Chapter 5. MySQL Server Administration

Table of Contents

5.1. The MySQL Server
5.1.1. Option and Variable Reference
5.1.2. Command Options
5.1.3. System Variables
5.1.4. Session System Variables
5.1.5. Using System Variables
5.1.6. Status Variables
5.1.7. 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. Selecting General Query and Slow Query Log Output Destinations
5.2.2. The Error Log
5.2.3. The General Query Log
5.2.4. The Binary Log
5.2.5. The Slow Query Log
5.2.6. Server Log Maintenance
5.3. General Security Issues
5.3.1. General Security Guidelines
5.3.2. Making MySQL Secure Against Attackers
5.3.3. Security-Related mysqld Options
5.3.4. Security Issues with LOAD DATA LOCAL
5.3.5. How to Run MySQL as a Normal User
5.4. The MySQL Access Privilege System
5.4.1. 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 Your Password Secure
5.5.7. Using SSL for Secure Connections
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 12.5.4.14, “SHOW ENGINES Syntax”.

5.1.1. 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.

Note

This table is part of an ongoing process to expand and simplify the information provided on these elements. Further improvements to the table, and corresponding descriptions will be applied over the coming months.

NameCmd-LineOption fileSystem VarDynamic  
Aborted_clients    YesNo 
Aborted_connects    YesNo 
abort-slave-event-count Yes Yes    
allow-suspicious-udfs Yes Yes    
ansi Yes Yes    
autocommit   Yes  Yes 
auto-increment-increment Yes Yes   Yes 
- Variable: auto_increment_increment   Yes  Yes 
auto-increment-offset Yes Yes   Yes 
- Variable: auto_increment_offset   Yes  Yes 
automatic_sp_privileges   Yes  Yes 
back_log Yes Yes Yes No 
basedir Yes Yes Yes No 
big-tables Yes Yes   Yes 
- Variable: big_tables   Yes  Yes 
bind-address Yes Yes    
Binlog_cache_disk_use    YesNo 
binlog_cache_size Yes Yes Yes  Yes 
Binlog_cache_use    YesNo 
binlog-do-db Yes Yes    
binlog-format Yes Yes   Yes 
- Variable: binlog_format   Yes  Yes 
binlog-ignore-db Yes Yes    
binlog-row-event-max-size Yes Yes    
bootstrap Yes Yes    
bulk_insert_buffer_size Yes Yes Yes  Yes 
Bytes_received    YesNo 
Bytes_sent    YesNo 
character_set_client   Yes  Yes 
character-set-client-handshake Yes     
character_set_connection   Yes  Yes 
character_set_database   Yes  Yes 
character-set-filesystem Yes Yes   Yes 
- Variable: character_set_filesystem   Yes  Yes 
character_set_results   Yes  Yes 
character-sets-dir Yes Yes  No 
- Variable: character_sets_dir   Yes No 
character-set-server Yes Yes   Yes 
- Variable: character_set_server   Yes  Yes 
character_set_system   Yes No 
chroot Yes Yes    
collation_connection   Yes  Yes 
collation_database   Yes  Yes 
collation-server Yes Yes   Yes 
- Variable: collation_server   Yes  Yes 
Com_admin_commands    YesNo 
Com_alter_db    YesNo 
Com_alter_event    YesNo 
Com_alter_table    YesNo 
Com_analyze    YesNo 
Com_backup_table    YesNo 
Com_begin    YesNo 
Com_call_procedure    YesNo 
Com_change_db    YesNo 
Com_change_master    YesNo 
Com_check    YesNo 
Com_checksum    YesNo 
Com_commit    YesNo 
Com_create_db    YesNo 
Com_create_event    YesNo 
Com_create_function    YesNo 
Com_create_index    YesNo 
Com_create_table    YesNo 
Com_create_user    YesNo 
Com_dealloc_sql    YesNo 
Com_delete    YesNo 
Com_delete_multi    YesNo 
Com_do    YesNo 
Com_drop_db    YesNo 
Com_drop_event    YesNo 
Com_drop_function    YesNo 
Com_drop_index    YesNo 
Com_drop_table    YesNo 
Com_drop_user    YesNo 
Com_execute_sql    YesNo 
Com_flush    YesNo 
Com_grant    YesNo 
Com_ha_close    YesNo 
Com_ha_open    YesNo 
Com_ha_read    YesNo 
Com_help    YesNo 
Com_insert    YesNo 
Com_insert_select    YesNo 
Com_kill    YesNo 
Com_load    YesNo 
Com_lock_tables    YesNo 
Com_optimize    YesNo 
completion_type Yes Yes Yes  Yes 
Com_preload_keys    YesNo 
Com_prepare_sql    YesNo 
Compression    YesNo 
Com_purge    YesNo 
Com_purge_before_date    YesNo 
Com_rename_table    YesNo 
Com_repair    YesNo 
Com_replace    YesNo 
Com_replace_select    YesNo 
Com_reset    YesNo 
Com_restore_table    YesNo 
Com_revoke    YesNo 
Com_revoke_all    YesNo 
Com_rollback    YesNo 
Com_savepoint    YesNo 
Com_select    YesNo 
Com_set_option    YesNo 
Com_show_binlog_events    YesNo 
Com_show_binlogs    YesNo 
Com_show_charsets    YesNo 
Com_show_collations    YesNo 
Com_show_column_types    YesNo 
Com_show_create_db    YesNo 
Com_show_create_event    YesNo 
Com_show_create_table    YesNo 
Com_show_databases    YesNo 
Com_show_engine_logs    YesNo 
Com_show_engine_mutex    YesNo 
Com_show_engine_status    YesNo 
Com_show_errors    YesNo 
Com_show_events    YesNo 
Com_show_fields    YesNo 
Com_show_grants    YesNo 
Com_show_innodb_status    YesNo 
Com_show_keys    YesNo 
Com_show_logs    YesNo 
Com_show_master_status    YesNo 
Com_show_ndb_status    YesNo 
Com_show_new_master    YesNo 
Com_show_open_tables    YesNo 
Com_show_plugins    YesNo 
Com_show_privileges    YesNo 
Com_show_processlist    YesNo 
Com_show_slave_hosts    YesNo 
Com_show_slave_status    YesNo 
Com_show_status    YesNo 
Com_show_storage_engines    YesNo 
Com_show_tables    YesNo 
Com_show_triggers    YesNo 
Com_show_variables    YesNo 
Com_show_warnings    YesNo 
Com_slave_start    YesNo 
Com_slave_stop    YesNo 
Com_stmt_close    YesNo 
Com_stmt_execute    YesNo 
Com_stmt_fetch    YesNo 
Com_stmt_prepare    YesNo 
Com_stmt_reprepare    YesNo 
Com_stmt_reset    YesNo 
Com_stmt_send_long_data    YesNo 
Com_truncate    YesNo 
Com_unlock_tables    YesNo 
Com_update    YesNo 
Com_update_multi    YesNo 
Com_xa_commit    YesNo 
Com_xa_end    YesNo 
Com_xa_prepare    YesNo 
Com_xa_recover    YesNo 
Com_xa_rollback    YesNo 
Com_xa_start    YesNo 
concurrent_insert Yes Yes Yes  Yes 
Connections    YesNo 
connect_timeout Yes Yes Yes  Yes 
console Yes Yes    
core-file Yes Yes    
Created_tmp_disk_tables    YesNo 
Created_tmp_files    YesNo 
Created_tmp_tables    YesNo 
datadir Yes Yes Yes No 
date_format   Yes  Yes 
datetime_format Yes Yes Yes  Yes 
debug Yes Yes Yes  Yes 
defaults-extra-file Yes     
defaults-file Yes     
defaults-group-suffix Yes     
default-storage-engine Yes Yes    
default-table-type Yes Yes    
default-time-zone Yes Yes    
