--standalone
    Platform SpecificWindows

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

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

    Command-Line Format--symbolic-links

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

  • --skip-safemalloc

    Command-Line Format--skip-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 do not need it by using the --skip-safemalloc option.

  • --skip-show-database

    Command-Line Format--skip-show-database
    System Variable Nameskip_show_database
    Variable ScopeGlobal
    Dynamic VariableNo

    This option sets the skip_show_database system variable that controls who is permitted to use the SHOW DATABASES statement. See Section 5.1.4, “Server System Variables”.

  • --skip-stack-trace

    Command-Line Format--skip-stack-trace

    Do not write stack traces. This option is useful when you are running mysqld under a debugger. On some systems, you also must use this option to get a core file. See Section 22.4, “Debugging and Porting MySQL”.

  • --skip-thread-priority

    Deprecated5.1.29
    Command-Line Format--skip-thread-priority

    Disable using thread priorities for faster response time. This option is deprecated as of MySQL 5.1.29 and is removed in MySQL 5.6.

    Prior to MySQL 5.1.29, mysqld makes a large number of invalid calls to thread scheduling routines on Linux. These calls do not affect performance noticeably but may be a source of noise for debugging tools. For example, they can overwhelm other information of more interest in kernel logs. To avoid these calls, start the server with the --skip-thread-priority option.

  • --slow-query-log[={0|1}]

    Introduced5.1.12
    Command-Line Format--slow-query-logfrom 5.1.29
    System Variable Nameslow_query_log
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    Specify the initial slow query log state. With no argument or an argument of 1, the --slow-query-log option enables the log. If omitted or given with an argument of 0, the option disables the log. This option was added in MySQL 5.1.12.

  • --socket=path

    Command-Line Format--socket=file_name
    System Variable Namesocket
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name
    Default/tmp/mysql.sock

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

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

    Command-Line Format--sql-mode=name
    System Variable Namesql_mode
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    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 5.1.7, “Server SQL Modes”.

    Note

    MySQL installation programs may configure the SQL mode during the installation process. If the SQL mode differs from the default or from what you expect, check for a setting in an option file that the server reads at startup.

  • --sysdate-is-now

    Introduced5.1.8
    Command-Line Format--sysdate-is-now
     Permitted Values
    Typeboolean
    DefaultFALSE

    SYSDATE() by default returns the time at which it executes, not the time at which the statement in which it occurs begins executing. This differs from the behavior of NOW(). This option causes SYSDATE() to be an alias for NOW(). For information about the implications for binary logging and replication, see the description for SYSDATE() in Section 12.7, “Date and Time Functions” and for SET TIMESTAMP in Section 5.1.4, “Server System Variables”.

    This option was added in MySQL 5.1.8.

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

    Command-Line Format--tc-heuristic-recover=name
     Permitted Values
    Typeenumeration
    DefaultCOMMIT
    Valid ValuesCOMMIT
    ROLLBACK

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

  • --temp-pool

    Command-Line Format--temp-pool
     Permitted Values
    Typeboolean
    DefaultTRUE

    This option causes most temporary files created by the server to use a small set of names, rather than a unique name for each new file. This works around a problem in the Linux kernel dealing with creating many new files with different names. With the old behavior, Linux seems to leak memory, because it is being allocated to the directory entry cache rather than to the disk cache. As of MySQL 5.1.31, this option is ignored except on Linux.

  • --transaction-isolation=level

    Command-Line Format--transaction-isolation=name
     Permitted Values
    Typeenumeration
    DefaultREPEATABLE-READ
    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 13.3.6, “SET TRANSACTION Syntax”.

    The default transaction isolation level can also be set at runtime using the SET TRANSACTION statement or by setting the tx_isolation system variable.

  • --tmpdir=path, -t path

    Command-Line Format--tmpdir=path
     -t
    System Variable Nametmpdir
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typedirectory name

    The path of the directory to use for creating temporary files. It might be useful if your default /tmp directory resides on a partition that is too small to hold temporary tables. This option accepts several paths that are used in round-robin fashion. Paths should be separated by colon characters (:) on Unix and semicolon characters (;) on Windows, 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.5.4.4, “Where MySQL Stores Temporary Files”. A replication slave needs some of its temporary files to survive a machine restart so that it can replicate temporary tables or LOAD DATA INFILE operations. If files in the temporary file directory are lost when the server restarts, replication fails.

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

    Command-Line Format--user=name
     -u name
     Permitted Values
    Typestring

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

    This option is mandatory when starting mysqld as root. The server changes its user ID during its startup sequence, causing it to run as that particular user rather than as root. See Section 6.1.1, “Security Guidelines”.

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

  • --verbose, -v

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

  • --version, -V

    Display version information and exit.

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

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

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

You can change the values of most system variables for a running server with the SET statement. See Section 13.7.4, “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 8.9.2, “Tuning Server Parameters”, includes information on optimizing the server by tuning system variables.

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 5.1 releases. For historical information concerning their implementation, please see http://dev.mysql.com/doc/refman/5.0/en/, and http://dev.mysql.com/doc/refman/4.1/en/.

The following table lists all available system variables.

