Chapter 5. MySQL Server Administration

Table of Contents

5.1. The MySQL Server
5.1.1. Server Option and Variable Reference
5.1.2. Server Command Options
5.1.3. Server System Variables
5.1.4. Session System Variables
5.1.5. Using System Variables
5.1.6. Server Status Variables
5.1.7. Server SQL Modes
5.1.8. Server-Side Help
5.1.9. Server Response to Signals
5.1.10. The Shutdown Process
5.2. MySQL Server Logs
5.2.1. The Error Log
5.2.2. The General Query Log
5.2.3. The Binary Log
5.2.4. The Slow Query Log
5.2.5. Server Log Maintenance
5.3. General Security Issues
5.3.1. General Security Guidelines
5.3.2. Making MySQL Secure Against Attackers
5.3.3. Security-Related mysqld Options
5.3.4. Security Issues with LOAD DATA LOCAL
5.3.5. How to Run MySQL as a Normal User
5.4. The MySQL Access Privilege System
5.4.1. What the Privilege System Does
5.4.2. How the Privilege System Works
5.4.3. Privileges Provided by MySQL
5.4.4. Access Control, Stage 1: Connection Verification
5.4.5. Access Control, Stage 2: Request Verification
5.4.6. When Privilege Changes Take Effect
5.4.7. Causes of Access denied Errors
5.4.8. Password Hashing as of MySQL 4.1
5.5. MySQL User Account Management
5.5.1. MySQL Usernames and Passwords
5.5.2. Adding New User Accounts to MySQL
5.5.3. Removing User Accounts from MySQL
5.5.4. Limiting Account Resources
5.5.5. Assigning Account Passwords
5.5.6. Keeping Passwords Secure
5.5.7. Using SSL for Secure Connections
5.5.8. Auditing MySQL Account Activity
5.6. Running Multiple MySQL Servers on the Same Machine
5.6.1. Running Multiple Servers on Windows
5.6.2. Running Multiple Servers on Unix
5.6.3. Using Client Programs in a Multiple-Server Environment

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

5.1. The MySQL Server

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

  • Startup options that the server supports

  • Server system variables

  • Server status variables

  • How to set the server SQL mode

  • The server shutdown process

Note

Not all storage engines are supported by all MySQL server binaries and configurations. To find out how to determine which storage engines are supported by your MySQL server installation, see Section 12.5.5.13, “SHOW ENGINES Syntax”.

5.1.1. Server Option and Variable Reference

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

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

Table 5.1. mysqld Option/Variable Summary

NameCmd-LineOption fileSystem VarStatus VarVar ScopeDynamic
Aborted_clients   YesBothNo
Aborted_connects   YesGlobalNo
abort-slave-event-countYesYes    
allow-suspicious-udfsYesYes    
ansiYesYes    
autocommit  Yes SessionYes
auto_increment_incrementYesYesYes BothYes
auto_increment_offsetYesYesYes BothYes
automatic_sp_privileges  Yes GlobalYes
back_logYesYesYes GlobalNo
basedirYesYesYes GlobalNo
bdb_cache_sizeYesYesYes GlobalNo
bdb-homeYesYesYes GlobalNo
bdb-lock-detectYesYes  GlobalNo
- Variable: bdb_lock_detect  Yes GlobalNo
bdb_log_buffer_sizeYesYesYes GlobalNo
bdb-logdirYesYesYes GlobalNo
bdb_max_lockYesYesYes GlobalNo
bdb-no-recoverYesYes    
bdb-shared-dataYesYes  GlobalNo
- Variable: bdb_shared_data  Yes GlobalNo
bdb-tmpdirYesYesYes GlobalNo
big-tablesYesYes  SessionYes
- Variable: big_tables  Yes SessionYes
bind-addressYesYes    
Binlog_cache_disk_use   YesBothNo
binlog_cache_sizeYesYesYes GlobalYes
Binlog_cache_use   YesBothNo
binlog-do-dbYesYes    
binlog-ignore-dbYesYes    
bootstrapYesYes    
bulk_insert_buffer_sizeYesYesYes BothYes
Bytes_received   YesBothNo
Bytes_sent   YesBothNo
character_set_client  Yes BothYes
character-set-client-handshakeYes     
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-sets-dirYesYes  GlobalNo
- Variable: character_sets_dir  Yes GlobalNo
character-set-serverYesYes  BothYes
- Variable: character_set_server  Yes BothYes
character_set_system  Yes GlobalNo
chrootYesYes    
collation_connection  Yes BothYes
collation_database[b]  Yes BothYes
collation-serverYesYes  BothYes
- Variable: collation_server  Yes BothYes
Com_admin_commands   YesBothNo
Com_alter_db   YesBothNo
Com_alter_event   YesBothNo
Com_alter_table   YesBothNo
Com_analyze   YesBothNo
Com_backup_table   YesBothNo
Com_begin   YesBothNo
Com_call_procedure   YesBothNo
Com_change_db   YesBothNo
Com_change_master   YesBothNo
Com_check   YesBothNo
Com_checksum   YesBothNo
Com_commit   YesBothNo
Com_create_db   YesBothNo
Com_create_event   YesBothNo
Com_create_function   YesBothNo
Com_create_index   YesBothNo
Com_create_table   YesBothNo
Com_create_user   YesBothNo
Com_dealloc_sql   YesBothNo
Com_delete   YesBothNo
Com_delete_multi   YesBothNo
Com_do   YesBothNo
Com_drop_db   YesBothNo
Com_drop_event   YesBothNo
Com_drop_function   YesBothNo
Com_drop_index   YesBothNo
Com_drop_table   YesBothNo
Com_drop_user   YesBothNo
Com_execute_sql   YesBothNo
Com_flush   YesBothNo
Com_grant   YesBothNo
Com_ha_close   YesBothNo
Com_ha_open   YesBothNo
Com_ha_read   YesBothNo
Com_help   YesBothNo
Com_insert   YesBothNo
Com_insert_select   YesBothNo
Com_kill   YesBothNo
Com_load   YesBothNo
Com_lock_tables   YesBothNo
Com_optimize   YesBothNo
completion_typeYesYesYes BothYes
Com_preload_keys   YesBothNo
Com_prepare_sql   YesBothNo
Compression   YesBothNo
Com_purge   YesBothNo
Com_purge_before_date   YesBothNo
Com_rename_table   YesBothNo
Com_repair   YesBothNo
Com_replace   YesBothNo
Com_replace_select   YesBothNo
Com_reset   YesBothNo
Com_restore_table   YesBothNo
Com_revoke   YesBothNo
Com_revoke_all   YesBothNo
Com_rollback   YesBothNo
Com_savepoint   YesBothNo
Com_select   YesBothNo
Com_set_option   YesBothNo
Com_show_binlog_events   YesBothNo
Com_show_binlogs   YesBothNo
Com_show_charsets   YesBothNo
Com_show_collations   YesBothNo
Com_show_column_types   YesBothNo
Com_show_create_db   YesBothNo
Com_show_create_event   YesBothNo
Com_show_create_table   YesBothNo
Com_show_databases   YesBothNo
Com_show_engine_logs   YesBothNo
Com_show_engine_mutex   YesBothNo
Com_show_engine_status   YesBothNo
Com_show_errors   YesBothNo
Com_show_events   YesBothNo
Com_show_fields   YesBothNo
Com_show_grants   YesBothNo
Com_show_innodb_status   YesBothNo
Com_show_keys   YesBothNo
Com_show_logs   YesBothNo
Com_show_master_status   YesBothNo
Com_show_ndb_status   YesBothNo
Com_show_new_master   YesBothNo
Com_show_open_tables   YesBothNo
Com_show_plugins   YesBothNo
Com_show_privileges   YesBothNo
Com_show_processlist   YesBothNo
Com_show_slave_hosts   YesBothNo
Com_show_slave_status   YesBothNo
Com_show_status   YesBothNo
Com_show_storage_engines   YesBothNo
Com_show_tables   YesBothNo
Com_show_triggers   YesBothNo
Com_show_variables   YesBothNo
Com_show_warnings   YesBothNo
Com_slave_start   YesBothNo
Com_slave_stop   YesBothNo
Com_stmt_close   YesBothNo
Com_stmt_execute   YesBothNo
Com_stmt_fetch   YesBothNo
Com_stmt_prepare   YesBothNo
Com_stmt_reset   YesBothNo
Com_stmt_send_long_data   YesBothNo
Com_truncate   YesBothNo
Com_unlock_tables   YesBothNo
Com_update   YesBothNo
Com_update_multi   YesBothNo
Com_xa_commit   YesBothNo
Com_xa_end   YesBothNo
Com_xa_prepare   YesBothNo
Com_xa_recover   YesBothNo
Com_xa_rollback   YesBothNo
Com_xa_start   YesBothNo
concurrent_insertYesYesYes GlobalYes
Connections   YesBothNo
connect_timeoutYesYesYes GlobalYes
consoleYesYes    
core-fileYesYes    
Created_tmp_disk_tables   YesBothNo
Created_tmp_files   YesBothNo
Created_tmp_tables   YesBothNo
datadirYesYesYes GlobalNo
date_format  Yes BothYes
datetime_formatYesYesYes BothYes
debugYesYesYes BothYes
default-character-setYesYes    
defaults-extra-fileYes     
defaults-fileYes     
defaults-group-suffixYes     
default-storage-engineYesYes    
default-table-typeYesYes    
default-time-zoneYesYes    
default_week_formatYesYesYes BothYes
Delayed_errors   YesBothNo
delayed_insert_limitYesYesYes GlobalYes
Delayed_insert_threads   YesBothNo
delayed_insert_timeoutYesYesYes GlobalYes
delayed_queue_sizeYesYesYes GlobalYes
Delayed_writes   YesBothNo
delay-key-writeYesYes  GlobalYes
- Variable: delay_key_write  Yes GlobalYes
des-key-fileYesYes    
disconnect-slave-event-countYesYes    
div_precision_incrementYesYesYes BothYes
enable-lockingYes     
enable-named-pipeYesYes    
enable-pstackYesYes    
engine-condition-pushdownYesYes  BothYes
- Variable: engine_condition_pushdown  Yes BothYes
error_count  Yes SessionNo
exit-infoYesYes    
expire_logs_daysYesYesYes GlobalYes
external-lockingYesYes    
- Variable: external_locking      
flushYesYesYes GlobalYes
Flush_commands   YesBothNo
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    
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_bdb  Yes GlobalNo
have_blackhole_engine  Yes GlobalNo
have_compress  Yes GlobalNo
have_crypt  Yes GlobalNo
have_csv  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_query_cache  Yes GlobalNo
have_raid  Yes GlobalNo
have_rtree_keys  Yes GlobalNo
have_ssl  Yes GlobalNo
have_symlink  Yes GlobalNo
helpYes     
hostname  Yes GlobalNo
identity  Yes SessionYes
init_connectYesYesYes GlobalYes
init-fileYesYes  GlobalNo
- Variable: init_file  Yes GlobalNo
init_slaveYesYesYes GlobalYes
innodbYesYes    
innodb_adaptive_hash_indexYesYesYes GlobalNo
innodb_additional_mem_pool_sizeYesYesYes GlobalNo
innodb_autoextend_incrementYesYesYes GlobalYes
innodb_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_rnd   YesGlobalNo
Innodb_buffer_pool_read_ahead_seq   YesGlobalNo
Innodb_buffer_pool_read_requests   YesGlobalNo
Innodb_buffer_pool_reads   YesGlobalNo
innodb_buffer_pool_sizeYesYesYes GlobalNo
Innodb_buffer_pool_wait_free   YesGlobalNo
Innodb_buffer_pool_write_requests   YesGlobalNo
innodb_checksumsYesYesYes GlobalNo
innodb_commit_concurrencyYesYesYes GlobalYes
innodb_concurrency_ticketsYesYesYes GlobalYes
innodb_data_file_pathYesYesYes GlobalNo
Innodb_data_fsyncs   YesGlobalNo
innodb_data_home_dirYesYesYes GlobalNo
Innodb_data_pending_fsyncs   YesGlobalNo
Innodb_data_pending_reads   YesGlobalNo
Innodb_data_pending_writes   YesGlobalNo
Innodb_data_read   YesGlobalNo
Innodb_data_reads   YesGlobalNo
Innodb_data_writes   YesGlobalNo
Innodb_data_written   YesGlobalNo
Innodb_dblwr_pages_written   YesGlobalNo
Innodb_dblwr_writes   YesGlobalNo
innodb_doublewriteYesYesYes GlobalNo
innodb_fast_shutdownYesYesYes GlobalYes
innodb_file_io_threadsYesYesYes GlobalNo
innodb_file_per_tableYesYesYes GlobalNo
innodb_flush_log_at_trx_commitYesYesYes GlobalYes
innodb_flush_methodYesYesYes GlobalNo
innodb_force_recoveryYesYesYes GlobalNo
innodb_locks_unsafe_for_binlogYesYesYes GlobalNo
innodb_lock_wait_timeoutYesYesYes GlobalNo
innodb_log_arch_dirYesYesYes GlobalNo
innodb_log_archiveYesYesYes GlobalNo
innodb_log_buffer_sizeYesYesYes GlobalNo
innodb_log_files_in_groupYesYesYes GlobalNo
innodb_log_file_sizeYesYesYes GlobalNo
innodb_log_group_home_dirYesYesYes GlobalNo
Innodb_log_waits   YesGlobalNo
Innodb_log_write_requests   YesGlobalNo
Innodb_log_writes   YesGlobalNo
innodb_max_dirty_pages_pctYesYesYes GlobalYes
innodb_max_purge_lagYesYesYes GlobalYes
innodb_mirrored_log_groupsYesYesYes GlobalNo
innodb_open_filesYesYesYes GlobalNo
Innodb_os_log_fsyncs   YesGlobalNo
Innodb_os_log_pending_fsyncs   YesGlobalNo
Innodb_os_log_pending_writes   YesGlobalNo
Innodb_os_log_written   YesGlobalNo
Innodb_pages_created   YesGlobalNo
Innodb_page_size   YesGlobalNo
Innodb_pages_read   YesGlobalNo
Innodb_pages_written   YesGlobalNo
innodb_rollback_on_timeoutYesYesYes GlobalNo
Innodb_row_lock_current_waits   YesGlobalNo
Innodb_row_lock_time   YesGlobalNo
Innodb_row_lock_time_avg   YesGlobalNo
Innodb_row_lock_time_max   YesGlobalNo
Innodb_row_lock_waits   YesGlobalNo
Innodb_rows_deleted   YesGlobalNo
Innodb_rows_inserted   YesGlobalNo
Innodb_rows_read   YesGlobalNo
Innodb_rows_updated   YesGlobalNo
innodb-safe-binlogYesYes    
innodb_status_fileYesYes    
innodb_support_xaYesYesYes BothYes
innodb_sync_spin_loopsYesYesYes GlobalYes
innodb_table_locksYesYesYes BothYes
innodb_thread_concurrencyYesYesYes GlobalYes
innodb_thread_sleep_delayYesYesYes GlobalYes
insert_id  Yes SessionYes
interactive_timeoutYesYesYes BothYes
join_buffer_sizeYesYesYes BothYes
keep_files_on_createYesYesYes BothYes
Key_blocks_not_flushed   YesBothNo
Key_blocks_unused   YesBothNo
Key_blocks_used   YesBothNo
key_buffer_sizeYesYesYes GlobalYes
key_cache_age_thresholdYesYesYes GlobalYes
key_cache_block_sizeYesYesYes GlobalYes
key_cache_division_limitYesYesYes GlobalYes
Key_read_requests   YesBothNo
Key_reads   YesBothNo
Key_write_requests   YesBothNo
Key_writes   YesBothNo
languageYesYesYes GlobalNo
large_files_support  Yes GlobalNo
large-pagesYesYes  GlobalNo
- Variable: large_pages  Yes GlobalNo
large_page_size  Yes GlobalNo
last_insert_id  Yes SessionYes
Last_query_cost   YesBothNo
lc_time_names  Yes BothYes
license  Yes GlobalNo
local_infile  Yes GlobalYes
local-infileYesYes    
locked_in_memory  Yes GlobalNo
logYesYesYes GlobalNo
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-errorYesYes  GlobalNo
- Variable: log_error  Yes GlobalNo
log-isamYesYes    
log-queries-not-using-indexesYesYes  GlobalYes
- Variable: log_queries_not_using_indexes  Yes GlobalYes
log-short-formatYesYes    
log-slave-updatesYesYes  GlobalNo
- Variable: log_slave_updates  Yes GlobalNo
log-slow-admin-statementsYesYes    
log-slow-queriesYesYes  GlobalNo
- Variable: log_slow_queries  Yes GlobalNo
log-tcYesYes    
log-tc-sizeYesYes    
log-warningsYesYes  BothYes
- Variable: log_warnings  Yes BothYes
long_query_timeYesYesYes BothYes
lower_case_file_systemYesYesYes GlobalNo
lower_case_table_namesYesYesYes GlobalNo
low-priority-updatesYesYes  BothYes
- Variable: low_priority_updates  Yes BothYes
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 BothYes
max_binlog_cache_sizeYesYesYes GlobalYes
max-binlog-dump-eventsYesYes    
max_binlog_sizeYesYesYes GlobalYes
max_connect_errorsYesYesYes GlobalYes
max_connectionsYesYesYes GlobalYes
max_delayed_threadsYesYesYes BothYes
max_error_countYesYesYes BothYes
max_heap_table_sizeYesYesYes BothYes
max_insert_delayed_threads  Yes BothYes
max_join_sizeYesYesYes BothYes
max_length_for_sort_dataYesYesYes BothYes
max_prepared_stmt_countYesYesYes GlobalYes
max_relay_log_sizeYesYesYes GlobalYes
max_seeks_for_keyYesYesYes BothYes
max_sort_lengthYesYesYes BothYes
max_sp_recursion_depthYesYesYes BothYes
max_tmp_tablesYesYesYes BothYes
Max_used_connections   YesBothNo
max_user_connectionsYesYesYes BothYes
max_write_lock_countYesYesYes GlobalYes
memlockYesYesYes GlobalNo
mergeYesYes    
multi_range_countYesYesYes BothYes
myisam_block_sizeYesYes    
myisam_data_pointer_sizeYesYesYes GlobalYes
myisam_max_extra_sort_file_sizeYesYesYes GlobalNo
myisam_max_sort_file_sizeYesYesYes GlobalYes
myisam-recoverYesYes    
myisam_recover_options  Yes GlobalNo
myisam_repair_threadsYesYesYes BothYes
myisam_sort_buffer_sizeYesYesYes BothYes
myisam_stats_methodYesYesYes BothYes
named_pipe  Yes GlobalNo
ndb_autoincrement_prefetch_szYesYesYes BothYes
ndb_cache_check_timeYesYesYes GlobalYes
ndbclusterYesYesYes BothYes
Ndb_cluster_node_id   YesBothNo
Ndb_config_from_host   YesBothNo
Ndb_config_from_port   YesBothNo
ndb_force_sendYesYesYes BothYes
ndb_index_stat_cache_entriesYesYes    
ndb_index_stat_enableYesYes    
ndb_index_stat_update_freqYesYes    
ndb-mgmd-hostYesYes    
ndb-nodeidYesYes Yes No
ndb_optimized_node_selectionYesYes    
ndb_report_thresh_binlog_epoch_slipYesYes    
ndb_report_thresh_binlog_mem_usageYesYes    
ndb-shmYesYes Yes No
ndb_use_exact_count  Yes BothYes
ndb_use_transactionsYesYes    
net_buffer_lengthYesYesYes BothYes
net_read_timeoutYesYesYes BothYes
net_retry_countYesYesYes BothYes
net_write_timeoutYesYesYes BothYes
newYesYesYes BothYes
no-defaultsYes     
Not_flushed_delayed_rows   YesBothNo
old-passwordsYesYes  BothYes
- Variable: old_passwords  Yes BothYes
old-style-user-limitsYesYes    
one-threadYesYes    
Opened_tables   YesBothNo
Open_files   YesBothNo
open-files-limitYesYes  GlobalNo
- Variable: open_files_limit  Yes GlobalNo
Open_streams   YesBothNo
Open_tables   YesBothNo
optimizer_prune_levelYesYesYes BothYes
optimizer_search_depthYesYesYes BothYes
pid-fileYesYes  GlobalNo
- Variable: pid_file  Yes GlobalNo
plugin_dirYesYesYes GlobalNo
portYesYesYes GlobalNo
port-open-timeoutYesYes    
preload_buffer_sizeYesYesYes BothYes
prepared_stmt_count  YesYesGlobalNo
print-defaultsYes     
profiling  Yes SessionYes
profiling_history_size  Yes BothYes
protocol_version  Yes GlobalNo
Qcache_free_blocks   YesBothNo
Qcache_free_memory   YesBothNo
Qcache_hits   YesBothNo
Qcache_inserts   YesBothNo
Qcache_lowmem_prunes   YesBothNo
Qcache_not_cached   YesBothNo
Qcache_queries_in_cache   YesBothNo
Qcache_total_blocks   YesBothNo
query_alloc_block_sizeYesYesYes BothYes
query_cache_limitYesYesYes GlobalYes
query_cache_min_res_unitYesYesYes GlobalYes
query_cache_sizeYesYesYes GlobalYes
query_cache_typeYesYesYes BothYes
query_cache_wlock_invalidateYesYesYes BothYes
query_prealloc_sizeYesYesYes BothYes
Questions   YesBothNo
rand_seed1  Yes SessionYes
rand_seed2  Yes SessionYes
range_alloc_block_sizeYesYesYes BothYes
read_buffer_sizeYesYesYes BothYes
read_onlyYesYesYes GlobalYes
read_rnd_buffer_sizeYesYesYes BothYes
relay-logYesYes    
relay-log-indexYesYes    
relay-log-info-fileYesYes    
relay_log_purgeYesYesYes GlobalYes
relay_log_space_limitYesYesYes GlobalNo
replicate-do-dbYesYes    
replicate-do-tableYesYes    
replicate-ignore-dbYesYes    
replicate-ignore-tableYesYes    
replicate-rewrite-dbYesYes    
replicate-same-server-idYesYes    
replicate-wild-do-tableYesYes    
replicate-wild-ignore-tableYesYes    
report-hostYesYes  GlobalNo
- Variable: report_host  Yes GlobalNo
report-passwordYesYes  GlobalNo
- Variable: report_password  Yes GlobalNo
report-portYesYes  GlobalNo
- Variable: report_port  Yes GlobalNo
report-userYesYes  GlobalNo
- Variable: report_user  Yes GlobalNo
rpl_recovery_rank  Yes GlobalYes
Rpl_status   YesBothNo
safemalloc-mem-limitYesYes    
safe-modeYesYes    
safe-user-createYesYes    
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
set-variableYesYes    
shared_memory  Yes GlobalNo
shared_memory_base_name  Yes GlobalNo
show-slave-auth-infoYesYes    
skip-bdbYesYes    
skip-character-set-client-handshakeYesYes    
skip-concurrent-insertYesYes    
- Variable: concurrent_insert      
skip-external-lockingYesYes  GlobalNo
- Variable: skip_external_locking  Yes GlobalNo
skip-grant-tablesYesYes    
skip-host-cacheYesYes    
skip-innodbYesYes    
skip-innodb-checksumsYesYes    
skip-lockingYesYes    
skip-log-warningsYes     
skip-mergeYesYes    
- Variable:       
skip-name-resolveYesYes    
skip-networkingYesYes  GlobalNo
- Variable: skip_networking  Yes GlobalNo
skip-newYesYes    
skip-safemallocYesYes    
skip-show-databaseYesYes  GlobalNo
- Variable: skip_show_database  Yes GlobalNo
skip-slave-startYesYes    
skip-sslYesYes    
skip-stack-traceYesYes    
skip-symbolic-linksYes     
skip-symlinkYesYes    
skip-sync-bdb-logsYesYesYes GlobalNo
skip-thread-priorityYesYes    
slave_compressed_protocolYesYesYes GlobalYes
slave-load-tmpdirYesYes  GlobalNo
- Variable: slave_load_tmpdir  Yes GlobalNo
slave-net-timeoutYesYes  GlobalYes
- Variable: slave_net_timeout  Yes GlobalYes
Slave_open_temp_tables   YesBothNo
Slave_retried_transactions   YesBothNo
Slave_running   YesBothNo
slave-skip-errorsYesYes  GlobalNo
- Variable: slave_skip_errors  Yes GlobalNo
slave_transaction_retriesYesYesYes GlobalYes
Slow_launch_threads   YesBothNo
slow_launch_timeYesYesYes GlobalYes
Slow_queries   YesBothNo
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 BothYes
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   YesBothNo
Ssl_accepts   YesBothNo
ssl-caYesYes  GlobalNo
- Variable: ssl_ca  Yes GlobalNo
Ssl_callback_cache_hits   YesBothNo
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   YesBothNo
Ssl_connect_renegotiates   YesBothNo
Ssl_ctx_verify_depth   YesBothNo
Ssl_ctx_verify_mode   YesBothNo
Ssl_default_timeout   YesBothNo
Ssl_finished_accepts   YesBothNo
Ssl_finished_connects   YesBothNo
ssl-keyYesYes  GlobalNo
- Variable: ssl_key  Yes GlobalNo
Ssl_session_cache_hits   YesBothNo
Ssl_session_cache_misses   YesBothNo
Ssl_session_cache_mode   YesBothNo
Ssl_session_cache_overflows   YesBothNo
Ssl_session_cache_size   YesBothNo
Ssl_session_cache_timeouts   YesBothNo
Ssl_sessions_reused   YesBothNo
Ssl_used_session_cache_entries   YesBothNo
Ssl_verify_depth   YesBothNo
Ssl_verify_mode   YesBothNo
Ssl_version   YesBothNo
standaloneYesYes    
storage_engine  Yes BothYes
symbolic-linksYesYes    
sync-bdb-logsYesYesYes GlobalNo
sync-binlogYesYes  GlobalYes
- Variable: sync_binlog  Yes GlobalYes
sync-frmYesYes  GlobalYes
- Variable: sync_frm  Yes GlobalYes
sysdate-is-nowYesYes    
system_time_zone  Yes GlobalNo
table_cacheYesYesYes GlobalYes
Table_locks_immediate   YesBothNo
Table_locks_waited   YesBothNo
table_lock_wait_timeoutYesYesYes GlobalYes
table_open_cache YesYes GlobalYes
table_type  Yes BothYes
tc-heuristic-recoverYesYes    
Tc_log_max_pages_used   YesBothNo
Tc_log_page_size   YesBothNo
Tc_log_page_waits   YesBothNo
temp-poolYesYes    
thread_cache_sizeYesYesYes GlobalYes
thread_concurrencyYesYesYes GlobalNo
Threads_cached   YesBothNo
Threads_connected   YesBothNo
Threads_created   YesBothNo
Threads_running   YesBothNo
thread_stackYesYesYes GlobalNo
timed_mutexesYesYesYes GlobalYes
time_formatYesYesYes BothYes
timestamp  Yes SessionYes
time_zoneYes Yes BothYes
tmpdirYesYesYes GlobalNo
tmp_table_sizeYesYesYes BothYes
transaction_alloc_block_sizeYesYesYes BothYes
transaction-isolationYesYes    
transaction_prealloc_sizeYesYesYes BothYes
tx_isolation  Yes BothYes
unique_checks  Yes SessionYes
updatable_views_with_limitYesYesYes BothYes
Uptime   YesBothNo
Uptime_since_flush_status   YesBothNo
userYesYes    
verboseYes     
versionYes Yes GlobalNo
version_comment  Yes GlobalNo
version_compile_machine  Yes GlobalNo
version_compile_os  Yes GlobalNo
wait_timeoutYesYesYes BothYes
warning_count  Yes SessionNo
warningsYesYes    

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

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

5.1.2. Server Command Options

When you start the mysqld server, you can specify program options using any of the methods described in Section 4.2.3, “Specifying Program Options”. The most common methods are to provide options in an option file or on the command line. However, in most cases it is desirable to make sure that the server uses the same options each time it runs. The best way to ensure this is to list them in an option file. See Section 4.2.3.2, “Using Option Files”.