default_week_format Yes Yes Yes  Yes 
Delayed_errors    YesNo 
delayed_insert_limit Yes Yes Yes  Yes 
Delayed_insert_threads    YesNo 
delayed_insert_timeout Yes Yes Yes  Yes 
delayed_queue_size Yes Yes Yes  Yes 
Delayed_writes    YesNo 
delay-key-write Yes Yes   Yes 
- Variable: delay_key_write   Yes  Yes 
des-key-file Yes Yes    
disconnect-slave-event-count Yes Yes    
div_precision_increment Yes Yes Yes  Yes 
enable-locking Yes     
enable-named-pipe Yes Yes    
enable-pstack Yes Yes    
engine-condition-pushdown Yes Yes   Yes 
- Variable: engine_condition_pushdown   Yes  Yes 
error_count   Yes No 
event-scheduler Yes Yes Yes  Yes 
exit-info Yes Yes    
expire_logs_days Yes Yes Yes  Yes 
external-locking Yes Yes    
- Variable: external_locking      
flush Yes Yes Yes  Yes 
Flush_commands    YesNo 
flush_time Yes Yes Yes  Yes 
foreign_key_checks   Yes  Yes 
ft_boolean_syntax Yes Yes Yes  Yes 
ft_max_word_len Yes Yes Yes No 
ft_min_word_len Yes Yes Yes No 
ft_query_expansion_limit Yes Yes Yes No 
ft_stopword_file Yes Yes Yes No 
gdb Yes Yes    
general-log Yes Yes   Yes 
- Variable: general_log   Yes  Yes 
general_log_file   Yes  Yes 
group_concat_max_len Yes Yes Yes  Yes 
Handler_commit    YesNo 
Handler_delete    YesNo 
Handler_discover    YesNo 
Handler_prepare    YesNo 
Handler_read_first    YesNo 
Handler_read_key    YesNo 
Handler_read_next    YesNo 
Handler_read_prev    YesNo 
Handler_read_rnd    YesNo 
Handler_read_rnd_next    YesNo 
Handler_rollback    YesNo 
Handler_savepoint    YesNo 
Handler_savepoint_rollback    YesNo 
Handler_update    YesNo 
Handler_write    YesNo 
have_archive   Yes No 
have_blackhole_engine   Yes No 
have_compress   Yes No 
have_crypt   Yes No 
have_csv   Yes No 
have_dynamic_loading   Yes No 
have_example_engine   Yes No 
have_federated_engine   Yes No 
have_geometry   Yes No 
have_innodb   Yes No 
have_isam   Yes No 
have_merge_engine   Yes No 
have_ndbcluster   Yes No 
have_openssl   Yes No 
have_partitioning   Yes No 
have_query_cache   Yes No 
have_raid   Yes No 
have_row_based_replication   Yes No 
have_rtree_keys   Yes No 
have_ssl   Yes No 
have_symlink   Yes No 
help Yes     
hostname   Yes No 
identity   Yes  Yes 
init_connect Yes Yes Yes  Yes 
init-file Yes Yes  No 
- Variable: init_file   Yes No 
init_slave Yes Yes Yes  Yes 
innodb Yes Yes    
innodb_adaptive_hash_index Yes Yes Yes No 
innodb_additional_mem_pool_size Yes Yes Yes No 
innodb_autoextend_increment Yes Yes Yes  Yes 
innodb_autoinc_lock_mode Yes Yes Yes No 
innodb_buffer_pool_awe_mem_mb Yes Yes Yes No 
Innodb_buffer_pool_pages_data    YesNo 
Innodb_buffer_pool_pages_dirty    YesNo 
Innodb_buffer_pool_pages_flushed    YesNo 
Innodb_buffer_pool_pages_free    YesNo 
Innodb_buffer_pool_pages_latched    YesNo 
Innodb_buffer_pool_pages_misc    YesNo 
Innodb_buffer_pool_pages_total    YesNo 
Innodb_buffer_pool_read_ahead_rnd    YesNo 
Innodb_buffer_pool_read_ahead_seq    YesNo 
Innodb_buffer_pool_read_requests    YesNo 
Innodb_buffer_pool_reads    YesNo 
innodb_buffer_pool_size Yes Yes Yes No 
Innodb_buffer_pool_wait_free    YesNo 
Innodb_buffer_pool_write_requests    YesNo 
innodb_checksums Yes Yes Yes No 
innodb_commit_concurrency Yes Yes Yes  Yes 
innodb_concurrency_tickets Yes Yes Yes  Yes 
innodb_data_file_path Yes Yes Yes No 
Innodb_data_fsyncs    YesNo 
innodb_data_home_dir Yes Yes Yes No 
Innodb_data_pending_fsyncs    YesNo 
Innodb_data_pending_reads    YesNo 
Innodb_data_pending_writes    YesNo 
Innodb_data_read    YesNo 
Innodb_data_reads    YesNo 
Innodb_data_writes    YesNo 
Innodb_data_written    YesNo 
Innodb_dblwr_pages_written    YesNo 
Innodb_dblwr_writes    YesNo 
innodb_doublewrite Yes Yes Yes No 
innodb_fast_shutdown Yes Yes Yes  Yes 
innodb_file_io_threads Yes Yes Yes No 
innodb_file_per_table Yes Yes Yes No 
innodb_flush_log_at_trx_commit Yes Yes Yes  Yes 
innodb_flush_method Yes Yes Yes No 
innodb_force_recovery Yes Yes Yes No 
innodb_locks_unsafe_for_binlog Yes Yes Yes No 
innodb_lock_wait_timeout Yes Yes Yes No 
innodb_log_arch_dir Yes Yes Yes No 
innodb_log_archive Yes Yes Yes No 
innodb_log_buffer_size Yes Yes Yes No 
innodb_log_files_in_group Yes Yes Yes No 
innodb_log_file_size Yes Yes Yes No 
innodb_log_group_home_dir Yes Yes Yes No 
Innodb_log_waits    YesNo 
Innodb_log_write_requests    YesNo 
Innodb_log_writes    YesNo 
innodb_max_dirty_pages_pct Yes Yes Yes  Yes 
innodb_max_purge_lag Yes Yes Yes  Yes 
innodb_mirrored_log_groups Yes Yes Yes No 
innodb_open_files Yes Yes Yes No 
Innodb_os_log_fsyncs    YesNo 
Innodb_os_log_pending_fsyncs    YesNo 
Innodb_os_log_pending_writes    YesNo 
Innodb_os_log_written    YesNo 
Innodb_pages_created    YesNo 
Innodb_page_size    YesNo 
Innodb_pages_read    YesNo 
Innodb_pages_written    YesNo 
innodb_rollback_on_timeout Yes Yes Yes No 
Innodb_row_lock_current_waits    YesNo 
Innodb_row_lock_time    YesNo 
Innodb_row_lock_time_avg    YesNo 
Innodb_row_lock_time_max    YesNo 
Innodb_row_lock_waits    YesNo 
Innodb_rows_deleted    YesNo 
Innodb_rows_inserted    YesNo 
Innodb_rows_read    YesNo 
Innodb_rows_updated    YesNo 
innodb_stats_on_metadata Yes Yes Yes No 
innodb_status_file Yes Yes Yes No 
innodb_support_xa Yes Yes Yes  Yes 
innodb_sync_spin_loops Yes Yes Yes  Yes 
innodb_table_locks Yes Yes Yes  Yes 
innodb_thread_concurrency Yes Yes Yes  Yes 
innodb_thread_sleep_delay Yes Yes Yes  Yes 
insert_id   Yes  Yes 
interactive_timeout Yes Yes Yes  Yes 
join_buffer_size Yes Yes Yes  Yes 
keep_files_on_create Yes Yes Yes  Yes 
Key_blocks_not_flushed    YesNo 
Key_blocks_unused    YesNo 
Key_blocks_used    YesNo 
key_buffer_size Yes Yes Yes  Yes 
key_cache_age_threshold Yes Yes Yes  Yes 
key_cache_block_size Yes Yes Yes  Yes 
key_cache_division_limit Yes Yes Yes  Yes 
Key_read_requests    YesNo 
Key_reads    YesNo 
Key_write_requests    YesNo 
Key_writes    YesNo 
language Yes Yes Yes No 
large-pages Yes Yes  No 
- Variable: large_pages   Yes No 
large_page_size   Yes No 
last_insert_id   Yes  Yes 
Last_query_cost    YesNo 
lc_time_names   Yes  Yes 
license   Yes No 
local_infile   Yes  Yes 
local-infile Yes Yes    
locked_in_memory   Yes No 
log Yes Yes Yes  Yes 
log_bin   Yes No 
log-bin Yes Yes    
log-bin-index Yes Yes    
log-bin-trust-function-creators Yes Yes   Yes 