Table 5.2 System Variable Summary

NameCmd-LineOption FileSystem VarVar ScopeDynamic
auto_increment_increment  YesBothYes
auto_increment_offset  YesBothYes
autocommitYesYesYesSessionYes
automatic_sp_privileges  YesGlobalYes
back_log  YesGlobalNo
basedirYesYesYesGlobalNo
big-tablesYesYes  Yes
- Variable: big_tables  YesSessionYes
bind-addressYesYesYesGlobalNo
binlog_cache_sizeYesYesYesGlobalYes
binlog_direct_non_transactional_updatesYesYesYesBothYes
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  YesBothNo
datetime_format  YesBothNo
debugYesYesYesBothYes
debug_sync  YesBothYes
default-storage-engineYesYesYesBothYes
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
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_archive  YesGlobalNo
have_blackhole_engine  YesGlobalNo
have_community_features  YesGlobalNo
have_compress  YesGlobalNo
have_crypt  YesGlobalNo
have_csv  YesGlobalNo
have_dynamic_loading  YesGlobalNo
have_example_engine  YesGlobalNo
have_federated_engine  YesGlobalNo
have_geometry  YesGlobalNo
have_innodb  YesGlobalNo
have_isam  YesGlobalNo
have_merge_engine  YesGlobalNo
have_ndbcluster  YesGlobalNo
have_openssl  YesGlobalNo
have_partition_engine  YesGlobalNo
have_partitioning  YesGlobalNo
have_query_cache  YesGlobalNo
have_raid  YesGlobalNo
have_row_based_replication  YesGlobalNo
have_rtree_keys  YesGlobalNo
have_ssl  YesGlobalNo
have_symlink  YesGlobalNo
hostname  YesGlobalNo
identity  YesSessionYes
ignore-builtin-innodbYesYes  No
- Variable: ignore_builtin_innodb  YesGlobalNo
init_connectYesYesYesGlobalYes
init-fileYesYes  No
- Variable: init_file  YesGlobalNo
init_slaveYesYesYesGlobalYes
innodb_adaptive_flushingYesYesYesGlobalYes
innodb_adaptive_hash_indexYesYesYesGlobalNo
innodb_additional_mem_pool_sizeYesYesYesGlobalNo
innodb_autoextend_incrementYesYesYesGlobalYes
innodb_autoinc_lock_modeYesYesYesGlobalNo
innodb_buffer_pool_awe_mem_mbYesYesYesGlobalNo
innodb_buffer_pool_sizeYesYesYesGlobalNo
innodb_change_bufferingYesYesYesGlobalYes
innodb_checksumsYesYesYesGlobalNo
innodb_commit_concurrencyYesYesYesGlobalYes
innodb_concurrency_ticketsYesYesYesGlobalYes
innodb_data_file_pathYesYesYesGlobalNo
innodb_data_home_dirYesYesYesGlobalNo
innodb_doublewriteYesYesYesGlobalNo
innodb_fast_shutdownYesYesYesGlobalYes
innodb_file_formatYesYesYesGlobalYes
innodb_file_format_checkYesYesYesGlobalYes
innodb_file_io_threadsYesYesYesGlobalNo
innodb_file_per_tableYesYesYesGlobalNo
innodb_flush_log_at_trx_commitYesYesYesGlobalYes
innodb_flush_methodYesYesYesGlobalNo
innodb_force_recoveryYesYesYesGlobalNo
innodb_io_capacityYesYesYesGlobalNo
innodb_lock_wait_timeoutYesYesYesBothNo
innodb_locks_unsafe_for_binlogYesYesYesGlobalNo
innodb_log_arch_dirYesYesYesGlobalNo
innodb_log_archiveYesYesYesGlobalNo
innodb_log_buffer_sizeYesYesYesGlobalNo
innodb_log_file_sizeYesYesYesGlobalNo
innodb_log_files_in_groupYesYesYesGlobalNo
innodb_log_group_home_dirYesYesYesGlobalNo
innodb_max_dirty_pages_pctYesYesYesGlobalYes
innodb_max_purge_lagYesYesYesGlobalYes
innodb_mirrored_log_groupsYesYesYesGlobalNo
innodb_old_blocks_pctYesYesYesGlobalYes
innodb_old_blocks_timeYesYesYesGlobalYes
innodb_open_filesYesYesYesGlobalNo
innodb_random_read_aheadYesYesYesGlobalYes
innodb_read_ahead_thresholdYesYesYesGlobalYes
innodb_read_io_threadsYesYesYesGlobalNo
innodb_replication_delayYesYesYesGlobalYes
innodb_rollback_on_timeoutYesYesYesGlobalNo
innodb_spin_wait_delayYesYesYesGlobalYes
innodb_stats_methodYesYesYesGlobalYes
innodb_stats_on_metadataYesYesYesGlobalYes
innodb_stats_sample_pagesYesYesYesGlobalYes
innodb_strict_modeYesYesYesBothYes
innodb_support_xaYesYesYesBothYes
innodb_sync_spin_loopsYesYesYesGlobalYes
innodb_table_locksYesYesYesBothYes
innodb_thread_concurrencyYesYesYesGlobalYes
innodb_thread_sleep_delayYesYesYesGlobalYes
innodb_use_legacy_cardinality_algorithmYesYesYesGlobalYes
innodb_use_sys_mallocYesYesYesGlobalNo
innodb_version  YesGlobalNo
innodb_write_io_threadsYesYesYesGlobalNo
insert_id  YesSessionYes
interactive_timeoutYesYesYesBothYes
join_buffer_sizeYesYesYesBothYes
keep_files_on_createYesYesYesBothYes
key_buffer_sizeYesYesYesGlobalYes
key_cache_age_thresholdYesYesYesGlobalYes
key_cache_block_sizeYesYesYesGlobalYes
key_cache_division_limitYesYesYesGlobalYes
languageYesYesYesGlobalNo
large_files_support  YesGlobalNo
large_page_size  YesGlobalNo
large-pagesYesYes  No
- Variable: large_pages  YesGlobalNo
last_insert_id  YesSessionYes
lc_time_names  YesBothYes
license  YesGlobalNo
local_infile  YesGlobalYes
locked_in_memory  YesGlobalNo
logYesYesYesGlobalYes
log_bin  YesGlobalNo
log-binYesYesYesGlobalNo
log-bin-trust-function-creatorsYesYes  Yes
- Variable: log_bin_trust_function_creators  YesGlobalYes
log-bin-trust-routine-creatorsYesYes  Yes
- Variable: log_bin_trust_routine_creators  YesGlobalYes
log_bin_use_v1_row_eventsYesYesYesGlobalNo
log-bin-use-v1-row-eventsYesYes  No
- Variable: log_bin_use_v1_row_events  YesGlobalNo
log-errorYesYes  No
- Variable: log_error  YesGlobalNo
log-outputYesYes  Yes
- Variable: log_output  YesGlobalYes
log-queries-not-using-indexesYesYes  Yes
- Variable: log_queries_not_using_indexes  YesGlobalYes
log-slave-updatesYesYes  No
- Variable: log_slave_updates  YesGlobalNo
log_slave_updatesYesYesYesGlobalNo
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_system  YesGlobalNo
lower_case_table_namesYesYesYesGlobalNo
max_allowed_packetYesYesYesGlobalYes
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_long_data_sizeYesYesYesGlobalNo
max_prepared_stmt_countYesYesYesGlobalYes
max_relay_log_sizeYesYesYesGlobalYes
max_seeks_for_keyYesYesYesBothYes
max_sort_lengthYesYesYesBothYes
max_sp_recursion_depthYesYesYesBothYes
max_user_connectionsYesYesYesBothYes
max_write_lock_countYesYesYesGlobalYes
memlockYesYesYesGlobalNo
min-examined-row-limitYesYesYesBothYes
multi_range_countYesYesYesBothYes
myisam_data_pointer_sizeYesYesYesGlobalYes
myisam_max_sort_file_sizeYesYesYesGlobalYes
myisam_mmap_sizeYesYesYesGlobalNo
myisam_recover_options  YesGlobalNo
myisam_repair_threadsYesYesYesBothYes
myisam_sort_buffer_sizeYesYesYesBothYes
myisam_stats_methodYesYesYesBothYes
myisam_use_mmapYesYesYesGlobalYes
named_pipe  YesGlobalNo
ndb_autoincrement_prefetch_szYesYesYesBothYes
ndb-batch-sizeYesYesYesGlobalNo
ndb-blob-read-batch-bytesYesYesYesBothYes
ndb-blob-write-batch-bytesYesYesYesBothYes
ndb_cache_check_timeYesYesYesGlobalYes
ndb-cluster-connection-poolYesYesYesGlobalNo
ndb-deferred-constraintsYesYes  Yes
- Variable: ndb_deferred_constraints  YesBothYes
ndb_deferred_constraintsYesYesYesBothYes
ndb_distributionYesYesYesGlobalYes
ndb-distributionYesYes  Yes
- Variable: ndb_distribution  YesGlobalYes
ndb_eventbuffer_max_allocYesYesYesGlobalYes
ndb_extra_loggingYesYesYesGlobalYes
ndb_force_sendYesYesYesBothYes
ndb_index_stat_cache_entriesYesYesYesBothYes
ndb_index_stat_enableYesYesYesBothYes
ndb_index_stat_optionYesYesYesBothYes
ndb_index_stat_update_freqYesYesYesBothYes
ndb_join_pushdown  YesBothYes
ndb-log-apply-statusYesYes  No
- Variable: ndb_log_apply_status  YesGlobalNo
ndb_log_apply_statusYesYesYesGlobalNo
ndb_log_binYes YesBothYes
ndb_log_binlog_indexYes YesGlobalYes
ndb_log_empty_epochsYesYesYesGlobalYes
ndb-log-empty-epochsYesYesYesGlobalYes
ndb-log-origYesYes  No
- Variable: ndb_log_orig  YesGlobalNo
ndb_log_origYesYesYesGlobalNo
ndb-log-transaction-idYesYes  No
- Variable: ndb_log_transaction_id  YesGlobalNo
ndb_log_transaction_id  YesGlobalNo
ndb-log-update-as-writeYesYesYesGlobalYes
ndb_log_updated_onlyYesYesYesGlobalYes
ndb_optimization_delay  YesGlobalYes
ndb_optimized_node_selectionYesYesYesGlobalNo
ndb_table_no_logging  YesSessionYes
ndb_table_temporary  YesSessionYes
ndb_use_copying_alter_table  YesBothNo
ndb_use_exact_count  YesBothYes
ndb_use_transactionsYesYesYesBothYes
ndb_version  YesGlobalNo
ndb_version_string  YesGlobalNo
ndb-wait-connectedYesYesYesGlobalNo
ndb-wait-setupYesYesYesGlobalNo
ndbinfo_database  YesGlobalNo
ndbinfo_max_bytesYes YesBothYes
ndbinfo_max_rowsYes YesBothYes
ndbinfo_offline  YesGlobalYes
ndbinfo_show_hiddenYes YesBothYes
ndbinfo_table_prefixYes YesBothYes
ndbinfo_version  YesGlobalNo
net_buffer_lengthYesYesYesBothYes
net_read_timeoutYesYesYesBothYes
net_retry_countYesYesYesBothYes
net_write_timeoutYesYesYesBothYes
newYesYesYesBothYes
oldYesYesYesGlobalNo
old-alter-tableYesYes  Yes
- Variable: old_alter_table  YesBothYes
old_passwords  YesBothYes
open-files-limitYesYes  No
- Variable: open_files_limit  YesGlobalNo
optimizer_prune_levelYesYesYesBothYes
optimizer_search_depthYesYesYesBothYes
optimizer_switchYesYesYesBothYes
pid-fileYesYes  No
- Variable: pid_file  YesGlobalNo
plugin_dirYesYesYesGlobalNo
portYesYesYesGlobalNo
preload_buffer_sizeYesYesYesBothYes
prepared_stmt_count  YesGlobalNo
profiling  YesSessionYes
profiling_history_sizeYesYesYesBothYes
protocol_version  YesGlobalNo
pseudo_thread_id  YesSessionYes
query_alloc_block_sizeYesYesYesBothYes
query_cache_limitYesYesYesGlobalYes
query_cache_min_res_unitYesYesYesGlobalYes
query_cache_sizeYesYesYesGlobalYes
query_cache_typeYesYesYesBothYes
query_cache_wlock_invalidateYesYesYesBothYes
query_prealloc_sizeYesYesYesBothYes
rand_seed1  YesSessionYes
rand_seed2  YesSessionYes
range_alloc_block_sizeYesYesYesBothYes
read_buffer_sizeYesYesYesBothYes
read_onlyYesYesYesGlobalYes
read_rnd_buffer_sizeYesYesYesBothYes
relay-logYesYes  No
- Variable: relay_log  YesGlobalNo
relay-log-indexYesYes  No
- Variable: relay_log_index  YesGlobalNo
relay_log_indexYesYesYesGlobalNo
relay_log_info_fileYesYesYesGlobalNo
relay_log_purgeYesYesYesGlobalYes
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
safe-show-databaseYesYesYesGlobalYes
secure-authYesYes  Yes
- Variable: secure_auth  YesGlobalYes
secure-file-privYesYes  No
- Variable: secure_file_priv  YesGlobalNo
server-idYesYes  Yes
- Variable: server_id  YesGlobalYes
server_id_bitsYesYesYesGlobalNo
server-id-bitsYesYes  No
- Variable: server_id_bits  YesGlobalNo
shared_memoryYesYesYesGlobalNo
shared_memory_base_name  YesGlobalNo
skip_external_lockingYesYesYesGlobalNo
skip-name-resolveYesYes  No
- Variable: skip_name_resolve  YesGlobalNo
skip-networkingYesYes  No
- Variable: skip_networking  YesGlobalNo
skip-show-databaseYesYes  No
- Variable: skip_show_database  YesGlobalNo
slave_allow_batchingYesYesYesGlobalYes
slave_compressed_protocolYesYesYesGlobalYes
slave_exec_modeYesYesYesGlobalYes
slave-load-tmpdirYesYes  No
- Variable: slave_load_tmpdir  YesGlobalNo
slave_max_allowed_packet  YesGlobalYes
slave-net-timeoutYesYes  Yes
- Variable: slave_net_timeout  YesGlobalYes
slave-skip-errorsYesYes  No
- Variable: slave_skip_errors  YesGlobalNo
slave_transaction_retriesYesYesYesGlobalYes
slave_type_conversionsYesYesYesGlobalNo
slow_launch_timeYesYesYesGlobalYes
slow-query-logYesYes  Yes
- Variable: slow_query_log  YesGlobalYes
slow_query_log_fileYesYesYesGlobalYes
socketYesYesYesGlobalNo
sort_buffer_sizeYesYesYesBothYes
sql_auto_is_null  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_binlogYesYesYesGlobalYes
sync_frmYesYesYesGlobalYes
system_time_zone  YesGlobalNo
table_cacheYesYesYesGlobalYes
table_definition_cache  YesGlobalYes
table_lock_wait_timeoutYesYesYesGlobalYes
table_open_cache  YesGlobalYes
table_type  YesBothYes
thread_cache_sizeYesYesYesGlobalYes
thread_concurrencyYesYesYesGlobalNo
thread_handlingYesYesYesGlobalNo
thread_stackYesYesYesGlobalNo
time_format  YesBothNo
time_zone  YesBothYes
timed_mutexesYesYesYesGlobalYes
timestamp  YesSessionYes
tmp_table_sizeYesYesYesBothYes
tmpdirYesYesYesGlobalNo
transaction_alloc_block_sizeYesYesYesBothYes
transaction_allow_batching  YesSessionYes
transaction_prealloc_sizeYesYesYesBothYes
tx_isolation  YesBothYes
unique_checks  YesSessionYes
updatable_views_with_limitYesYesYesBothYes
version  YesGlobalNo
version_comment  YesGlobalNo
version_compile_machine  YesGlobalNo
version_compile_os  YesGlobalNo
wait_timeoutYesYesYesBothYes
warning_count  YesSessionNo

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

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


For additional system variable information, see these sections:

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.