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

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

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

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

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

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

  • --help, -?

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

  • --abort-slave-event-count

    Value Set
    Typenumeric
    Default0
    Min Value0

    When this option is set to some positive integer value other than 0 (the default) it affects replication behavior as follows: After the slave SQL thread has started, value log events are allowed to be executed; after that, the slave SQL thread does not receive any more events, just as if the network connection from the master were cut. The slave thread continues to run, and the output from SHOW SLAVE STATUS displays Yes in both the Slave_IO_Running and the Slave_SQL_Running columns, but no further events are read from the relay log.

    This option is used internally by the MySQL test suite for replication testing and debugging. It is not intended for use in a production setting.

  • --allow-suspicious-udfs

    Version Introduced5.0.3
    Value Set
    Typeboolean
    DefaultFALSE

    This option controls whether user-defined functions that have only an xxx symbol for the main function can be loaded. By default, the option is off and only UDFs that have at least one auxiliary symbol can be loaded; this prevents attempts at loading functions from shared object files other than those containing legitimate UDFs. This option was added in version 5.0.3. See Section 21.2.2.6, “User-Defined Function Security Precautions”.

  • --ansi

    Use standard (ANSI) SQL syntax instead of MySQL syntax. For more precise control over the server SQL mode, use the --sql-mode option instead. See Section 1.7.3, “Running MySQL in ANSI Mode”, and Section 5.1.7, “Server SQL Modes”.

  • --basedir=path, -b path

    Option Sets VariableYes, basedir
    Variable Namebasedir
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

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

  • --big-tables

    Option Sets VariableYes, big_tables
    Variable Namebig-tables
    Variable ScopeSession
    Dynamic VariableYes
    Value Set
    Typeboolean

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

  • --bind-address=IP

    Value Set
    Typestring

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

  • --bootstrap

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

    This option is unavailable if MySQL was configured with the --disable-grant-options option. See Section 2.16.2, “Typical configure Options”.

  • --character-sets-dir=path

    Option Sets VariableYes, character_sets_dir
    Variable Namecharacter-sets-dir
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

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

  • --character-set-client-handshake

    Value Set
    Typeboolean
    DefaultTRUE

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

  • --character-set-filesystem=charset_name

    Version Introduced5.0.19
    Option Sets VariableYes, character_set_filesystem
    Variable Namecharacter_set_filesystem
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typestring

    The filesystem character set. This option sets the character_set_filesystem system variable. It was added in MySQL 5.0.19.

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

    Option Sets VariableYes, character_set_server
    Variable Namecharacter_set_server
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typestring

    Use charset_name as the default server character set. See Section 9.2, “The Character Set Used for Data and Sorting”. If you use this option to specify a non-default character set, you should also use --collation-server to specify the collation.

  • --chroot=path, -r path

    Value Set
    Typefilename

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

  • --collation-server=collation_name

    Option Sets VariableYes, collation_server
    Variable Namecollation_server
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typestring

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

  • --console

    Option Sets VariableYes, console
    Platform Specificwindows

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

  • --core-file

    Value Set
    Typeboolean
    DefaultTRUE

    Write a core file if mysqld dies. For some systems, you must also specify the --core-file-size option to mysqld_safe. See Section 4.3.2, “mysqld_safe — MySQL Server Startup Script”. Note that on some systems, such as Solaris, you do not get a core file if you are also using the --user option.

  • --datadir=path, -h path

    Option Sets VariableYes, datadir
    Variable Namedatadir
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    The path to the data directory.

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

    Variable Namedebug
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typestring
    Default'd:t:o,/tmp/mysqld.trace

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

    As of MySQL 5.0.25, 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.

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

    Deprecated5.0
    Value Set
    Typestring

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

  • --default-collation=collation_name

    Variable Namedefault-collation
    Variable Scope 
    Dynamic VariableNo
    Deprecated4.1.3
    Value Set
    Typestring

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

  • --default-storage-engine=type

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

  • --default-table-type=type

    Deprecated5.0, by default-storage-engine
    Value Set
    Typestring

    This option is a deprecated synonym for --default-storage-engine.

  • --default-time-zone=timezone

    Value Set
    Typestring

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

  • --delay-key-write[={OFF|ON|ALL}]

    Option Sets VariableYes, delay_key_write
    Variable Namedelay-key-write
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typeenumeration
    DefaultON
    Valid ValuesON, OFF, ALL

    Specify how to use delayed key writes. Delayed key writing causes key buffers not to be flushed between writes for MyISAM tables. OFF disables delayed key writes. ON enables delayed key writes for those tables that were created with the DELAY_KEY_WRITE option. ALL delays key writes for all MyISAM tables. See Section 7.5.2, “Tuning Server Parameters”, and Section 13.1.1, “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

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

  • --enable-named-pipe

    Platform Specificwindows

    Enable support for named pipes. This option can be used only with the mysqld-nt and mysqld-debug servers that support named-pipe connections.

  • --enable-pstack

    Value Set
    Typeboolean
    DefaultFALSE

    Print a symbolic stack trace on failure.

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

    Version Introduced5.0.3
    Option Sets VariableYes, engine_condition_pushdown
    Variable Nameengine_condition_pushdown
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set (>= 5.0.3)
    Typeboolean
    DefaultOFF

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

    In MySQL 5.0, this option is useful only with the NDBCLUSTER storage engine. However, we intend to implement it for additional storage engines in future MySQL releases.

    Setting this option to ON 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 means the amount of cluster data that must be sent over the network is greatly reduced, increasing the efficiency with which results are returned.

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

    This variable was added in MySQL 5.0.3.

  • --exit-info[=flags], -T [flags]

    Value Set
    Typenumeric

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

  • --external-locking

    Option Sets VariableYes, external_locking
    Disabled byskip-external-locking
    Value Set
    Typeboolean
    DefaultFALSE

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

    For more information about external locking, including conditions under which it can and cannot be used, see Section 7.3.4, “External Locking”.

  • --flush

    Variable Nameflush
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typeboolean
    DefaultOFF

    Flush (synchronize) all changes to disk after each SQL statement. Normally, MySQL does a write of all changes to disk only after each SQL statement and lets the operating system handle the synchronizing to disk. See Section B.1.4.2, “What to Do If MySQL Keeps Crashing”.

  • --gdb

    Value Set
    Typeboolean
    DefaultFALSE

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

  • --init-file=file_name

    Option Sets VariableYes, init_file
    Variable Nameinit_file
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

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

    This option is unavailable if MySQL was configured with the --disable-grant-options option. See Section 2.16.2, “Typical configure Options”.

  • --innodb-safe-binlog

    Version Introduced5.0.1
    Deprecated5.0.3
    Value Set (<= 5.0.3)
    Typeboolean

    Adds consistency guarantees between the content of InnoDB tables and the binary log. See Section 5.2.3, “The Binary Log”. This option was removed in MySQL 5.0.3, having been made obsolete by the introduction of XA transaction support.

  • --innodb-xxx

    The InnoDB options are listed in Section 13.2.4, “InnoDB Startup Options and System Variables”.

  • --language=lang_name, -L lang_name

    Option Sets VariableYes, language
    Variable Namelanguage
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename
    Default/usr/local/mysql/share/mysql/english/

    Return client error messages in the given language. lang_name can be given as the language name or as the full pathname to the directory where the language files are installed. See Section 9.3, “Setting the Error Message Language”.

  • --large-pages

    Version Introduced5.0.3
    Option Sets VariableYes, large_pages
    Variable Namelarge_pages
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform Specificlinux
    Value Set
    Typelinuxboolean
    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 OS. 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 pages support (which is called HugeTLB in Linux). We have plans to extend this support to FreeBSD, Solaris and possibly other platforms.

    Before large pages can be used on Linux, it is necessary to configure the HugeTLB memory pool. For reference, consult the hugetlbpage.txt file in the Linux kernel source.

    This option is disabled by default. It was added in MySQL 5.0.3.

  • --log[=file_name], -l [file_name]

    Option Sets VariableYes, log
    Variable Namelog
    Variable ScopeGlobal
    Dynamic VariableNo
    Deprecated5.1.29, by general-log
    Value Set
    Typestring
    DefaultOFF

    Log connections and SQL statements received from clients to this file. See Section 5.2.2, “The General Query Log”. If you omit the filename, MySQL uses host_name.log as the filename.

  • --log-error[=file_name]

    Option Sets VariableYes, log_error
    Variable Namelog_error
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    Log errors and startup messages to this file. See Section 5.2.1, “The Error Log”. If you omit the filename, MySQL uses host_name.err. If the filename has no extension, the server adds an extension of .err.

  • --log-isam[=file_name]

    Value Set
    Typefilename

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

  • --log-long-format (DEPRECATED)

    Deprecated4.1

    Log extra information to the update log, binary update log, and slow query log, if they have been activated. For example, the username 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-queries-not-using-indexes

    Option Sets VariableYes, log_queries_not_using_indexes
    Variable Namelog_queries_not_using_indexes
    Variable ScopeGlobal
    Dynamic VariableYes
    Deprecated5.1.29, by slow-query-log
    Value Set
    Typeboolean

    If you are using this option with the slow query log enabled, queries that are expected to retrieve all rows are logged. See Section 5.2.4, “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

    Value Set
    Typeboolean
    DefaultFALSE

    Log less information to the update log, binary update log, and slow query log, if they have been activated. For example, the username and timestamp are not logged for queries.

  • --log-slow-admin-statements

    Value Set
    Typeboolean
    DefaultFALSE

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

  • --log-slow-queries[=file_name]

    Option Sets VariableYes, log_slow_queries
    Variable Namelog_slow_queries
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typeboolean

    Log all queries that have taken more than long_query_time seconds to execute to this file. See Section 5.2.4, “The Slow Query Log”. See the descriptions of the --log-long-format and --log-short-format options for details.

  • --log-tc=file_name

    Version Introduced5.0.3
    Value Set
    Typefilename
    Defaulttc.log

    The name of the memory-mapped transaction coordinator log file (for XA transactions that affect multiple storage engines when the binary log is disabled). The default name is tc.log. The file is created under the data directory if not given as a full pathname. Currently, this option is unused. Added in MySQL 5.0.3.

  • --log-tc-size=size

    Version Introduced5.0.3
    Value Set
    Typenumeric
    Default24576
    Max Value4294967295

    The size in bytes of the memory-mapped transaction coordinator log. The default size is 24KB. Added in MySQL 5.0.3.

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

    Option Sets VariableYes, log-warnings
    Variable Namelog_warnings
    Variable ScopeBoth
    Dynamic VariableYes
    Disabled byskip-log-warnings
    Value Set
    Typenumeric
    Default1

    Print out warnings such as Aborted connection... to the error log. Enabling this option is recommended, for example, if you use replication (you get more information about what is happening, such as messages about network failures and reconnections). This option is enabled (1) by default, and the default level value if omitted is 1. To disable this option, use --log-warnings=0. If the value is greater than 1, aborted connections are written to the error log. See Section B.1.2.11, “Communication Errors and Aborted Connections”.

    If a slave server was started with --log-warnings enabled, the slave prints messages to the error log to provide information about its status, such as the binary log and relay log coordinates where it starts its job, when it is switching to another relay log, when it reconnects after a disconnect, and so forth.

  • --low-priority-updates

    Option Sets VariableYes, low_priority_updates
    Variable Namelow_priority_updates
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeboolean
    DefaultFALSE

    Give table-modifying operations (INSERT, REPLACE, DELETE, UPDATE) lower priority than selects. This can also be done via {INSERT | REPLACE | DELETE | UPDATE} LOW_PRIORITY ... to lower the priority of only one query, or by SET LOW_PRIORITY_UPDATES=1 to change the priority in one thread. This affects only storage engines that use only table-level locking (MyISAM, MEMORY, MERGE). See Section 7.3.2, “Table Locking Issues”.

  • --memlock

    Variable Namelocked_in_memory
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typeboolean
    DefaultFALSE

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

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

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

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

    extern int mlockall (int __flags) __THROW;
    

    Important

    Using this option requires that you run the server as root, which, for reasons of security, is normally not a good idea. See Section 5.3.5, “How to Run MySQL as a Normal User”.

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

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

    Value Set
    Typeenumeration
    DefaultOFF
    Valid ValuesDEFAULT, BACKUP, FORCE, QUICK

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

    The following options affect how the repair works:

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

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

    See Section 13.1.1, “MyISAM Startup Options”.

  • --old-passwords

    Option Sets VariableYes, old_passwords
    Variable Nameold_passwords
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeboolean
    DefaultFALSE

    Force the server to generate short (pre-4.1) password hashes for new passwords. This is useful for compatibility when the server must support older client programs. See Section 5.4.8, “Password Hashing as of MySQL 4.1”.

  • --old-style-user-limits

    Version Introduced5.0.3
    Value Set
    Typeboolean
    DefaultFALSE

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

  • --one-thread

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

  • --open-files-limit=count

    Option Sets VariableYes, open_files_limit
    Variable Nameopen_files_limit
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typenumeric
    Default0
    Range0-65535

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

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

  • --pid-file=path

    Option Sets VariableYes, pid_file
    Variable Namepid_file
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

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

  • --port=port_num, -P port_num

    Option Sets VariableYes, port
    Variable Nameport
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typenumeric
    Default3306

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

  • --port-open-timeout=num

    Version Introduced5.0.19
    Value Set
    Typenumeric
    Default0

    On some systems, when the server is stopped, the TCP/IP port might not become available immediately. If the server is restarted quickly afterward, its attempt to reopen the port can fail. This option indicates how many seconds the server should wait for the TCP/IP port to become free if it cannot be opened. The default is not to wait. This option was added in MySQL 5.0.19.

  • --safe-mode

    Deprecated5.0

    Skip some optimization stages.

  • --safe-show-database (DEPRECATED)

    Option Sets VariableYes, safe_show_database
    Variable Namesafe_show_database
    Variable ScopeGlobal
    Dynamic VariableYes
    Deprecated4.0.2
    Value Set
    Typeboolean

    See Section 5.4.3, “Privileges Provided by MySQL”.

  • --safe-user-create

    Option Sets VariableYes, safe-user-create
    Value Set
    Typeboolean
    DefaultFALSE

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

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

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

  • --secure-auth

    Option Sets VariableYes, secure_auth
    Variable Namesecure_auth
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typeboolean
    DefaultFALSE

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

  • --secure-file-priv=path

    Version Introduced5.0.38
    Option Sets VariableYes, secure_file_priv
    Variable Namesecure_file_priv
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typestring

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

    This option was added in MySQL 5.0.38.

  • --shared-memory

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

  • --shared-memory-base-name=name

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

  • --skip-bdb

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

  • --skip-concurrent-insert

    Turn off the ability to select and insert at the same time on MyISAM tables. (This is to be used only if you think you have found a bug in this feature.) See Section 7.3.3, “Concurrent Inserts”.

  • --skip-external-locking

    Do not use external locking (system locking). For more information about external locking, including conditions under which it can and cannot be used, see Section 7.3.4, “External Locking”.

    External locking has been disabled by default since MySQL 4.0.

  • --skip-grant-tables

    This option causes the server not to use 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 user-defined functions (UDFs).

    This option is unavailable if MySQL was configured with the --disable-grant-options option. See Section 2.16.2, “Typical configure Options”.

  • --skip-host-cache

    Do not use the internal hostname cache for faster name-to-IP resolution. Instead, query the DNS server every time a client connects. See Section 7.5.10, “How MySQL Uses DNS”.

  • --skip-innodb

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

  • --skip-merge

    Disable the MERGE storage engine. This option was added in MySQL 5.0.24. It can be used if the following behavior is undesirable: If a user has access to MyISAM table t, that user can create a MERGE table m that accesses t. However, if the user's privileges on t are subsequently revoked, the user can continue to access t by doing so through m.

  • --skip-name-resolve

    Do not resolve hostnames when checking client connections. Use only IP numbers. If you use this option, all Host column values in the grant tables must be IP numbers or localhost. See Section 7.5.10, “How MySQL Uses DNS”.

  • --skip-networking

    Don't listen for TCP/IP connections at all. All interaction with mysqld must be made via named pipes or shared memory (on Windows) or Unix socket files (on Unix). This option is highly recommended for systems where only local clients are allowed. See Section 7.5.10, “How MySQL Uses DNS”.

  • --ssl*

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

  • --standalone

    Platform Specificwindows

    Instructs the MySQL server not to run as a service.

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

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

  • --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 don't need it by using the --skip-safemalloc option.

  • --skip-show-database

    Option Sets VariableYes, skip_show_database
    Variable Nameskip_show_database
    Variable ScopeGlobal
    Dynamic VariableNo

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

  • --skip-stack-trace

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

  • --skip-thread-priority

    Deprecated5.1.29

    Disable using thread priorities for faster response time.

  • --socket=path

    Option Sets VariableYes, socket
    Variable Namesocket
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typelinuxfilename
    Default/tmp/mysql.sock 

    On Unix, this option specifies the Unix socket file to use when listening for local connections. The default value is /tmp/mysql.sock. On Windows, the option specifies the pipe name to use when listening for local connections that use a named pipe. The default value is MySQL (not case sensitive).

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

    Option Sets VariableYes, sql_mode
    Variable Namesql_mode
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeset
    Default''
    Valid ValuesALLOW_INVALID_DATES, ANSI_QUOTES, ERROR_FOR_DIVISION_BY_ZERO, HIGH_NOT_PRECEDENCE, IGNORE_SPACE, NO_AUTO_CREATE_USER, NO_AUTO_VALUE_ON_ZERO, NO_BACKSLASH_ESCAPES, NO_DIR_IN_CREATE, NO_ENGINE_SUBSTITUTION, NO_FIELD_OPTIONS, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_UNSIGNED_SUBTRACTION, NO_ZERO_DATE, NO_ZERO_IN_DATE, ONLY_FULL_GROUP_BY, PAD_CHAR_TO_FULL_LENGTH, PIPES_AS_CONCAT, REAL_AS_FLOAT, STRICT_ALL_TABLES, STRICT_TRANS_TABLES

    Set the SQL mode. See Section 5.1.7, “Server SQL Modes”.

  • --sysdate-is-now

    Version Introduced5.0.20
    Value Set
    Typeboolean
    DefaultFALSE

    As of MySQL 5.0.13, SYSDATE() by default returns the time at which it executes, not the time at which the statement in which it occurs begins executing. This differs from the behavior of NOW(). This option causes SYSDATE() to be an alias for NOW(). For information about the implications for binary logging and replication, see the description for SYSDATE() in Section 11.6, “Date and Time Functions” and for SET TIMESTAMP in Section 5.1.4, “Session System Variables”.

    This option was added in MySQL 5.0.20.

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

    Version Introduced5.0.3
    Value Set
    Typeenumeration
    Valid ValuesCOMMIT, RECOVER

    The type of decision to use in the heuristic recovery process. Currently, this option is unused. Added in MySQL 5.0.3.

  • --temp-pool

    Value Set
    Typeboolean
    DefaultTRUE

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

  • --transaction-isolation=level

    Value Set
    Typeenumeration
    Valid ValuesREAD-UNCOMMITTED, READ-COMMITTED, REPEATABLE-READ, SERIALIZABLE

    Sets the default transaction isolation level. The level value can be READ-UNCOMMITTED, READ-COMMITTED, REPEATABLE-READ, or SERIALIZABLE. See Section 12.4.6, “SET TRANSACTION Syntax”.

  • --tmpdir=path, -t path

    Option Sets VariableYes, tmpdir
    Variable Nametmpdir
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    The path of the directory to use for creating temporary files. It might be useful if your default /tmp directory resides on a partition that is too small to hold temporary tables. This option accepts several paths that are used in round-robin fashion. Paths should be separated by colon characters (“:”) on Unix and semicolon characters (“;”) on Windows, NetWare, and OS/2. If the MySQL server is acting as a replication slave, you should not set --tmpdir to point to a directory on a memory-based filesystem or to a directory that is cleared when the server host restarts. For more information about the storage location of temporary files, see Section B.1.4.4, “Where MySQL Stores Temporary Files”. A replication slave needs some of its temporary files to survive a machine restart so that it can replicate temporary tables or LOAD DATA INFILE operations. If files in the temporary file directory are lost when the server restarts, replication fails.

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

    Value Set
    Typestring

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

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

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

  • --version, -V

    Variable Nameversion
    Variable ScopeGlobal
    Dynamic VariableNo

    Display version information and exit.

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

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

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

It is also possible to set variables by using --set-variable=var_name=value or -O var_name=value syntax. This syntax is deprecated.

You can change the values of most system variables for a running server with the SET statement. See Section 12.5.4, “SET Syntax”.

Section 5.1.3, “Server System Variables”, provides a full description for all variables, and additional information for setting them at server startup and runtime. Section 7.5.2, “Tuning Server Parameters”, includes information on optimizing the server by tuning system variables.