- Variable: log_bin_trust_function_creators   Yes  Yes 
log-bin-trust-routine-creators Yes Yes   Yes 
- Variable: log_bin_trust_routine_creators   Yes  Yes 
log-error Yes Yes  No 
- Variable: log_error   Yes No 
log-isam Yes Yes    
log-output Yes Yes   Yes 
- Variable: log_output   Yes  Yes 
log-queries-not-using-indexes Yes Yes   Yes 
- Variable: log_queries_not_using_indexes   Yes  Yes 
log-short-format Yes Yes    
log-slave-updates Yes Yes  No 
- Variable: log_slave_updates   Yes No 
log-slow-admin-statements Yes Yes    
log-slow-queries Yes Yes   Yes 
- Variable: log_slow_queries   Yes  Yes 
log-slow-slave-statements Yes Yes    
log-tc Yes Yes    
log-tc-size Yes Yes    
log-warnings Yes Yes   Yes 
- Variable: log_warnings   Yes  Yes 
long_query_time Yes Yes Yes  Yes 
lower_case_file_system Yes Yes Yes No 
lower_case_table_names Yes Yes Yes No 
low-priority-updates Yes Yes   Yes 
- Variable: low_priority_updates   Yes  Yes 
master-bind Yes Yes Yes No 
master-connect-retry Yes Yes    
master-host Yes Yes    
master-info-file Yes Yes    
master-password Yes Yes    
master-port Yes Yes    
master-retry-count Yes Yes    
master-ssl Yes Yes    
master-ssl-ca Yes Yes    
master-ssl-capath Yes Yes    
master-ssl-cert Yes Yes    
master-ssl-cipher Yes Yes    
master-ssl-key Yes Yes    
master-user Yes Yes    
max_allowed_packet Yes Yes Yes  Yes 
max_binlog_cache_size Yes Yes Yes  Yes 
max-binlog-dump-events Yes Yes    
max_binlog_size Yes Yes Yes  Yes 
max_connect_errors Yes Yes Yes  Yes 
max_connections Yes Yes Yes  Yes 
max_delayed_threads Yes Yes Yes  Yes 
max_error_count Yes Yes Yes  Yes 
max_heap_table_size Yes Yes Yes  Yes 
max_insert_delayed_threads   Yes  Yes 
max_join_size Yes Yes Yes  Yes 
max_length_for_sort_data Yes Yes Yes  Yes 
max_prepared_stmt_count Yes Yes Yes  Yes 
max_relay_log_size Yes Yes Yes  Yes 
max_seeks_for_key Yes Yes Yes  Yes 
max_sort_length Yes Yes Yes  Yes 
max_sp_recursion_depth Yes Yes Yes  Yes 
max_tmp_tables Yes Yes Yes  Yes 
Max_used_connections    YesNo 
max_user_connections Yes Yes Yes  Yes 
max_write_lock_count Yes Yes Yes  Yes 
memlock Yes Yes Yes No 
merge Yes Yes    
min-examined-row-limit Yes Yes Yes  Yes 
multi_range_count Yes Yes Yes  Yes 
myisam_block_size Yes Yes Yes  Yes 
myisam_data_pointer_size Yes Yes Yes  Yes 
myisam_max_sort_file_size Yes Yes Yes  Yes 
myisam-recover Yes Yes    
myisam_recover_options   Yes No 
myisam_repair_threads Yes Yes Yes  Yes 
myisam_sort_buffer_size Yes Yes Yes  Yes 
myisam_stats_method Yes Yes Yes  Yes 
myisam_use_mmap Yes Yes Yes  Yes 
named_pipe   Yes No 
ndb_autoincrement_prefetch_sz Yes Yes Yes  Yes 
ndb-batch-size Yes Yes    
ndb_cache_check_time Yes Yes Yes  Yes 
ndbcluster Yes Yes Yes  Yes 
ndb-cluster-connection-pool Yes Yes  YesNo 
Ndb_cluster_node_id    YesNo 
Ndb_config_from_host    YesNo 
Ndb_config_from_port    YesNo 
Ndb_conflict_fn_max    YesNo 
Ndb_conflict_fn_old    YesNo 
ndb-connectstring Yes Yes    
ndb_execute_count    YesNo 
ndb_extra_logging Yes Yes Yes  Yes 
ndb_force_send Yes Yes Yes  Yes 
ndb_index_stat_cache_entries Yes Yes    
ndb_index_stat_enable Yes Yes    
ndb_index_stat_update_freq Yes Yes    
ndb_log_orig   Yes No 
ndb_log_update_as_write Yes Yes Yes  Yes 
ndb_log_updated_only Yes Yes Yes  Yes 
Ndb_number_of_data_nodes    YesNo 
ndb_optimization_delay   Yes  Yes 
ndb_optimized_node_selection Yes Yes    
ndb_report_thresh_binlog_epoch_slip Yes Yes    
ndb_report_thresh_binlog_mem_usage Yes Yes    
ndb_table_no_logging   Yes  Yes 
ndb_table_temporary   Yes  Yes 
ndb_use_copying_alter_table   Yes No 
ndb_use_exact_count   Yes  Yes 
ndb_use_transactions Yes Yes    
ndb_wait_connected Yes Yes Yes No 
net_buffer_length Yes Yes Yes  Yes 
net_read_timeout Yes Yes Yes  Yes 
net_retry_count Yes Yes Yes  Yes 
net_write_timeout Yes Yes Yes  Yes 
new Yes Yes Yes  Yes 
no-defaults Yes     
Not_flushed_delayed_rows    YesNo 
old Yes Yes Yes No 
old-alter-table Yes Yes    
old-passwords Yes Yes   Yes 
- Variable: old_passwords   Yes  Yes 
old-style-user-limits Yes Yes    
one-thread Yes Yes    
Opened_files    YesNo 
Opened_tables    YesNo 
Open_files    YesNo 
open-files-limit Yes Yes  No 
- Variable: open_files_limit   Yes No 
Open_streams    YesNo 
Open_table_definitions    YesNo 
Open_tables    YesNo 
optimizer_prune_level Yes Yes Yes  Yes 
optimizer_search_depth Yes Yes Yes  Yes 
pid-file Yes Yes  No 
- Variable: pid_file   Yes No 
plugin_dir Yes Yes Yes No 
plugin-innodb Yes Yes    
plugin_innodb_additional_mem_pool_size Yes Yes Yes No 
plugin_innodb_autoextend_increment Yes Yes Yes  Yes 
plugin_innodb_buffer_pool_awe_mem_mb Yes Yes  No 
- Variable: innodb_buffer_pool_awe_mem_mb   Yes No 
plugin_innodb_buffer_pool_size Yes Yes Yes No 
plugin_innodb_checksums Yes Yes Yes  Yes 
plugin_innodb_commit_concurrency Yes Yes Yes  Yes 
plugin_innodb_concurrency_tickets Yes Yes Yes  Yes 
plugin_innodb_data_file_path Yes Yes Yes No 
plugin_innodb_data_home_dir Yes Yes Yes No 
plugin-innodb-doublewrite Yes Yes  No 
- Variable: plugin_innodb_doublewrite   Yes No 
plugin_innodb_fast_shutdown Yes Yes Yes No 
plugin_innodb_file_io_threads Yes Yes Yes No 
plugin_innodb_file_per_table Yes Yes Yes No 
plugin_innodb_flush_log_at_trx_commit Yes Yes Yes  Yes 
plugin_innodb_flush_method Yes Yes Yes No 
plugin_innodb_force_recovery Yes Yes Yes No 
plugin_innodb_locks_unsafe_for_binlog Yes Yes Yes No 
plugin_innodb_lock_wait_timeout Yes Yes Yes No 
plugin_innodb_log_archive Yes Yes Yes No 
plugin_innodb_log_buffer_size Yes Yes Yes No 
plugin_innodb_log_files_in_group Yes Yes Yes No 
plugin_innodb_log_file_size Yes Yes Yes No 
plugin_innodb_log_group_home_dir Yes Yes Yes No 
plugin_innodb_max_dirty_pages_pct Yes Yes Yes  Yes 
plugin_innodb_max_purge_lag Yes Yes Yes  Yes 
plugin_innodb_mirrored_log_groups Yes Yes Yes No 
plugin_innodb_open_files Yes Yes Yes No 
plugin_innodb_rollback_on_timeout Yes Yes Yes No 
plugin_innodb_stats_on_metadata Yes Yes Yes No 
plugin_innodb_status_file Yes Yes Yes No 
plugin_innodb_support_xa Yes Yes Yes  Yes 
plugin_innodb_sync_spin_loops Yes Yes Yes  Yes 
plugin_innodb_table_locks Yes Yes Yes  Yes 
plugin_innodb_thread_concurrency Yes Yes Yes  Yes 
plugin_innodb_thread_sleep_delay Yes Yes Yes  Yes 
port Yes Yes Yes No 