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

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

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

  • autocommit

    System Variable Nameautocommit
    Variable ScopeSession
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultON

    The autocommit mode. If set to 1, all changes to a table take effect immediately. If set to 0, you must use COMMIT to accept a transaction or ROLLBACK to cancel it. If autocommit is 0 and you change it to 1, MySQL performs an automatic COMMIT of any open transaction. Another way to begin a transaction is to use a START TRANSACTION or BEGIN statement. See Section 13.3.1, “START TRANSACTION, COMMIT, and ROLLBACK Syntax”.

    By default, client connections begin with autocommit set to 1. To cause clients to begin with a default of 0, set the server's init_connect system variable:

    SET GLOBAL init_connect='SET autocommit=0';
    

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

    [mysqld]
    init_connect='SET autocommit=0'
    

    The content of init_connect is not executed for users that have the SUPER privilege.

  • automatic_sp_privileges

    System Variable Nameautomatic_sp_privileges
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultTRUE

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

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

    See also Section 19.2.2, “Stored Routines and MySQL Privileges”.

  • back_log

    System Variable Nameback_log
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default50
    Min Value1
    Max Value65535

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

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

  • basedir

    Command-Line Format--basedir=path
     -b
    System Variable Namebasedir
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typedirectory name

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

  • big_tables

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

    Note

    This variable was formerly named sql_big_tables.

  • bulk_insert_buffer_size

    Command-Line Format--bulk_insert_buffer_size=#
    System Variable Namebulk_insert_buffer_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default8388608
    Min Value0
    Max Value18446744073709547520

    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

    System Variable Namecharacter_set_client
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring

    The character set for statements that arrive from the client. The session value of this variable is set using the character set requested by the client when the client connects to the server. (Many clients support a --default-character-set option to enable this character set to be specified explicitly. See also Section 10.1.4, “Connection Character Sets and Collations”.) The global value of the variable is used to set the session value in cases when the client-requested value is unknown or not available, or the server is configured to ignore client requests:

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

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

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

    ucs2 cannot be used as a client character set, which means that it also does not work for SET NAMES or SET CHARACTER SET.

  • character_set_connection

    System Variable Namecharacter_set_connection
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring

    The character set for the current connection. Used for literals that do not have an explicit character set specification and for number-to-string conversion.

  • character_set_database

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

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

  • character_set_filesystem

    Introduced5.1.6
    Command-Line Format--character-set-filesystem=name
    System Variable Namecharacter_set_filesystem
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring
    Defaultbinary

    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 multibyte file names are permitted, a different value may be more appropriate. For example, if the system represents file names using UTF-8, set character_set_filesystem to 'utf8'. This variable was added in MySQL 5.1.6.

  • character_set_results

    System Variable Namecharacter_set_results
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring

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

  • character_set_server

    Command-Line Format--character-set-server
    System Variable Namecharacter_set_server
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring
    Defaultlatin1

    The server's default character set.

  • character_set_system

    System Variable Namecharacter_set_system
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring
    Defaultutf8

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

  • character_sets_dir

    Command-Line Format--character-sets-dir=path
    System Variable Namecharacter_sets_dir
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typedirectory name

    The directory where character sets are installed.

  • collation_connection

    System Variable Namecollation_connection
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring

    The collation of the connection character set.

  • collation_database

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

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

  • collation_server

    Command-Line Format--collation-server
    System Variable Namecollation_server
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring
    Defaultlatin1_swedish_ci

    The server's default collation.

  • completion_type

    Command-Line Format--completion_type=#
    System Variable Namecompletion_type
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default0
    Valid Values0
    1
    2

    The transaction completion type. This variable can take the values shown in the following table.

    ValueDescription
    0COMMIT and ROLLBACK are unaffected. This is the default value.
    1COMMIT 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.)
    2COMMIT and ROLLBACK are equivalent to COMMIT RELEASE and ROLLBACK RELEASE, respectively. (The server disconnects after terminating the transaction.)

    completion_type affects transactions that begin with START TRANSACTION or BEGIN and end with COMMIT or ROLLBACK. It does not apply to implicit commits resulting from execution of the statements listed in Section 13.3.3, “Statements That Cause an Implicit Commit”. It also does not apply for XA COMMIT, XA ROLLBACK, or when autocommit=1.

  • concurrent_insert

    Command-Line Format--concurrent_insert[=#]
    System Variable Nameconcurrent_insert
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultTRUE

    If 1 (the default), MySQL permits INSERT and SELECT statements to run concurrently for MyISAM tables that have no free blocks in the middle of the data file. If you start mysqld with --skip-new, this variable is set to 0.

    This variable can take three integer values.

    ValueDescription
    0Disables concurrent inserts
    1(Default) Enables concurrent insert for MyISAM tables that do not 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 8.7.3, “Concurrent Inserts”.

  • connect_timeout

    Command-Line Format--connect_timeout=#
    System Variable Nameconnect_timeout
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values (<= 5.1.22)
    Typenumeric
    Default5
    Min Value2
    Max Value31536000
     Permitted Values (>= 5.1.23)
    Typenumeric
    Default10
    Min Value2
    Max Value31536000

    The number of seconds that the mysqld server waits for a connect packet before responding with Bad handshake. The default value is 10 seconds as of MySQL 5.1.23 and 5 seconds before that.

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

  • datadir

    Command-Line Format--datadir=path
     -h
    System Variable Namedatadir
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typedirectory name

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

  • date_format

    This variable is unused.

  • datetime_format

    This variable is unused.

  • debug

    Command-Line Format--debug[=debug_options]
    System Variable Namedebug
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Type (Unix)string
    Defaultd:t:i:o,/tmp/mysqld.trace
     Permitted Values
    Type (Windows)string
    Defaultd:t:i:O,\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       |
    +---------+
    

    This variable was added in MySQL 5.1.7.

  • debug_sync

    Introduced5.1.41
    System Variable Namedebug_sync
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring

    This variable is the user interface to the Debug Sync facility. Use of Debug Sync requires that MySQL be configured with the --enable-debug-sync option (see Section 2.11.4, “MySQL Source-Configuration Options”). If Debug Sync is not compiled in, this system variable is not available.

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

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

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

    This variable was added in MySQL 5.1.41.

  • default_week_format

    Command-Line Format--default_week_format=#
    System Variable Namedefault_week_format
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default0
    Min Value0
    Max Value7

    The default mode value to use for the WEEK() function. See Section 12.7, “Date and Time Functions”.

  • delay_key_write

    Command-Line Format--delay-key-write[=name]
    System Variable Namedelay_key_write
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    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 5.1.3, “Server Command Options”, and Section 14.5.1, “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=#
    System Variable Namedelayed_insert_limit
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default100
    Min Value1
    Max Value18446744073709547520

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

  • delayed_insert_timeout

    Command-Line Format--delayed_insert_timeout=#
    System Variable Namedelayed_insert_timeout
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default300

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

  • delayed_queue_size

    Command-Line Format--delayed_queue_size=#
    System Variable Namedelayed_queue_size
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default1000
    Min Value1
    Max Value18446744073709547520

    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=#
    System Variable Namediv_precision_increment
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default4
    Min Value0
    Max Value30

    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 |
    +----------------+
    

    For more information, see Section 22.4.3, “The DBUG Package”.

  • engine_condition_pushdown

    Command-Line Format--engine-condition-pushdown
    System Variable Nameengine_condition_pushdown
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultON

    The engine condition pushdown optimization enables processing for certain comparisons to be pushed down to the storage engine level for more efficient execution. For more information, see Section 8.3.1.5, “Engine Condition Pushdown Optimization”.

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

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

  • error_count

    The number of errors that resulted from the last statement that generated messages. This variable is read only. See Section 13.7.5.18, “SHOW ERRORS Syntax”.

  • event_scheduler

    Introduced5.1.6
    Command-Line Format--event-scheduler[=value]
    System Variable Nameevent_scheduler
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeenumeration
    DefaultOFF
    Valid ValuesON
    OFF
    DISABLED

    This variable indicates the status of the Event Scheduler; as of MySQL 5.1.12, 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.

    This variable was added in MySQL 5.1.6.

  • expire_logs_days

    Command-Line Format--expire_logs_days=#
    System Variable Nameexpire_logs_days
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default0
    Min Value0
    Max Value99

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

    To remove binary log files manually, use the PURGE BINARY LOGS statement. See Section 13.4.1.1, “PURGE BINARY LOGS Syntax”.

  • flush

    Command-Line Format--flush
    System Variable Nameflush
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

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

  • flush_time

    Command-Line Format--flush_time=#
    System Variable Nameflush_time
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default0
    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 systems with minimal resources.

  • foreign_key_checks

    If set to 1 (the default), foreign key constraints for InnoDB tables are checked. If set to 0, they are ignored. Disabling foreign key checking can be useful for reloading InnoDB tables in an order different from that required by their parent/child relationships. See Section 14.6.5.6, “InnoDB and 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.

  • ft_boolean_syntax

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

    The list of operators supported by boolean full-text searches performed using IN BOOLEAN MODE. See Section 12.9.2, “Boolean Full-Text Searches”.

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

    • Operator function is determined by position within the string.

    • The replacement value must be 14 characters.

    • Each character must be an ASCII nonalphanumeric character.

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

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

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

  • ft_max_word_len

    Command-Line Format--ft_max_word_len=#
    System Variable Nameft_max_word_len
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Min Value10

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

    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=#
    System Variable Nameft_min_word_len
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default4
    Min Value1

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

    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=#
    System Variable Nameft_query_expansion_limit
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default20
    Min Value0
    Max Value1000

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

  • ft_stopword_file

    Command-Line Format--ft_stopword_file=file_name
    System Variable Nameft_stopword_file
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

    The file from which to read the list of stopwords for full-text searches. The server looks for the file in the data directory unless an absolute path name is given to specify a different directory. All the words from the file are used; comments are not honored. By default, a built-in list of stopwords is used (as defined in the storage/myisam/ft_static.c file). Setting this variable to the empty string ('') disables stopword filtering. See also Section 12.9.4, “Full-Text Stopwords”.

    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

    Introduced5.1.12
    Command-Line Format--general-log
    System Variable Namegeneral_log
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    Whether the general query log is enabled. The value can be 0 (or OFF) to disable the log or 1 (or ON) to enable the log. The default value depends on whether the --general_log option is given (--log before MySQL 5.1.29). 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. The general_log variable was added in MySQL 5.1.12.