5.1.3. Server System Variables

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

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

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

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

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

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

The following table lists all available system variables:

Table 5.2. mysqld System Variable Summary

NameCmd-LineOption fileSystem VarVar ScopeDynamic
autocommit  YesSessionYes
auto_increment_incrementYesYesYesBothYes
auto_increment_offsetYesYesYesBothYes
automatic_sp_privileges  YesGlobalYes
back_logYesYesYesGlobalNo
basedirYesYesYesGlobalNo
bdb_cache_sizeYesYesYesGlobalNo
bdb-homeYesYesYesGlobalNo
bdb-lock-detectYesYes  No
- Variable: bdb_lock_detect  YesGlobalNo
bdb_log_buffer_sizeYesYesYesGlobalNo
bdb-logdirYesYesYesGlobalNo
bdb_max_lockYesYesYesGlobalNo
bdb-shared-dataYesYes  No
- Variable: bdb_shared_data  YesGlobalNo
bdb-tmpdirYesYesYesGlobalNo
big-tablesYesYes  Yes
- Variable: big_tables  YesSessionYes
binlog_cache_sizeYesYesYesGlobalYes
bulk_insert_buffer_sizeYesYesYesBothYes
character_set_client  YesBothYes
character_set_connection  YesBothYes
character_set_database[a]  YesBothYes
character-set-filesystemYesYes  Yes
- Variable: character_set_filesystem  YesBothYes
character_set_results  YesBothYes
character-sets-dirYesYes  No
- Variable: character_sets_dir  YesGlobalNo
character-set-serverYesYes  Yes
- Variable: character_set_server  YesBothYes
character_set_system  YesGlobalNo
collation_connection  YesBothYes
collation_database[b]  YesBothYes
collation-serverYesYes  Yes
- Variable: collation_server  YesBothYes
completion_typeYesYesYesBothYes
concurrent_insertYesYesYesGlobalYes
connect_timeoutYesYesYesGlobalYes
datadirYesYesYesGlobalNo
date_format  YesBothYes
datetime_formatYesYesYesBothYes
debugYesYesYesBothYes
default_week_formatYesYesYesBothYes
delayed_insert_limitYesYesYesGlobalYes
delayed_insert_timeoutYesYesYesGlobalYes
delayed_queue_sizeYesYesYesGlobalYes
delay-key-writeYesYes  Yes
- Variable: delay_key_write  YesGlobalYes
div_precision_incrementYesYesYesBothYes
engine-condition-pushdownYesYes  Yes
- Variable: engine_condition_pushdown  YesBothYes
error_count  YesSessionNo
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
group_concat_max_lenYesYesYesBothYes
have_archive  YesGlobalNo
have_bdb  YesGlobalNo
have_blackhole_engine  YesGlobalNo
have_compress  YesGlobalNo
have_crypt  YesGlobalNo
have_csv  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_query_cache  YesGlobalNo
have_raid  YesGlobalNo
have_rtree_keys  YesGlobalNo
have_ssl  YesGlobalNo
have_symlink  YesGlobalNo
hostname  YesGlobalNo
identity  YesSessionYes
init_connectYesYesYesGlobalYes
init-fileYesYes  No
- Variable: init_file  YesGlobalNo
init_slaveYesYesYesGlobalYes
innodb_adaptive_hash_indexYesYesYesGlobalNo
innodb_additional_mem_pool_sizeYesYesYesGlobalNo
innodb_autoextend_incrementYesYesYesGlobalYes
innodb_buffer_pool_awe_mem_mbYesYesYesGlobalNo
innodb_buffer_pool_sizeYesYesYesGlobalNo
innodb_checksumsYesYesYesGlobalNo
innodb_commit_concurrencyYesYesYesGlobalYes
innodb_concurrency_ticketsYesYesYesGlobalYes
innodb_data_file_pathYesYesYesGlobalNo
innodb_data_home_dirYesYesYesGlobalNo
innodb_doublewriteYesYesYesGlobalNo
innodb_fast_shutdownYesYesYesGlobalYes
innodb_file_io_threadsYesYesYesGlobalNo
innodb_file_per_tableYesYesYesGlobalNo
innodb_flush_log_at_trx_commitYesYesYesGlobalYes
innodb_flush_methodYesYesYesGlobalNo
innodb_force_recoveryYesYesYesGlobalNo
innodb_locks_unsafe_for_binlogYesYesYesGlobalNo
innodb_lock_wait_timeoutYesYesYesGlobalNo
innodb_log_arch_dirYesYesYesGlobalNo
innodb_log_archiveYesYesYesGlobalNo
innodb_log_buffer_sizeYesYesYesGlobalNo
innodb_log_files_in_groupYesYesYesGlobalNo
innodb_log_file_sizeYesYesYesGlobalNo
innodb_log_group_home_dirYesYesYesGlobalNo
innodb_max_dirty_pages_pctYesYesYesGlobalYes
innodb_max_purge_lagYesYesYesGlobalYes
innodb_mirrored_log_groupsYesYesYesGlobalNo
innodb_open_filesYesYesYesGlobalNo
innodb_rollback_on_timeoutYesYesYesGlobalNo
innodb_support_xaYesYesYesBothYes
innodb_sync_spin_loopsYesYesYesGlobalYes
innodb_table_locksYesYesYesBothYes
innodb_thread_concurrencyYesYesYesGlobalYes
innodb_thread_sleep_delayYesYesYesGlobalYes
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-pagesYesYes  No
- Variable: large_pages  YesGlobalNo
large_page_size  YesGlobalNo
last_insert_id  YesSessionYes
lc_time_names  YesBothYes
license  YesGlobalNo
local_infile  YesGlobalYes
locked_in_memory  YesGlobalNo
logYesYesYesGlobalNo
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-errorYesYes  No
- Variable: log_error  YesGlobalNo
log-queries-not-using-indexesYesYes  Yes
- Variable: log_queries_not_using_indexes  YesGlobalYes
log-slave-updatesYesYes  No
- Variable: log_slave_updates  YesGlobalNo
log-slow-queriesYesYes  No
- Variable: log_slow_queries  YesGlobalNo
log-warningsYesYes  Yes
- Variable: log_warnings  YesBothYes
long_query_timeYesYesYesBothYes
lower_case_file_systemYesYesYesGlobalNo
lower_case_table_namesYesYesYesGlobalNo
low-priority-updatesYesYes  Yes
- Variable: low_priority_updates  YesBothYes
max_allowed_packetYesYesYesBothYes
max_binlog_cache_sizeYesYesYesGlobalYes
max_binlog_sizeYesYesYesGlobalYes
max_connect_errorsYesYesYesGlobalYes
max_connectionsYesYesYesGlobalYes
max_delayed_threadsYesYesYesBothYes
max_error_countYesYesYesBothYes
max_heap_table_sizeYesYesYesBothYes
max_insert_delayed_threads  YesBothYes
max_join_sizeYesYesYesBothYes
max_length_for_sort_dataYesYesYesBothYes
max_prepared_stmt_countYesYesYesGlobalYes
max_relay_log_sizeYesYesYesGlobalYes
max_seeks_for_keyYesYesYesBothYes
max_sort_lengthYesYesYesBothYes
max_sp_recursion_depthYesYesYesBothYes
max_tmp_tablesYesYesYesBothYes
max_user_connectionsYesYesYesBothYes
max_write_lock_countYesYesYesGlobalYes
memlockYesYesYesGlobalNo
multi_range_countYesYesYesBothYes
myisam_data_pointer_sizeYesYesYesGlobalYes
myisam_max_extra_sort_file_sizeYesYesYesGlobalNo
myisam_max_sort_file_sizeYesYesYesGlobalYes
myisam_recover_options  YesGlobalNo
myisam_repair_threadsYesYesYesBothYes
myisam_sort_buffer_sizeYesYesYesBothYes
myisam_stats_methodYesYesYesBothYes
named_pipe  YesGlobalNo
ndb_autoincrement_prefetch_szYesYesYesBothYes
ndb_cache_check_timeYesYesYesGlobalYes
ndbclusterYesYesYesBothYes
ndb_force_sendYesYesYesBothYes
ndb_use_exact_count  YesBothYes
net_buffer_lengthYesYesYesBothYes
net_read_timeoutYesYesYesBothYes
net_retry_countYesYesYesBothYes
net_write_timeoutYesYesYesBothYes
newYesYesYesBothYes
old-passwordsYesYes  Yes
- Variable: old_passwords  YesBothYes
open-files-limitYesYes  No
- Variable: open_files_limit  YesGlobalNo
optimizer_prune_levelYesYesYesBothYes
optimizer_search_depthYesYesYesBothYes
pid-fileYesYes  No
- Variable: pid_file  YesGlobalNo
plugin_dirYesYesYesGlobalNo
portYesYesYesGlobalNo
preload_buffer_sizeYesYesYesBothYes
prepared_stmt_count  YesGlobalNo
profiling  YesSessionYes
profiling_history_size  YesBothYes
protocol_version  YesGlobalNo
query_alloc_block_sizeYesYesYesBothYes
query_cache_limitYesYesYesGlobalYes
query_cache_min_res_unitYesYesYesGlobalYes
query_cache_sizeYesYesYesGlobalYes
query_cache_typeYesYesYesBothYes
query_cache_wlock_invalidateYesYesYesBothYes
query_prealloc_sizeYesYesYesBothYes
rand_seed1  YesSessionYes
rand_seed2  YesSessionYes
range_alloc_block_sizeYesYesYesBothYes
read_buffer_sizeYesYesYesBothYes
read_onlyYesYesYesGlobalYes
read_rnd_buffer_sizeYesYesYesBothYes
relay_log_purgeYesYesYesGlobalYes
relay_log_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
secure-authYesYes  Yes
- Variable: secure_auth  YesGlobalYes
secure-file-privYesYes  No
- Variable: secure_file_priv  YesGlobalNo
server-idYesYes  Yes
- Variable: server_id  YesGlobalYes
shared_memory  YesGlobalNo
shared_memory_base_name  YesGlobalNo
skip-external-lockingYesYes  No
- Variable: skip_external_locking  YesGlobalNo
skip-networkingYesYes  No
- Variable: skip_networking  YesGlobalNo
skip-show-databaseYesYes  No
- Variable: skip_show_database  YesGlobalNo
skip-sync-bdb-logsYesYesYesGlobalNo
slave_compressed_protocolYesYesYesGlobalYes
slave-load-tmpdirYesYes  No
- Variable: slave_load_tmpdir  YesGlobalNo
slave-net-timeoutYesYes  Yes
- Variable: slave_net_timeout  YesGlobalYes
slave-skip-errorsYesYes  No
- Variable: slave_skip_errors  YesGlobalNo
slave_transaction_retriesYesYesYesGlobalYes
slow_launch_timeYesYesYesGlobalYes
socketYesYesYesGlobalNo
sort_buffer_sizeYesYesYesBothYes
sql_auto_is_null  YesSessionYes
sql_big_selects  YesBothYes
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-bdb-logsYesYesYesGlobalNo
sync-binlogYesYes  Yes
- Variable: sync_binlog  YesGlobalYes
sync-frmYesYes  Yes
- Variable: sync_frm  YesGlobalYes
system_time_zone  YesGlobalNo
table_cacheYesYesYesGlobalYes
table_lock_wait_timeoutYesYesYesGlobalYes
table_open_cache YesYesGlobalYes
table_type  YesBothYes
thread_cache_sizeYesYesYesGlobalYes
thread_concurrencyYesYesYesGlobalNo
thread_stackYesYesYesGlobalNo
timed_mutexesYesYesYesGlobalYes
time_formatYesYesYesBothYes
timestamp  YesSessionYes
time_zoneYes YesBothYes
tmpdirYesYesYesGlobalNo
tmp_table_sizeYesYesYesBothYes
transaction_alloc_block_sizeYesYesYesBothYes
transaction_prealloc_sizeYesYesYesBothYes
tx_isolation  YesBothYes
unique_checks  YesSessionYes
updatable_views_with_limitYesYesYesBothYes
versionYes 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.

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

  • automatic_sp_privileges

    Version Introduced5.0.3
    Variable Nameautomatic_sp_privileges
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typeboolean
    DefaultTRUE

    When this variable has a value of 1 (the default), the server automatically grants the EXECUTE and ALTER ROUTINE privileges to the creator of a stored routine, if the user cannot already execute and alter or drop the routine. (The ALTER ROUTINE privilege is required to drop the routine.) The server also automatically drops those privileges when the creator drops the routine. If automatic_sp_privileges is 0, the server does not automatically add or drop these privileges. This variable was added in MySQL 5.0.3.

  • back_log

    Option Sets VariableYes, back_log
    Variable Nameback_log
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typenumeric
    Default50
    Range1-65535

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

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

  • basedir

    Option Sets VariableYes, basedir
    Variable Namebasedir
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

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

  • bdb_cache_size

    Command Line Format--bdb_cache_size=#
    Config File Formatbdb_cache_size
    Option Sets VariableYes, bdb_cache_size
    Variable Namebdb_cache_size
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typenumeric
    Min Value20480

    The size of the buffer that is allocated for caching indexes and rows for BDB tables. If you don't use BDB tables, you should start mysqld with --skip-bdb to not allocate memory for this cache.

  • bdb_home

    Command Line Format--bdb-home=name
    Variable Namebdb_home
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    The base directory for BDB tables. This should be assigned the same value as the datadir variable.

  • bdb_log_buffer_size

    Command Line Format--bdb_log_buffer_size=#
    Config File Formatbdb_log_buffer_size
    Option Sets VariableYes, bdb_log_buffer_size
    Variable Namebdb_log_buffer_size
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typenumeric
    Range262144-4294967295

    The size of the buffer that is allocated for caching indexes and rows for BDB tables. If you don't use BDB tables, you should set this to 0 or start mysqld with --skip-bdb to not allocate memory for this cache.

  • bdb_logdir

    Command Line Format--bdb-logdir=file_name
    Variable Namebdb_logdir
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    The directory where the BDB storage engine writes its log files. This variable can be set with the --bdb-logdir option.

  • bdb_max_lock

    Command Line Format--bdb_max_lock=#
    Config File Formatbdb_max_lock
    Option Sets VariableYes, bdb_max_lock
    Variable Namebdb_max_lock
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typenumeric
    Default10000

    The maximum number of locks that can be active for a BDB table (10,000 by default). You should increase this value if errors such as the following occur when you perform long transactions or when mysqld has to examine many rows to calculate a query:

    bdb: Lock table is out of available locks
    Got error 12 from ...
    
  • bdb_shared_data

    Command Line Format--bdb-shared-data
    Option Sets VariableYes, bdb_shared_data
    Variable Namebdb_shared_data
    Variable ScopeGlobal
    Dynamic VariableNo

    This is ON if you are using --bdb-shared-data to start Berkeley DB in multi-process mode. (Do not use DB_PRIVATE when initializing Berkeley DB.)

  • bdb_tmpdir

    Command Line Format--bdb-tmpdir=name
    Config File Formatbdb-tmpdir
    Variable Namebdb_tmpdir
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    The BDB temporary file directory.

  • binlog_cache_size

    Option Sets VariableYes, binlog_cache_size
    Variable Namebinlog_cache_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default32768
    Range4096-4294967295

    The size of the cache to hold the SQL statements for the binary log during a transaction. A binary log cache is allocated for each client if the server supports any transactional storage engines and if the server has the binary log enabled (--log-bin option). If you often use large, multiple-statement transactions, you can increase this cache size to get more performance. The Binlog_cache_use and Binlog_cache_disk_use status variables can be useful for tuning the size of this variable. See Section 5.2.3, “The Binary Log”.

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

  • bulk_insert_buffer_size

    Option Sets VariableYes, bulk_insert_buffer_size
    Variable Namebulk_insert_buffer_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default8388608
    Range0-4294967295

    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 non-empty tables. This variable limits the size of the cache tree in bytes per thread. Setting it to 0 disables this optimization. The default value is 8MB.

  • character_set_client

    Variable Namecharacter_set_client
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typestring

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

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

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

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

  • character_set_connection

    Variable Namecharacter_set_connection
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typestring

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

  • character_set_database

    Variable Namecharacter_set_database
    Variable ScopeBoth
    Dynamic VariableYes
    FootnoteThis option is dynamic, but only the server should set this information. You should not set the value of this variable manually.
    Value Set
    Typestring

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

  • character_set_filesystem

    Version Introduced5.0.19
    Option Sets VariableYes, character_set_filesystem
    Variable Namecharacter_set_filesystem
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typestring

    The filesystem character set. This variable is used to interpret string literals that refer to filenames, such as in the LOAD DATA INFILE and SELECT ... INTO OUTFILE statements and the LOAD_FILE() function. Such filenames are converted from character_set_client to character_set_filesystem before the file opening attempt occurs. The default value is binary, which means that no conversion occurs. For systems on which multi-byte filenames are allowed, a different value may be more appropriate. For example, if the system represents filenames using UTF-8, set character_set_filesystem to 'utf8'. This variable was added in MySQL 5.0.19.

  • character_set_results

    Variable Namecharacter_set_results
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typestring

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

  • character_set_server

    Option Sets VariableYes, character_set_server
    Variable Namecharacter_set_server
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typestring

    The server's default character set.

  • character_set_system

    Variable Namecharacter_set_system
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typestring

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

  • character_sets_dir

    Option Sets VariableYes, character_sets_dir
    Variable Namecharacter-sets-dir
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    The directory where character sets are installed.

  • collation_connection

    Variable Namecollation_connection
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typestring

    The collation of the connection character set.

  • collation_database

    Variable Namecollation_database
    Variable ScopeBoth
    Dynamic VariableYes
    FootnoteThis option is dynamic, but only the server should set this information. You should not set the value of this variable manually.
    Value Set
    Typestring

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

  • collation_server

    Option Sets VariableYes, collation_server
    Variable Namecollation_server
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typestring

    The server's default collation.

  • completion_type

    Version Introduced5.0.3
    Option Sets VariableYes, completion_type
    Variable Namecompetion_type
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default0
    Valid Values0, 1, 2

    The transaction completion type:

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

    • If the value is 1, COMMIT and ROLLBACK are equivalent to COMMIT AND CHAIN and ROLLBACK AND CHAIN, respectively. (A new transaction starts immediately with the same isolation level as the just-terminated transaction.)

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

    This variable was added in MySQL 5.0.3

  • concurrent_insert

    Option Sets VariableYes, concurrent_insert
    Variable Nameconcurrent_insert
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set (<= 5.0.6)
    Typeboolean
    DefaultTRUE
    Value Set (>= 5.0.6)
    Typenumeric
    Default1
    Valid Values0, 1, 2

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

    In MySQL 5.0.6, this variable was changed to take three integer values:

    ValueDescription
    0Off
    1(Default) Enables concurrent insert for MyISAM tables that don't have holes
    2Enables concurrent inserts for all MyISAM tables, even those that have holes. For a table with a hole, new rows are inserted at the end of the table if it is in use by another thread. Otherwise, MySQL acquires a normal write lock and inserts the row into the hole.

    See also Section 7.3.3, “Concurrent Inserts”.

  • connect_timeout

    Option Sets VariableYes, connect_timeout
    Variable Nameconnect_timeout
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set (<= 5.0.52)
    Typenumeric
    Default5
    Min Value2
    Value Set (>= 5.0.52)
    Typenumeric
    Default10

    The number of seconds that the mysqld server waits for a connect packet before responding with Bad handshake. The default value is 10 seconds as of MySQL 5.0.52 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

    Option Sets VariableYes, datadir
    Variable Namedatadir
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

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

  • date_format

    This variable is unused.

  • datetime_format

    This variable is unused.

  • default_week_format

    Option Sets VariableYes, default_week_format
    Variable Namedefault_week_format
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default0
    Range0-7

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

  • delay_key_write

    Option Sets VariableYes, delay_key_write
    Variable Namedelay-key-write
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typeenumeration
    DefaultON
    Valid ValuesON, OFF, ALL

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

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

    If DELAY_KEY_WRITE is enabled for a table, the key buffer is not flushed for the table on every index update, but only when the table is closed. This speeds up writes on keys a lot, but if you use this feature, you should add automatic checking of all MyISAM tables by starting the server with the --myisam-recover option (for example, --myisam-recover=BACKUP,FORCE). See Section 5.1.2, “Server Command Options”, and Section 13.1.1, “MyISAM Startup Options”.

    Note that 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

    Option Sets VariableYes, delayed_insert_limit
    Variable Namedelayed_insert_limit
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default100
    Range1-4294967295

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

  • delayed_insert_timeout

    Option Sets VariableYes, delayed_insert_timeout
    Variable Namedelayed_insert_timeout
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default300

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

  • delayed_queue_size

    Option Sets VariableYes, delayed_queue_size
    Variable Namedelayed_queue_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default1000
    Range1-4294967295

    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

    Version Introduced5.0.6
    Option Sets VariableYes, div_precision_increment
    Variable Namediv_precision_increment
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default4
    Range0-30

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

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

    This variable was added in MySQL 5.0.6.

  • expire_logs_days

    Option Sets VariableYes, expire_logs_days
    Variable Nameexpire_logs_days
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default0
    Range0-99

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

  • flush

    Variable Nameflush
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typeboolean
    DefaultOFF

    If ON, the server flushes (synchronizes) all changes to disk after each SQL statement. Normally, MySQL does a write of all changes to disk only after each SQL statement and lets the operating system handle the synchronizing to disk. See Section B.1.4.2, “What to Do If MySQL Keeps Crashing”. This variable is set to ON if you start mysqld with the --flush option.

  • flush_time

    Option Sets VariableYes, flush_time
    Variable Nameflush_time
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typelinuxnumeric
    Default0 
    Min Value0 

    If this is set to a non-zero value, all tables are closed every flush_time seconds to free up resources and synchronize unflushed data to disk. We recommend that this option be used only on systems with minimal resources.

  • ft_boolean_syntax

    Variable Nameft_boolean_syntax
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typestring
    Default+-><()~*:""&

    The list of operators supported by boolean full-text searches performed using IN BOOLEAN MODE. See Section 11.8.2, “Boolean Full-Text Searches”.

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

    • Operator function is determined by position within the string.

    • The replacement value must be 14 characters.

    • Each character must be an ASCII non-alphanumeric character.

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

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

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

  • ft_max_word_len

    Option Sets VariableYes, ft_max_word_len
    Variable Nameft_max_word_len
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typenumeric
    Min Value10

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

    Note

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

  • ft_min_word_len

    Option Sets VariableYes, ft_min_word_len
    Variable Nameft_min_word_len
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typenumeric
    Default4
    Min Value1

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

    Note

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

  • ft_query_expansion_limit

    Option Sets VariableYes, ft_query_expansion_limit
    Variable Nameft_query_expansion_limit
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typenumeric
    Default20
    Range0-1000

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

  • ft_stopword_file

    Option Sets VariableYes, ft_stopword_file
    Variable Nameft_stopword_file
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    The file from which to read the list of stopwords for full-text searches. All the words from the file are used; comments are not honored. By default, a built-in list of stopwords is used (as defined in the myisam/ft_static.c file). Setting this variable to the empty string ('') disables stopword filtering.

    Note

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

  • group_concat_max_len

    Option Sets VariableYes, group_concat_max_len
    Variable Namegroup_concat_max_len
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default1024
    Min Value4

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

  • have_archive

    YES if mysqld supports ARCHIVE tables, NO if not.

  • have_bdb

    YES if mysqld supports BDB tables. DISABLED if --skip-bdb is used.

  • have_blackhole_engine

    YES if mysqld supports BLACKHOLE tables, NO if not.

  • have_compress

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

  • have_crypt

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

  • have_csv

    YES if mysqld supports CSV tables, NO if not.

  • have_example_engine

    YES if mysqld supports EXAMPLE tables, NO if not.

  • have_federated_engine

    YES if mysqld supports FEDERATED tables, NO if not. This variable was added in MySQL 5.0.3.

  • have_geometry

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

  • have_innodb

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

  • have_isam

    In MySQL 5.0, this variable appears only for reasons of backward compatibility. It is always NO because ISAM tables are no longer supported.

  • have_merge_engine

    YES if mysqld supports MERGE tables. DISABLED if --skip-merge is used. This variable was added in MySQL 5.0.24.

  • have_openssl

    YES if mysqld supports SSL connections, NO if not. As of MySQL 5.0.38, this variable is an alias for have_ssl.

  • have_query_cache

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

  • have_raid

    In MySQL 5.0, this variable appears only for reasons of backward compatibility. It is always NO because RAID tables are no longer supported.

  • 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. This variable was added in MySQL 5.0.38. 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.

  • hostname

    Version Introduced5.0.38
    Variable Namehostname
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typestring

    The server sets this variable to the server hostname at startup. This variable was added in MySQL 5.0.38.

  • init_connect

    Option Sets VariableYes, init_connect
    Variable Nameinit_connect
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typestring

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

    SET GLOBAL init_connect='SET autocommit=0';
    

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

    [mysqld]
    init_connect='SET autocommit=0'
    

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

  • init_file

    Option Sets VariableYes, init_file
    Variable Nameinit_file
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    The name of the file specified with the --init-file option when you start the server. This should be a file containing SQL statements that you want the server to execute when it starts. Each statement must be on a single line and should not include comments.

    Note that the --init-file option is unavailable if MySQL was configured with the --disable-grant-options option. See Section 2.16.2, “Typical configure Options”.

  • innodb_xxx

    InnoDB system variables are listed in Section 13.2.4, “InnoDB Startup Options and System Variables”.

  • interactive_timeout

    Option Sets VariableYes, interactive_timeout
    Variable Nameinteractive_timeout
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default28800
    Min Value1

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

  • join_buffer_size

    Option Sets VariableYes, join_buffer_size
    Variable Namejoin_buffer_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default131072
    Range8200-4294967295

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

    The maximum allowable setting for join_buffer_size is 4GB.

  • keep_files_on_create

    Version Introduced5.0.48
    Option Sets VariableYes, keep_files_on_create
    Variable Namekeep_files_on_create
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeboolean
    DefaultOFF

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

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

    This variable was added in MySQL 5.0.48.

  • key_buffer_size

    Option Sets VariableYes, key_buffer_size
    Variable Namekey_buffer_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default8388608
    Range8-4294967295

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

    The maximum allowable setting for key_buffer_size is 4GB on 32-bit platforms. As of MySQL 5.0.52, values larger than 4GB are allowed for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB with a warning). The effective maximum size might be less, depending on your available physical RAM and per-process RAM limits imposed by your operating system or hardware platform. The value of this variable indicates the amount of memory requested. Internally, the server allocates as much memory as possible up to this amount, but the actual allocation might be less.

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

    For even more speed when writing many rows at the same time, use LOCK TABLES. See Section 7.2.18, “Speed of INSERT Statements”.

    You can check the performance of the key buffer by issuing a SHOW STATUS statement and examining the Key_read_requests, Key_reads, Key_write_requests, and Key_writes status variables. (See Section 12.5.5, “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 may be allocated internally for administrative structures.

    It is possible to create multiple MyISAM key caches. The size limit of 4GB applies to each cache individually, not as a group. See Section 7.4.6, “The MyISAM Key Cache”.

  • key_cache_age_threshold

    Option Sets VariableYes, key_cache_age_threshold
    Variable Namekey_cache_age_threshold
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default300
    Range100-4294967295

    This value controls the demotion of buffers from the hot sub-chain of a key cache to the warm sub-chain. Lower values cause demotion to happen more quickly. The minimum value is 100. The default value is 300. See Section 7.4.6, “The MyISAM Key Cache”.

  • key_cache_block_size

    Option Sets VariableYes, key_cache_block_size
    Variable Namekey_cache_block_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default1024
    Range512-16384

    The size in bytes of blocks in the key cache. The default value is 1024. See Section 7.4.6, “The MyISAM Key Cache”.

  • key_cache_division_limit

    Option Sets VariableYes, key_cache_division_limit
    Variable Namekey_cache_division_limit
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default100
    Range1-100

    The division point between the hot and warm sub-chains of the key cache buffer chain. The value is the percentage of the buffer chain to use for the warm sub-chain. Allowable values range from 1 to 100. The default value is 100. See Section 7.4.6, “The MyISAM Key Cache”.

  • language

    Option Sets VariableYes, language
    Variable Namelanguage
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename
    Default/usr/local/mysql/share/mysql/english/

    The language used for error messages.

  • large_files_support

    Variable Namelarge_files_support
    Variable ScopeGlobal
    Dynamic VariableNo

    Whether mysqld was compiled with options for large file support.

  • large_pages

    Version Introduced5.0.3
    Option Sets VariableYes, large_pages
    Variable Namelarge_pages
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform Specificlinux
    Value Set
    Typelinuxboolean
    DefaultFALSE 

    Whether large page support is enabled. This variable was added in MySQL 5.0.3.