port-open-timeout Yes Yes    
preload_buffer_size Yes Yes Yes  Yes 
prepared_stmt_count   Yes YesNo 
print-defaults Yes     
protocol_version   Yes No 
Qcache_free_blocks    YesNo 
Qcache_free_memory    YesNo 
Qcache_hits    YesNo 
Qcache_inserts    YesNo 
Qcache_lowmem_prunes    YesNo 
Qcache_not_cached    YesNo 
Qcache_queries_in_cache    YesNo 
Qcache_total_blocks    YesNo 
query_alloc_block_size Yes Yes Yes  Yes 
query_cache_limit Yes Yes Yes  Yes 
query_cache_min_res_unit Yes Yes Yes  Yes 
query_cache_size Yes Yes Yes  Yes 
query_cache_type Yes Yes Yes  Yes 
query_cache_wlock_invalidate Yes Yes Yes  Yes 
query_prealloc_size Yes Yes Yes  Yes 
Questions    YesNo 
range_alloc_block_size Yes Yes Yes  Yes 
read_buffer_size Yes Yes Yes  Yes 
read_only Yes Yes Yes  Yes 
read_rnd_buffer_size Yes Yes Yes  Yes 
relay-log Yes Yes    
relay-log-index Yes Yes    
relay-log-info-file Yes Yes    
relay_log_purge Yes Yes Yes  Yes 
relay_log_space_limit Yes Yes Yes No 
replicate-do-db Yes Yes    
replicate-do-table Yes Yes    
replicate-ignore-db Yes Yes    
replicate-ignore-table Yes Yes    
replicate-rewrite-db Yes Yes    
replicate-same-server-id Yes Yes    
replicate-wild-do-table Yes Yes    
replicate-wild-ignore-table Yes Yes    
report-host Yes Yes  No 
- Variable: report_host   Yes No 
report-password Yes Yes  No 
- Variable: report_password   Yes No 
report-port Yes Yes  No 
- Variable: report_port   Yes No 
report-user Yes Yes  No 
- Variable: report_user   Yes No 
rpl_recovery_rank   Yes  Yes 
Rpl_status    YesNo 
safemalloc-mem-limit Yes Yes    
safe-mode Yes Yes    
safe-user-create Yes Yes    
secure-auth Yes Yes   Yes 
- Variable: secure_auth   Yes  Yes 
secure-file-priv Yes Yes  No 
- Variable: secure_file_priv   Yes No 
Select_full_join    YesNo 
Select_full_range_join    YesNo 
Select_range    YesNo 
Select_range_check    YesNo 
Select_scan    YesNo 
server-id Yes Yes   Yes 
- Variable: server_id   Yes  Yes 
shared_memory   Yes No 
shared_memory_base_name   Yes No 
show-slave-auth-info Yes Yes    
skip-character-set-client-handshake Yes Yes    
skip-concurrent-insert Yes Yes    
- Variable: concurrent_insert      
skip-external-locking Yes Yes  No 
- Variable: skip_external_locking   Yes No 
skip-grant-tables Yes Yes    
skip-host-cache Yes Yes    
skip-innodb Yes Yes    
skip-innodb-checksums Yes Yes    
skip-locking Yes Yes    
skip-log-warnings Yes     
skip-merge Yes Yes    
- Variable:       
skip-name-resolve Yes Yes    
skip-ndbcluster Yes Yes    
skip-networking Yes Yes  No 
- Variable: skip_networking   Yes No 
skip-new Yes Yes    
skip-plugin-innodb Yes Yes    
skip-plugin-innodb-checksums Yes Yes    
skip-safemalloc Yes Yes    
skip-show-database Yes Yes  No 
- Variable: skip_show_database   Yes No 
skip-slave-start Yes Yes    
skip-ssl Yes Yes    
skip-stack-trace Yes Yes    
skip-symbolic-links Yes     
skip-symlink Yes Yes    
skip-thread-priority Yes Yes    
slave-allow-batching Yes    Yes 
- Variable: slave_allow_batching   Yes  Yes 
slave_compressed_protocol Yes Yes Yes  Yes 
slave_exec_mode   Yes  Yes 
Slave_heartbeat_period    YesNo 
slave-load-tmpdir Yes Yes  No 
- Variable: slave_load_tmpdir   Yes No 
slave-net-timeout Yes Yes   Yes 
- Variable: slave_net_timeout   Yes  Yes 
Slave_open_temp_tables    YesNo 
Slave_received_heartbeats    YesNo 
Slave_retried_transactions    YesNo 
Slave_running    YesNo 
slave-skip-errors Yes Yes  No 
- Variable: slave_skip_errors   Yes No 
slave_transaction_retries Yes Yes Yes  Yes 
Slow_launch_threads    YesNo 
slow_launch_time Yes Yes Yes  Yes 
Slow_queries    YesNo 
slow-query-log Yes Yes   Yes 
- Variable: slow_query_log   Yes  Yes 
slow_query_log_file   Yes  Yes 
socket Yes Yes Yes No 
sort_buffer_size Yes Yes Yes  Yes 
Sort_merge_passes    YesNo 
Sort_range    YesNo 
Sort_rows    YesNo 
Sort_scan    YesNo 
sporadic-binlog-dump-fail Yes Yes    
sql_auto_is_null   Yes  Yes 
sql_big_selects   Yes  Yes 
sql_big_tables   Yes  Yes 
sql_buffer_result   Yes  Yes 
sql_log_bin   Yes  Yes 
sql_log_off   Yes  Yes 
sql_log_update   Yes  Yes 
sql_low_priority_updates   Yes  Yes 
sql_max_join_size   Yes  Yes 
sql-mode Yes Yes   Yes 
- Variable: sql_mode   Yes  Yes 
sql_notes   Yes  Yes 
sql_quote_show_create   Yes  Yes 
sql_safe_updates   Yes  Yes 
sql_select_limit Yes Yes Yes  Yes 
sql_slave_skip_counter   Yes  Yes 
sql_warnings   Yes  Yes 
ssl Yes Yes    
ssl-ca Yes Yes  No 
- Variable: ssl_ca   Yes No 
ssl-capath Yes Yes  No 
- Variable: ssl_capath   Yes No 
ssl-cert Yes Yes  No 
- Variable: ssl_cert   Yes No 
ssl-cipher Yes Yes  No 
- Variable: ssl_cipher   Yes No 
ssl-key Yes Yes  No 
- Variable: ssl_key   Yes No 
ssl-verify-server-cert Yes Yes    
standalone Yes Yes    
storage_engine   Yes  Yes 
symbolic-links Yes Yes    
sync-binlog Yes Yes   Yes 
- Variable: sync_binlog   Yes  Yes 
sync-frm Yes Yes   Yes 
- Variable: sync_frm   Yes  Yes 
sysdate-is-now Yes Yes    
system_time_zone   Yes No 
table_cache Yes Yes Yes  Yes 
table_definition_cache Yes Yes Yes  Yes 
Table_locks_immediate    YesNo 
Table_locks_waited    YesNo 
table_lock_wait_timeout Yes Yes Yes  Yes 
table_open_cache  Yes Yes  Yes 
table_type   Yes  Yes 
tc-heuristic-recover Yes Yes    
Tc_log_max_pages_used    YesNo 
Tc_log_page_size    YesNo 
Tc_log_page_waits    YesNo 
temp-pool Yes Yes    
thread_cache_size Yes Yes Yes  Yes 
thread_concurrency Yes Yes Yes No 
thread_handling Yes Yes Yes No 
Threads_cached    YesNo 
Threads_connected    YesNo 
Threads_created    YesNo 
Threads_running    YesNo 
thread_stack Yes Yes Yes No 
timed_mutexes Yes Yes Yes  Yes 
time_format Yes Yes Yes  Yes 
timestamp   Yes  Yes 
time_zone Yes  Yes  Yes 
tmpdir Yes Yes Yes No 
tmp_table_size Yes Yes Yes  Yes 
transaction_alloc_block_size Yes Yes Yes  Yes 
transaction_allow_batching   Yes  Yes 
transaction-isolation Yes Yes    
transaction_prealloc_size Yes Yes Yes  Yes 
tx_isolation   Yes  Yes 
unique_checks   Yes  Yes 
updatable_views_with_limit Yes Yes Yes  Yes 
Uptime    YesNo 
Uptime_since_flush_status    YesNo 
user Yes Yes    
use-symbolic-links Yes Yes    
verbose Yes     
version Yes  Yes No 
version_comment   Yes No 
version_compile_machine   Yes No 
version_compile_os   Yes No 
wait_timeout Yes Yes Yes  Yes 
warning_count   Yes No 