  • general_log_file

    Introduced5.1.12
    Command-Line Format--general-log-file=file_namefrom 5.1.29
    System Variable Namegeneral_log_file
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typefile name
    Defaulthost_name.log

    The name of the general query log file. The default value is host_name.log, but the initial value can be changed with the --general_log_file option (--log before MySQL 5.1.29). This variable was added in MySQL 5.1.12.

  • group_concat_max_len

    Command-Line Format--group_concat_max_len=#
    System Variable Namegroup_concat_max_len
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default1024
    Min Value4
    Max Value18446744073709547520

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

  • have_archive

    YES if mysqld supports ARCHIVE tables, NO if not. This variable was removed in MySQL 5.1.14.

  • have_blackhole_engine

    YES if mysqld supports BLACKHOLE tables, NO if not. This variable was removed in MySQL 5.1.14.

  • 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_community_features

    YES if statement profiling capability is present, NO if not. If present, the profiling system variable controls whether this capability is enabled or disabled. See Section 13.7.5.33, “SHOW PROFILES Syntax”.

    This variable was added in MySQL 5.1.24. It is renamed to have_profiling in MySQL 5.5.

  • have_crypt

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

  • have_csv

    YES if mysqld supports CSV tables, NO if not.

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

  • have_dynamic_loading

    YES if mysqld supports dynamic loading of plugins, NO if not. This variable was added in MySQL 5.1.10.

  • have_example_engine

    YES if mysqld supports EXAMPLE tables, NO if not. This variable was removed in MySQL 5.1.14.

  • have_federated_engine

    YES if mysqld supports FEDERATED tables, NO if not. This variable was removed in MySQL 5.1.14.

  • have_geometry

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

  • have_innodb

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

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

  • have_isam

    In MySQL 5.1, this variable appears only for reasons of backward compatibility. It is always NO because ISAM tables are no longer supported. This variable was removed in MySQL 5.1.7.

  • have_merge_engine

    YES if mysqld supports MERGE tables. DISABLED if --skip-merge is used. This variable was removed in MySQL 5.1.3.

  • have_openssl

    YES if mysqld supports SSL connections, NO if not. As of MySQL 5.1.17, this variable is an alias for have_ssl.

  • have_partitioning

    YES if mysqld supports partitioning. Added in MySQL 5.1.1 as have_partition_engine and renamed to have_partioning in 5.1.6.

    This variable is deprecated and is removed in MySQL 5.6. Use SHOW PLUGINS instead. For more information, see Chapter 18, Partitioning.

  • have_query_cache

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

  • have_row_based_replication

    Introduced5.1.5
    Removed5.1.15
    System Variable Namehave_row_based_replication
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typeboolean

    YES if the server can perform replication using row-based binary logging. If the value is NO, the server can use only statement-based logging. See Section 16.1.2, “Replication Formats”. This variable was added in MySQL 5.1.5 and removed in 5.1.15.

  • have_raid

    In MySQL 5.1, this variable appears only for reasons of backward compatibility. It is always NO because RAID tables are no longer supported. This variable was removed in MySQL 5.1.7.

  • have_rtree_keys

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

  • have_ssl

    YES if mysqld supports SSL connections, NO if not. DISABLED indicates that the server was compiled with SSL support, but was not started with the appropriate --ssl-xxx options. For more information, see Section 6.3.6.2, “Configuring MySQL for SSL”.

    This variable was added in MySQL 5.1.17. Before that, use have_openssl.

  • 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. If the server is started with the --skip-symbolic-links option, the value is DISABLED.

  • hostname

    Introduced5.1.17
    System Variable Namehostname
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring

    The server sets this variable to the server host name at startup. This variable was added in MySQL 5.1.17.

  • identity

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

  • init_connect

    Command-Line Format--init-connect=name
    System Variable Nameinit_connect
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typestring

    A string to be executed by the server for each client that connects. The string consists of one or more SQL statements, separated by semicolon characters. For example, each client session begins by default with autocommit mode enabled. There is no global autocommit 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';
    

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

    [mysqld]
    init_connect='SET autocommit=0'
    

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

  • init_file

    Command-Line Format--init-file=file_name
    System Variable Nameinit_file
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

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

    Note that the --init-file option is unavailable if MySQL was configured with the --disable-grant-options option. See Section 2.11.4, “MySQL Source-Configuration Options”.

  • innodb_xxx

    InnoDB system variables are listed in Section 14.6.7, “InnoDB Startup Options and System Variables”. These variables control many aspects of storage, memory use, and I/O patterns for InnoDB tables, and are especially important in MySQL 5.5 and higher, where InnoDB is the default storage engine.

  • insert_id

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

  • interactive_timeout

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

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

  • join_buffer_size

    Command-Line Format--join_buffer_size=#
    System Variable Namejoin_buffer_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Type (Other)numeric
    Default131072
    Min Value8200
    Max Value4294967295
     Permitted Values
    Platform Bit Size64
    Type (Other)numeric
    Default131072
    Min Value8228
    Max Value18446744073709547520
     Permitted Values
    Platform Bit Size32
    Type (Windows)numeric
    Default131072
    Min Value8200
    Max Value4294967295
     Permitted Values
    Platform Bit Size64
    Type (Windows)numeric
    Default131072
    Min Value8228
    Max Value4294967295

    The minimum size of the buffer that is used for plain index scans, range index scans, and joins that do not use indexes and thus perform full table scans. Normally, the best way to get fast joins is to add indexes. Increase the value of join_buffer_size to get a faster full join when adding indexes is not possible. One join buffer is allocated for each full join between two tables. For a complex join between several tables for which indexes are not used, multiple join buffers might be necessary.

    There is no gain from setting the buffer larger than required to hold each matching row, and all joins allocate at least the minimum size, so use caution in setting this variable to a large value globally. It is better to keep the global setting small and change to a larger setting only in sessions that are doing large joins. Memory allocation time can cause substantial performance drops if the global size is larger than needed by most queries that use it.

    The maximum permissible setting for join_buffer_size is 4GB–1. As of MySQL 5.1.23, larger values are permitted for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB–1 with a warning).

    For additional information about join buffering, see Section 8.3.1.8, “Nested-Loop Join Algorithms”.

  • keep_files_on_create

    Introduced5.1.21
    Command-Line Format--keep_files_on_create=#
    System Variable Namekeep_files_on_create
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

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

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

    This variable was added in MySQL 5.1.23.

  • key_buffer_size

    Command-Line Format--key_buffer_size=#
    System Variable Namekey_buffer_size
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values (<= 5.1.22)
    Typenumeric
    Default8388608
    Min Value8
    Max Value4294967295
     Permitted Values (>= 5.1.23)
    Platform Bit Size32
    Typenumeric
    Default8388608
    Min Value8
    Max Value4294967295
     Permitted Values (>= 5.1.23)
    Platform Bit Size64
    Typenumeric
    Default8388608
    Min Value8
    Max ValueOS_PER_PROCESS_LIMIT

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

    The maximum permissible setting for key_buffer_size is 4GB–1 on 32-bit platforms. As of MySQL 5.1.23, larger values are permitted for 64-bit platforms, except 64-bit Windows prior to MySQL 5.1.31, for which large values are truncated to 4GB–1 with a warning. As of MySQL 5.1.31, larger values are also permitted for 64-bit Windows. The effective maximum size might be less, depending on your available physical RAM and per-process RAM limits imposed by your operating system or hardware platform. The value of this variable indicates the amount of memory requested. Internally, the server allocates as much memory as possible up to this amount, but the actual allocation might be less.

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

    For even more speed when writing many rows at the same time, use LOCK TABLES. See Section 8.3.2.1, “Speed of INSERT Statements”.

    You can check the performance of the key buffer by issuing a SHOW STATUS statement and examining the Key_read_requests, Key_reads, Key_write_requests, and Key_writes status variables. (See Section 13.7.5, “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 is allocated internally for administrative structures. Factors that influence the amount of overhead for these structures include block size and pointer size. As block size increases, the percentage of the key buffer lost to overhead tends to decrease. Larger blocks results in a smaller number of read operations (because more keys are obtained per read), but conversely an increase in reads of keys that are not examined (if not all keys in a block are relevant to a query).

    It is possible to create multiple MyISAM key caches. The size limit of 4GB applies to each cache individually, not as a group. See Section 8.6.1, “The MyISAM Key Cache”.

  • key_cache_age_threshold

    Command-Line Format--key_cache_age_threshold=#
    System Variable Namekey_cache_age_threshold
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default300
    Min Value100
    Max Value18446744073709547520

    This value controls the demotion of buffers from the hot sublist of a key cache to the warm sublist. Lower values cause demotion to happen more quickly. The minimum value is 100. The default value is 300. See Section 8.6.1, “The MyISAM Key Cache”.

  • key_cache_block_size

    Command-Line Format--key_cache_block_size=#
    System Variable Namekey_cache_block_size
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default1024
    Min Value512
    Max Value16384

    The size in bytes of blocks in the key cache. The default value is 1024. See Section 8.6.1, “The MyISAM Key Cache”.

  • key_cache_division_limit

    Command-Line Format--key_cache_division_limit=#
    System Variable Namekey_cache_division_limit
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default100
    Min Value1
    Max Value100

    The division point between the hot and warm sublists of the key cache buffer list. The value is the percentage of the buffer list to use for the warm sublist. Permissible values range from 1 to 100. The default value is 100. See Section 8.6.1, “The MyISAM Key Cache”.

  • language

    Command-Line Format--language=name
     -L
    System Variable Namelanguage
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typedirectory name
    Default/usr/local/mysql/share/mysql/english/

    The directory where error messages are located. See Section 10.2, “Setting the Error Message Language”.

  • large_files_support

    System 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
    System Variable Namelarge_pages
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform SpecificLinux
     Permitted Values
    Type (Linux)boolean
    DefaultFALSE

    Whether large page support is enabled (via the --large-pages option). See Section 8.9.7, “Enabling Large Page Support”.

  • large_page_size

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

    If large page support is enabled, this shows the size of memory pages. Currently, large memory pages are supported only on Linux; on other platforms, the value of this variable is always 0. See Section 8.9.7, “Enabling Large Page Support”.

  • last_insert_id

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

  • lc_time_names

    Introduced5.1.12
    System Variable Namelc_time_names
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring

    This variable specifies the locale that controls the language used to display day and month names and abbreviations. This variable affects the output from the DATE_FORMAT(), DAYNAME() and MONTHNAME() functions. Locale names are POSIX-style values such as 'ja_JP' or 'pt_BR'. The default value is 'en_US' regardless of your system's locale setting. For further information, see Section 10.7, “MySQL Server Locale Support”. This variable was added in MySQL 5.1.12.