    For more information, see the entry for the --large-pages server option.

  • large_page_size

    Version Introduced5.0.3
    Variable Namelarge_page_size
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typelinuxnumeric
    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. This variable was added in MySQL 5.0.3.

    For more information, see the entry for the --large-pages server option.

  • lc_time_names

    Version Introduced5.0.25
    Variable Namelc_time_names
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typestring

    This variable specifies the locale that controls the language used to display day and month names and abbreviations. This variable affects the output from the DATE_FORMAT(), DAYNAME() and MONTHNAME() functions. Locale names are POSIX-style values such as 'ja_JP' or 'pt_BR'. The default value is 'en_US' regardless of your system's locale setting. For further information, see Section 9.8, “MySQL Server Locale Support”. This variable was added in MySQL 5.0.25.

  • license

    Variable Namelicense
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typestring
    DefaultGPL

    The type of license the server has.

  • local_infile

    Variable Namelocal_infile
    Variable ScopeGlobal
    Dynamic VariableYes

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

  • locked_in_memory

    Variable Namelocked_in_memory
    Variable ScopeGlobal
    Dynamic VariableNo

    Whether mysqld was locked in memory with --memlock.

  • log

    Whether logging of all statements to the general query log is enabled. See Section 5.2.2, “The General Query Log”.

  • log_bin

    Variable Namelog_bin
    Variable ScopeGlobal
    Dynamic VariableNo

    Whether the binary log is enabled. See Section 5.2.3, “The Binary Log”.

  • log_bin_trust_function_creators

    Version Introduced5.0.16
    Option Sets VariableYes, log_bin_trust_function_creators
    Variable Namelog_bin_trust_function_creators
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typeboolean
    DefaultFALSE

    This variable applies when binary logging is enabled. It controls whether stored function creators can be trusted not to create stored functions that will cause unsafe events to be written to the binary log. If set to 0 (the default), users are not allowed to create or alter stored functions unless they have the SUPER privilege in addition to the CREATE ROUTINE or ALTER ROUTINE privilege. A setting of 0 also enforces the restriction that a function must be declared with the DETERMINISTIC characteristic, or with the READS SQL DATA or NO SQL characteristic. If the variable is set to 1, MySQL does not enforce these restrictions on stored function creation. This variable also applies to trigger creation. See Section 18.5, “Binary Logging of Stored Programs”.

    This variable was added in MySQL 5.0.16.

  • log_bin_trust_routine_creators

    This is the old name for log_bin_trust_function_creators. Before MySQL 5.0.16, it also applies to stored procedures, not just stored functions. As of 5.0.16, this variable is deprecated. It is recognized for backward compatibility but its use results in a warning.

    This variable was added in MySQL 5.0.6.

  • log_error

    Option Sets VariableYes, log_error
    Variable Namelog_error
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    The location of the error log.

  • log_queries_not_using_indexes

    Option Sets VariableYes, log_queries_not_using_indexes
    Variable Namelog_queries_not_using_indexes
    Variable ScopeGlobal
    Dynamic VariableYes
    Deprecated5.1.29, by slow-query-log
    Value Set
    Typeboolean

    Whether queries that do not use indexes are logged to the slow query log. See Section 5.2.4, “The Slow Query Log”. This variable was added in MySQL 5.0.23.

  • log_slow_queries

    Option Sets VariableYes, log_slow_queries
    Variable Namelog_slow_queries
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typeboolean

    Whether slow queries should be logged. “Slow” is determined by the value of the long_query_time variable. See Section 5.2.4, “The Slow Query Log”.

  • log_warnings

    Option Sets VariableYes, log-warnings
    Variable Namelog_warnings
    Variable ScopeBoth
    Dynamic VariableYes
    Disabled byskip-log-warnings
    Value Set
    Typenumeric
    Default1

    Whether to produce additional warning messages. It is enabled (1) by default and can be disabled by setting it to 0. Aborted connections are not logged to the error log unless the value is greater than 1.

  • long_query_time

    Option Sets VariableYes, long_query_time
    Variable Namelong_query_time
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set (<= 5.0.20)
    Typenumeric
    Default10
    Min Value1

    If a query takes longer than this many seconds, the server increments the Slow_queries status variable. If you are using the --log-slow-queries option, the query is logged to the slow query log file. This value is measured in real time, not CPU time, so a query that is under the threshold on a lightly loaded system might be above the threshold on a heavily loaded one. The minimum value is 1. The default is 10. See Section 5.2.4, “The Slow Query Log”.

  • low_priority_updates

    Option Sets VariableYes, low_priority_updates
    Variable Namelow_priority_updates
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeboolean
    DefaultFALSE

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

  • lower_case_file_system

    Option Sets VariableYes, lower_case_file_system
    Variable Namelower_case_file_system
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typeboolean

    This variable describes the case sensitivity of filenames on the filesystem where the data directory is located. OFF means filenames are case sensitive, ON means they are not case sensitive.

  • lower_case_table_names

    Option Sets VariableYes, lower_case_table_names
    Variable Namelower_case_table_names
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typenumeric
    Default0
    Range0-2

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

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

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

  • max_allowed_packet

    Option Sets VariableYes, max_allowed_packet
    Variable Namemax_allowed_packet
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default1048576
    Range1024-1073741824

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

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

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

  • max_connect_errors

    Option Sets VariableYes, max_connect_errors
    Variable Namemax_connect_errors
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default10
    Range1-4294967295

    If there are more than this number of interrupted connections from a host, that host is blocked from further connections. You can unblock blocked hosts with the FLUSH HOSTS statement.

  • max_connections

    Option Sets VariableYes, max_connections
    Variable Namemax_connections
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default100

    The number of simultaneous client connections allowed. By default, this is 100. See Section B.1.2.7, “Too many connections, for more information.

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

    Increasing this value increases the number of file descriptors that mysqld requires. See Section 7.4.8, “How MySQL Opens and Closes Tables”, for comments on file descriptor limits.

  • max_delayed_threads

    Option Sets VariableYes, max_delayed_threads
    Variable Namemax_delayed_threads
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default20
    Range0-16384

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

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

  • max_error_count

    Option Sets VariableYes, max_error_count
    Variable Namemax_error_count
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default64
    Range0-65535

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

  • max_heap_table_size

    Option Sets VariableYes, max_heap_table_size
    Variable Namemax_heap_table_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default16777216
    Range16384-4294967295

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

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

  • max_insert_delayed_threads

    Variable Namemax_insert_delayed_threads
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric

    This variable is a synonym for max_delayed_threads.

  • max_join_size

    Option Sets VariableYes, max_join_size
    Variable Namemax_join_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default4294967295
    Range1-4294967295

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

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

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

    This variable previously was named sql_max_join_size.

  • max_length_for_sort_data

    Option Sets VariableYes, max_length_for_sort_data
    Variable Namemax_length_for_sort_data
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default1024
    Range4-8388608

    The cutoff on the size of index values that determines which filesort algorithm to use. See Section 7.2.12, “ORDER BY Optimization”.

  • max_prepared_stmt_count

    Version Introduced5.0.21
    Command Line Format--max_prepared_stmt_count=#
    Config File Formatmax_prepared_stmt_count
    Option Sets VariableYes, max_prepared_stmt_count
    Variable Namemax_prepared_stmt_count
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default16382
    Range0-1048576

    This variable limits the total number of prepared statements in the server. It can be used in environments where there is the potential for denial-of-service attacks based on running the server out of memory by preparing huge numbers of statements. The default value is 16,382. The allowable range of values is from 0 to 1 million. 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. This variable was added in MySQL 5.0.21.

  • max_relay_log_size

    Option Sets VariableYes, max_relay_log_size
    Variable Namemax_relay_log_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default0
    Range0-1073741824

    If a write by a replication slave to its relay log causes the current log file size to exceed the value of this variable, the slave rotates the relay logs (closes the current file and opens the next one). If max_relay_log_size is 0, the server uses max_binlog_size for both the binary log and the relay log. If max_relay_log_size is greater than 0, it constrains the size of the relay log, which enables you to have different sizes for the two logs. You must set max_relay_log_size to between 4096 bytes and 1GB (inclusive), or to 0. The default value is 0. See Section 16.4.1, “Replication Implementation Details”.

  • max_seeks_for_key

    Option Sets VariableYes, max_seeks_for_key
    Variable Namemax_seeks_for_key
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default4294967295
    Range1-4294967295

    Limit the assumed maximum number of seeks when looking up rows based on a key. The MySQL optimizer assumes that no more than this number of key seeks are required when searching for matching rows in a table by scanning an index, regardless of the actual cardinality of the index (see Section 12.5.5.18, “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

    Option Sets VariableYes, max_sort_length
    Variable Namemax_sort_length
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default1024
    Range4-8388608

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

  • max_sp_recursion_depth

    Version Introduced5.0.17
    Option Sets VariableYes, max_sp_recursion_depth
    Variable Namemax_sp_recursion_depth
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default0
    Max Value255

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

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

    This variable was added in MySQL 5.0.17.

  • max_tmp_tables

    Option Sets VariableYes, max_tmp_tables
    Variable Namemax_tmp_tables
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default32
    Range1-4294967295

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

  • max_user_connections

    Option Sets VariableYes, max_user_connections
    Variable Namemax_user_connections
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Range1-4294967295

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

    Before MySQL 5.0.3, this variable has only global scope. Beginning with MySQL 5.0.3, it also has a read-only session scope. The session variable has the same value as the global variable unless the current account has a non-zero MAX_USER_CONNECTIONS resource limit. In that case, the session value reflects the account limit.

  • max_write_lock_count

    Option Sets VariableYes, max_write_lock_count
    Variable Namemax_write_lock_count
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default4294967295
    Range1-4294967295

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

  • myisam_block_size

    Value Set
    Typenumeric
    Default1024
    Range1024-16384

    The block size to be used for MyISAM index pages.

  • myisam_data_pointer_size

    Option Sets VariableYes, myisam_data_pointer_size
    Variable Namemyisam_data_pointer_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set (<= 5.0.6)
    Typenumeric
    Default4
    Range2-8
    Value Set (>= 5.0.6)
    Typenumeric
    Default6
    Range2-7

    The default pointer size in bytes, to be used by CREATE TABLE for MyISAM tables when no MAX_ROWS option is specified. This variable cannot be less than 2 or larger than 7. The default value is 6 (4 before MySQL 5.0.6). See Section B.1.2.12, “The table is full.

  • myisam_max_extra_sort_file_size (DEPRECATED)

    This variable is not used. It was removed in MySQL 5.0.6.

  • myisam_max_sort_file_size

    Option Sets VariableYes, myisam_max_sort_file_size
    Variable Namemyisam_max_sort_file_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default2147483648

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

    The default value is 2GB. If MyISAM index files exceed this size and disk space is available, increasing the value may help performance.

  • myisam_recover_options

    Variable Namemyisam_recover_options
    Variable ScopeGlobal
    Dynamic VariableNo

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

  • myisam_repair_threads

    Option Sets VariableYes, myisam_repair_threads
    Variable Namemyisam_repair_threads
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default1
    Range1-4294967295

    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

    Option Sets VariableYes, myisam_sort_buffer_size
    Variable Namemyisam_sort_buffer_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default8388608
    Range4-4294967295

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

    The maximum allowable setting for myisam_sort_buffer_size is 4GB.

  • myisam_stats_method

    Version Introduced5.0.14
    Option Sets VariableYes, myisam_stats_method
    Variable Namemyisam_stats_method
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set (<= 5.0)
    Typeenumeration
    Defaultnulls_unequal
    Value Set (>= 5.0)
    Typeenumeration
    Valid Valuesnulls_equal, nulls_unequal

    How the server treats NULL values when collecting statistics about the distribution of index values for MyISAM tables. This variable has two possible values, nulls_equal and nulls_unequal. 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.

    The method that is used for generating table statistics influences how the optimizer chooses indexes for query execution, as described in Section 7.4.7, “MyISAM Index Statistics Collection”.

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

    This variable was added in MySQL 5.0.14. For older versions, the statistics collection method is equivalent to nulls_equal.

  • named_pipe

    Variable Namenamed_pipe
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform Specificwindows

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

  • net_buffer_length

    Option Sets VariableYes, net_buffer_length
    Variable Namenet_buffer_length
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default16384
    Range1024-1048576

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

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

  • net_read_timeout

    Option Sets VariableYes, net_read_timeout
    Variable Namenet_read_timeout
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default30
    Min Value1

    The number of seconds to wait for more data from a connection before aborting the read. This timeout applies only to TCP/IP connections, not to connections made via Unix socket files, named pipes, or shared memory. When the server is reading from the client, net_read_timeout is the timeout value controlling when to abort. When the server is writing to the client, net_write_timeout is the timeout value controlling when to abort. See also slave_net_timeout.

  • net_retry_count

    Option Sets VariableYes, net_retry_count
    Variable Namenet_retry_count
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default10
    Range1-4294967295

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

  • net_write_timeout

    Option Sets VariableYes, net_write_timeout
    Variable Namenet_write_timeout
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default60
    Min Value1

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

  • new

    Option Sets VariableYes, new
    Variable Namenew
    Variable ScopeBoth
    Dynamic VariableYes
    Disabled byskip-new
    Value Set
    Typeboolean
    DefaultFALSE

    This variable was used in MySQL 4.0 to turn on some 4.1 behaviors, and is retained for backward compatibility. In MySQL 5.0, its value is always OFF.

  • old_passwords

    Option Sets VariableYes, old_passwords
    Variable Nameold_passwords
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeboolean
    DefaultFALSE

    Whether the server should use pre-4.1-style passwords for MySQL user accounts. See Section B.1.2.4, “Client does not support authentication protocol.

  • one_shot

    This is not a variable, but it can be used when setting some variables. It is described in Section 12.5.4, “SET Syntax”.

  • open_files_limit

    Option Sets VariableYes, open_files_limit
    Variable Nameopen_files_limit
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typenumeric
    Default0
    Range0-65535

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

  • optimizer_prune_level

    Version Introduced5.0.1
    Option Sets VariableYes, optimizer_prune_level
    Variable Nameoptimizer_prune_level
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeboolean
    Default1

    Controls the heuristics applied during query optimization to prune less-promising partial plans from the optimizer search space. A value of 0 disables heuristics so that the optimizer performs an exhaustive search. A value of 1 causes the optimizer to prune plans based on the number of rows retrieved by intermediate plans. This variable was added in MySQL 5.0.1.

  • optimizer_search_depth

    Version Introduced5.0.1
    Option Sets VariableYes, optimizer_search_depth
    Variable Nameoptimizer_search_depth
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default62

    The maximum depth of search performed by the query optimizer. Values larger than the number of relations in a query result in better query plans, but take longer to generate an execution plan for a query. Values smaller than the number of relations in a query return an execution plan quicker, but the resulting plan may be far from being optimal. If set to 0, the system automatically picks a reasonable value. If set to the maximum number of tables used in a query plus 2, the optimizer switches to the algorithm used in MySQL 5.0.0 (and previous versions) for performing searches. This variable was added in MySQL 5.0.1.

  • pid_file

    Option Sets VariableYes, pid_file
    Variable Namepid_file
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

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

  • plugin_dir

    Version Introduced5.0.67
    Option Sets VariableYes, plugin_dir
    Variable Nameplugin_dir
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename
    Default/usr/local/mysql/lib/mysql

    The pathname of the plugin directory. This variable was added in MySQL 5.0.67. If the value is non-empty, user-defined function object files must be located in this directory. If the value is empty, the behavior that is used before 5.0.67 applies: The UDF object files must be located in a directory that is searched by your system's dynamic linker.

  • port

    Option Sets VariableYes, port
    Variable Nameport
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typenumeric
    Default3306

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

  • preload_buffer_size

    Option Sets VariableYes, preload_buffer_size
    Variable Namepreload_buffer_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default32768
    Range1024-1073741824

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

  • prepared_stmt_count

    Version Introduced5.0.21
    Variable Nameprepared_stmt_count
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    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 5.0.21. In MySQL 5.0.32, it was converted to the global Prepared_stmt_count status variable.

  • protocol_version

    Variable Nameprotocol_version
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typenumeric

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

  • query_alloc_block_size

    Option Sets VariableYes, query_alloc_block_size
    Variable Namequery_alloc_block_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default8192
    Range1024-4294967295

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

  • query_cache_limit

    Option Sets VariableYes, query_cache_limit
    Variable Namequery_cache_limit
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default1048576
    Min Value0

    Don't cache results that are larger than this number of bytes. The default value is 1MB.

  • query_cache_min_res_unit

    Option Sets VariableYes, query_cache_min_res_unit
    Variable Namequery_cache_min_res_unit
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default4096
    Min Value512

    The minimum size (in bytes) for blocks allocated by the query cache. The default value is 4096 (4KB). Tuning information for this variable is given in Section 7.5.4.3, “Query Cache Configuration”.

  • query_cache_size

    Option Sets VariableYes, query_cache_size
    Variable Namequery_cache_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default0

    The amount of memory allocated for caching query results. The default value is 0, which disables the query cache. The allowable values are multiples of 1024; other values are rounded down to the nearest multiple. Note that query_cache_size bytes of memory are allocated even if query_cache_type is set to 0. See Section 7.5.4.3, “Query Cache Configuration”, for more information.

    The query cache needs a minimum size of about 40KB to allocate its structures. (The exact size depends on system architecture.) If you set the value of query_cache_size too small, you'll get a warning, as described in Section 7.5.4.3, “Query Cache Configuration”.

  • query_cache_type

    Option Sets VariableYes, query_cache_type
    Variable Namequery_cache_type
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeenumeration
    Default1
    Valid Values0, 1, 2

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

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

    This variable defaults to ON.

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

  • query_cache_wlock_invalidate

    Option Sets VariableYes, query_cache_wlock_invalidate
    Variable Namequery_cache_wlock_invalidate
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeboolean
    DefaultFALSE

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

  • query_prealloc_size

    Option Sets VariableYes, query_prealloc_size
    Variable Namequery_prealloc_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default8192
    Range8192-4294967295

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

  • range_alloc_block_size

    Option Sets VariableYes, range_alloc_block_size
    Variable Namerange_alloc_block_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set (>= 5.0.54)
    Typenumeric
    Default4096
    Max Value4294967295

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

  • read_buffer_size

    Option Sets VariableYes, read_buffer_size
    Variable Nameread_buffer_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default131072
    Range8200-2147479552

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

    The maximum allowable setting for read_buffer_size is 2GB.

    read_buffer_size and read_rnd_buffer_size are not specific to any storage engine and apply in a general manner for optimization. See Section 7.5.8, “How MySQL Uses Memory”, for example.

  • read_only

    Option Sets VariableYes, read_only
    Variable Nameread_only
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default0

    This variable is off by default. When it is enabled, the server allows no updates except from users that have the SUPER privilege or (on a slave server) from updates performed by slave threads. On a slave server, this can be useful to ensure that the slave accepts updates only from its master server and not from clients. As of MySQL 5.0.16, this variable does not apply to TEMPORARY tables.

    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.

  • read_rnd_buffer_size

    Option Sets VariableYes, read_rnd_buffer_size
    Variable Nameread_rnd_buffer_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default262144
    Range8200-4294967295

    When reading rows in sorted order following a key-sorting operation, the rows are read through this buffer to avoid disk seeks. See Section 7.2.12, “ORDER BY Optimization”. Setting the variable to a large value can improve ORDER BY performance by a lot. However, this is a buffer allocated for each client, so you should not set the global variable to a large value. Instead, change the session variable only from within those clients that need to run large queries.

    The maximum allowable setting for read_rnd_buffer_size is 2GB.

    read_buffer_size and read_rnd_buffer_size are not specific to any storage engine and apply in a general manner for optimization. See Section 7.5.8, “How MySQL Uses Memory”, for example.

  • secure_auth

    Option Sets VariableYes, secure_auth
    Variable Namesecure_auth
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typeboolean
    DefaultFALSE

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

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

    Server startup fails with an error if this option is enabled and the privilege tables are in pre-4.1 format. See Section B.1.2.4, “Client does not support authentication protocol.

  • secure_file_priv

    Version Introduced5.0.38
    Option Sets VariableYes, secure_file_priv
    Variable Namesecure_file_priv
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typestring

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

    This variable was added in MySQL 5.0.38.

  • shared_memory

    Variable Nameshared_memory
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform Specificwindows

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

  • shared_memory_base_name

    Variable Nameshared_memory_base_name
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform Specificwindows

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

  • skip_external_locking

    This is OFF if mysqld uses external locking, ON if external locking is disabled.

  • skip_networking

    This is ON if the server allows only local (non-TCP/IP) connections. On Unix, local connections use a Unix socket file. On Windows, local connections use a named pipe or shared memory. On NetWare, only TCP/IP connections are supported, so do not set this variable to ON. This variable can be set to ON with the --skip-networking option.

  • skip_show_database

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

  • slow_launch_time

    Option Sets VariableYes, slow_launch_time
    Variable Nameslow_launch_time
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default2

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

  • socket

    Option Sets VariableYes, socket
    Variable Namesocket
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typelinuxfilename
    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

    Option Sets VariableYes, sort_buffer_size
    Variable Namesort_buffer_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default2097144
    Max Value4294967295

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

    The maximum allowable setting for sort_buffer_size is 4GB.

  • sql_mode

    Option Sets VariableYes, sql_mode
    Variable Namesql_mode
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeset
    Default''
    Valid ValuesALLOW_INVALID_DATES, ANSI_QUOTES, ERROR_FOR_DIVISION_BY_ZERO, HIGH_NOT_PRECEDENCE, IGNORE_SPACE, NO_AUTO_CREATE_USER, NO_AUTO_VALUE_ON_ZERO, NO_BACKSLASH_ESCAPES, NO_DIR_IN_CREATE, NO_ENGINE_SUBSTITUTION, NO_FIELD_OPTIONS, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_UNSIGNED_SUBTRACTION, NO_ZERO_DATE, NO_ZERO_IN_DATE, ONLY_FULL_GROUP_BY, PAD_CHAR_TO_FULL_LENGTH, PIPES_AS_CONCAT, REAL_AS_FLOAT, STRICT_ALL_TABLES, STRICT_TRANS_TABLES

    The current server SQL mode, which can be set dynamically. See Section 5.1.7, “Server SQL Modes”.

  • sql_select_limit

    Variable Namesql_select_limit
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric

    The maximum number of rows to return from SELECT statements. The default value for a new connection is the maximum number of rows that the server allows per table, which depends on the server configuration and may be affected if the server build was configured with --with-big-tables. Typical default values are (232)–1 or (264)–1. If you have changed the limit, the default value can be restored by assigning a value of DEFAULT.

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

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

  • ssl_ca

    Version Introduced5.0.23
    Option Sets VariableYes, ssl_ca
    Variable Namessl_ca
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    The path to a file with a list of trusted SSL CAs. This variable was added in MySQL 5.0.23.

  • ssl_capath

    Version Introduced5.0.23
    Option Sets VariableYes, ssl_capath
    Variable Namessl_capath
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    The path to a directory that contains trusted SSL CA certificates in PEM format. This variable was added in MySQL 5.0.23.

  • ssl_cert

    Version Introduced5.0.23
    Option Sets VariableYes, ssl_cert
    Variable Namessl_cert
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    The name of the SSL certificate file to use for establishing a secure connection. This variable was added in MySQL 5.0.23.

  • ssl_cipher

    Version Introduced5.0.23
    Option Sets VariableYes, ssl_cipher
    Variable Namessl_cipher
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    A list of allowable ciphers to use for SSL encryption. This variable was added in MySQL 5.0.23.

  • ssl_key

    Version Introduced5.0.23
    Option Sets VariableYes, ssl_key
    Variable Namessl_key
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typestring

    The name of the SSL key file to use for establishing a secure connection. This variable was added in MySQL 5.0.23.

  • storage_engine

    Variable Namestorage_engine
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeenumeration

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

  • sync_frm

    Option Sets VariableYes, sync_frm
    Variable Namesync_frm
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typeboolean
    DefaultTRUE

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

  • system_time_zone

    Variable Namesystem_time_zone
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typestring

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

    The system_time_zone variable differs from time_zone. Although they might have the same value, the latter variable is used to initialize the time zone for each client that connects. See Section 9.7, “MySQL Server Time Zone Support”.

  • table_cache

    Option Sets VariableYes, table_cache
    Variable Nametable_cache
    Variable ScopeGlobal
    Dynamic VariableYes
    Deprecated5.1.3, by table_open_cache
    Value Set
    Typenumeric
    Default64
    Range1-524288

    The number of open tables for all threads. Increasing this value increases the number of file descriptors that mysqld requires. You can check whether you need to increase the table cache by checking the Opened_tables status variable. See Section 5.1.6, “Server Status Variables”. If the value of Opened_tables is large and you don't do FLUSH TABLES often (which just forces all tables to be closed and reopened), then you should increase the value of the table_cache variable. For more information about the table cache, see Section 7.4.8, “How MySQL Opens and Closes Tables”.

  • table_lock_wait_timeout

    Version Introduced5.0.10
    Option Sets VariableYes, table_lock_wait_timeout
    Variable Nametable_lock_wait_timeout
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default50
    Range1-1073741824

    Specifies a wait timeout for table-level locks, in seconds. The default timeout is 50 seconds. The timeout is active only if the connection has open cursors. This variable can also be set globally at runtime (you need the SUPER privilege to do this). It's available as of MySQL 5.0.10.

  • table_type

    Variable Nametable_type
    Variable ScopeBoth
    Dynamic VariableYes
    Deprecated5.2.5, by storage_engine
    Value Set
    Typeenumeration

    This variable is a synonym for storage_engine. In MySQL 5.0, storage_engine is the preferred name.