5.1.2. 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

    Value Set
    Typeboolean
    DefaultFALSE

    This option controls whether user-defined functions that have only an xxx symbol for the main function can be loaded. By default, the option is off and only UDFs that have at least one auxiliary symbol can be loaded; this prevents attempts at loading functions from shared object files other than those containing legitimate UDFs. See Section 31.3.4.6, “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 1.8.3, “Running MySQL in ANSI Mode”, and Section 5.1.7, “SQL Modes”.

  • --basedir=path, -b path

    Option Sets Variable Yes, 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 Variable Yes, big_tables
    Variable Namebig-tables
    Variable ScopeSession
    Dynamic Variable Yes
    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.

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

    Version Introduced5.1.5
    Option Sets Variable Yes, binlog_format
    Variable Namebinlog_format
    Variable ScopeBoth
    Dynamic Variable Yes
    Value Set
    Typeenumeration
    DefaultMIXED
    Valid ValuesROW, STATEMENT, MIXED

    Specify whether to use row-based, statement-based, or mixed replication (statement-based was the default prior to MySQL 5.1.12; beginning with MySQL 5.1.12, mixed replication is the default). See Section 19.1.2, “Replication Formats”. This option was added in MySQL 5.1.5.

  • --binlog-row-event-max-size=N

    Version Introduced5.1.5
    Value Set
    Typenumeric
    Default1024
    Min Value256

    Specify the maximum size of a row-based binary log event, in bytes. Rows are grouped into events smaller than this size if possible. The value should be a multiple of 256. The default is 1024. See Section 19.1.2, “Replication Formats”. This option was added in MySQL 5.1.5.

  • --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 2.9.2, “Typical configure Options”.

  • --character-sets-dir=path

    Option Sets Variable Yes, 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 Introduced5.1.6
    Option Sets Variable Yes, character_set_filesystem
    Variable Namecharacter_set_filesystem
    Variable ScopeBoth
    Dynamic Variable Yes
    Value Set
    Typestring

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

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

    Option Sets Variable Yes, character_set_server
    Variable Namecharacter_set_server
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, collation_server
    Variable Namecollation_server
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, 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 Variable Yes, 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 Variable Yes
    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 5.1.12, using --with-debug to configure MySQL with debugging support enables you to use the --debug="d,parser_debug" option when you start the server. This causes the Bison parser that is used to process SQL statements to dump a parser trace to the server's standard error output. Typically, this output is written to the error log.

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

  • --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 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 Variable Yes, delay_key_write
    Variable Namedelay-key-write
    Variable ScopeGlobal
    Dynamic Variable Yes
    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 13.4.1, “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.

  • --disconnect-slave-event-count

    Value Set
    Typenumeric
    Default0

    This option is used internally by the MySQL test suite for replication testing and debugging.

  • --enable-named-pipe

    Platform Specificwindows

    Enable support for named pipes. This option applies only on Windows NT, 2000, XP, and 2003 systems. For MySQL 5.1.20 and earler, this option is available only when using the mysqld-nt and mysqld-debug servers that support named-pipe connections. For MySQL 5.1.21 and later, mysqld-nt is not available, but support is included in the standard mysqld and mysqld-debug servers.

  • --enable-pstack

    Value Set
    Typeboolean
    DefaultFALSE

    Print a symbolic stack trace on failure.

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

    Option Sets Variable Yes, engine_condition_pushdown
    Variable Nameengine_condition_pushdown
    Variable ScopeBoth
    Dynamic Variable Yes
    Value Set (>= 5.1.0)
    Typeboolean
    DefaultON

    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 5.1, 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”.

  • --event-scheduler[=value]

    Version Introduced5.1.6
    Option Sets Variable Yes, event-scheduler
    Variable Nameevent_scheduler
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typeenumeration
    DefaultOFF
    Valid ValuesON, OFF, DISABLED

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

    For detailed information, see The event-scheduler Option.

  • --exit-info[=flags], -T [flags]

    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 Variable Yes, 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 Variable Yes
    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.

  • --general-log[={0|1}]

    Version Introduced5.1.12
    Option Sets Variable Yes, general_log
    Variable Namegeneral_log
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typeboolean
    DefaultOFF

    Specify the initial general log state, if the --log or -l option is given. With no argument or an argument of 0, the --general-log option disables the log. If omitted or given with an argument of 1, the option enables the log. If --log or -l is not specified, --general-log has no effect. This option was added in MySQL 5.1.12.

  • --init-file=file_name

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

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

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

  • --innodb-xxx

    The InnoDB options are listed in Section 13.5.4, “InnoDB Startup Options and System Variables”.

  • --language=lang_name, -L lang_name

    Option Sets Variable Yes, 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

    Option Sets Variable Yes, 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.