  • license

    System Variable Namelicense
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring
    DefaultGPL

    The type of license the server has.

  • local_infile

    System Variable Namelocal_infile
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean

    Whether LOCAL is supported for LOAD DATA INFILE statements. If this variable is disabled, clients cannot use LOCAL in LOAD DATA statements. See Section 6.1.6, “Security Issues with LOAD DATA LOCAL”.

  • locked_in_memory

    System Variable Namelocked_in_memory
    Variable ScopeGlobal
    Dynamic VariableNo

    Whether mysqld was locked in memory with --memlock.

  • log

    Deprecated5.1.29, by general-log
    Command-Line Format--log[=file_name]
     -l
    System Variable Namelog
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typefile name

    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 5.1.29 and is removed in MySQL 5.6. Use general_log instead.

  • log_bin_trust_function_creators

    Command-Line Format--log-bin-trust-function-creators
    System Variable Namelog_bin_trust_function_creators
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultFALSE

    This variable applies when binary logging is enabled. It controls whether stored function creators can be trusted not to create stored functions that will cause unsafe events to be written to the binary log. If set to 0 (the default), users are not permitted to create or alter stored functions unless they have the SUPER privilege in addition to the CREATE ROUTINE or ALTER ROUTINE privilege. A setting of 0 also enforces the restriction that a function must be declared with the DETERMINISTIC characteristic, or with the READS SQL DATA or NO SQL characteristic. If the variable is set to 1, MySQL does not enforce these restrictions on stored function creation. This variable also applies to trigger creation. See Section 19.7, “Binary Logging of Stored Programs”.

  • log_error

    Command-Line Format--log-error[=file_name]
    System Variable Namelog_error
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

    The location of the error log, or empty if the server is writing error message to the standard error output. See Section 5.2.2, “The Error Log”.

  • log_output

    Introduced5.1.6
    Command-Line Format--log-output=name
    System Variable Namelog_output
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeset
    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 FILE. 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”. This variable was added in MySQL 5.1.6.

  • log_queries_not_using_indexes

    Command-Line Format--log-queries-not-using-indexes
    System Variable Namelog_queries_not_using_indexes
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    Whether queries that do not use indexes are logged to the slow query log. See Section 5.2.5, “The Slow Query Log”. This variable was added in MySQL 5.1.11.

  • log_slow_queries

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

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

    This variable is deprecated as of MySQL 5.1.29 and is removed in MySQL 5.6. Use slow_query_log instead.

  • log_warnings

    Command-Line Format--log-warnings[=#]
     -W [#]
    System Variable Namelog_warnings
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default1
    Min Value0
    Max Value18446744073709547520

    Whether to produce additional warning messages to the error log. This variable is enabled (1) by default and can be disabled by setting it to 0. As of MySQL 5.1.38, the server logs messages about statements that are unsafe for statement-based logging if the value is greater than 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=#
    System Variable Namelong_query_time
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values (>= 5.1.21)
    Typenumeric
    Default10
    Min Value0

    If a query takes longer than this many seconds, the server increments the Slow_queries status variable. If the slow query log is enabled, the query is logged to the slow query log file. This value is measured in real time, not CPU time, so a query that is under the threshold on a lightly loaded system might be above the threshold on a heavily loaded one. The default value of long_query_time is 10. Beginning with MySQL 5.1.21, the minimum is 0, and the value can be specified to a resolution of microseconds. For logging to a file, times are written including the microseconds part. For logging to tables, only integer times are written; the microseconds part is ignored. Prior to MySQL 5.1.21, the minimum value is 1, and the value for this variable must be an integer. See Section 5.2.5, “The Slow Query Log”.

  • low_priority_updates

    Command-Line Format--low-priority-updates
    System Variable Namelow_priority_updates
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultFALSE

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

  • lower_case_file_system

    System Variable Namelower_case_file_system
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typeboolean

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

  • lower_case_table_names

    Command-Line Format--lower_case_table_names[=#]
    System Variable Namelower_case_table_names
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default0
    Min Value0
    Max Value2

    If set to 0, table names are stored as specified and comparisons are case sensitive. If set to 1, table names are stored in lowercase on disk and comparisons are not case sensitive. If set to 2, table names are stored as given but compared in lowercase. This option also applies to database names and table aliases. For additional information, see Section 9.2.2, “Identifier Case Sensitivity”.

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

    If you are using InnoDB tables, you should set this variable to 1 on all platforms to force names to be converted to lowercase. Prior to MySQL Cluster NDB 6.3.35, MySQL Cluster NDB 7.0.15, and MySQL Cluster NDB 7.1.4, this is also true for tables using the NDB storage engine.

    The setting of this variable has no effect on replication filtering options. See Section 16.2.3, “How Servers Evaluate Replication Filtering Rules”, for more information.

    You should not use different settings for lower_case_table_names on replication masters and slaves. In particular, you should not do this when the slave uses a case-sensitive file system, as this can cause replication to fail. For more information, see Section 16.4.1.36, “Replication and Variables”.

  • max_allowed_packet

    Command-Line Format--max_allowed_packet=#
    System Variable Namemax_allowed_packet
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default1048576
    Min Value1024
    Max Value1073741824

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

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

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

    When you change the message buffer size by changing the value of the max_allowed_packet variable, you should also change the buffer size on the client side if your client program permits it. The default max_allowed_packet value built in to the client library is 1GB, but individual client programs might override this. For example, mysql and mysqldump have defaults of 16MB and 24MB, respectively. They also 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 5.1.31, the session value of this variable is read only. Before 5.1.31, setting the session value is permitted but has no effect.

  • max_connect_errors

    Command-Line Format--max_connect_errors=#
    System Variable Namemax_connect_errors
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default10
    Min Value1
    Max Value18446744073709547520

    If more than this many successive connection requests from a host are interrupted without a successful connection, the server blocks that host from further connections. You can unblock blocked hosts by flushing the host cache. To do so, issue a FLUSH HOSTS statement or execute a mysqladmin flush-hosts command. If a connection is established successfully within fewer than max_connect_errors attempts after a previous connection was interrupted, the error count for the host is cleared to zero. However, once a host is blocked, flushing the host cache is the only way to unblock it.

  • max_connections

    Command-Line Format--max_connections=#
    System Variable Namemax_connections
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values (<= 5.1.14)
    Typenumeric
    Default100
     Permitted Values (>= 5.1.15)
    Typenumeric
    Default151
    Min Value1
    Max Value16384
     Permitted Values (>= 5.1.17)
    Typenumeric
    Default151
    Min Value1
    Max Value100000

    The maximum permitted number of simultaneous client connections. By default, this is 151, beginning with MySQL 5.1.15. (Previously, the default was 100.) See Section B.5.2.7, “Too many connections”, for more information.

    Increasing this value increases the number of file descriptors that mysqld requires. See Section 8.8.3, “How MySQL Opens and Closes Tables”, for comments on file descriptor limits.

  • max_delayed_threads

    Command-Line Format--max_delayed_threads=#
    System Variable Namemax_delayed_threads
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default20
    Min Value0
    Max Value16384

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

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

  • max_error_count

    Command-Line Format--max_error_count=#
    System Variable Namemax_error_count
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default64
    Min Value0
    Max Value65535

    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=#
    System Variable Namemax_heap_table_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default16777216
    Min Value16384
    Max Value4294967295
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default16777216
    Min Value16384
    Max Value1844674407370954752

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

    This variable is also used in conjunction with tmp_table_size to limit the size of internal in-memory tables. See Section 8.8.5, “How MySQL Uses Internal Temporary Tables”.

    max_heap_table_size is not replicated. See Section 16.4.1.21, “Replication and MEMORY Tables”, and Section 16.4.1.36, “Replication and Variables”, for more information.

  • max_insert_delayed_threads

    System Variable Namemax_insert_delayed_threads
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric

    This variable is a synonym for max_delayed_threads.

  • max_join_size

    Command-Line Format--max_join_size=#
    System Variable Namemax_join_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default4294967295
    Min Value1
    Max Value4294967295

    Do not permit 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 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=#
    System Variable Namemax_length_for_sort_data
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default1024
    Min Value4
    Max Value8388608

    The cutoff on the size of index values that determines which filesort algorithm to use. See Section 8.3.1.11, “ORDER BY Optimization”.

  • max_long_data_size

    Introduced5.1.57
    Deprecated5.1.57
    Command-Line Format--max_long_data_size=#
    System Variable Namemax_long_data_size
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default1048576
    Min Value1024
    Max Value4294967295

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

  • max_prepared_stmt_count

    Introduced5.1.10
    Command-Line Format--max_prepared_stmt_count=#
    System Variable Namemax_prepared_stmt_count
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default16382
    Min Value0
    Max Value1048576

    This variable limits the total number of prepared statements in the server. (The sum of the number of prepared statements across all sessions.) It can be used in environments where there is the potential for denial-of-service attacks based on running the server out of memory by preparing huge numbers of statements. If the value is set lower than the current number of prepared statements, existing statements are not affected and can be used, but no new statements can be prepared until the current number drops below the limit. The default value is 16,382. The permissible range of values is from 0 to 1 million. Setting the value to 0 disables prepared statements. This variable was added in MySQL 5.1.10.

  • max_relay_log_size

    Command-Line Format--max_relay_log_size=#
    System Variable Namemax_relay_log_size
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default0
    Min Value0
    Max Value1073741824

    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 16.2.1, “Replication Implementation Details”.

  • max_seeks_for_key

    Command-Line Format--max_seeks_for_key=#
    System Variable Namemax_seeks_for_key
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default4294967295
    Min Value1
    Max Value4294967295

    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 13.7.5.23, “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=#
    System Variable Namemax_sort_length
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default1024
    Min Value4
    Max Value8388608

    The number of bytes to use when sorting data 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[=#]
    System Variable Namemax_sp_recursion_depth
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default0
    Max Value255

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

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

  • max_tmp_tables

    This variable is unused.

  • max_user_connections

    Command-Line Format--max_user_connections=#
    System Variable Namemax_user_connections
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default0
    Min Value0
    Max Value4294967295

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

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

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

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

    Account resource limits are specified using the GRANT statement. See Section 6.3.4, “Setting Account Resource Limits”, and Section 13.7.1.3, “GRANT Syntax”.

  • max_write_lock_count

    Command-Line Format--max_write_lock_count=#
    System Variable Namemax_write_lock_count
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default4294967295
    Min Value1
    Max Value4294967295

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

  • min_examined_row_limit

    Introduced5.1.21
    Command-Line Format--min-examined-row-limit=#
    System Variable Namemin_examined_row_limit
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default0
    Min Value0
    Max Value4294967295

    Queries that examine fewer than this number of rows are not logged to the slow query log. This variable was added in MySQL 5.1.21.