  • thread_cache_size

    Option Sets VariableYes, thread_cache_size
    Variable Namethread_cache_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default0
    Range0-16384

    How many threads the server should cache for reuse. When a client disconnects, the client's threads are put in the cache if there are fewer than thread_cache_size threads there. Requests for threads are satisfied by reusing threads taken from the cache if possible, and only when the cache is empty is a new thread created. This variable can be increased to improve performance if you have a lot of new connections. (Normally, this doesn't provide a notable performance improvement if you have a good thread implementation.) By examining the difference between the Connections and Threads_created status variables, you can see how efficient the thread cache is. For details, see Section 5.1.6, “Server Status Variables”.

  • thread_concurrency

    Option Sets VariableYes, thread_concurrency
    Variable Namethread_concurrency
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typenumeric
    Default10
    Range1-512

    On Solaris, mysqld calls thr_setconcurrency() with this 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. This variable does not apply on other systems.

  • thread_stack

    Option Sets VariableYes, thread_stack
    Variable Namethread_stack
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typenumeric
    Default196608
    Range131072-4294967295

    The stack size for each thread. Many of the limits detected by the crash-me test are dependent on this value. See Section 7.1.4, “The MySQL Benchmark Suite”. The default (192KB) is large enough for normal operation. If the thread stack size is too small, it limits the complexity of the SQL statements that the server can handle, the recursion depth of stored procedures, and other memory-consuming actions.

  • time_format

    This variable is unused.

  • time_zone

    Variable Nametime_zone
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typestring

    The current time zone. This variable is used to initialize the time zone for each client that connects. By default, the initial value of this is 'SYSTEM' (which means, “use the value of system_time_zone”). The value can be specified explicitly at server startup with the --default-time-zone option. See Section 9.7, “MySQL Server Time Zone Support”.

  • timed_mutexes

    Version Introduced5.0.3
    Option Sets VariableYes, timed_mutexes
    Variable Nametimed_mutexes
    Variable ScopeGlobal
    Dynamic VariableYes
    Value Set
    Typeboolean
    DefaultOFF

    This variable controls whether InnoDB mutexes are timed. If this variable is set to 0 or OFF (the default), mutex timing is disabled. If the variable is set to 1 or ON, mutex timing is enabled. With timing enabled, the os_wait_times value in the output from SHOW ENGINE INNODB MUTEX indicates the amount of time (in ms) spent in operating system waits. Otherwise, the value is 0. This variable was added in MySQL 5.0.3.

  • tmp_table_size

    Option Sets VariableYes, tmp_table_size
    Variable Nametmp_table_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Defaultsystem dependent
    Range1024-4294967295

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

  • tmpdir

    Option Sets VariableYes, tmpdir
    Variable Nametmpdir
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

    The directory used for temporary files and temporary tables. This variable can be set to a list of several paths that are used in round-robin fashion. Paths should be separated by colon characters (“:”) on Unix and semicolon characters (“;”) on Windows, NetWare, and OS/2.

    The multiple-directory feature can be used to spread the load between several physical disks. If the MySQL server is acting as a replication slave, you should not set tmpdir to point to a directory on a memory-based filesystem or to a directory that is cleared when the server host restarts. A replication slave needs some of its temporary files to survive a machine restart so that it can replicate temporary tables or LOAD DATA INFILE operations. If files in the temporary file directory are lost when the server restarts, replication fails. However, if you are using MySQL 4.0.0 or later, you can set the slave's temporary directory using the slave_load_tmpdir variable. In that case, the slave won't use the general tmpdir value and you can set tmpdir to a non-permanent location.

  • transaction_alloc_block_size

    Option Sets VariableYes, transaction_alloc_block_size
    Variable Nametransaction_alloc_block_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default8192
    Range1024-4294967295

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

  • transaction_prealloc_size

    Option Sets VariableYes, transaction_prealloc_size
    Variable Nametransaction_prealloc_size
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default4096

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

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

  • tx_isolation

    Variable Nametx_isolation
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeenumeration
    DefaultREPEATABLE-READ
    Valid ValuesREAD-UNCOMMITTED, READ-COMMITTED, REPEATABLE-READ, SERIALIZABLE

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

    This variable is set by the SET TRANSACTION ISOLATION LEVEL statement. See Section 12.4.6, “SET TRANSACTION Syntax”. If you set tx_isolation directly to an isolation level name that contains a space, the name should be enclosed within quotes, with the space replaced by a dash. For example:

    SET tx_isolation = 'READ-COMMITTED';
    

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

  • updatable_views_with_limit

    Version Introduced5.0.2
    Option Sets VariableYes, updatable_views_with_limit
    Variable Nameupdatable_views_with_limit
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typeboolean
    Default1

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

    The variable can have two values:

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

    • 0 or NO: Prohibit the update.

    This variable was added in MySQL 5.0.2.

  • version

    Variable Nameversion
    Variable ScopeGlobal
    Dynamic VariableNo

    The version number for the server.

    Variable Nameversion
    Variable ScopeGlobal
    Dynamic VariableNo

    Starting with MySQL 5.0.24, the version number will also indicate whether the server is a standard release (Community) or Enterprise release (for example, 5.0.28-enterprise-gpl-nt).

  • version_bdb

    The BDB storage engine version.

  • version_comment

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

    For precompiled binaries, this variable will hold the server version and license information. Starting with MySQL 5.0.24, version_comment will include the full server type and license. For community users this will appear as MySQL Community Edition - Standard (GPL). For Enterprise users, the version might be displayed as MySQL Enterprise Server (GPL). The corresponding license for your MySQL binary is shown in parentheses. For server compiled from source, the default value will be the same as that for Community releases.

  • version_compile_machine

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

  • version_compile_os

    Variable Nameversion_compile_os
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typestring

    The type of operating system on which MySQL was built.

  • wait_timeout

    Option Sets VariableYes, wait_timeout
    Variable Namewait_timeout
    Variable ScopeBoth
    Dynamic VariableYes
    Value Set
    Typenumeric
    Default28800

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

    On thread startup, the session wait_timeout value is initialized from the global wait_timeout value or from the global interactive_timeout value, depending on the type of client (as defined by the CLIENT_INTERACTIVE connect option to mysql_real_connect()). See also interactive_timeout.

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

5.1.4. Session System Variables

Several system variables exist only as session variables. These cannot be set at server startup but can be assigned values at runtime using the SET statement (except for those that are read only). Most of them are not displayed by SHOW VARIABLES, but you can obtain their values using SELECT. This section describes the session system variables. For information about setting or displaying their values, see Section 5.1.5, “Using System Variables”. For example:

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

The lettercase of these variables does not matter.

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

Table 5.3. mysqld Session System Variable Summary

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

    The autocommit mode. If set to 1, all changes to a table take effect immediately. If set to 0, you must use COMMIT to accept a transaction or ROLLBACK to cancel it. By default, client connections begin with autocommit set to 1. If you change autocommit mode from 0 to 1, MySQL performs an automatic COMMIT of any open transaction. Another way to begin a transaction is to use a START TRANSACTION or BEGIN statement. See Section 12.4.1, “START TRANSACTION, COMMIT, and ROLLBACK Syntax”.

  • big_tables

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

    Note

    This variable was formerly named sql_big_tables.

  • error_count

    The number of errors that resulted from the last statement that generated messages. This variable is read only. See Section 12.5.5.14, “SHOW ERRORS Syntax”.

  • foreign_key_checks

    If set to 1 (the default), foreign key constraints for InnoDB tables are checked. If set to 0, they are ignored. Disabling foreign key checking can be useful for reloading InnoDB tables in an order different from that required by their parent/child relationships. See Section 13.2.5.4, “FOREIGN KEY Constraints”.

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

    Note

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

  • identity

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

  • insert_id

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

  • last_insert_id

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

  • profiling

    If set to 0 (the default), statement profiling is disabled. If set to 1, statement profiling is enabled and the SHOW PROFILES and SHOW PROFILE statements provide access to profiling information. See Section 12.5.5.29, “SHOW PROFILES Syntax”. This variable was added in MySQL 5.0.37. Note: This option does not apply to MySQL Enterprise Server users.

  • profiling_history_size

    The number of statements for which to maintain profiling information if profiling is enabled. The default value is 15. The maximum value is 100. Setting the value to 0 effectively disables profiling. See Section 12.5.5.29, “SHOW PROFILES Syntax”. This variable was added in MySQL 5.0.37. Note: This option does not apply to MySQL Enterprise Server users.

  • rand_seed1

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

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

  • rand_seed2

    See the description for rand_seed1.

  • sql_auto_is_null

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

    WHERE auto_increment_column IS NULL
    

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

  • sql_big_selects

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

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

  • sql_buffer_result

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

  • sql_log_bin

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

  • sql_log_off

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

  • sql_log_update

    This variable is deprecated, and is mapped to sql_log_bin.

  • sql_notes

    If set to 1 (the default), warnings of Note level are recorded. If set to 0, Note warnings are suppressed. mysqldump includes output to set this variable to 0 so that reloading the dump file does not produce warnings for events that do not affect the integrity of the reload operation. sql_notes was added in MySQL 5.0.3.

  • sql_quote_show_create

    If set to 1 (the default), the server quotes identifiers for SHOW CREATE TABLE and SHOW CREATE DATABASE statements. If set to 0, quoting is disabled. This option is enabled by default so that replication works for identifiers that require quoting. See Section 12.5.5.9, “SHOW CREATE TABLE Syntax”, and Section 12.5.5.6, “SHOW CREATE DATABASE Syntax”.

  • sql_safe_updates

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

  • sql_warnings

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

  • timestamp = {timestamp_value | DEFAULT}

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

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

  • unique_checks

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

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

  • warning_count

    The number of errors, warnings, and notes that resulted from the last statement that generated messages. This variable is read only. See Section 12.5.5.37, “SHOW WARNINGS Syntax”.

5.1.5. Using System Variables

The MySQL server maintains many system variables that indicate how it is configured. Section 5.1.3, “Server System Variables”, describes the meaning of these variables. Each system variable has a default value. System variables can be set at server startup using options on the command line or in an option file. Most of them can be changed dynamically while the server is running by means of the SET statement, which enables you to modify operation of the server without having to stop and restart it. You can refer to system variable values in expressions.

The server maintains two kinds of system variables. Global variables affect the overall operation of the server. Session variables affect its operation for individual client connections. A given system variable can have both a global and a session value. Global and session system variables are related as follows:

  • When the server starts, it initializes all global variables to their default values. These defaults can be changed by options specified on the command line or in an option file. (See Section 4.2.3, “Specifying Program Options”.)

  • The server also maintains a set of session variables for each client that connects. The client's session variables are initialized at connect time using the current values of the corresponding global variables. For example, the client's SQL mode is controlled by the session sql_mode value, which is initialized when the client connects to the value of the global sql_mode value.

System variable values can be set globally at server startup by using options on the command line or in an option file. When you use a startup option to set a variable that takes a numeric value, the value can be given with a suffix of K, M, or G (either uppercase or lowercase) to indicate a multiplier of 1024, 10242 or 10243; that is, units of kilobytes, megabytes, or gigabytes, respectively. Thus, the following command starts the server with a query cache size of 16 megabytes and a maximum packet size of one gigabyte:

mysqld --query_cache_size=16M --max_allowed_packet=1G

Within an option file, those variables are set like this:

[mysqld]
query_cache_size=16M
max_allowed_packet=1G

The lettercase of suffix letters does not matter; 16M and 16m are equivalent, as are 1G and 1g.

If you want to restrict the maximum value to which a system variable can be set at runtime with the SET statement, you can specify this maximum by using an option of the form --maximum-var_name=value at server startup. For example, to prevent the value of query_cache_size from being increased to more than 32MB at runtime, use the option --maximum-query_cache_size=32M.

Many system variables are dynamic and can be changed while the server runs by using the SET statement. For a list, see Section 5.1.5.2, “Dynamic System Variables”. To change a system variable with SET, refer to it as var_name, optionally preceded by a modifier:

  • To indicate explicitly that a variable is a global variable, precede its name by GLOBAL or @@global.. The SUPER privilege is required to set global variables.

  • To indicate explicitly that a variable is a session variable, precede its name by SESSION, @@session., or @@. Setting a session variable requires no special privilege, but a client can change only its own session variables, not those of any other client.

  • LOCAL and @@local. are synonyms for SESSION and @@session..

  • If no modifier is present, SET changes the session variable.

A SET statement can contain multiple variable assignments, separated by commas. If you set several system variables, the most recent GLOBAL or SESSION modifier in the statement is used for following variables that have no modifier specified.

Examples:

SET sort_buffer_size=10000;
SET @@local.sort_buffer_size=10000;
SET GLOBAL sort_buffer_size=1000000, SESSION sort_buffer_size=1000000;
SET @@sort_buffer_size=1000000;
SET @@global.sort_buffer_size=1000000, @@local.sort_buffer_size=1000000;

The @@var_name syntax for system variables is supported for compatibility with some other database systems.

If you change a session system variable, the value remains in effect until your session ends or until you change the variable to a different value. The change is not visible to other clients.

If you change a global system variable, the value is remembered and used for new connections until the server restarts. (To make a global system variable setting permanent, you should set it in an option file.) The change is visible to any client that accesses that global variable. However, the change affects the corresponding session variable only for clients that connect after the change. The global variable change does not affect the session variable for any client that is currently connected (not even that of the client that issues the SET GLOBAL statement).

To prevent incorrect usage, MySQL produces an error if you use SET GLOBAL with a variable that can only be used with SET SESSION or if you do not specify GLOBAL (or @@global.) when setting a global variable.

To set a SESSION variable to the GLOBAL value or a GLOBAL value to the compiled-in MySQL default value, use the DEFAULT keyword. For example, the following two statements are identical in setting the session value of max_join_size to the global value:

SET max_join_size=DEFAULT;
SET @@session.max_join_size=@@global.max_join_size;

Not all system variables can be set to DEFAULT. In such cases, use of DEFAULT results in an error.

You can refer to the values of specific global or sesson system variables in expressions by using one of the @@-modifiers. For example, you can retrieve values in a SELECT statement like this:

SELECT @@global.sql_mode, @@session.sql_mode, @@sql_mode;

When you refer to a system variable in an expression as @@var_name (that is, when you do not specify @@global. or @@session.), MySQL returns the session value if it exists and the global value otherwise. (This differs from SET @@var_name = value, which always refers to the session value.)

Suffixes for specifying a value multiplier can be used when setting a variable at server startup, but not to set the value with SET at runtime. On the other hand, with SET you can assign a variable's value using an expression, which is not true when you set a variable at server startup. For example, the first of the following lines is legal at server startup, but the second is not:

shell> mysql --max_allowed_packet=16M
shell> mysql --max_allowed_packet=16*1024*1024

Conversely, the second of the following lines is legal at runtime, but the first is not:

mysql> SET GLOBAL max_allowed_packet=16M;
mysql> SET GLOBAL max_allowed_packet=16*1024*1024;

Note

Some system variables can be enabled with the SET statement by setting them to ON or 1, or disabled by setting them to OFF or 0. However, to set such a variable on the command line or in an option file, you must set it to 1 or 0; setting it to ON or OFF will not work. For example, on the command line, --delay_key_write=1 works but --delay_key_write=ON does not.

To display system variable names and values, use the SHOW VARIABLES statement:

mysql> SHOW VARIABLES;
+--------+--------------------------------------------------------------+
| Variable_name                   | Value                               |
+--------+--------------------------------------------------------------+
| auto_increment_increment        | 1                                   |
| auto_increment_offset           | 1                                   |
| automatic_sp_privileges         | ON                                  |
| back_log                        | 50                                  |
| basedir                         | /                                   |
| bdb_cache_size                  | 8388600                             |
| bdb_home                        | /var/lib/mysql/                     |
| bdb_log_buffer_size             | 32768                               |
| bdb_logdir                      |                                     |
| bdb_max_lock                    | 10000                               |
| bdb_shared_data                 | OFF                                 |
| bdb_tmpdir                      | /tmp/                               |
| binlog_cache_size               | 32768                               |
| bulk_insert_buffer_size         | 8388608                             |
| character_set_client            | latin1                              |
| character_set_connection        | latin1                              |
| character_set_database          | latin1                              |
| character_set_results           | latin1                              |
| character_set_server            | latin1                              |
| character_set_system            | utf8                                |
| character_sets_dir              | /usr/share/mysql/charsets/          |
| collation_connection            | latin1_swedish_ci                   |
| collation_database              | latin1_swedish_ci                   |
| collation_server                | latin1_swedish_ci                   |
...
| innodb_additional_mem_pool_size | 1048576                             |
| innodb_autoextend_increment     | 8                                   |
| innodb_buffer_pool_awe_mem_mb   | 0                                   |
| innodb_buffer_pool_size         | 8388608                             |
| innodb_checksums                | ON                                  |
| innodb_commit_concurrency       | 0                                   |
| innodb_concurrency_tickets      | 500                                 |
| innodb_data_file_path           | ibdata1:10M:autoextend              |
| innodb_data_home_dir            |                                     |
...
| version                         | 5.0.19                              |
| version_comment                 | MySQL Community Edition - (GPL)     |
| version_compile_machine         | i686                                |
| version_compile_os              | pc-linux-gnu                        |
| wait_timeout                    | 28800                               |
+--------+--------------------------------------------------------------+

With a LIKE clause, the statement displays only those variables that match the pattern. To obtain a specific variable name, use a LIKE clause as shown:

SHOW VARIABLES LIKE 'max_join_size';
SHOW SESSION VARIABLES LIKE 'max_join_size';

To get a list of variables whose name match a pattern, use the “%” wildcard character in a LIKE clause:

SHOW VARIABLES LIKE '%size%';
SHOW GLOBAL VARIABLES LIKE '%size%';

Wildcard characters can be used in any position within the pattern to be matched. Strictly speaking, because “_” is a wildcard that matches any single character, you should escape it as “\_” to match it literally. In practice, this is rarely necessary.

For SHOW VARIABLES, if you specify neither GLOBAL nor SESSION, MySQL returns SESSION values.

The reason for requiring the GLOBAL keyword when setting GLOBAL-only variables but not when retrieving them is to prevent problems in the future. If we were to remove a SESSION variable that has the same name as a GLOBAL variable, a client with the SUPER privilege might accidentally change the GLOBAL variable rather than just the SESSION variable for its own connection. If we add a SESSION variable with the same name as a GLOBAL variable, a client that intends to change the GLOBAL variable might find only its own SESSION variable changed.

5.1.5.1. Structured System Variables

A structured variable differs from a regular system variable in two respects:

  • Its value is a structure with components that specify server parameters considered to be closely related.

  • There might be several instances of a given type of structured variable. Each one has a different name and refers to a different resource maintained by the server.

MySQL 5.0 supports one structured variable type, which specifies parameters governing the operation of key caches. A key cache structured variable has these components:

This section describes the syntax for referring to structured variables. Key cache variables are used for syntax examples, but specific details about how key caches operate are found elsewhere, in Section 7.4.6, “The MyISAM Key Cache”.

To refer to a component of a structured variable instance, you can use a compound name in instance_name.component_name format. Examples:

hot_cache.key_buffer_size
hot_cache.key_cache_block_size
cold_cache.key_cache_block_size

For each structured system variable, an instance with the name of default is always predefined. If you refer to a component of a structured variable without any instance name, the default instance is used. Thus, default.key_buffer_size and key_buffer_size both refer to the same system variable.

Structured variable instances and components follow these naming rules:

  • For a given type of structured variable, each instance must have a name that is unique within variables of that type. However, instance names need not be unique across structured variable types. For example, each structured variable has an instance named default, so default is not unique across variable types.

  • The names of the components of each structured variable type must be unique across all system variable names. If this were not true (that is, if two different types of structured variables could share component member names), it would not be clear which default structured variable to use for references to member names that are not qualified by an instance name.

  • If a structured variable instance name is not legal as an unquoted identifier, refer to it as a quoted identifier using backticks. For example, hot-cache is not legal, but `hot-cache` is.

  • global, session, and local are not legal instance names. This avoids a conflict with notation such as @@global.var_name for referring to non-structured system variables.

Currently, the first two rules have no possibility of being violated because the only structured variable type is the one for key caches. These rules will assume greater significance if some other type of structured variable is created in the future.

With one exception, you can refer to structured variable components using compound names in any context where simple variable names can occur. For example, you can assign a value to a structured variable using a command-line option:

shell> mysqld --hot_cache.key_buffer_size=64K

In an option file, use this syntax:

[mysqld]
hot_cache.key_buffer_size=64K

If you start the server with this option, it creates a key cache named hot_cache with a size of 64KB in addition to the default key cache that has a default size of 8MB.

Suppose that you start the server as follows:

shell> mysqld --key_buffer_size=256K \
         --extra_cache.key_buffer_size=128K \
         --extra_cache.key_cache_block_size=2048

In this case, the server sets the size of the default key cache to 256KB. (You could also have written --default.key_buffer_size=256K.) In addition, the server creates a second key cache named extra_cache that has a size of 128KB, with the size of block buffers for caching table index blocks set to 2048 bytes.

The following example starts the server with three different key caches having sizes in a 3:1:1 ratio:

shell> mysqld --key_buffer_size=6M \
         --hot_cache.key_buffer_size=2M \
         --cold_cache.key_buffer_size=2M

Structured variable values may be set and retrieved at runtime as well. For example, to set a key cache named hot_cache to a size of 10MB, use either of these statements:

mysql> SET GLOBAL hot_cache.key_buffer_size = 10*1024*1024;
mysql> SET @@global.hot_cache.key_buffer_size = 10*1024*1024;

To retrieve the cache size, do this:

mysql> SELECT @@global.hot_cache.key_buffer_size;

However, the following statement does not work. The variable is not interpreted as a compound name, but as a simple string for a LIKE pattern-matching operation:

mysql> SHOW GLOBAL VARIABLES LIKE 'hot_cache.key_buffer_size';

This is the exception to being able to use structured variable names anywhere a simple variable name may occur.

5.1.5.2. Dynamic System Variables

Many server system variables are dynamic and can be set at runtime using SET GLOBAL or SET SESSION. You can also obtain their values using SELECT. See Section 5.1.5, “Using System Variables”.

The following table shows the full list of all dynamic system variables. The last column indicates for each variable whether GLOBAL or SESSION (or both) apply. The table also lists session options that can be set with the SET statement. Section 5.1.4, “Session System Variables”, discusses these options.

Variables that have a type of “string” take a string value. Variables that have a type of “numeric” take a numeric value. Variables that have a type of “boolean” can be set to 0, 1, ON or OFF. (If you set them on the command line or in an option file, use the numeric values.) Variables that are marked as “enumeration” normally should be set to one of the available values for the variable, but can also be set to the number that corresponds to the desired enumeration value. For enumerated system variables, the first enumeration value corresponds to 0. This differs from ENUM columns, for which the first enumeration value corresponds to 1.