  • --log[=file_name], -l [file_name]

    Option Sets Variable Yes, log
    Variable Namelog
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typestring
    DefaultOFF

    This option enables logging to the general query log, which contains entries that record client connections and SQL statements received from clients. The log output destination can be selected with the --log-output option as of MySQL 5.1.6. Before 5.1.6, logging occurs to the general query log file. If you omit the filename, MySQL uses host_name.log as the filename. See Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”, and Section 5.2.3, “The General Query Log”.

  • --log-bin[=base_name]

    Value Set
    Typefilename

    Enable binary logging. The server logs all statements that change data to the binary log, which is used for backup and replication. See Section 5.2.4, “The Binary Log”.

    The option value, if given, is the basename for the log sequence. The server creates binary log files in sequence by adding a numeric suffix to the basename. It is recommended that you specify a basename (see Section B.1.8.1, “Open Issues in MySQL”, for the reason). Otherwise, MySQL uses host_name-bin as the basename.

  • --log-bin-index[=file_name]

    Value Set
    Typefilename

    The index file for binary log filenames. See Section 5.2.4, “The Binary Log”. If you omit the filename, and if you didn't specify one with --log-bin, MySQL uses host_name-bin.index as the filename.

  • --log-bin-trust-function-creators[={0|1}]

    Option Sets Variable Yes, log_bin_trust_function_creators
    Variable Namelog_bin_trust_function_creators
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typeboolean
    DefaultFALSE

    With no argument or an argument of 1, this option sets the log_bin_trust_function_creators system variable to 1. With an argument of 0, this option sets the system variable to 0. log_bin_trust_function_creators affects how MySQL enforces restrictions on stored function and trigger creation. See Section 23.4, “Binary Logging of Stored Routines and Triggers”.

  • --log-error[=file_name]

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

    Log errors and startup messages to this file. See Section 5.2.2, “The Error Log”. If you omit the 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 binary 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-output[=value,...]

    Version Introduced5.1.6
    Option Sets Variable Yes, log_output
    Variable Namelog_output
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typeenumeration
    DefaultFILE
    Valid ValuesTABLE, FILE, NONE

    This option determines the destination for general query log and slow query log output. The option value can be given as one or more of the words TABLE, FILE, or NONE. If the option is given without a value, the default is FILE. (For MySQL 5.1.6 through 5.1.20, the default is TABLE.) TABLE select logging to the general_log and slow_log tables in the mysql database as a destination. FILE selects logging to log files as a destination. (For FILE logging, the --log and -slow-log options determine the log file location.) NONE disables logging. If NONE is present in the option value, it takes precedence over any other words that are present. TABLE and FILE can both be given to select to both log output destinations.

    This option selects log output destinations, but does not enable log output. To do that, use the --log and --log-slow-queries options. For more information, see Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”.

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

  • --log-queries-not-using-indexes

    Option Sets Variable Yes, log_queries_not_using_indexes
    Variable Namelog_queries_not_using_indexes
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typeboolean

    If you are using this option with --log-slow-queries, queries that do not use indexes are logged to the slow query log. See Section 5.2.5, “The Slow Query Log”.

  • --log-short-format

    Value Set
    Typeboolean
    DefaultFALSE

    Log less information to the binary 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 Variable Yes, log_slow_queries
    Variable Namelog_slow_queries
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typeboolean

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

    The log output destination can be selected with the --log-output option as of MySQL 5.1.6. Before 5.1.6, logging occurs to the slow query log file. If you omit the filename, MySQL uses host_name-slow.log as the filename. See Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”, and Section 5.2.5, “The Slow Query Log”.

  • --log-slow-slave-statements

    Version Introduced5.1.21
    Value Set
    Typeboolean
    Defaultoff

    When the slow query log is enabled, this option enables logging for queries that have taken more than long_query_time seconds to execute on the slave.

    This option was added in MySQL 5.1.21.

  • --log-tc=file_name

    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.

  • --log-tc-size=size

    Value Set
    Typenumeric
    Default24576
    Max Value4294967295

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

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

    Option Sets Variable Yes, log-warnings
    Variable Namelog_warnings
    Variable ScopeBoth
    Dynamic Variable Yes
    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”.

  • --low-priority-updates

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

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

  • --min-examined-row-limit=number

    Version Introduced5.1.21
    Variable Namemin_examined_row_limit
    Variable ScopeBoth
    Dynamic Variable Yes
    Value Set
    Typenumeric
    Default0
    Range0-4294967295

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

    This option was introduced in MySQL 5.1.21.

  • --max-binlog-dump-events

    Value Set
    Typenumeric
    Default0

    This option is used internally by the MySQL test suite for replication testing and debugging.

  • --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 13.4.1, “MyISAM Startup Options”.

  • --old-passwords

    Option Sets Variable Yes, old_passwords
    Variable Nameold_passwords
    Variable ScopeBoth
    Dynamic Variable Yes
    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

    Value Set
    Typeboolean
    DefaultFALSE

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

  • --one-thread

    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.

    As of MySQL 5.1.17, this option is deprecated; use --thread_handling=one-thread instead.

  • --open-files-limit=count

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

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

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

  • --pid-file=path

    Option Sets Variable Yes, 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 Variable Yes, 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 Introduced5.1.5
    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 5.1.5.

  • --safe-mode

    Deprecated5.0

    Skip some optimization stages.

  • --safe-show-database (DEPRECATED)

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

    See Section 5.4.3, “Privileges Provided by MySQL”.

  • --safe-user-create

    Option Sets Variable Yes, 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 Variable Yes, secure_auth
    Variable Namesecure_auth
    Variable ScopeGlobal
    Dynamic Variable Yes
    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 Introduced5.1.17
    Option Sets Variable Yes, 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 5.1.17.

  • --shared-memory

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

  • --shared-memory-base-name=name

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

  • --skip-concurrent-insert

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

  • --skip-external-locking

    Do not use external locking (system locking). For more information about external locking, including conditions under which it can and cannot be used, see Section 7.3.4, “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 plugins and user-defined functions (UDFs). Beginning with MySQL 5.1.17, it also suppresses loading of scheduled events (Bug#28607).

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

  • --skip-host-cache

    Do not use the internal 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-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”.

  • --sporadic-binlog-dump-fail

    Value Set
    Typeboolean
    DefaultFALSE

    This option is used internally by the MySQL test suite for replication testing and debugging.

  • --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

    Available on Windows NT-based systems only; 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 Variable Yes, 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

    Disable using thread priorities for faster response time.

  • --slow-query-log[={0|1}]

    Version Introduced5.1.12
    Option Sets Variable Yes, slow_query_log
    Variable Nameslow_query_log
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typeboolean
    DefaultOFF

    Specify the initial slow query log state, if the --log-slow-queries option is given. With no argument or an argument of 0, the --slow-query-log option disables the log. If omitted or given with an argument of 1, the option enables the log. If --log or -l is not specified, --slow-query-log has no effect. This option was added in MySQL 5.1.12.

  • --socket=path

    Option Sets Variable Yes, socket
    Variable Namesocket
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typelinuxfilename
    Default/tmp/mysql.sock 
    Value Set
    Typehpuxfilename
    Default/tmp/mysql.sock 
    Value Set
    Typesolarisfilename
    Default/tmp/mysql.sock 
    Value Set
    Typemacosxfilename
    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 Variable Yes, sql_mode
    Variable Namesql_mode
    Variable ScopeBoth
    Dynamic Variable Yes
    Value Set
    Typeenumeration
    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, “SQL Modes”.

  • --sysdate-is-now

    Version Introduced5.1.8
    Value Set
    Typeboolean
    DefaultFALSE

    SYSDATE() by default returns the time at which it executes, not the time at which the statement in which it occurs begins executing. This differs from the behavior of NOW(). This option causes SYSDATE() to be an alias for NOW(). For information about the implications for binary logging and replication, see the description for SYSDATE() in Section 11.6, “Date and Time Functions” and for SET TIMESTAMP in Section 12.5.3, “SET Syntax”.