  • multi_range_count

    Command-Line Format--multi_range_count=#
    System Variable Namemulti_range_count
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default256
    Min Value1
    Max Value4294967295

    The maximum number of ranges to send to a table handler at once during range selects. The default value is 256. Sending multiple ranges to a handler at once can improve the performance of certain selects dramatically. This is especially true for the NDBCLUSTER table handler, which needs to send the range requests to all nodes. Sending a batch of those requests at once reduces communication costs significantly.

    This variable is deprecated in MySQL 5.1, and is no longer supported in MySQL 5.5, in which arbitrarily long lists of ranges can be processed.

  • myisam_data_pointer_size

    Command-Line Format--myisam_data_pointer_size=#
    System Variable Namemyisam_data_pointer_size
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default6
    Min Value2
    Max Value7

    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.5.2.12, “The table is full”.

  • myisam_max_sort_file_size

    Command-Line Format--myisam_max_sort_file_size=#
    System Variable Namemyisam_max_sort_file_size
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default2147483648
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default9223372036854775807

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

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

  • myisam_mmap_size

    Introduced5.1.43
    Command-Line Format--myisam_mmap_size=#
    System Variable Namemyisam_mmap_size
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default4294967295
    Min Value7
    Max Value4294967295

    The maximum amount of memory to use for memory mapping compressed MyISAM files. If many compressed MyISAM tables are used, the value can be decreased to reduce the likelihood of memory-swapping problems. This variable was added in MySQL 5.1.43.

  • myisam_recover_options

    System Variable Namemyisam_recover_options
    Variable ScopeGlobal
    Dynamic VariableNo

    The value of the --myisam-recover option. See Section 5.1.3, “Server Command Options”.

  • myisam_repair_threads

    Command-Line Format--myisam_repair_threads=#
    System Variable Namemyisam_repair_threads
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default1
    Min Value1
    Max Value4294967295

    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=#
    System Variable Namemyisam_sort_buffer_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Type (Windows)numeric
    Default8388608
    Min Value4096
    Max Value4294967295

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

    The maximum permissible setting for myisam_sort_buffer_size is 4GB–1. As of MySQL 5.1.23, larger values are permitted for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB–1 with a warning).

  • myisam_stats_method

    Command-Line Format--myisam_stats_method=name
    System Variable Namemyisam_stats_method
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeenumeration
    Defaultnulls_unequal
    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 8.5.4, “InnoDB and MyISAM Index Statistics Collection”.

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

  • myisam_use_mmap

    Introduced5.1.4
    Command-Line Format--myisam_use_mmap
    System Variable Namemyisam_use_mmap
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    Use memory mapping for reading and writing MyISAM tables. This variable was added in MySQL 5.1.4.

  • named_pipe

    System Variable Namenamed_pipe
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform SpecificWindows
     Permitted Values
    Type (Windows)boolean
    DefaultOFF

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

  • net_buffer_length

    Command-Line Format--net_buffer_length=#
    System Variable Namenet_buffer_length
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default16384
    Min Value1024
    Max Value1048576

    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 5.1.31, the session value of this variable is read only. Before 5.1.31, setting the session value is permitted but has no effect.

  • net_read_timeout

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

    The number of seconds to wait for more data from a connection before aborting the read. Before MySQL 5.1.41, this timeout applies only to TCP/IP connections, not to connections made through 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.

    On Linux, the NO_ALARM build flag affects timeout behavior as indicated in the description of the net_retry_count system variable.

  • net_retry_count

    Command-Line Format--net_retry_count=#
    System Variable Namenet_retry_count
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default10
    Min Value1
    Max Value4294967295

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

    On Linux, the NO_ALARM build flag (-DNO_ALARM) modifies how the binary treats both net_read_timeout and net_write_timeout. With this flag enabled, neither timer cancels the current statement until after the failing connection has been waited on an additional net_retry_count times. This means that the effective timeout value becomes (timeout setting) × (net_retry_count+1).

  • net_write_timeout

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

    The number of seconds to wait for a block to be written to a connection before aborting the write. Before MySQL 5.1.41, this timeout applies only to TCP/IP connections, not to connections made using Unix socket files, named pipes, or shared memory. See also net_read_timeout.

    On Linux, the NO_ALARM build flag affects timeout behavior as indicated in the description of the net_retry_count system variable.

  • new

    Command-Line Format--new
     -n
    System Variable Namenew
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Disabled byskip-new
     Permitted Values
    Typeboolean
    DefaultFALSE

    This variable was used in MySQL 4.0 to turn on some 4.1 behaviors, and is retained for backward compatibility. In MySQL 5.1, its value is always OFF.

  • old

    Introduced5.1.18
    Command-Line Format--old
    System 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 13.2.8.3, “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.

    This variable was added as old_mode in MySQL 5.1.17 and renamed to old in MySQL 5.1.18.

  • old_alter_table

    Command-Line Format--old-alter-table
    System Variable Nameold_alter_table
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    When this variable is enabled, the server does not use the optimized method of processing an ALTER TABLE operation. It reverts to using a temporary table, copying over the data, and then renaming the temporary table to the original, as used by MySQL 5.0 and earlier. For more information on the operation of ALTER TABLE, see Section 13.1.7, “ALTER TABLE Syntax”.

  • old_passwords

    System Variable Nameold_passwords
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    Default0

    This variable controls the password hashing method used by the PASSWORD() function. It also influences password hashing performed by CREATE USER and GRANT statements that specify a password using an IDENTIFIED BY clause.

    The value determines whether or not to use old native MySQL password hashing. A value of 0 (or OFF) causes passwords to be encrypted using the format available from MySQL 4.1 on. A value of 1 (or ON) causes password encryption to use the older pre-4.1 format.

    If old_passwords=1, PASSWORD(str) returns the same value as OLD_PASSWORD(str). The latter function is not affected by the value of old_passwords.

    For information about hashing formats, see Section 6.1.2.4, “Password Hashing in MySQL”.

  • one_shot

    This is not a variable, but it can be used when setting some variables. It is described in Section 13.7.4, “SET Syntax”.

  • open_files_limit

    Command-Line Format--open-files-limit=#
    System Variable Nameopen_files_limit
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default0
    Min Value0
    Max Valueplatform dependent

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

  • optimizer_prune_level

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

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

  • optimizer_search_depth

    Command-Line Format--optimizer_search_depth[=#]
    System Variable Nameoptimizer_search_depth
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default62
    Min Value0
    Max Value63

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

  • optimizer_switch

    Introduced5.1.34
    Command-Line Format--optimizer_switch=value
    System Variable Nameoptimizer_switch
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeset
    Valid Valuesindex_merge={on|off}
    index_merge_intersection={on|off}
    index_merge_sort_union={on|off}
    index_merge_union={on|off}

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

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

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

    For more information about the syntax of this variable and the optimizer behaviors that it controls, see Section 8.4.2, “Controlling Switchable Optimizations”.

  • pid_file

    Command-Line Format--pid-file=file_name
    System Variable Namepid_file
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

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

  • plugin_dir

    Introduced5.1.2
    Command-Line Format--plugin_dir=path
    System Variable Nameplugin_dir
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values (>= 5.1.2)
    Type (Windows)directory name
    DefaultBASEDIR/lib/plugin
     Permitted Values (>= 5.1.2)
    Type (Other)directory name
    DefaultBASEDIR/lib/mysql/plugin

    The path name of the plugin directory. This variable was added in MySQL 5.1.2.

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

  • port

    Command-Line Format--port=#
     -P
    System Variable Nameport
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default3306
    Min Value0
    Max Value65535

    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=#
    System Variable Namepreload_buffer_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default32768
    Min Value1024
    Max Value1073741824

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

  • prepared_stmt_count

    Introduced5.1.10
    Removed5.1.13
    System Variable Nameprepared_stmt_count
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric

    The current number of prepared statements. (The maximum number of statements is given by the max_prepared_stmt_count system variable.) This variable was added in MySQL 5.1.10. In MySQL 5.1.14, it was converted to the global Prepared_stmt_count status variable.

  • profiling

    If set to 0 or OFF (the default), statement profiling is disabled. If set to 1 or ON, statement profiling is enabled and the SHOW PROFILE and SHOW PROFILES statements provide access to profiling information. See Section 13.7.5.33, “SHOW PROFILES Syntax”. This variable was added in MySQL 5.1.24.

  • 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 13.7.5.33, “SHOW PROFILES Syntax”. This variable was added in MySQL 5.1.24.

  • protocol_version

    System Variable Nameprotocol_version
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric

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

  • pseudo_thread_id

    System Variable Namepseudo_thread_id
    Variable ScopeSession
    Dynamic VariableYes
     Permitted Values
    Typenumeric

    This variable is for internal server use.

  • query_alloc_block_size

    Command-Line Format--query_alloc_block_size=#
    System Variable Namequery_alloc_block_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default8192
    Min Value1024
    Max Value4294967295
    Block Size1024

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

  • query_cache_limit

    Command-Line Format--query_cache_limit=#
    System Variable Namequery_cache_limit
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default1048576
    Min Value0
    Max Value4294967295

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

  • query_cache_min_res_unit

    Command-Line Format--query_cache_min_res_unit=#
    System Variable Namequery_cache_min_res_unit
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default4096
    Min Value512
    Max Value4294967295

    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 8.6.3.3, “Query Cache Configuration”.

  • query_cache_size

    Command-Line Format--query_cache_size=#
    System Variable Namequery_cache_size
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default0
    Min Value0
    Max Value18446744073709547520

    The amount of memory allocated for caching query results. The default value is 0, which disables the query cache. The permissible values are multiples of 1024; other values are rounded down to the nearest multiple. Note that query_cache_size bytes of memory are allocated even if query_cache_type is set to 0. See Section 8.6.3.3, “Query Cache Configuration”, for more information.

    The query cache needs a minimum size of about 40KB to allocate its structures. (The exact size depends on system architecture.) If you set the value of query_cache_size too small, a warning will occur, as described in Section 8.6.3.3, “Query Cache Configuration”.

  • query_cache_type

    Command-Line Format--query_cache_type=#
    System Variable Namequery_cache_type
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    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 OFFDo not cache results in or retrieve results from the query cache. Note that this does not deallocate the query cache buffer. To do that, you should set query_cache_size to 0.
    1 or ONCache all cacheable query results except for those that begin with SELECT SQL_NO_CACHE.
    2 or DEMANDCache results only for cacheable queries that begin with SELECT SQL_CACHE.

    This variable defaults to ON.