Variable NameVariable TypeVariable Scope
autocommitbooleanSESSION
auto_increment_incrementnumericGLOBAL | SESSION
auto_increment_offsetnumericGLOBAL | SESSION
automatic_sp_privilegesbooleanGLOBAL
big_tablesbooleanSESSION
binlog_cache_sizenumericGLOBAL
bulk_insert_buffer_sizenumericGLOBAL | SESSION
character_set_clientstringGLOBAL | SESSION
character_set_connectionstringGLOBAL | SESSION
character_set_databasestringGLOBAL | SESSION
character_set_filesystemstringGLOBAL | SESSION
character_set_resultsstringGLOBAL | SESSION
character_set_serverstringGLOBAL | SESSION
collation_connectionstringGLOBAL | SESSION
collation_databasestringGLOBAL | SESSION
collation_serverstringGLOBAL | SESSION
completion_typenumericGLOBAL | SESSION
concurrent_insertbooleanGLOBAL
connect_timeoutnumericGLOBAL
date_formatstringGLOBAL | SESSION
datetime_formatstringGLOBAL | SESSION
debugstringGLOBAL | SESSION
default_week_formatnumericGLOBAL | SESSION
delayed_insert_limitnumericGLOBAL
delayed_insert_timeoutnumericGLOBAL
delayed_queue_sizenumericGLOBAL
delay_key_writeenumerationGLOBAL
div_precision_incrementnumericGLOBAL | SESSION
engine_condition_pushdownbooleanGLOBAL | SESSION
expire_logs_daysnumericGLOBAL
flushbooleanGLOBAL
flush_timenumericGLOBAL
foreign_key_checksbooleanSESSION
ft_boolean_syntaxstringGLOBAL
group_concat_max_lennumericGLOBAL | SESSION
identitynumericSESSION
init_connectstringGLOBAL
init_slavestringGLOBAL
innodb_autoextend_incrementnumericGLOBAL
innodb_commit_concurrencynumericGLOBAL
innodb_concurrency_ticketsnumericGLOBAL
innodb_fast_shutdownbooleanGLOBAL
innodb_flush_log_at_trx_commitnumericGLOBAL
innodb_max_dirty_pages_pctnumericGLOBAL
innodb_max_purge_lagnumericGLOBAL
innodb_support_xabooleanGLOBAL | SESSION
innodb_sync_spin_loopsnumericGLOBAL
innodb_table_locksbooleanGLOBAL | SESSION
innodb_thread_concurrencynumericGLOBAL
innodb_thread_sleep_delaynumericGLOBAL
insert_idnumericSESSION
interactive_timeoutnumericGLOBAL | SESSION
join_buffer_sizenumericGLOBAL | SESSION
keep_files_on_createbooleanGLOBAL | SESSION
key_buffer_sizenumericGLOBAL
key_cache_age_thresholdnumericGLOBAL
key_cache_block_sizenumericGLOBAL
key_cache_division_limitnumericGLOBAL
last_insert_idnumericSESSION
lc_time_namesstringGLOBAL | SESSION
local_infile GLOBAL
log_bin_trust_function_creatorsbooleanGLOBAL
log_bin_trust_routine_creatorsbooleanGLOBAL
log_queries_not_using_indexesbooleanGLOBAL
log-warningsnumericGLOBAL | SESSION
long_query_timenumericGLOBAL | SESSION
low_priority_updatesbooleanGLOBAL | SESSION
max_allowed_packetnumericGLOBAL | SESSION
max_binlog_cache_sizenumericGLOBAL
max_binlog_sizenumericGLOBAL
max_connect_errorsnumericGLOBAL
max_connectionsnumericGLOBAL
max_delayed_threadsnumericGLOBAL | SESSION
max_error_countnumericGLOBAL | SESSION
max_heap_table_sizenumericGLOBAL | SESSION
max_insert_delayed_threadsnumericGLOBAL | SESSION
max_join_sizenumericGLOBAL | SESSION
max_length_for_sort_datanumericGLOBAL | SESSION
max_prepared_stmt_countnumericGLOBAL
max_relay_log_sizenumericGLOBAL
max_seeks_for_keynumericGLOBAL | SESSION
max_sort_lengthnumericGLOBAL | SESSION
max_sp_recursion_depthnumericGLOBAL | SESSION
max_tmp_tablesnumericGLOBAL | SESSION
max_user_connectionsnumericGLOBAL | SESSION
max_write_lock_countnumericGLOBAL
multi_range_countnumericGLOBAL | SESSION
myisam_data_pointer_sizenumericGLOBAL
myisam_max_sort_file_sizenumericGLOBAL
myisam_repair_threadsnumericGLOBAL | SESSION
myisam_sort_buffer_sizenumericGLOBAL | SESSION
myisam_stats_methodenumerationGLOBAL | SESSION
ndb_autoincrement_prefetch_sznumericGLOBAL | SESSION
ndb_cache_check_timenumericGLOBAL
ndbclusterbooleanGLOBAL | SESSION
ndb_force_sendbooleanGLOBAL | SESSION
ndb_use_exact_countbooleanGLOBAL | SESSION
net_buffer_lengthnumericGLOBAL | SESSION
net_read_timeoutnumericGLOBAL | SESSION
net_retry_countnumericGLOBAL | SESSION
net_write_timeoutnumericGLOBAL | SESSION
newbooleanGLOBAL | SESSION
old_passwordsbooleanGLOBAL | SESSION
optimizer_prune_levelbooleanGLOBAL | SESSION
optimizer_search_depthnumericGLOBAL | SESSION
preload_buffer_sizenumericGLOBAL | SESSION
profilingbooleanSESSION
profiling_history_sizenumericGLOBAL | SESSION
query_alloc_block_sizenumericGLOBAL | SESSION
query_cache_limitnumericGLOBAL
query_cache_min_res_unitnumericGLOBAL
query_cache_sizenumericGLOBAL
query_cache_typeenumerationGLOBAL | SESSION
query_cache_wlock_invalidatebooleanGLOBAL | SESSION
query_prealloc_sizenumericGLOBAL | SESSION
rand_seed1numericSESSION
rand_seed2numericSESSION
range_alloc_block_sizenumericGLOBAL | SESSION
read_buffer_sizenumericGLOBAL | SESSION
read_onlynumericGLOBAL
read_rnd_buffer_sizenumericGLOBAL | SESSION
relay_log_purgebooleanGLOBAL
rpl_recovery_ranknumericGLOBAL
secure_authbooleanGLOBAL
server_idnumericGLOBAL
slave_compressed_protocolbooleanGLOBAL
slave_net_timeoutnumericGLOBAL
slave_transaction_retriesnumericGLOBAL
slow_launch_timenumericGLOBAL
sort_buffer_sizenumericGLOBAL | SESSION
sql_auto_is_nullbooleanSESSION
sql_big_selectsbooleanGLOBAL | SESSION
sql_big_tablesbooleanSESSION
sql_buffer_resultbooleanSESSION
sql_log_binbooleanSESSION
sql_log_offbooleanSESSION
sql_log_updatebooleanSESSION
sql_low_priority_updatesbooleanGLOBAL | SESSION
sql_max_join_sizenumericGLOBAL | SESSION
sql_modesetGLOBAL | SESSION
sql_notesbooleanSESSION
sql_quote_show_createbooleanSESSION
sql_safe_updatesbooleanSESSION
sql_select_limitnumericGLOBAL | SESSION
sql_slave_skip_counternumericGLOBAL
sql_warningsbooleanSESSION
storage_engineenumerationGLOBAL | SESSION
sync_binlognumericGLOBAL
sync_frmbooleanGLOBAL
table_cachenumericGLOBAL
table_lock_wait_timeoutnumericGLOBAL
table_open_cachenumericGLOBAL
table_typeenumerationGLOBAL | SESSION
thread_cache_sizenumericGLOBAL
timed_mutexesbooleanGLOBAL
time_formatstringGLOBAL | SESSION
timestampstringSESSION
time_zonestringGLOBAL | SESSION
tmp_table_sizenumericGLOBAL | SESSION
transaction_alloc_block_sizenumericGLOBAL | SESSION
transaction_prealloc_sizenumericGLOBAL | SESSION
tx_isolationenumerationGLOBAL | SESSION
unique_checksbooleanSESSION
updatable_views_with_limitbooleanGLOBAL | SESSION
wait_timeoutnumericGLOBAL | SESSION

MySQL Enterprise Improper configuration of system variables can adversely affect performance and security. The MySQL Enterprise Monitor continually monitors system variables and provides expert advice about appropriate settings. For more information see http://www.mysql.com/products/enterprise/advisors.html.

5.1.6. Server Status Variables

The server maintains many status variables that provide information about its operation. You can view these variables and their values by using the SHOW [GLOBAL | SESSION] STATUS statement (see Section 12.5.5.32, “SHOW STATUS Syntax”). The optional GLOBAL keyword aggregates the values over all connections, and SESSION shows the values for the current connection.

mysql> SHOW GLOBAL STATUS;
+-----------------------------------+------------+
| Variable_name                     | Value      |
+-----------------------------------+------------+
| Aborted_clients                   | 0          |
| Aborted_connects                  | 0          |
| Bytes_received                    | 155372598  |
| Bytes_sent                        | 1176560426 |
...
| Connections                       | 30023      |
| Created_tmp_disk_tables           | 0          |
| Created_tmp_files                 | 3          |
| Created_tmp_tables                | 2          |
...
| Threads_created                   | 217        |
| Threads_running                   | 88         |
| Uptime                            | 1389872    |
+-----------------------------------+------------+

The following table lists all available server status variables:

Variable NameVariable TypeVariable Scope
Aborted_clientsnumericGLOBAL | SESSION
Aborted_connectsnumericGLOBAL
Binlog_cache_disk_usenumericGLOBAL | SESSION
Binlog_cache_usenumericGLOBAL | SESSION
Bytes_receivednumericGLOBAL | SESSION
Bytes_sentnumericGLOBAL | SESSION
Com_admin_commandsnumericGLOBAL | SESSION
Com_alter_dbnumericGLOBAL | SESSION
Com_alter_eventnumericGLOBAL | SESSION
Com_alter_tablenumericGLOBAL | SESSION
Com_analyzenumericGLOBAL | SESSION
Com_backup_tablenumericGLOBAL | SESSION
Com_beginnumericGLOBAL | SESSION
Com_call_procedurenumericGLOBAL | SESSION
Com_change_dbnumericGLOBAL | SESSION
Com_change_masternumericGLOBAL | SESSION
Com_checknumericGLOBAL | SESSION
Com_checksumnumericGLOBAL | SESSION
Com_commitnumericGLOBAL | SESSION
Com_create_dbnumericGLOBAL | SESSION
Com_create_eventnumericGLOBAL | SESSION
Com_create_functionnumericGLOBAL | SESSION
Com_create_indexnumericGLOBAL | SESSION
Com_create_tablenumericGLOBAL | SESSION
Com_create_usernumericGLOBAL | SESSION
Com_dealloc_sqlnumericGLOBAL | SESSION
Com_deletenumericGLOBAL | SESSION
Com_delete_multinumericGLOBAL | SESSION
Com_donumericGLOBAL | SESSION
Com_drop_dbnumericGLOBAL | SESSION
Com_drop_eventnumericGLOBAL | SESSION
Com_drop_functionnumericGLOBAL | SESSION
Com_drop_indexnumericGLOBAL | SESSION
Com_drop_tablenumericGLOBAL | SESSION
Com_drop_usernumericGLOBAL | SESSION
Com_execute_sqlnumericGLOBAL | SESSION
Com_flushnumericGLOBAL | SESSION
Com_grantnumericGLOBAL | SESSION
Com_ha_closenumericGLOBAL | SESSION
Com_ha_opennumericGLOBAL | SESSION
Com_ha_readnumericGLOBAL | SESSION
Com_helpnumericGLOBAL | SESSION
Com_insertnumericGLOBAL | SESSION
Com_insert_selectnumericGLOBAL | SESSION
Com_killnumericGLOBAL | SESSION
Com_loadnumericGLOBAL | SESSION
Com_lock_tablesnumericGLOBAL | SESSION
Com_optimizenumericGLOBAL | SESSION
Com_preload_keysnumericGLOBAL | SESSION
Com_prepare_sqlnumericGLOBAL | SESSION
CompressionnumericGLOBAL | SESSION
Com_purgenumericGLOBAL | SESSION
Com_purge_before_datenumericGLOBAL | SESSION
Com_rename_tablenumericGLOBAL | SESSION
Com_repairnumericGLOBAL | SESSION
Com_replacenumericGLOBAL | SESSION
Com_replace_selectnumericGLOBAL | SESSION
Com_resetnumericGLOBAL | SESSION
Com_restore_tablenumericGLOBAL | SESSION
Com_revokenumericGLOBAL | SESSION
Com_revoke_allnumericGLOBAL | SESSION
Com_rollbacknumericGLOBAL | SESSION
Com_savepointnumericGLOBAL | SESSION
Com_selectnumericGLOBAL | SESSION
Com_set_optionnumericGLOBAL | SESSION
Com_show_binlog_eventsnumericGLOBAL | SESSION
Com_show_binlogsnumericGLOBAL | SESSION
Com_show_charsetsnumericGLOBAL | SESSION
Com_show_collationsnumericGLOBAL | SESSION
Com_show_column_typesnumericGLOBAL | SESSION
Com_show_create_dbnumericGLOBAL | SESSION
Com_show_create_eventnumericGLOBAL | SESSION
Com_show_create_tablenumericGLOBAL | SESSION
Com_show_databasesnumericGLOBAL | SESSION
Com_show_engine_logsnumericGLOBAL | SESSION
Com_show_engine_mutexnumericGLOBAL | SESSION
Com_show_engine_statusnumericGLOBAL | SESSION
Com_show_errorsnumericGLOBAL | SESSION
Com_show_eventsnumericGLOBAL | SESSION
Com_show_fieldsnumericGLOBAL | SESSION
Com_show_grantsnumericGLOBAL | SESSION
Com_show_innodb_statusnumericGLOBAL | SESSION
Com_show_keysnumericGLOBAL | SESSION
Com_show_logsnumericGLOBAL | SESSION
Com_show_master_statusnumericGLOBAL | SESSION
Com_show_ndb_statusnumericGLOBAL | SESSION
Com_show_new_masternumericGLOBAL | SESSION
Com_show_open_tablesnumericGLOBAL | SESSION
Com_show_pluginsnumericGLOBAL | SESSION
Com_show_privilegesnumericGLOBAL | SESSION
Com_show_processlistnumericGLOBAL | SESSION
Com_show_slave_hostsnumericGLOBAL | SESSION
Com_show_slave_statusnumericGLOBAL | SESSION
Com_show_statusnumericGLOBAL | SESSION
Com_show_storage_enginesnumericGLOBAL | SESSION
Com_show_tablesnumericGLOBAL | SESSION
Com_show_triggersnumericGLOBAL | SESSION
Com_show_variablesnumericGLOBAL | SESSION
Com_show_warningsnumericGLOBAL | SESSION
Com_slave_startnumericGLOBAL | SESSION
Com_slave_stopnumericGLOBAL | SESSION
Com_stmt_closenumericGLOBAL | SESSION
Com_stmt_executenumericGLOBAL | SESSION
Com_stmt_fetchnumericGLOBAL | SESSION
Com_stmt_preparenumericGLOBAL | SESSION
Com_stmt_resetnumericGLOBAL | SESSION
Com_stmt_send_long_datanumericGLOBAL | SESSION
Com_truncatenumericGLOBAL | SESSION
Com_unlock_tablesnumericGLOBAL | SESSION
Com_updatenumericGLOBAL | SESSION
Com_update_multinumericGLOBAL | SESSION
Com_xa_commitnumericGLOBAL | SESSION
Com_xa_endnumericGLOBAL | SESSION
Com_xa_preparenumericGLOBAL | SESSION
Com_xa_recovernumericGLOBAL | SESSION
Com_xa_rollbacknumericGLOBAL | SESSION
Com_xa_startnumericGLOBAL | SESSION
ConnectionsnumericGLOBAL | SESSION
Created_tmp_disk_tablesnumericGLOBAL | SESSION
Created_tmp_filesnumericGLOBAL | SESSION
Created_tmp_tablesnumericGLOBAL | SESSION
Delayed_errorsnumericGLOBAL | SESSION
Delayed_insert_threadsnumericGLOBAL | SESSION
Delayed_writesnumericGLOBAL | SESSION
Flush_commandsnumericGLOBAL | SESSION
Handler_commitnumericGLOBAL | SESSION
Handler_deletenumericGLOBAL | SESSION
Handler_discovernumericGLOBAL | SESSION
Handler_preparenumericGLOBAL | SESSION
Handler_read_firstnumericGLOBAL | SESSION
Handler_read_keynumericGLOBAL | SESSION
Handler_read_nextnumericGLOBAL | SESSION
Handler_read_prevnumericGLOBAL | SESSION
Handler_read_rndnumericGLOBAL | SESSION
Handler_read_rnd_nextnumericGLOBAL | SESSION
Handler_rollbacknumericGLOBAL | SESSION
Handler_savepointnumericGLOBAL | SESSION
Handler_savepoint_rollbacknumericGLOBAL | SESSION
Handler_updatenumericGLOBAL | SESSION
Handler_writenumericGLOBAL | SESSION
Innodb_buffer_pool_pages_datanumericGLOBAL
Innodb_buffer_pool_pages_dirtynumericGLOBAL
Innodb_buffer_pool_pages_flushednumericGLOBAL
Innodb_buffer_pool_pages_freenumericGLOBAL
Innodb_buffer_pool_pages_latchednumericGLOBAL
Innodb_buffer_pool_pages_miscnumericGLOBAL
Innodb_buffer_pool_pages_totalnumericGLOBAL
Innodb_buffer_pool_read_ahead_rndnumericGLOBAL
Innodb_buffer_pool_read_ahead_seqnumericGLOBAL
Innodb_buffer_pool_read_requestsnumericGLOBAL
Innodb_buffer_pool_readsnumericGLOBAL
Innodb_buffer_pool_wait_freenumericGLOBAL
Innodb_buffer_pool_write_requestsnumericGLOBAL
Innodb_data_fsyncsnumericGLOBAL
Innodb_data_pending_fsyncsnumericGLOBAL
Innodb_data_pending_readsnumericGLOBAL
Innodb_data_pending_writesnumericGLOBAL
Innodb_data_readnumericGLOBAL
Innodb_data_readsnumericGLOBAL
Innodb_data_writesnumericGLOBAL
Innodb_data_writtennumericGLOBAL
Innodb_dblwr_pages_writtennumericGLOBAL
Innodb_dblwr_writesnumericGLOBAL
Innodb_log_waitsnumericGLOBAL
Innodb_log_write_requestsnumericGLOBAL
Innodb_log_writesnumericGLOBAL
Innodb_os_log_fsyncsnumericGLOBAL
Innodb_os_log_pending_fsyncsnumericGLOBAL
Innodb_os_log_pending_writesnumericGLOBAL
Innodb_os_log_writtennumericGLOBAL
Innodb_pages_creatednumericGLOBAL
Innodb_page_sizenumericGLOBAL
Innodb_pages_readnumericGLOBAL
Innodb_pages_writtennumericGLOBAL
Innodb_row_lock_current_waitsnumericGLOBAL
Innodb_row_lock_timenumericGLOBAL
Innodb_row_lock_time_avgnumericGLOBAL
Innodb_row_lock_time_maxnumericGLOBAL
Innodb_row_lock_waitsnumericGLOBAL
Innodb_rows_deletednumericGLOBAL
Innodb_rows_insertednumericGLOBAL
Innodb_rows_readnumericGLOBAL
Innodb_rows_updatednumericGLOBAL
Key_blocks_not_flushednumericGLOBAL | SESSION
Key_blocks_unusednumericGLOBAL | SESSION
Key_blocks_usednumericGLOBAL | SESSION
Key_read_requestsnumericGLOBAL | SESSION
Key_readsnumericGLOBAL | SESSION
Key_write_requestsnumericGLOBAL | SESSION
Key_writesnumericGLOBAL | SESSION
Last_query_costnumericGLOBAL | SESSION
Max_used_connectionsnumericGLOBAL | SESSION
Ndb_cluster_node_idnumericGLOBAL | SESSION
Ndb_config_from_hostnumericGLOBAL | SESSION
Ndb_config_from_portnumericGLOBAL | SESSION
ndb-nodeidnumeric 
ndb-shmboolean 
Not_flushed_delayed_rowsnumericGLOBAL | SESSION
Opened_tablesnumericGLOBAL | SESSION
Open_filesnumericGLOBAL | SESSION
Open_streamsnumericGLOBAL | SESSION
Open_tablesnumericGLOBAL | SESSION
prepared_stmt_countnumericGLOBAL
Qcache_free_blocksnumericGLOBAL | SESSION
Qcache_free_memorynumericGLOBAL | SESSION
Qcache_hitsnumericGLOBAL | SESSION
Qcache_insertsnumericGLOBAL | SESSION
Qcache_lowmem_prunesnumericGLOBAL | SESSION
Qcache_not_cachednumericGLOBAL | SESSION
Qcache_queries_in_cachenumericGLOBAL | SESSION
Qcache_total_blocksnumericGLOBAL | SESSION
QuestionsnumericGLOBAL | SESSION
Rpl_statusstringGLOBAL | SESSION
Select_full_joinnumericGLOBAL | SESSION
Select_full_range_joinnumericGLOBAL | SESSION
Select_rangenumericGLOBAL | SESSION
Select_range_checknumericGLOBAL | SESSION
Select_scannumericGLOBAL | SESSION
Slave_open_temp_tablesnumericGLOBAL | SESSION
Slave_retried_transactionsnumericGLOBAL | SESSION
Slave_runningbooleanGLOBAL | SESSION
Slow_launch_threadsnumericGLOBAL | SESSION
Slow_queriesnumericGLOBAL | SESSION
Sort_merge_passesnumericGLOBAL | SESSION
Sort_rangenumericGLOBAL | SESSION
Sort_rowsnumericGLOBAL | SESSION
Sort_scannumericGLOBAL | SESSION
Ssl_accept_renegotiatesnumericGLOBAL | SESSION
Ssl_acceptsnumericGLOBAL | SESSION
Ssl_callback_cache_hitsnumericGLOBAL | SESSION
Ssl_cipherstringGLOBAL | SESSION
Ssl_cipher_liststringGLOBAL | SESSION
Ssl_client_connectsnumericGLOBAL | SESSION
Ssl_connect_renegotiatesnumericGLOBAL | SESSION
Ssl_ctx_verify_depthnumericGLOBAL | SESSION
Ssl_ctx_verify_modenumericGLOBAL | SESSION
Ssl_default_timeoutnumericGLOBAL | SESSION
Ssl_finished_acceptsnumericGLOBAL | SESSION
Ssl_finished_connectsnumericGLOBAL | SESSION
Ssl_session_cache_hitsnumericGLOBAL | SESSION
Ssl_session_cache_missesnumericGLOBAL | SESSION
Ssl_session_cache_modestringGLOBAL | SESSION
Ssl_session_cache_overflowsnumericGLOBAL | SESSION
Ssl_session_cache_sizenumericGLOBAL | SESSION
Ssl_session_cache_timeoutsnumericGLOBAL | SESSION
Ssl_sessions_reusednumericGLOBAL | SESSION
Ssl_used_session_cache_entriesnumericGLOBAL | SESSION
Ssl_verify_depthnumericGLOBAL | SESSION
Ssl_verify_modenumericGLOBAL | SESSION
Ssl_versionstringGLOBAL | SESSION
Table_locks_immediatenumericGLOBAL | SESSION
Table_locks_waitednumericGLOBAL | SESSION
Tc_log_max_pages_usednumericGLOBAL | SESSION
Tc_log_page_sizenumericGLOBAL | SESSION
Tc_log_page_waitsnumericGLOBAL | SESSION
Threads_cachednumericGLOBAL | SESSION
Threads_connectednumericGLOBAL | SESSION
Threads_creatednumericGLOBAL | SESSION
Threads_runningnumericGLOBAL | SESSION
UptimenumericGLOBAL | SESSION
Uptime_since_flush_statusnumericGLOBAL | SESSION

Note

Before MySQL 5.0.2, SHOW STATUS returned global status values. Because the default as of 5.0.2 is to return session values, this is incompatible with previous versions. To issue a SHOW STATUS statement that will retrieve global status values for all versions of MySQL, write it like this:

SHOW /*!50002 GLOBAL */ STATUS;

Many status variables are reset to 0 by the FLUSH STATUS statement.

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

The status variables have the following meanings. Variables with no version indicated were already present prior to MySQL 5.0. For information regarding their implementation history, see MySQL 3.23, 4.0, 4.1 Reference Manual.

For meanings of status variables specific to MySQL Cluster, see Section 17.4.4, “MySQL Cluster Status Variables”.

  • Aborted_clients

    The number of connections that were aborted because the client died without closing the connection properly. See Section B.1.2.11, “Communication Errors and Aborted Connections”.

  • Aborted_connects

    The number of failed attempts to connect to the MySQL server. See Section B.1.2.11, “Communication Errors and Aborted Connections”.

  • Binlog_cache_disk_use

    The number of transactions that used the temporary binary log cache but that exceeded the value of binlog_cache_size and used a temporary file to store statements from the transaction.

  • Binlog_cache_use

    The number of transactions that used the temporary binary log cache.

  • Bytes_received

    The number of bytes received from all clients.

  • Bytes_sent

    The number of bytes sent to all clients.

  • Com_xxx

    The Com_xxx statement counter variables indicate the number of times each xxx statement has been executed. There is one status variable for each type of statement. For example, Com_delete and Com_insert count DELETE and INSERT statements, respectively. However, if a query result is returned from query cache, the server increments the Qcache_hits status variable, not Com_select. See Section 7.5.4.4, “Query Cache Status and Maintenance”.

    All of the Com_stmt_xxx variables are increased even if a prepared statement argument is unknown or an error occurred during execution. In other words, their values correspond to the number of requests issued, not to the number of requests successfully completed.

    The Com_stmt_xxx status variables were added in 5.0.8:

    • Com_stmt_prepare

    • Com_stmt_execute

    • Com_stmt_fetch

    • Com_stmt_send_long_data

    • Com_stmt_reset

    • Com_stmt_close

    Those variables stand for prepared statement commands. Their names refer to the COM_xxx command set used in the network layer. In other words, their values increase whenever prepared statement API calls such as mysql_stmt_prepare(), mysql_stmt_execute(), and so forth are executed. However, Com_stmt_prepare, Com_stmt_execute and Com_stmt_close also increase for PREPARE, EXECUTE, or DEALLOCATE PREPARE, respectively. Additionally, the values of the older (available since MySQL 4.1.3) statement counter variables Com_prepare_sql, Com_execute_sql, and Com_dealloc_sql increase for the PREPARE, EXECUTE, and DEALLOCATE PREPARE statements. Com_stmt_fetch stands for the total number of network round-trips issued when fetching from cursors.

  • Compression

    Whether the client connection uses compression in the client/server protocol. Added in MySQL 5.0.16.

  • Connections

    The number of connection attempts (successful or not) to the MySQL server.

  • Created_tmp_disk_tables

    The number of temporary tables on disk created automatically by the server while executing statements.

  • Created_tmp_files

    How many temporary files mysqld has created.

  • Created_tmp_tables

    The number of in-memory temporary tables created automatically by the server while executing statements. If Created_tmp_disk_tables is large, you may want to increase the tmp_table_size value to cause temporary tables to be memory-based instead of disk-based.

  • Delayed_errors

    The number of rows written with INSERT DELAYED for which some error occurred (probably duplicate key).

  • Delayed_insert_threads

    The number of INSERT DELAYED handler threads in use.

  • Delayed_writes

    The number of INSERT DELAYED rows written.

  • Flush_commands

    The number of executed FLUSH statements.

  • Handler_commit

    The number of internal COMMIT statements.

  • Handler_delete

    The number of times that rows have been deleted from tables.

  • Handler_prepare

    A counter for the prepare phase of two-phase commit operations. Added in MySQL 5.0.3.

  • Handler_read_first

    The number of times the first entry was read from an index. If this value is high, it suggests that the server is doing a lot of full index scans; for example, SELECT col1 FROM foo, assuming that col1 is indexed.

  • Handler_read_key

    The number of requests to read a row based on a key. If this value is high, it is a good indication that your tables are properly indexed for your queries.

  • Handler_read_next

    The number of requests to read the next row in key order. This value is incremented if you are querying an index column with a range constraint or if you are doing an index scan.

  • Handler_read_prev

    The number of requests to read the previous row in key order. This read method is mainly used to optimize ORDER BY ... DESC.

  • Handler_read_rnd

    The number of requests to read a row based on a fixed position. This value is high if you are doing a lot of queries that require sorting of the result. You probably have a lot of queries that require MySQL to scan entire tables or you have joins that don't use keys properly.

  • Handler_read_rnd_next

    The number of requests to read the next row in the data file. This value is high if you are doing a lot of table scans. Generally this suggests that your tables are not properly indexed or that your queries are not written to take advantage of the indexes you have.

  • Handler_rollback

    The number of requests for a storage engine to perform a rollback operation.