    This option was added in MySQL 5.1.8.

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

    Value Set
    Typeenumeration
    Valid ValuesCOMMIT, RECOVER

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

  • --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-UNCOMMTTED, 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 Variable Yes, 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

    Display version information and exit.

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

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

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

You can change the values of most system variables for a running server with the SET statement. See Section 12.5.3, “SET Syntax”.

Section 5.1.3, “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. System Variables

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

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

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

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

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

This section provides a description of each system variable. Variables with no version indicated are present in all MySQL 5.1 releases. For historical information concerning their implementation, please see MySQL 5.0 Reference Manual and MySQL 3.23, 4.0, 4.1 Reference Manual.

The following table lists all available system variables:

NameCmd-LineOption fileSystem VarVar ScopeDynamic
autocommit   YesSession Yes
auto-increment-increment Yes Yes   Yes
- Variable: auto_increment_increment   YesBoth Yes
auto-increment-offset Yes Yes   Yes
- Variable: auto_increment_offset   YesBoth Yes
automatic_sp_privileges   YesGlobal Yes
back_log Yes Yes YesGlobalNo
basedir Yes Yes YesGlobalNo
big-tables Yes Yes   Yes
- Variable: big_tables   YesSession Yes
binlog_cache_size Yes Yes YesGlobal Yes
binlog-format Yes Yes   Yes
- Variable: binlog_format   YesBoth Yes
bulk_insert_buffer_size Yes Yes YesBoth Yes
character_set_client   YesBoth Yes
character_set_connection   YesBoth Yes
character_set_database   YesBoth Yes
character-set-filesystem Yes Yes   Yes
- Variable: character_set_filesystem   YesBoth Yes
character_set_results   YesBoth Yes
character-sets-dir Yes Yes  No
- Variable: character_sets_dir   YesGlobalNo
character-set-server Yes Yes   Yes
- Variable: character_set_server   YesBoth Yes
character_set_system   YesGlobalNo
collation_connection   YesBoth Yes
collation_database   YesBoth Yes
collation-server Yes Yes   Yes
- Variable: collation_server   YesBoth Yes
completion_type Yes Yes YesBoth Yes
concurrent_insert Yes Yes YesGlobal Yes
connect_timeout Yes Yes YesGlobal Yes
datadir Yes Yes YesGlobalNo
date_format   YesBoth Yes
datetime_format Yes Yes YesBoth Yes
debug Yes Yes YesBoth Yes
default_week_format Yes Yes YesBoth Yes
delayed_insert_limit Yes Yes YesGlobal Yes
delayed_insert_timeout Yes Yes YesGlobal Yes
delayed_queue_size Yes Yes YesGlobal Yes
delay-key-write Yes Yes   Yes
- Variable: delay_key_write   YesGlobal Yes
div_precision_increment Yes Yes YesBoth Yes
engine-condition-pushdown Yes Yes   Yes
- Variable: engine_condition_pushdown   YesBoth Yes
error_count   YesSessionNo
event-scheduler Yes Yes YesGlobal Yes
expire_logs_days Yes Yes YesGlobal Yes
flush Yes Yes YesGlobal Yes
flush_time Yes Yes YesGlobal Yes
foreign_key_checks   YesSession Yes
ft_boolean_syntax Yes Yes YesGlobal Yes
ft_max_word_len Yes Yes YesGlobalNo
ft_min_word_len Yes Yes YesGlobalNo
ft_query_expansion_limit Yes Yes YesGlobalNo
ft_stopword_file Yes Yes YesGlobalNo
general-log Yes Yes   Yes
- Variable: general_log   YesGlobal Yes
general_log_file   YesGlobal Yes
group_concat_max_len Yes Yes YesBoth Yes
have_archive   YesGlobalNo
have_blackhole_engine   YesGlobalNo
have_compress   YesGlobalNo
have_crypt   YesGlobalNo
have_csv   YesGlobalNo
have_dynamic_loading   YesGlobalNo
have_example_engine   YesGlobalNo
have_federated_engine   YesGlobalNo
have_geometry   YesGlobalNo
have_innodb   YesGlobalNo
have_isam   YesGlobalNo
have_merge_engine   YesGlobalNo
have_ndbcluster   YesGlobalNo
have_openssl   YesGlobalNo
have_partitioning   YesGlobalNo
have_query_cache   YesGlobalNo
have_raid   YesGlobalNo
have_row_based_replication   YesGlobalNo
have_rtree_keys   YesGlobalNo
have_ssl   YesGlobalNo
have_symlink   YesGlobalNo
hostname   YesGlobalNo
identity   YesSession Yes
init_connect Yes Yes YesGlobal Yes
init-file Yes Yes  No
- Variable: init_file   YesGlobalNo
init_slave Yes Yes YesGlobal Yes
innodb_adaptive_hash_index Yes Yes YesGlobalNo
innodb_additional_mem_pool_size Yes Yes YesGlobalNo
innodb_autoextend_increment Yes Yes YesGlobal Yes
innodb_autoinc_lock_mode Yes Yes YesGlobalNo
innodb_buffer_pool_awe_mem_mb Yes Yes YesGlobalNo
innodb_buffer_pool_size Yes Yes YesGlobalNo
innodb_checksums Yes Yes YesGlobalNo
innodb_commit_concurrency Yes Yes YesGlobal Yes
innodb_concurrency_tickets Yes Yes YesGlobal Yes
innodb_data_file_path Yes Yes YesGlobalNo
innodb_data_home_dir Yes Yes YesGlobalNo
innodb_doublewrite Yes Yes YesGlobalNo
innodb_fast_shutdown Yes Yes YesGlobal Yes
innodb_file_io_threads Yes Yes YesGlobalNo
innodb_file_per_table Yes Yes YesGlobalNo
innodb_flush_log_at_trx_commit Yes Yes YesGlobal Yes
innodb_flush_method Yes Yes YesGlobalNo
innodb_force_recovery Yes Yes YesGlobalNo
innodb_locks_unsafe_for_binlog Yes Yes YesGlobalNo
innodb_lock_wait_timeout Yes Yes YesGlobalNo
innodb_log_arch_dir Yes Yes YesGlobalNo
innodb_log_archive Yes Yes YesGlobalNo
innodb_log_buffer_size Yes Yes YesGlobalNo
innodb_log_files_in_group Yes Yes YesGlobalNo
innodb_log_file_size Yes Yes YesGlobalNo
innodb_log_group_home_dir Yes Yes YesGlobalNo
innodb_max_dirty_pages_pct Yes Yes YesGlobal Yes
innodb_max_purge_lag Yes Yes YesGlobal Yes
innodb_mirrored_log_groups Yes Yes YesGlobalNo
innodb_open_files Yes Yes YesGlobalNo
innodb_rollback_on_timeout Yes Yes YesGlobalNo
innodb_stats_on_metadata Yes Yes YesGlobalNo