    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
    System Variable Namequery_cache_wlock_invalidate
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultFALSE

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

  • query_prealloc_size

    Command-Line Format--query_prealloc_size=#
    System Variable Namequery_prealloc_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default8192
    Min Value8192
    Max Value18446744073709551615
    Block Size1024

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

  • rand_seed1

    The rand_seed1 and rand_seed2 variables exist as session variables only, and can be set but not read. Beginning with MySQL 5.1.18, the variables—but not their values—are shown in the output of SHOW VARIABLES.

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

  • rand_seed2

    See the description for rand_seed1.

  • range_alloc_block_size

    Command-Line Format--range_alloc_block_size=#
    System Variable Namerange_alloc_block_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default4096
    Min Value4096
    Max Value4294967295
    Block Size1024
     Permitted Values
    Platform Bit Size64
    Typenumeric
    Default4096
    Min Value4096
    Max Value18446744073709547520
    Block Size1024

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

  • read_buffer_size

    Command-Line Format--read_buffer_size=#
    System Variable Nameread_buffer_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default131072
    Min Value8200
    Max Value2147479552

    Each thread that does a sequential scan for a MyISAM table 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.

    This option is also used in the following context for all search engines:

    • For caching the indexes in a temporary file (not a temporary table), when sorting rows for ORDER BY.

    • For bulk insert into partitions.

    • For caching results of nested queries.

    and in one other storage engine-specific way: to determine the memory block size for MEMORY tables.

    The maximum permissible setting for read_buffer_size is 2GB.

    For more information about memory use during different operations, see Section 8.9.4, “How MySQL Uses Memory”.

  • read_only

    Command-Line Format--read-only
    System Variable Nameread_only
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    Defaultfalse

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

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

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

    Important

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

    As of MySQL 5.1.15, 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.

  • read_rnd_buffer_size

    Command-Line Format--read_rnd_buffer_size=#
    System Variable Nameread_rnd_buffer_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default262144
    Min Value8200
    Max Value2147483647

    When reading rows from a MyISAM table in sorted order following a key-sorting operation, the rows are read through this buffer to avoid disk seeks. See Section 8.3.1.11, “ORDER BY Optimization”. Setting the variable to a large value can improve ORDER BY performance by a lot. However, this is a buffer allocated for each client, so you should not set the global variable to a large value. Instead, change the session variable only from within those clients that need to run large queries.

    The maximum permissible setting for read_rnd_buffer_size is 2GB.

    For more information about memory use during different operations, see Section 8.9.4, “How MySQL Uses Memory”.

  • relay_log_purge

    Command-Line Format--relay_log_purge
    System Variable Namerelay_log_purge
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultTRUE

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

  • relay_log_space_limit

    Command-Line Format--relay_log_space_limit=#
    System Variable Namerelay_log_space_limit
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default0
    Min Value0
    Max Value4294967295

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

  • report_host

    Command-Line Format--report-host=host_name
    System Variable Namereport_host
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring

    The value of the --report-host option. This variable was added in MySQL 5.1.24.

  • report_password

    Command-Line Format--report-password=name
    System Variable Namereport_password
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring

    The value of the --report-password option. Not the same as the password for the MySQL replication user account. This variable was added in MySQL 5.1.24.

  • report_port

    Command-Line Format--report-port=#
    System Variable Namereport_port
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default3306
    Min Value0
    Max Value65535

    The value of the --report-port option. This variable was added in MySQL 5.1.24.

  • report_user

    Command-Line Format--report-user=name
    System Variable Namereport_user
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring

    The value of the --report-user option. This variable was added in MySQL 5.1.24.

  • secure_auth

    Command-Line Format--secure-auth
    System Variable Namesecure_auth
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    If this variable is enabled, the server blocks connections by clients that attempt to use accounts that have passwords stored in the old (pre-4.1) format.

    Enable this variable 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 variable is enabled and the privilege tables are in pre-4.1 format. See Section B.5.2.4, “Client does not support authentication protocol”.

  • secure_file_priv

    Introduced5.1.17
    Command-Line Format--secure-file-priv=path
    System Variable Namesecure_file_priv
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring

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

    This variable was added in MySQL 5.1.17.

  • server_id

    Command-Line Format--server-id=#
    System Variable Nameserver_id
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default0
    Min Value0
    Max Value4294967295

    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

    Command-Line Format--shared-memory-base-name=name
    System Variable Nameshared_memory
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform SpecificWindows

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

  • shared_memory_base_name

    System 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

    Command-Line Format--skip-external-locking
    System Variable Nameskip_external_locking
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typeboolean
    DefaultON

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

    This variable is set by the --external-locking or --skip-external-locking option. External locking has been disabled by default as of MySQL 4.0.

    External locking affects only MyISAM table access. For more information, including conditions under which it can and cannot be used, see Section 8.7.4, “External Locking”.

  • skip_name_resolve

    Command-Line Format--skip-name-resolve
    System Variable Nameskip_name_resolve
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typeboolean
    DefaultOFF

    This variable is set from the value of the --skip-name-resolve option. If it is OFF, mysqld resolves host names when checking client connections. If it is ON, mysqld uses only IP numbers; in this case, all Host column values in the grant tables must be IP addresses or localhost. See Section 8.9.8, “DNS Lookup Optimization and the Host Cache”.

    This variable was added in MySQL 5.1.46.

  • skip_networking

    Command-Line Format--skip-networking
    System Variable Nameskip_networking
    Variable ScopeGlobal
    Dynamic VariableNo

    This is ON if the server permits only local (non-TCP/IP) connections. On Unix, local connections use a Unix socket file. On Windows, local connections use a named pipe or shared memory. 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

    Command-Line Format--skip-show-database
    System Variable Nameskip_show_database
    Variable ScopeGlobal
    Dynamic VariableNo

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

  • slow_launch_time

    Command-Line Format--slow_launch_time=#
    System Variable Nameslow_launch_time
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default2

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

  • slow_query_log

    Introduced5.1.12
    Command-Line Format--slow-query-logfrom 5.1.29
    System Variable Nameslow_query_log
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

    Whether the slow query log is enabled. The value can be 0 (or OFF) to disable the log or 1 (or ON) to enable the log. The default value depends on whether the --slow_query_log option is given (--log-slow-queries before MySQL 5.1.29). 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. The slow_query_log variable was added in MySQL 5.1.12.

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

  • slow_query_log_file

    Introduced5.1.12
    Command-Line Format--slow-query-log-file=file_name
    System Variable Nameslow_query_log_file
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typefile name
    Defaulthost_name-slow.log

    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 5.1.29). This variable was added in MySQL 5.1.12.

  • socket

    Command-Line Format--socket=file_name
    System Variable Namesocket
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name
    Default/tmp/mysql.sock

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

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

  • sort_buffer_size

    Command-Line Format--sort_buffer_size=#
    System Variable Namesort_buffer_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Type (Other)numeric
    Default2097144
    Min Value32768
    Max Value4294967295
     Permitted Values
    Platform Bit Size64
    Type (Other)numeric
    Default2097144
    Min Value32768
    Max Value18446744073709551615
     Permitted Values
    Type (Windows)numeric
    Default2097144
    Min Value32768
    Max Value4294967295

    Each session that needs to do a sort allocates a buffer of this size. sort_buffer_size is not specific to any storage engine and applies in a general manner for optimization. See Section 8.3.1.11, “ORDER BY Optimization”, for example.

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

    The maximum permissible setting for sort_buffer_size is 4GB–1. As of MySQL 5.1.23, larger values are permitted for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB–1 with a warning).

  • sql_auto_is_null

    System Variable Namesql_auto_is_null
    Variable ScopeSession
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    Default1

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

    SELECT * FROM tbl_name WHERE auto_col IS NULL
    

    If the statement returns a row, the value returned is the same as if you invoked the LAST_INSERT_ID() function. For details, including the return value after a multiple-row insert, see Section 12.14, “Information Functions”. If no AUTO_INCREMENT value was successfully inserted, the SELECT statement returns no row.

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

  • sql_big_selects

    System Variable Namesql_big_selects
    Variable ScopeSession
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    Default1

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

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

  • sql_buffer_result

    System Variable Namesql_buffer_result
    Variable ScopeSession
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    Default0

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

  • sql_log_bin

    System Variable Namesql_log_bin
    Variable ScopeSession
    Dynamic VariableYes
     Permitted Values
    Typeboolean

    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

    System Variable Namesql_log_off
    Variable ScopeSession
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    Default0

    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

    Deprecated5.0.0, by sql_log_bin
    System Variable Namesql_log_update
    Variable ScopeSession
    Dynamic VariableYes
     Permitted Values
    Typeboolean

    This variable is deprecated, and is mapped to sql_log_bin. It is removed in MySQL 5.5.

  • sql_mode

    Command-Line Format--sql-mode=name
    System Variable Namesql_mode
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    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 5.1.7, “Server SQL Modes”.

    Note

    MySQL installation programs may configure the SQL mode during the installation process. If the SQL mode differs from the default or from what you expect, check for a setting in an option file that the server reads at startup.

  • sql_notes

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

  • sql_quote_show_create

    If set to 1 (the default), the server quotes identifiers for SHOW CREATE TABLE and SHOW CREATE DATABASE statements. If set to 0, quoting is disabled. This option is enabled by default so that replication works for identifiers that require quoting. See Section 13.7.5.12, “SHOW CREATE TABLE Syntax”, and Section 13.7.5.8, “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. (Specifically, UPDATE statements must have a WHERE clause that uses a key or a LIMIT clause, or both. DELETE statements must have both.) This makes it possible to catch UPDATE or DELETE statements where keys are not used properly and that would probably change or delete a large number of rows. The default value is 0.

  • sql_select_limit

    System Variable Namesql_select_limit
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typenumeric

    The maximum number of rows to return from SELECT statements. The default value for a new connection is the maximum number of rows that the server permits per table, 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_warnings

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

  • ssl_ca

    Introduced5.1.11
    Command-Line Format--ssl-ca=file_name
    System Variable Namessl_ca
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

    The path to a file with a list of trusted SSL CAs. This variable was added in MySQL 5.1.11.

  • ssl_capath

    Introduced5.1.11
    Command-Line Format--ssl-capath=dir_name
    System Variable Namessl_capath
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typedirectory name

    The path to a directory that contains trusted SSL CA certificates in PEM format. This variable was added in MySQL 5.1.11.

  • ssl_cert

    Introduced5.1.11
    Command-Line Format--ssl-cert=file_name
    System Variable Namessl_cert
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

    The name of the SSL certificate file to use for establishing a secure connection. This variable was added in MySQL 5.1.11.