  • Handler_savepoint

    The number of requests for a storage engine to place a savepoint. Added in MySQL 5.0.3.

  • Handler_savepoint_rollback

    The number of requests for a storage engine to roll back to a savepoint. Added in MySQL 5.0.3.

  • Handler_update

    The number of requests to update a row in a table.

  • Handler_write

    The number of requests to insert a row in a table.

  • Innodb_buffer_pool_pages_data

    The number of pages containing data (dirty or clean). Added in MySQL 5.0.2.

  • Innodb_buffer_pool_pages_dirty

    The number of pages currently dirty. Added in MySQL 5.0.2.

  • Innodb_buffer_pool_pages_flushed

    The number of buffer pool page-flush requests. Added in MySQL 5.0.2.

  • Innodb_buffer_pool_pages_free

    The number of free pages. Added in MySQL 5.0.2.

  • Innodb_buffer_pool_pages_latched

    The number of latched pages in InnoDB buffer pool. These are pages currently being read or written or that cannot be flushed or removed for some other reason. Added in MySQL 5.0.2.

  • Innodb_buffer_pool_pages_misc

    The number of pages that are busy because they have been allocated for administrative overhead such as row locks or the adaptive hash index. This value can also be calculated as Innodb_buffer_pool_pages_totalInnodb_buffer_pool_pages_freeInnodb_buffer_pool_pages_data. Added in MySQL 5.0.2.

  • Innodb_buffer_pool_pages_total

    The total size of buffer pool, in pages. Added in MySQL 5.0.2.

  • Innodb_buffer_pool_read_ahead_rnd

    The number of “random” read-aheads initiated by InnoDB. This happens when a query scans a large portion of a table but in random order. Added in MySQL 5.0.2.

  • Innodb_buffer_pool_read_ahead_seq

    The number of sequential read-aheads initiated by InnoDB. This happens when InnoDB does a sequential full table scan. Added in MySQL 5.0.2.

  • Innodb_buffer_pool_read_requests

    The number of logical read requests InnoDB has done. Added in MySQL 5.0.2.

  • Innodb_buffer_pool_reads

    The number of logical reads that InnoDB could not satisfy from the buffer pool and had to do a single-page read. Added in MySQL 5.0.2.

  • Innodb_buffer_pool_wait_free

    Normally, writes to the InnoDB buffer pool happen in the background. However, if it is necessary to read or create a page and no clean pages are available, it is also necessary to wait for pages to be flushed first. This counter counts instances of these waits. If the buffer pool size has been set properly, this value should be small. Added in MySQL 5.0.2.

  • Innodb_buffer_pool_write_requests

    The number writes done to the InnoDB buffer pool. Added in MySQL 5.0.2.

  • Innodb_data_fsyncs

    The number of fsync() operations so far. Added in MySQL 5.0.2.

  • Innodb_data_pending_fsyncs

    The current number of pending fsync() operations. Added in MySQL 5.0.2.

  • Innodb_data_pending_reads

    The current number of pending reads. Added in MySQL 5.0.2.

  • Innodb_data_pending_writes

    The current number of pending writes. Added in MySQL 5.0.2.

  • Innodb_data_read

    The amount of data read so far, in bytes. Added in MySQL 5.0.2.

  • Innodb_data_reads

    The total number of data reads. Added in MySQL 5.0.2.

  • Innodb_data_writes

    The total number of data writes. Added in MySQL 5.0.2.

  • Innodb_data_written

    The amount of data written so far, in bytes. Added in MySQL 5.0.2.

  • Innodb_dblwr_writes

    The number of doublewrite operations that have been performed. Added in MySQL 5.0.2. See Section 13.2.13.1, “InnoDB Disk I/O”.

  • Innodb_dblwr_pages_written

    The number of pages that have been written for doublewrite operations. Added in MySQL 5.0.2. See Section 13.2.13.1, “InnoDB Disk I/O”.

  • Innodb_log_waits

    The number of times that the log buffer was too small and a wait was required for it to be flushed before continuing. Added in MySQL 5.0.2.

  • Innodb_log_write_requests

    The number of log write requests. Added in MySQL 5.0.2.

  • Innodb_log_writes

    The number of physical writes to the log file. Added in MySQL 5.0.2.

  • Innodb_os_log_fsyncs

    The number of fsync() writes done to the log file. Added in MySQL 5.0.2.

  • Innodb_os_log_pending_fsyncs

    The number of pending log file fsync() operations. Added in MySQL 5.0.2.

  • Innodb_os_log_pending_writes

    The number of pending log file writes. Added in MySQL 5.0.2.

  • Innodb_os_log_written

    The number of bytes written to the log file. Added in MySQL 5.0.2.

  • Innodb_page_size

    The compiled-in InnoDB page size (default 16KB). Many values are counted in pages; the page size allows them to be easily converted to bytes. Added in MySQL 5.0.2.

  • Innodb_pages_created

    The number of pages created. Added in MySQL 5.0.2.

  • Innodb_pages_read

    The number of pages read. Added in MySQL 5.0.2.

  • Innodb_pages_written

    The number of pages written. Added in MySQL 5.0.2.

  • Innodb_row_lock_current_waits

    The number of row locks currently being waited for. Added in MySQL 5.0.3.

  • Innodb_row_lock_time

    The total time spent in acquiring row locks, in milliseconds. Added in MySQL 5.0.3.

  • Innodb_row_lock_time_avg

    The average time to acquire a row lock, in milliseconds. Added in MySQL 5.0.3.

  • Innodb_row_lock_time_max

    The maximum time to acquire a row lock, in milliseconds. Added in MySQL 5.0.3.

  • Innodb_row_lock_waits

    The number of times a row lock had to be waited for. Added in MySQL 5.0.3.

  • Innodb_rows_deleted

    The number of rows deleted from InnoDB tables. Added in MySQL 5.0.2.

  • Innodb_rows_inserted

    The number of rows inserted into InnoDB tables. Added in MySQL 5.0.2.

  • Innodb_rows_read

    The number of rows read from InnoDB tables. Added in MySQL 5.0.2.

  • Innodb_rows_updated

    The number of rows updated in InnoDB tables. Added in MySQL 5.0.2.

  • Key_blocks_not_flushed

    The number of key blocks in the key cache that have changed but have not yet been flushed to disk.

  • Key_blocks_unused

    The number of unused blocks in the key cache. You can use this value to determine how much of the key cache is in use; see the discussion of key_buffer_size in Section 5.1.3, “Server System Variables”.

  • Key_blocks_used

    The number of used blocks in the key cache. This value is a high-water mark that indicates the maximum number of blocks that have ever been in use at one time.

  • Key_read_requests

    The number of requests to read a key block from the cache.

  • Key_reads

    The number of physical reads of a key block from disk. If Key_reads is large, then your key_buffer_size value is probably too small. The cache miss rate can be calculated as Key_reads/Key_read_requests.

  • Key_write_requests

    The number of requests to write a key block to the cache.

  • Key_writes

    The number of physical writes of a key block to disk.

  • Last_query_cost

    The total cost of the last compiled query as computed by the query optimizer. This is useful for comparing the cost of different query plans for the same query. The default value of 0 means that no query has been compiled yet. This variable was added in MySQL 5.0.1, with a default value of -1. In MySQL 5.0.7, the default was changed to 0; also in version 5.0.7, the scope of Last_query_cost was changed to session rather than global.

    The Last_query_cost value can be computed accurately only for simple “flat” queries, not complex queries such as those with subqueries or UNION. For the latter, the value is set to 0.

    Prior to MySQL 5.0.16, this variable was not updated for queries served from the query cache.

  • Max_used_connections

    The maximum number of connections that have been in use simultaneously since the server started.

  • Not_flushed_delayed_rows

    The number of rows waiting to be written in INSERT DELAY queues.

  • Open_files

    The number of files that are open.

  • Open_streams

    The number of streams that are open (used mainly for logging).

  • Open_tables

    The number of tables that are open.

  • Opened_tables

    The number of tables that have been opened. If Opened_tables is big, your table_cache value is probably too small.

  • Prepared_stmt_count

    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 5.0.32.

  • Qcache_free_blocks

    The number of free memory blocks in the query cache.

  • Qcache_free_memory

    The amount of free memory for the query cache.

  • Qcache_hits

    The number of query cache hits.

  • Qcache_inserts

    The number of queries added to the query cache.

  • Qcache_lowmem_prunes

    The number of queries that were deleted from the query cache because of low memory.

  • Qcache_not_cached

    The number of non-cached queries (not cacheable, or not cached due to the query_cache_type setting).

  • Qcache_queries_in_cache

    The number of queries registered in the query cache.

  • Qcache_total_blocks

    The total number of blocks in the query cache.

  • Questions

    The number of statements that clients have sent to the server.

  • Rpl_status

    The status of fail-safe replication (not yet implemented).

  • Select_full_join

    The number of joins that perform table scans because they do not use indexes. If this value is not 0, you should carefully check the indexes of your tables.

  • Select_full_range_join

    The number of joins that used a range search on a reference table.

  • Select_range

    The number of joins that used ranges on the first table. This is normally not a critical issue even if the value is quite large.

  • Select_range_check

    The number of joins without keys that check for key usage after each row. If this is not 0, you should carefully check the indexes of your tables.

  • Select_scan

    The number of joins that did a full scan of the first table.

  • Slave_open_temp_tables

    The number of temporary tables that the slave SQL thread currently has open.

  • Slave_retried_transactions

    The total number of times since startup that the replication slave SQL thread has retried transactions. This variable was added in version 5.0.4.

  • Slave_running

    This is ON if this server is a slave that is connected to a master, and both the I/O SQL and threads are running.

  • Slow_launch_threads

    The number of threads that have taken more than slow_launch_time seconds to create.

  • Slow_queries

    The number of queries that have taken more than long_query_time seconds. See Section 5.2.4, “The Slow Query Log”.

  • Sort_merge_passes

    The number of merge passes that the sort algorithm has had to do. If this value is large, you should consider increasing the value of the sort_buffer_size system variable.

  • Sort_range

    The number of sorts that were done using ranges.

  • Sort_rows

    The number of sorted rows.

  • Sort_scan

    The number of sorts that were done by scanning the table.

  • Ssl_accept_renegotiates

    The number of negotiates needed to establish the connection.

  • Ssl_accepts

    The number of accepted SSL connections.

  • Ssl_callback_cache_hits

    The number of callback cache hits.

  • Ssl_cipher

    The current SSL cipher (empty for non-SSL connections).

  • Ssl_cipher_list

    The list of possible SSL ciphers.

  • Ssl_client_connects

    The number of SSL connection attempts to an SSL-enabled master.

  • Ssl_connect_renegotiates

    The number of negotiates needed to establish the connection to an SSL-enabled master.

  • Ssl_ctx_verify_depth

    The SSL context verification depth (how many certificates in the chain are tested).

  • Ssl_ctx_verify_mode

    The SSL context verification mode.

  • Ssl_default_timeout

    The default SSL timeout.

  • Ssl_finished_accepts

    The number of successful SSL connections to the server.

  • Ssl_finished_connects

    The number of successful slave connections to an SSL-enabled master.

  • Ssl_session_cache_hits

    The number of SSL session cache hits.

  • Ssl_session_cache_misses

    The number of SSL session cache misses.

  • Ssl_session_cache_mode

    The SSL session cache mode.

  • Ssl_session_cache_overflows

    The number of SSL session cache overflows.

  • Ssl_session_cache_size

    The SSL session cache size.

  • Ssl_session_cache_timeouts

    The number of SSL session cache timeouts.

  • Ssl_sessions_reused

    How many SSL connections were reused from the cache.

  • Ssl_used_session_cache_entries

    How many SSL session cache entries were used.

  • Ssl_verify_depth

    The verification depth for replication SSL connections.

  • Ssl_verify_mode

    The verification mode for replication SSL connections.

  • Ssl_version

    The SSL version number.

  • Table_locks_immediate

    The number of times that a request for a table lock could be granted immediately.

  • Table_locks_waited

    The number of times that a request for a table lock could not be granted immediately and a wait was needed. If this is high and you have performance problems, you should first optimize your queries, and then either split your table or tables or use replication.

  • Tc_log_max_pages_used

    For the memory-mapped implementation of the log that is used by mysqld when it acts as the transaction coordinator for recovery of internal XA transactions, this variable indicates the largest number of pages used for the log since the server started. If the product of Tc_log_max_pages_used and Tc_log_page_size is always significantly less than the log size, the size is larger than necessary and can be reduced. (The size is set by the --log-tc-size option. Currently, this variable is unused: It is unneeded for binary log-based recovery, and the memory-mapped recovery log method is not used unless the number of storage engines capable of two-phase commit is greater than one. (InnoDB is the only applicable engine.) Added in MySQL 5.0.3.

  • Tc_log_page_size

    The page size used for the memory-mapped implementation of the XA recovery log. The default value is determined using getpagesize(). Currently, this variable is unused for the same reasons as described for Tc_log_max_pages_used. Added in MySQL 5.0.3.

  • Tc_log_page_waits

    For the memory-mapped implementation of the recovery log, this variable increments each time the server was not able to commit a transaction and had to wait for a free page in the log. If this value is large, you might want to increase the log size (with the --log-tc-size option). For binary log-based recovery, this variable increments each time the binary log cannot be closed because there are two-phase commits in progress. (The close operation waits until all such transactions are finished.) Added in MySQL 5.0.3.

  • Threads_cached

    The number of threads in the thread cache.

  • Threads_connected

    The number of currently open connections.

  • Threads_created

    The number of threads created to handle connections. If Threads_created is big, you may want to increase the thread_cache_size value. The cache miss rate can be calculated as Threads_created/Connections.

  • Threads_running

    The number of threads that are not sleeping.

  • Uptime

    The number of seconds that the server has been up.

  • Uptime_since_flush_status

    The number of seconds since the most recent FLUSH STATUS statement. This variable was added in 5.0.35. (MySQL Community only)

5.1.7. Server SQL Modes

The MySQL server can operate in different SQL modes, and can apply these modes differently for different clients. This capability enables each application to tailor the server's operating mode to its own requirements.

For answers to some questions that are often asked about server SQL modes in MySQL, see Section A.3, “MySQL 5.0 FAQ — Server SQL Mode”.

Modes define what SQL syntax MySQL should support and what kind of data validation checks it should perform. This makes it easier to use MySQL in different environments and to use MySQL together with other database servers.

You can set the default SQL mode by starting mysqld with the --sql-mode="modes" option, or by using sql-mode="modes" in my.cnf (Unix operating systems) or my.ini (Windows). modes is a list of different modes separated by comma (“,”) characters. The default value is empty (no modes set). The modes value also can be empty (--sql-mode="" on the command line, or sql-mode="" in my.cnf on Unix systems or in my.ini on Windows) if you want to clear it explicitly.

You can change the SQL mode at runtime by using a SET [GLOBAL|SESSION] sql_mode='modes' statement to set the sql_mode system value. Setting the GLOBAL variable requires the SUPER privilege and affects the operation of all clients that connect from that time on. Setting the SESSION variable affects only the current client. Any client can change its own session sql_mode value at any time.

You can retrieve the current global or session sql_mode value with the following statements:

SELECT @@GLOBAL.sql_mode;
SELECT @@SESSION.sql_mode;

The most important sql_mode values are probably these:

  • ANSI

    This mode changes syntax and behavior to conform more closely to standard SQL.

  • STRICT_TRANS_TABLES

    If a value could not be inserted as given into a transactional table, abort the statement. For a non-transactional table, abort the statement if the value occurs in a single-row statement or the first row of a multiple-row statement. More detail is given later in this section. (Implemented in MySQL 5.0.2)

  • TRADITIONAL

    Make MySQL behave like a “traditional” SQL database system. A simple description of this mode is “give an error instead of a warning” when inserting an incorrect value into a column.

    Note

    The INSERT/UPDATE aborts as soon as the error is noticed. This may not be what you want if you are using a non-transactional storage engine, because data changes made prior to the error may not be rolled back, resulting in a “partially done” update. (Added in MySQL 5.0.2)

When this manual refers to “strict mode,” it means a mode where at least one of STRICT_TRANS_TABLES or STRICT_ALL_TABLES is enabled.

The following list describes all supported modes:

  • ALLOW_INVALID_DATES

    Don't do full checking of dates. Check only that the month is in the range from 1 to 12 and the day is in the range from 1 to 31. This is very convenient for Web applications where you obtain year, month, and day in three different fields and you want to store exactly what the user inserted (without date validation). This mode applies to DATE and DATETIME columns. It does not apply TIMESTAMP columns, which always require a valid date.

    This mode is implemented in MySQL 5.0.2. Before 5.0.2, this was the default MySQL date-handling mode. As of 5.0.2, the server requires that month and day values be legal, and not merely in the range 1 to 12 and 1 to 31, respectively. With strict mode disabled, invalid dates such as '2004-04-31' are converted to '0000-00-00' and a warning is generated. With strict mode enabled, invalid dates generate an error. To allow such dates, enable ALLOW_INVALID_DATES.

  • ANSI_QUOTES

    Treat “"” as an identifier quote character (like the “`” quote character) and not as a string quote character. You can still use “`” to quote identifiers with this mode enabled. With ANSI_QUOTES enabled, you cannot use double quotes to quote literal strings, because it is interpreted as an identifier.

  • ERROR_FOR_DIVISION_BY_ZERO

    Produce an error in strict mode (otherwise a warning) when a division by zero (or MOD(X,0)) occurs during an INSERT or UPDATE. If this mode is not enabled, MySQL instead returns NULL for divisions by zero. For INSERT IGNORE or UPDATE IGNORE, MySQL generates a warning for divisions by zero, but the result of the operation is NULL. (Implemented in MySQL 5.0.2)

  • HIGH_NOT_PRECEDENCE

    From MySQL 5.0.2 on, the precedence of the NOT operator is such that expressions such as NOT a BETWEEN b AND c are parsed as NOT (a BETWEEN b AND c). Before MySQL 5.0.2, the expression is parsed as (NOT a) BETWEEN b AND c. The old higher-precedence behavior can be obtained by enabling the HIGH_NOT_PRECEDENCE SQL mode. (Added in MySQL 5.0.2)

    mysql> SET sql_mode = '';
    mysql> SELECT NOT 1 BETWEEN -5 AND 5;
            -> 0
    mysql> SET sql_mode = 'HIGH_NOT_PRECEDENCE';
    mysql> SELECT NOT 1 BETWEEN -5 AND 5;
            -> 1
    
  • IGNORE_SPACE

    Allow spaces between a function name and the “(” character. This causes built-in function names to be treated as reserved words. As a result, identifiers that are the same as function names must be quoted as described in Section 8.2, “Schema Object Names”. For example, because there is a COUNT() function, the use of count as a table name in the following statement causes an error:

    mysql> CREATE TABLE count (i INT);
    ERROR 1064 (42000): You have an error in your SQL syntax
    

    The table name should be quoted:

    mysql> CREATE TABLE `count` (i INT);
    Query OK, 0 rows affected (0.00 sec)
    

    The IGNORE_SPACE SQL mode applies to built-in functions, not to user-defined functions or stored functions. It is always allowable to have spaces after a UDF or stored function name, regardless of whether IGNORE_SPACE is enabled.

    For further discussion of IGNORE_SPACE, see Section 8.2.3, “Function Name Parsing and Resolution”.

  • NO_AUTO_CREATE_USER

    Prevent the GRANT statement from automatically creating new users if it would otherwise do so, unless a non-empty password also is specified. (Added in MySQL 5.0.2)

  • NO_AUTO_VALUE_ON_ZERO

    NO_AUTO_VALUE_ON_ZERO affects handling of AUTO_INCREMENT columns. Normally, you generate the next sequence number for the column by inserting either NULL or 0 into it. NO_AUTO_VALUE_ON_ZERO suppresses this behavior for 0 so that only NULL generates the next sequence number.

    This mode can be useful if 0 has been stored in a table's AUTO_INCREMENT column. (Storing 0 is not a recommended practice, by the way.) For example, if you dump the table with mysqldump and then reload it, MySQL normally generates new sequence numbers when it encounters the 0 values, resulting in a table with contents different from the one that was dumped. Enabling NO_AUTO_VALUE_ON_ZERO before reloading the dump file solves this problem. mysqldump now automatically includes in its output a statement that enables NO_AUTO_VALUE_ON_ZERO, to avoid this problem.

  • NO_BACKSLASH_ESCAPES

    Disable the use of the backslash character (“\”) as an escape character within strings. With this mode enabled, backslash becomes an ordinary character like any other. (Implemented in MySQL 5.0.1)

  • NO_DIR_IN_CREATE

    When creating a table, ignore all INDEX DIRECTORY and DATA DIRECTORY directives. This option is useful on slave replication servers.

  • NO_ENGINE_SUBSTITUTION

    Control automatic substitution of the default storage engine when a statement such as CREATE TABLE or ALTER TABLE specifies a storage engine that is disabled or not compiled in. (Implemented in MySQL 5.0.8)

    With NO_ENGINE_SUBSTITUTION disabled, the default engine is used and a warning occurs if the desired engine is known but disabled or not compiled in. If the desired engine is invalid (not a known engine name), an error occurs and the table is not created or altered.

    With NO_ENGINE_SUBSTITUTION enabled, an error occurs and the table is not created or altered if the desired engine is unavailable for any reason (whether disabled or invalid).

  • NO_FIELD_OPTIONS

    Do not print MySQL-specific column options in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode.

  • NO_KEY_OPTIONS

    Do not print MySQL-specific index options in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode.

  • NO_TABLE_OPTIONS

    Do not print MySQL-specific table options (such as ENGINE) in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode.

  • NO_UNSIGNED_SUBTRACTION

    In integer subtraction operations, do not mark the result as UNSIGNED if one of the operands is unsigned. In other words, the result of a subtraction is always signed whenever this mode is in effect, even if one of the operands is unsigned. For example, compare the type of column c2 in table t1 with that of column c2 in table t2:

    mysql> SET SQL_MODE='';
    mysql> CREATE TABLE test (c1 BIGINT UNSIGNED NOT NULL);
    mysql> CREATE TABLE t1 SELECT c1 - 1 AS c2 FROM test;
    mysql> DESCRIBE t1;
    +-------+---------------------+------+-----+---------+-------+
    | Field | Type                | Null | Key | Default | Extra |
    +-------+---------------------+------+-----+---------+-------+
    | c2    | bigint(21) unsigned |      |     | 0       |       |
    +-------+---------------------+------+-----+---------+-------+
    
    mysql> SET SQL_MODE='NO_UNSIGNED_SUBTRACTION';
    mysql> CREATE TABLE t2 SELECT c1 - 1 AS c2 FROM test;
    mysql> DESCRIBE t2;
    +-------+------------+------+-----+---------+-------+
    | Field | Type       | Null | Key | Default | Extra |
    +-------+------------+------+-----+---------+-------+
    | c2    | bigint(21) |      |     | 0       |       |
    +-------+------------+------+-----+---------+-------+
    

    Note that this means that BIGINT UNSIGNED is not 100% usable in all contexts. See Section 11.9, “Cast Functions and Operators”.

    mysql> SET SQL_MODE = '';
    mysql> SELECT CAST(0 AS UNSIGNED) - 1;
    +-------------------------+
    | CAST(0 AS UNSIGNED) - 1 |
    +-------------------------+
    |    18446744073709551615 |
    +-------------------------+
    
    mysql> SET SQL_MODE = 'NO_UNSIGNED_SUBTRACTION';
    mysql> SELECT CAST(0 AS UNSIGNED) - 1;
    +-------------------------+
    | CAST(0 AS UNSIGNED) - 1 |
    +-------------------------+
    |                      -1 |
    +-------------------------+
    
  • NO_ZERO_DATE

    In strict mode, don't allow '0000-00-00' as a valid date. You can still insert zero dates with the IGNORE option. When not in strict mode, the date is accepted but a warning is generated. (Added in MySQL 5.0.2)

  • NO_ZERO_IN_DATE

    In strict mode, do not accept dates where the year part is non-zero but the month or day part is 0 (for example, '0000-00-00' is legal but '2010-00-01' and '2010-01-00' are not). If used with the IGNORE option, MySQL inserts a '0000-00-00' date for any such date. When not in strict mode, the date is accepted but a warning is generated. (Added in MySQL 5.0.2)

  • ONLY_FULL_GROUP_BY

    Do not allow queries for which the SELECT list refers to non-aggregated columns that are not named in the GROUP BY clause. The following query is invalid with this mode enabled because address is not named in the GROUP BY clause:

    SELECT name, address, MAX(age) FROM t GROUP BY name;
    

    As of MySQL 5.0.23, this mode also restricts references to non-aggregated columns in the HAVING clause that are not named in the GROUP BY clause.

  • PIPES_AS_CONCAT

    Treat || as a string concatenation operator (same as CONCAT()) rather than as a synonym for OR.

  • REAL_AS_FLOAT

    Treat REAL as a synonym for FLOAT. By default, MySQL treats REAL as a synonym for DOUBLE.

  • STRICT_ALL_TABLES

    Enable strict mode for all storage engines. Invalid data values are rejected. Additional detail follows. (Added in MySQL 5.0.2)

  • STRICT_TRANS_TABLES

    Enable strict mode for transactional storage engines, and when possible for non-transactional storage engines. Additional details follow. (Implemented in MySQL 5.0.2)

Strict mode controls how MySQL handles input values that are invalid or missing. A value can be invalid for several reasons. For example, it might have the wrong data type for the column, or it might be out of range. A value is missing when a new row to be inserted does not contain a value for a non-NULL column that has no explicit DEFAULT clause in its definition. (For a NULL column, NULL is inserted if the value is missing.)

For transactional tables, an error occurs for invalid or missing values in a statement when either of the STRICT_ALL_TABLES or STRICT_TRANS_TABLES modes are enabled. The statement is aborted and rolled back.

For non-transactional tables, the behavior is the same for either mode, if the bad value occurs in the first row to be inserted or updated. The statement is aborted and the table remains unchanged. If the statement inserts or modifies multiple rows and the bad value occurs in the second or later row, the result depends on which strict option is enabled:

  • For STRICT_ALL_TABLES, MySQL returns an error and ignores the rest of the rows. However, in this case, the earlier rows still have been inserted or updated. This means that you might get a partial update, which might not be what you want. To avoid this, it's best to use single-row statements because these can be aborted without changing the table.

  • For STRICT_TRANS_TABLES, MySQL converts an invalid value to the closest valid value for the column and insert the adjusted value. If a value is missing, MySQL inserts the implicit default value for the column data type. In either case, MySQL generates a warning rather than an error and continues processing the statement. Implicit defaults are described in Section 10.1.4, “Data Type Default Values”.

Strict mode disallows invalid date values such as '2004-04-31'. It does not disallow dates with zero month or day parts such as '2004-04-00' or “zero” dates. To disallow these as well, enable the NO_ZERO_IN_DATE and NO_ZERO_DATE SQL modes in addition to strict mode.

If you are not using strict mode (that is, neither STRICT_TRANS_TABLES nor STRICT_ALL_TABLES is enabled), MySQL inserts adjusted values for invalid or missing values and produces warnings. In strict mode, you can produce this behavior by using INSERT IGNORE or UPDATE IGNORE. See Section 12.5.5.37, “SHOW WARNINGS Syntax”.

Strict mode does not affect whether foreign key constraints are checked. foreign_key_checks can be used for that. (See Section 5.1.4, “Session System Variables”.)

The following special modes are provided as shorthand for combinations of mode values from the preceding list. All are available in MySQL 5.0 beginning with version 5.0.0, except for TRADITIONAL, which was implemented in MySQL 5.0.2.

The descriptions include all mode values that are available in the most recent version of MySQL. For older versions, a combination mode does not include individual mode values that are not available except in newer versions.

  • ANSI

    Equivalent to REAL_AS_FLOAT, PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE. Before MySQL 5.0.3, ANSI also includes ONLY_FULL_GROUP_BY.

    As of MySQL 5.0.40, ANSI mode also causes the server to return an error for queries where a set function S with an outer reference S(outer_ref) cannot be aggregated in the outer query against which the outer reference has been resolved. This is such a query:

    SELECT * FROM t1 WHERE t1.a IN (SELECT MAX(t1.b) FROM t2 WHERE ...);
    

    Here, MAX(t1.b) cannot aggregated in the outer query because it appears in the WHERE clause of that query. Standard SQL requires an error in this situation. If ANSI mode is not enabled, the server treats S(outer_ref) in such queries the same way that it would interpret S(const), as was always done prior to 5.0.40.

    See Section 1.7.3, “Running MySQL in ANSI Mode”.

  • DB2

    Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS.

  • MAXDB

    Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS, NO_AUTO_CREATE_USER.

  • MSSQL

    Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS.

  • MYSQL323

    Equivalent to NO_FIELD_OPTIONS, HIGH_NOT_PRECEDENCE.

  • MYSQL40

    Equivalent to NO_FIELD_OPTIONS, HIGH_NOT_PRECEDENCE.

  • ORACLE

    Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS, NO_AUTO_CREATE_USER.

  • POSTGRESQL

    Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS.

  • TRADITIONAL

    Equivalent to STRICT_TRANS_TABLES, STRICT_ALL_TABLES, NO_ZERO_IN_DATE, NO_ZERO_DATE, ERROR_FOR_DIVISION_BY_ZERO, NO_AUTO_CREATE_USER.

5.1.8. Server-Side Help

MySQL Server supports a HELP statement that returns online information from the MySQL Reference manual (see Section 12.3.3, “HELP Syntax”). The proper operation of this statement requires that the help tables in the mysql database be initialized with help topic information, which is done by processing the contents of the fill_help_tables.sql script.

For a MySQL binary distribution on Unix, help table setup occurs when you run mysql_install_db. For an RPM distribution on Linux or binary distribution on Windows, help table setup occurs as part of the MySQL installation process.

For a MySQL source distribution, you can find the fill_help_tables.sql file in the scripts directory. To load the file manually, make sure that you have initialized the mysql database by running mysql_install_db, and then process the file with the mysql client as follows:

shell> mysql -u root mysql < fill_help_tables.sql

If you are working with Bazaar and a MySQL development source tree, the tree doesn't contain fill_help_tables.sql. You can download the proper file for your version of MySQL from http://dev.mysql.com/doc/. After downloading and uncompressing the file, process it with mysql as just described.

5.1.9. Server Response to Signals

On Unix, signals can be sent to processes. mysqld responds to signals sent to it as follows:

  • SIGTERM causes the server to shut down.

  • SIGHUP causes the server to reload the grant tables and flush the logs (like FLUSH PRIVILEGES and FLUSH LOGS). It also writes a status report to the error log that has this format:

    Status information:
    
    Current dir: /var/mysql/data/
    Running threads: 0  Stack size: 196608
    Current locks:
    
    Key caches:
    default
    Buffer_size:       8388600
    Block_size:           1024
    Division_limit:        100
    Age_limit:             300
    blocks used:             0
    not flushed:             0
    w_requests:              0
    writes:                  0
    r_requests:              0
    reads:                   0
    
    handler status:
    read_key:            0
    read_next:           0
    read_rnd             0
    read_first:          1
    write:               0
    delete               0
    update:              0
    
    Table status:
    Opened tables:          5
    Open tables:            0
    Open files:             7
    Open streams:           0
    
    Alarm status:
    Active alarms:   1
    Max used alarms: 2
    Next alarm time: 67
    

On some Mac OS X 10.3 versions, mysqld ignores SIGHUP and SIGQUIT.

5.1.10. The Shutdown Process

The server shutdown process takes place as follows:

  1. The shutdown process is initiated.

    Server shutdown can be initiated several ways. For example, a user with the SHUTDOWN privilege can execute a mysqladmin shutdown command. mysqladmin can be used on any platform supported by MySQL. Other operating system-specific shutdown initiation methods are possible as well: The server shuts down on Unix when it receives a SIGTERM signal. A server running as a service on Windows shuts down when the services manager tells it to.

  2. The server creates a shutdown thread if necessary.

    Depending on how shutdown was initiated, the server might create a thread to handle the shutdown process. If shutdown was requested by a client, a shutdown thread is created. If shutdown is the result of receiving a SIGTERM signal, the signal thread might handle shutdown itself, or it might create a separate thread to do so. If the server tries to create a shutdown thread and cannot (for example, if memory is exhausted), it issues a diagnostic message that appears in the error log:

    Error: Can't create thread to kill server
    
  3. The server stops accepting new connections.

    To prevent new activity from being initiated during shutdown, the server stops accepting new client connections. It does this by closing the network connections to which it normally listens for connections: the TCP/IP port, the Unix socket file, the Windows named pipe, and shared memory on Windows.

  4. The server terminates current activity.

    For each thread that is associated with a client connection, the connection to the client is broken and the thread is marked as killed. Threads die when they notice that they are so marked. Threads for idle connections die quickly. Threads that currently are processing statements check their state periodically and take longer to die. For additional information about thread termination, see Section 12.5.6.3, “KILL Syntax”, in particular for the instructions about killed REPAIR TABLE or OPTIMIZE TABLE operations on MyISAM tables.

    For threads that have an open transaction, the transaction is rolled back. Note that if a thread is updating a non-transactional table, an operation such as a multiple-row UPDATE or INSERT may leave the table partially updated, because the operation can terminate before completion.

    If the server is a master replication server, threads associated with currently connected slaves are treated like other client threads. That is, each one is marked as killed and exits when it next checks its state.

    If the server is a slave replication server, the I/O and SQL threads, if active, are stopped before client threads are marked as killed. The SQL thread is allowed to finish its current statement (to avoid causing replication problems), and then stops. If the SQL thread was in the middle of a transaction at this point, the transaction is rolled back.

  5. Storage engines are shut down or closed.

    At this stage, the table cache is flushed and all open tables are closed.

    Each storage engine performs any actions necessary for tables that it manages. For example, MyISAM flushes any pending index writes for a table. InnoDB flushes its buffer pool to disk (starting from 5.0.5: unless innodb_fast_shutdown is 2), writes the current LSN to the tablespace, and terminates its own internal threads.

  6. The server exits.

5.2. MySQL Server Logs

MySQL has several different logs that can help you find out what is going on inside mysqld:

Log TypeInformation Written to Log
The error logProblems encountered starting, running, or stopping mysqld
The general query logEstablished client connections and statements received from clients
The binary logAll statements that change data (also used for replication)
The slow query logAll queries that took more than long_query_time seconds to execute or didn't use indexes

By default, all log files are created in the mysqld data directory. You can force mysqld to close and reopen the log files (or in some cases switch to a new log) by flushing the logs. Log flushing occurs when you issue a FLUSH LOGS statement or execute mysqladmin flush-logs or mysqladmin refresh. See Section 12.5.6.2, “FLUSH Syntax”, and Section 4.5.2, “mysqladmin — Client for Administering a MySQL Server”.

If you are using MySQL replication capabilities, slave replication servers maintain additional log files called relay logs. Chapter 16, Replication, discusses relay log contents and configuration.

MySQL Enterprise The MySQL Enterprise Monitor provides a number of advisors specifically related to the various log files. For more information see http://www.mysql.com/products/enterprise/advisors.html.

5.2.1. The Error Log

The error log contains information indicating when mysqld was started and stopped and also any critical errors that occur while the server is running. If mysqld notices a table that needs to be automatically checked or repaired, it writes a message to the error log.

On some operating systems, the error log contains a stack trace if mysqld dies. The trace can be used to determine where mysqld died. See MySQL Internals: Porting.

You can specify where mysqld writes the error log with the --log-error[=file_name] option. If no file_name value is given, mysqld uses the name host_name.err by default and writes the file in the data directory. If you execute FLUSH LOGS, the error log is renamed with the suffix -old and mysqld creates a new empty log file. (No renaming occurs if the --log-error option was not given to mysqld.)

If you do not specify --log-error, or (on Windows) if you use the --console option, errors are written to stderr, the standard error output. Usually this is your terminal.

On Windows, error output is always written to the .err file if --console is not given.

The --log-warnings option or log_warnings system variable can be used to control warning logging to the error log. The default value is enabled (1). Warning logging can be disabled using a value of 0. If the value is greater than 1, aborted connections are written to the error log. See Section B.1.2.11, “Communication Errors and Aborted Connections”.

If you use mysqld_safe to start mysqld, mysqld_safe arranges for mysqld to write error messages to a log file. If you specify a filename via --log-error to mysqld_safe or mysqld, that filename is used. Otherwise, mysqld_safe uses the default error log file.

If mysqld_safe is used to start mysqld and mysqld dies unexpectedly, mysqld_safe notices that it needs to restart mysqld and writes a restarted mysqld message to the error log.

5.2.2. The General Query Log

The general query log is a general record of what mysqld is doing. The server writes information to this log when clients connect or disconnect, and it logs each SQL statement received from clients. The general query log can be very useful when you suspect an error in a client and want to know exactly what the client sent to mysqld.

mysqld writes statements to the query log in the order that it receives them, which might differ from the order in which they are executed. This logging order contrasts to the binary log, for which statements are written after they are executed but before any locks are released. (Also, the query log contains all statements, whereas the binary log does not contain statements that only select data.)

To enable the general query log, start mysqld with the --log[=file_name] or -l [file_name] option.

If no file_name value is given for --log or -l, the default name is host_name.log in the data directory.

Server restarts and log flushing do not cause a new general query log file to be generated (although flushing closes and reopens it). On Unix, you can rename the file and create a new one by using the following commands:

shell> mv host_name.log host_name-old.log
shell> mysqladmin flush-logs
shell> cp host_name-old.log backup-directory
shell> rm host_name-old.log

Before 5.0.17, you cannot rename a log file on Windows while the server has it open. You must stop the server and rename the file, and then restart the server to create a new log file. As of 5.0.17, this applies only to the error log. However, a stop and restart can be avoided by using FLUSH LOGS, which causes the server to rename the error log with an -old suffix and open a new error log.

5.2.3. The Binary Log

The binary log contains all statements that update data or potentially could have updated it (for example, a DELETE which matched no rows). Statements are stored in the form of “events” that describe the modifications. The binary log also contains information about how long each statement took that updated data. The binary log has two important purposes:

  • For replication, the binary log is used on master replication servers as a record of the statements to be sent to slave servers. The master server sends the events contained in its binary log to its slaves, which execute those events to make the same data changes that were made on the master. See Section 16.4, “Replication Implementation Overview”.

  • Certain data recovery operations require use of the binary log. After a backup file has been restored, the events in the binary log that were recorded after the backup was made are re-executed. These events bring databases up to date from the point of the backup. See Section 6.2.2, “Using Backups for Recovery”.

Note

The binary log has replaced the old update log, which is no longer available as of MySQL 5.0. The binary log contains all information that is available in the update log in a more efficient format and in a manner that is transaction-safe. If you are using transactions, you must use the MySQL binary log for backups instead of the old update log.

For information about server options and variables affecting the operation of binary logging, see Section 16.1.2.4, “Binary Log Options and Variables”.

The binary log is not used for statements such as SELECT or SHOW that do not modify data. If you want to log all statements (for example, to identify a problem query), use the general query log. See Section 5.2.2, “The General Query Log”.

MySQL Enterprise The binary log can also be used to track significant DDL events. Analyzing the binary log in this way is an integral part of the MySQL Enterprise Monitor. For more information, see http://www.mysql.com/products/enterprise/advisors.html.

Running the server with the binary log enabled makes performance about 1% slower. However, the benefits of the binary log for restore operations and in allowing you to set up replication generally outweigh this minor performance decrement.

When started with the --log-bin[=base_name] option, mysqld writes a log file containing all SQL statements that update data (both DDL and DML statements). If no base_name value is given, the default name is the value of the pid-file option (which by default is the name of host machine) followed by -bin. If the basename is given, but not as an absolute pathname, the server writes the file in the data directory. It is recommended that you specify a basename; see Section B.1.8.1, “Open Issues in MySQL”, for the reason.

Note

From MySQL 5.0.41 through 5.0.52, “mysql” was used when no base_name was specified. Also in these versions, a path given as part of the --log-bin options was treated as absolute rather than relative. The previous behaviors were restored in MySQL 5.0.54. (See Bug#28603 and Bug#28597.)

If you supply an extension in the log name (for example, --log-bin=base_name.extension), the extension is silently removed and ignored.

mysqld appends a numeric extension to the binary log basename to generate binary log filenames. The number increases each time the server creates a new log file, thus creating an ordered series of files. The server creates a new file in the series each time it starts or flushes the logs. The server also creates a new binary log file automatically when the current log's size reaches max_binlog_size. A binary log file may become larger than max_binlog_size if you are using large transactions because a transaction is written to the file in one piece, never split between files.

To keep track of which binary log files have been used, mysqld also creates a binary log index file that contains the names of all used binary log files. By default, this has the same basename as the binary log file, with the extension '.index'. You can change the name of the binary log index file with the --log-bin-index[=file_name] option. You should not manually edit this file while mysqld is running; doing so would confuse mysqld.

You can delete all binary log files with the RESET MASTER statement, or a subset of them with PURGE BINARY LOGS. See Section 12.5.6.5, “RESET Syntax”, and Section 12.6.1.1, “PURGE BINARY LOGS Syntax”.

Writes to the binary log file and binary log index file are handled in the same way as writes to MyISAM tables. See Section B.1.4.3, “How MySQL Handles a Full Disk”.

The binary log format has some known limitations that can affect recovery from backups. See Section 16.3.1, “Replication Features and Issues”.

Binary logging for stored routines and triggers is done as described in Section 18.5, “Binary Logging of Stored Programs”.

A replication slave server by default does not write to its own binary log any data modifications that are received from the replication master. To log these modifications, start the slave with the --log-slave-updates option (see also Section 16.1.2.3, “Replication Slave Options and Variables”).

Evaluation of update selection options.  The server evaluates the options for logging or ignoring updates to the binary log according to the following rules:

  1. Are there --binlog-do-db or --binlog-ignore-db rules?

    • No: Write the statement to the binary log and exit.

    • Yes: Go to the next step.

  2. There are some rules (--binlog-do-db, --binlog-ignore-db, or both). Is there a default database (has any database been selected by USE?)?

    • No: Do not write the statement, and exit.

    • Yes: Go to the next step.

  3. There is a default database. Are there some --binlog-do-db rules?

    • Yes: Does the default database match any of the --binlog-do-db rules?

      • Yes: Write the statement and exit.

      • No: Do not write the statement, and exit.

    • No: Go to the next step.

  4. There are some --binlog-ignore-db rules. Does the default database match any of the --binlog-ignore-db rules?

    • Yes: Do not write the statement, and exit.

    • No: Write the query and exit.

Important

An exception is made in the rules just given for the CREATE DATABASE, ALTER DATABASE, and DROP DATABASE statements (see Section 16.1.2.4, “Binary Log Options and Variables”). In those cases, the database being created, altered, or dropped replaces the default database when determining whether to log or ignore updates.

For example, a slave running with only --binlog-do-db=sales does not write to the binary log any statement for which the default database is different from sales (in other words, --binlog-do-db can sometimes mean “ignore other databases”).

If you are using replication, you should not delete old binary log files until you are sure that no slave still needs to use them. For example, if your slaves never run more than three days behind, once a day you can execute mysqladmin flush-logs on the master and then remove any logs that are more than three days old. You can remove the files manually, but it is preferable to use PURGE BINARY LOGS, which also safely updates the binary log index file for you (and which can take a date argument). See Section 12.6.1.1, “PURGE BINARY LOGS Syntax”.

A client that has the SUPER privilege can disable binary logging of its own statements by using a SET sql_log_bin=0 statement. See Section 5.1.4, “Session System Variables”.

You can display the contents of binary log files with the mysqlbinlog utility. This can be useful when you want to reprocess statements in the log. For example, you can update a MySQL server from the binary log as follows:

shell> mysqlbinlog log_file | mysql -h server_name

See Section 4.6.7, “mysqlbinlog — Utility for Processing Binary Log Files”, for more information on the mysqlbinlog utility and how to use it. mysqlbinlog also can be used with relay log files because they are written using the same format as binary log files.

Binary logging is done immediately after a statement completes but before any locks are released or any commit is done. This ensures that the log is logged in execution order.

Updates to non-transactional tables are stored in the binary log immediately after execution. In MySQL 5.0.53 and earlier versions of MySQL 5.0, an UPDATE statement using a stored function that modified a non-transactional table was not logged if it failed, and an INSERT ... ON DUPLICATE KEY UPDATE statement that encountered a duplicate key constraint — but which did not actually change any data — was not logged. Beginning with MySQL 5.0.54, both of these statements are written to the binary log. (Bug#23333)

Within an uncommitted transaction, all updates (UPDATE, DELETE, or INSERT) that change transactional tables such as BDB or InnoDB tables are cached until a COMMIT statement is received by the server. At that point, mysqld writes the entire transaction to the binary log before the COMMIT is executed. When the thread that handles the transaction starts, it allocates a buffer of binlog_cache_size to buffer statements. If a statement is bigger than this, the thread opens a temporary file to store the transaction. The temporary file is deleted when the thread ends.

Modifications to non-transactional tables cannot be rolled back. If a transaction that is rolled back includes modifications to non-transactional tables, the entire transaction is logged with a ROLLBACK statement at the end to ensure that the modifications to those tables are replicated.

The Binlog_cache_use status variable shows the number of transactions that used this buffer (and possibly a temporary file) for storing statements. The Binlog_cache_disk_use status variable shows how many of those transactions actually had to use a temporary file. These two variables can be used for tuning binlog_cache_size to a large enough value that avoids the use of temporary files.

The max_binlog_cache_size system variable (default 4GB, which is also the maximum) can be used to restrict the total size used to cache a multiple-statement transaction. If a transaction is larger than this many bytes, it fails and rolls back. The minimum value is 4096.

Note that the binary log format is different in MySQL 5.0 from previous versions of MySQL, due to enhancements in replication. See Section 16.3.2, “Replication Compatibility Between MySQL Versions”.

By default, the binary log is not synchronized to disk at each write. So if the operating system or machine (not only the MySQL server) crashes, there is a chance that the last statements of the binary log are lost. To prevent this, you can make the binary log be synchronized to disk after every N writes to the binary log, with the sync_binlog system variable. See Section 5.1.3, “Server System Variables”. 1 is the safest value for sync_binlog, but also the slowest. Even with sync_binlog set to 1, there is still the chance of an inconsistency between the table content and binary log content in case of a crash. For example, if you are using InnoDB tables and the MySQL server processes a COMMIT statement, it writes the whole transaction to the binary log and then commits this transaction into InnoDB. If the server crashes between those two operations, the transaction is rolled back by InnoDB at restart but still exists in the binary log. This problem can be solved with the --innodb-safe-binlog option, which adds consistency between the content of InnoDB tables and the binary log. (Note: --innodb-safe-binlog is unneeded as of MySQL 5.0; it was made obsolete by the introduction of XA transaction support.)

For this option to provide a greater degree of safety, the MySQL server should also be configured to synchronize the binary log and the InnoDB logs to disk at every transaction. The InnoDB logs are synchronized by default, and sync_binlog=1 can be used to synchronize the binary log. The effect of this option is that at restart after a crash, after doing a rollback of transactions, the MySQL server cuts rolled back InnoDB transactions from the binary log. This ensures that the binary log reflects the exact data of InnoDB tables, and so, that the slave remains in synchrony with the master (not receiving a statement which has been rolled back).

Note that --innodb-safe-binlog can be used even if the MySQL server updates other storage engines than InnoDB. Only statements and transactions that affect InnoDB tables are subject to removal from the binary log at InnoDB's crash recovery. If the MySQL server discovers at crash recovery that the binary log is shorter than it should have been, it lacks at least one successfully committed InnoDB transaction. This should not happen if sync_binlog=1 and the disk/filesystem do an actual sync when they are requested to (some don't), so the server prints an error message The binary log <name> is shorter than its expected size. In this case, this binary log is not correct and replication should be restarted from a fresh snapshot of the master's data.

For MySQL 5.0.46, the session values of the following system variables are written to the binary log and honored by the replication slave when parsing the binary log:

5.2.4. The Slow Query Log

The slow query log consists of all SQL statements that took more than long_query_time seconds to execute. The time to acquire the initial table locks is not counted as execution time. mysqld writes a statement to the slow query log after it has been executed and after all locks have been released, so log order might be different from execution order. The minimum and default values of long_query_time are 1 and 10, respectively.

To enable the slow query log, start mysqld with the --log-slow-queries[=file_name] option.

If no file_name value is given for --log-slow-queries, the default name is host_name-slow.log. If a filename is given, but not as an absolute pathname, the server writes the file in the data directory.

The slow query log can be used to find queries that take a long time to execute and are therefore candidates for optimization. However, examining a long slow query log can become a difficult task. To make this easier, you can process the slow query log using the mysqldumpslow command to summarize the queries that appear in the log. Use mysqldumpslow --help to see the options that this command supports.

In MySQL 5.0, queries that do not use indexes are logged in the slow query log if the --log-queries-not-using-indexes option is specified. See Section 5.1.2, “Server Command Options”.

MySQL Enterprise Excessive table scans are indicative of missing or poorly optimized indexes. Using an advisor specifically designed for the task, the MySQL Enterprise Monitor can identify such problems and offer advice on resolution. For more information, see http://www.mysql.com/products/enterprise/advisors.html.

In MySQL 5.0, the --log-slow-admin-statements server option enables you to request logging of slow administrative statements such as OPTIMIZE TABLE, ANALYZE TABLE, and ALTER TABLE to the slow query log.

Queries handled by the query cache are not added to the slow query log, nor are queries that would not benefit from the presence of an index because the table has zero rows or one row.

Replication slaves do not write replicated queries to the slow query log, even if the same queries were written to the slow query log on the master. This is a known issue which we intend to fix in a future version of MySQL. (Bug#23300)

5.2.5. Server Log Maintenance

MySQL Server can create a number of different log files that make it easy to see what is going on. See Section 5.2, “MySQL Server Logs”. However, you must clean up these files regularly to ensure that the logs do not take up too much disk space.

When using MySQL with logging enabled, you may want to back up and remove old log files from time to time and tell MySQL to start logging to new files. See Section 6.1, “Database Backups”.

On a Linux (Red Hat) installation, you can use the mysql-log-rotate script for this. If you installed MySQL from an RPM distribution, this script should have been installed automatically. You should be careful with this script if you are using the binary log for replication. You should not remove binary logs until you are certain that their contents have been processed by all slaves.

On other systems, you must install a short script yourself that you start from cron (or its equivalent) for handling log files.

For the binary log, you can set the expire_logs_days system variable to expire binary log files automatically after a given number of days (see Section 5.1.3, “Server System Variables”). If you are using replication, you should set the variable no lower than the maximum number of days your slaves might lag behind the master.

You can force MySQL to start using new log files by issuing a FLUSH LOGS statement or executing mysqladmin flush-logs or mysqladmin refresh. See Section 12.5.6.2, “FLUSH Syntax”, and Section 4.5.2, “mysqladmin — Client for Administering a MySQL Server”.

A log flushing operation does the following:

  • If general query logging (--log) or slow query logging (--log-slow-queries) to a log file is enabled, the server closes and reopens the general query log file or slow query log file.

  • If binary logging (--log-bin) is used, the server closes the current log file and opens a new log file with the next sequence number.

  • If the server was given an error log filename with the --log-error option, it renames the error log with the suffix -old and creates a new empty error log file.

The server creates a new binary log file when you flush the logs. However, it just closes and reopens the general and slow query log files. To cause new files to be created on Unix, rename the current logs before flushing them. At flush time, the server will open new logs with the original names. For example, if the general and slow query logs are named mysql.log and mysql-slow.log, you can use a series of