  • ssl_cipher

    Introduced5.1.11
    Command-Line Format--ssl-cipher=name
    System Variable Namessl_cipher
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring

    A list of permissible ciphers to use for SSL encryption. This variable was added in MySQL 5.1.11.

  • ssl_key

    Introduced5.1.11
    Command-Line Format--ssl-key=file_name
    System Variable Namessl_key
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typefile name

    The name of the SSL key file to use for establishing a secure connection. This variable was added in MySQL 5.1.11.

  • storage_engine

    System Variable Namestorage_engine
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeenumeration
    DefaultMyISAM

    The default storage engine (table type). To set the storage engine at server startup, use the --default-storage-engine option. See Section 5.1.3, “Server Command Options”.

    To see which storage engines are available and enabled, use the SHOW ENGINES statement or query the INFORMATION_SCHEMA ENGINES table.

  • sync_frm

    Command-Line Format--sync-frm
    System Variable Namesync_frm
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultTRUE

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

  • system_time_zone

    System Variable Namesystem_time_zone
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring

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

    The system_time_zone variable differs from time_zone. Although they might have the same value, the latter variable is used to initialize the time zone for each client that connects. See Section 10.6, “MySQL Server Time Zone Support”.

  • table_cache

    Deprecated5.1.3, by table_open_cache
    Removed5.1.3
    Command-Line Format--table_cache=#
    System Variable Nametable_cache
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default64
    Min Value1
    Max Value524288

    This is the old name of table_open_cache before MySQL 5.1.3. From 5.1.3 on, use table_open_cache instead.

  • table_definition_cache

    Introduced5.1.3
    System Variable Nametable_definition_cache
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values (<= 5.1.24)
    Typenumeric
    Default128
    Min Value1
    Max Value524288
     Permitted Values (>= 5.1.25)
    Typenumeric
    Default256
    Min Value256
    Max Value524288

    The number of table definitions (from .frm files) 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. This variable was added in MySQL 5.1.3. The minimum and default values are 1 and 128 before MySQL 5.1.25. The minimum and default are both 256 as of MySQL 5.1.25.

  • table_lock_wait_timeout

    Command-Line Format--table_lock_wait_timeout=#
    System Variable Nametable_lock_wait_timeout
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default50
    Min Value1
    Max Value1073741824

    This variable is unused.

  • table_open_cache

    Introduced5.1.3
    System Variable Nametable_open_cache
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default64
    Min Value1
    Max Value524288

    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 5.1.6, “Server Status Variables”. If the value of Opened_tables is large and you do not use FLUSH TABLES often (which just forces all tables to be closed and reopened), then you should increase the value of the table_open_cache variable. For more information about the table cache, see Section 8.8.3, “How MySQL Opens and Closes Tables”. Before MySQL 5.1.3, this variable is called table_cache.

  • table_type

    System Variable Nametable_type
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeenumeration

    This variable is a synonym for storage_engine. In MySQL 5.1, storage_engine is the preferred name; table_type is deprecated and is removed in MySQL 5.5.

  • thread_cache_size

    Command-Line Format--thread_cache_size=#
    System Variable Namethread_cache_size
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typenumeric
    Default0
    Min Value0
    Max Value16384

    How many threads the server should cache for reuse. When a client disconnects, the client's threads are put in the cache if there are fewer than thread_cache_size threads there. Requests for threads are satisfied by reusing threads taken from the cache if possible, and only when the cache is empty is a new thread created. This variable can be increased to improve performance if you have a lot of new connections. Normally, this does not provide a notable performance improvement if you have a good thread implementation. However, if your server sees hundreds of connections per second you should normally set thread_cache_size high enough so that most new connections use cached threads. By examining the difference between the Connections and Threads_created status variables, you can see how efficient the thread cache is. For details, see Section 5.1.6, “Server Status Variables”.

  • thread_concurrency

    Command-Line Format--thread_concurrency=#
    System Variable Namethread_concurrency
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typenumeric
    Default10
    Min Value1
    Max Value512

    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

    Introduced5.1.17
    Command-Line Format--thread_handling=name
    System Variable Namethread_handling
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typeenumeration
    Defaultone-thread-per-connection
    Valid Valuesno-threads
    one-thread-per-connection

    The thread-handling model used by the server for connection threads. The permissible values are no-threads (the server uses a single thread to handle one connection) and one-thread-per-connection (the server uses one thread to handle each client connection). no-threads is useful for debugging under Linux; see Section 22.4, “Debugging and Porting MySQL”. This variable was added in MySQL 5.1.17

  • thread_stack

    Command-Line Format--thread_stack=#
    System Variable Namethread_stack
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default196608
    Min Value131072
    Max Value4294967295
    Block Size1024

    The stack size for each thread. Many of the limits detected by the crash-me test are dependent on this value. See Section 8.1.3, “The MySQL Benchmark Suite”. The default of 192KB (256KB for 64-bit systems) is large enough for normal operation. If the thread stack size is too small, it limits the complexity of the SQL statements that the server can handle, the recursion depth of stored procedures, and other memory-consuming actions.

  • time_format

    This variable is unused.

  • time_zone

    System Variable Nametime_zone
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typestring

    The current time zone. This variable is used to initialize the time zone for each client that connects. By default, the initial value of this is 'SYSTEM' (which means, use the value of system_time_zone). The value can be specified explicitly at server startup with the --default-time-zone option. See Section 10.6, “MySQL Server Time Zone Support”.

  • timed_mutexes

    Command-Line Format--timed_mutexes
    System Variable Nametimed_mutexes
    Variable ScopeGlobal
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    DefaultOFF

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

  • timestamp

    System Variable Nametimestamp
    Variable ScopeSession
    Dynamic VariableYes
     Permitted Values
    Typenumeric

    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 (a value like that returned by UNIX_TIMESTAMP(), not a value in 'YYYY-MM-DD hh:mm:ss' format) or DEFAULT.

    Setting timestamp to a constant value causes it to retain that value until it is changed again. Setting timestamp to DEFAULT causes its value to be the current date and time as of the time it is accessed.

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

  • tmp_table_size

    Command-Line Format--tmp_table_size=#
    System Variable Nametmp_table_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values (<= 5.1.11)
    Typenumeric
    Default33554432
    Min Value1024
    Max Value4294967295
     Permitted Values (>= 5.1.12, <= 5.1.36)
    Typenumeric
    Default16777216
    Min Value1024
    Max Value4294967295
     Permitted Values (>= 5.1.37, <= 5.1.55)
    Typenumeric
    Default16777216
    Min Value1024
    Max Value9223372036854775807
     Permitted Values (>= 5.1.56)
    Typenumeric
    Default16777216
    Min Value1024
    Max Value18446744073709551615

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

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

    See also Section 8.8.5, “How MySQL Uses Internal Temporary Tables”.

  • tmpdir

    Command-Line Format--tmpdir=path
     -t
    System Variable Nametmpdir
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typedirectory name

    The directory used for temporary files and temporary tables. This variable can be set to a list of several paths that are used in round-robin fashion. Paths should be separated by colon characters (:) on Unix and semicolon characters (;) on Windows, 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. You can set the slave's temporary directory using the slave_load_tmpdir variable. In that case, the slave will not use the general tmpdir value and you can set tmpdir to a nonpermanent location.

  • transaction_alloc_block_size

    Command-Line Format--transaction_alloc_block_size=#
    System Variable Nametransaction_alloc_block_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default8192
    Min Value1024
    Max Value4294967295
    Block Size1024

    The amount in bytes by which to increase a per-transaction memory pool which needs memory. See the description of transaction_prealloc_size.

  • transaction_prealloc_size

    Command-Line Format--transaction_prealloc_size=#
    System Variable Nametransaction_prealloc_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Platform Bit Size32
    Typenumeric
    Default4096
    Min Value1024
    Max Value4294967295
    Block Size1024

    There is a per-transaction memory pool from which various transaction-related allocations take memory. The initial size of the pool in bytes is transaction_prealloc_size. For every allocation that cannot be satisfied from the pool because it has insufficient memory available, the pool is increased by transaction_alloc_block_size bytes. When the transaction ends, the pool is truncated to transaction_prealloc_size bytes.

    By making transaction_prealloc_size sufficiently large to contain all statements within a single transaction, you can avoid many malloc() calls.

  • tx_isolation

    System Variable Nametx_isolation
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeenumeration
    DefaultREPEATABLE-READ
    Valid ValuesREAD-UNCOMMITTED
    READ-COMMITTED
    REPEATABLE-READ
    SERIALIZABLE

    The default transaction isolation level. Defaults to REPEATABLE-READ.

    This variable can be set directly, or indirectly using the SET TRANSACTION statement. See Section 13.3.6, “SET TRANSACTION Syntax”. If you set tx_isolation directly to an isolation level name that contains a space, the name should be enclosed within quotation marks, with the space replaced by a dash. For example:

    SET tx_isolation = 'READ-COMMITTED';
    

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

    The default transaction isolation level can also be set at startup using the --transaction-isolation server option.

  • unique_checks

    System Variable Nameunique_checks
    Variable ScopeSession
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    Default1

    If set to 1 (the default), uniqueness checks for secondary indexes in InnoDB tables are performed. If set to 0, storage engines are permitted to assume that duplicate keys are not present in input data. If you know for certain that your data does not contain uniqueness violations, you can set this to 0 to speed up large table imports to InnoDB.

    Note that setting this variable to 0 does not require storage engines to ignore duplicate keys. An engine is still permitted to check for them and issue duplicate-key errors if it detects them.

  • updatable_views_with_limit

    Command-Line Format--updatable_views_with_limit=#
    System Variable Nameupdatable_views_with_limit
    Variable ScopeGlobal, Session
    Dynamic VariableYes
     Permitted Values
    Typeboolean
    Default1

    This variable controls whether updates to a view can be made when the view does not contain all columns of the primary key defined in the underlying table, if the update statement contains a LIMIT clause. (Such updates often are generated by GUI tools.) An update is an UPDATE or DELETE statement. Primary key here means a PRIMARY KEY, or a UNIQUE index in which no column can contain NULL.

    The variable can have two values:

    • 1 or YES: Issue a warning only (not an error message). This is the default value.

    • 0 or NO: Prohibit the update.

  • version

    The version number for the server. The value might also include a suffix indicating server build or configuration information. -log indicates that one or more of the general log, slow query log, or binary log are enabled. -debug indicates that the server was built with debugging support enabled.

  • version_comment

    System Variable Nameversion_comment
    Variable ScopeGlobal
    Dynamic VariableNo
     Permitted Values
    Typestring

    The configure script has a <