innodb_status_file Yes Yes YesGlobalNo
innodb_support_xa Yes Yes YesBoth Yes
innodb_sync_spin_loops Yes Yes YesGlobal Yes
innodb_table_locks Yes Yes YesBoth Yes
innodb_thread_concurrency Yes Yes YesGlobal Yes
innodb_thread_sleep_delay Yes Yes YesGlobal Yes
insert_id   YesSession Yes
interactive_timeout Yes Yes YesBoth Yes
join_buffer_size Yes Yes YesBoth Yes
keep_files_on_create Yes Yes YesBoth Yes
key_buffer_size Yes Yes YesGlobal Yes
key_cache_age_threshold Yes Yes YesGlobal Yes
key_cache_block_size Yes Yes YesGlobal Yes
key_cache_division_limit Yes Yes YesGlobal Yes
language Yes Yes YesGlobalNo
large-pages Yes Yes  No
- Variable: large_pages   YesGlobalNo
large_page_size   YesGlobalNo
last_insert_id   YesSession Yes
lc_time_names   YesBoth Yes
license   YesGlobalNo
local_infile   YesGlobal Yes
locked_in_memory   YesGlobalNo
log Yes Yes YesGlobal Yes
log_bin   YesGlobalNo
log-bin-trust-function-creators Yes Yes   Yes
- Variable: log_bin_trust_function_creators   YesGlobal Yes
log-bin-trust-routine-creators Yes Yes   Yes
- Variable: log_bin_trust_routine_creators   YesGlobal Yes
log-error Yes Yes  No
- Variable: log_error   YesGlobalNo
log-output Yes Yes   Yes
- Variable: log_output   YesGlobal Yes
log-queries-not-using-indexes Yes Yes   Yes
- Variable: log_queries_not_using_indexes   YesGlobal Yes
log-slave-updates Yes Yes  No
- Variable: log_slave_updates   YesGlobalNo
log-slow-queries Yes Yes   Yes
- Variable: log_slow_queries   YesGlobal Yes
log-warnings Yes Yes   Yes
- Variable: log_warnings   YesBoth Yes
long_query_time Yes Yes YesBoth Yes
lower_case_file_system Yes Yes YesGlobalNo
lower_case_table_names Yes Yes YesGlobalNo
low-priority-updates Yes Yes   Yes
- Variable: low_priority_updates   YesBoth Yes
master-bind Yes Yes Yes No
max_allowed_packet Yes Yes YesBoth Yes
max_binlog_cache_size Yes Yes YesGlobal Yes
max_binlog_size Yes Yes YesGlobal Yes
max_connect_errors Yes Yes YesGlobal Yes
max_connections Yes Yes YesGlobal Yes
max_delayed_threads Yes Yes YesBoth Yes
max_error_count Yes Yes YesBoth Yes
max_heap_table_size Yes Yes YesBoth Yes
max_insert_delayed_threads   YesBoth Yes
max_join_size Yes Yes YesBoth Yes
max_length_for_sort_data Yes Yes YesBoth Yes
max_prepared_stmt_count Yes Yes YesGlobal Yes
max_relay_log_size Yes Yes YesGlobal Yes
max_seeks_for_key Yes Yes YesBoth Yes
max_sort_length Yes Yes YesBoth Yes
max_sp_recursion_depth Yes Yes YesBoth Yes
max_tmp_tables Yes Yes YesBoth Yes
max_user_connections Yes Yes YesBoth Yes
max_write_lock_count Yes Yes YesGlobal Yes
memlock Yes Yes YesGlobalNo
min-examined-row-limit Yes Yes YesBoth Yes
multi_range_count Yes Yes YesBoth Yes
myisam_block_size Yes Yes YesBoth Yes
myisam_data_pointer_size Yes Yes YesGlobal Yes
myisam_max_sort_file_size Yes Yes YesGlobal Yes
myisam_recover_options   YesGlobalNo
myisam_repair_threads Yes Yes YesBoth Yes
myisam_sort_buffer_size Yes Yes YesBoth Yes
myisam_stats_method Yes Yes YesBoth Yes
myisam_use_mmap Yes Yes YesGlobal Yes
named_pipe   YesGlobalNo
ndb_autoincrement_prefetch_sz Yes Yes YesBoth Yes
ndb_cache_check_time Yes Yes YesGlobal Yes
ndbcluster Yes Yes YesBoth Yes
ndb_extra_logging Yes Yes YesGlobal Yes
ndb_force_send Yes Yes YesBoth Yes
ndb_log_orig   YesGlobalNo
ndb_log_update_as_write Yes Yes YesGlobal Yes
ndb_log_updated_only Yes Yes YesGlobal Yes
ndb_optimization_delay   YesGlobal Yes
ndb_table_no_logging   YesSession Yes
ndb_table_temporary   YesSession Yes
ndb_use_copying_alter_table   YesBothNo
ndb_use_exact_count   YesBoth Yes
ndb_wait_connected Yes Yes Yes No
net_buffer_length Yes Yes YesBoth Yes
net_read_timeout Yes Yes YesBoth Yes
net_retry_count Yes Yes YesBoth Yes
net_write_timeout Yes Yes YesBoth Yes
new Yes Yes YesBoth Yes
old Yes Yes YesGlobalNo
old-passwords Yes Yes   Yes
- Variable: old_passwords   YesBoth Yes
open-files-limit Yes Yes  No
- Variable: open_files_limit   YesGlobalNo
optimizer_prune_level Yes Yes YesBoth Yes
optimizer_search_depth Yes Yes YesBoth Yes
pid-file Yes Yes  No
- Variable: pid_file   YesGlobalNo
plugin_dir Yes Yes YesGlobalNo
plugin_innodb_additional_mem_pool_size Yes Yes YesBothNo
plugin_innodb_autoextend_increment Yes Yes YesBoth Yes
plugin_innodb_buffer_pool_awe_mem_mb Yes Yes  No
- Variable: innodb_buffer_pool_awe_mem_mb   YesBothNo
plugin_innodb_buffer_pool_size Yes Yes YesBothNo
plugin_innodb_checksums Yes Yes YesBoth Yes
plugin_innodb_commit_concurrency Yes Yes YesGlobal Yes
plugin_innodb_concurrency_tickets Yes Yes YesGlobal Yes
plugin_innodb_data_file_path Yes Yes YesGlobalNo
plugin_innodb_data_home_dir Yes Yes YesGlobalNo
plugin-innodb-doublewrite Yes Yes  No
- Variable: plugin_innodb_doublewrite   YesGlobalNo
plugin_innodb_fast_shutdown Yes Yes YesGlobalNo
plugin_innodb_file_io_threads Yes Yes YesGlobalNo
plugin_innodb_file_per_table Yes Yes YesGlobalNo
plugin_innodb_flush_log_at_trx_commit Yes Yes YesGlobal Yes
plugin_innodb_flush_method Yes Yes YesGlobalNo
plugin_innodb_force_recovery Yes Yes YesGlobalNo
plugin_innodb_locks_unsafe_for_binlog Yes Yes YesGlobalNo
plugin_innodb_lock_wait_timeout Yes Yes YesGlobalNo
plugin_innodb_log_archive Yes Yes YesGlobalNo
plugin_innodb_log_buffer_size Yes Yes YesGlobalNo
plugin_innodb_log_files_in_group Yes Yes YesGlobalNo
plugin_innodb_log_file_size Yes Yes YesGlobalNo
plugin_innodb_log_group_home_dir Yes Yes YesGlobalNo
plugin_innodb_max_dirty_pages_pct Yes Yes YesGlobal Yes
plugin_innodb_max_purge_lag Yes Yes YesGlobal Yes
plugin_innodb_mirrored_log_groups Yes Yes YesGlobalNo
plugin_innodb_open_files Yes Yes YesGlobalNo
plugin_innodb_rollback_on_timeout Yes Yes Yes No
plugin_innodb_stats_on_metadata Yes Yes Yes No
plugin_innodb_status_file Yes Yes Yes No
plugin_innodb_support_xa Yes Yes YesBoth Yes
plugin_innodb_sync_spin_loops Yes Yes YesGlobal Yes
plugin_innodb_table_locks Yes Yes YesBoth Yes
plugin_innodb_thread_concurrency Yes Yes YesGlobal Yes
plugin_innodb_thread_sleep_delay Yes Yes YesGlobal Yes
port Yes Yes YesGlobalNo
preload_buffer_size Yes Yes YesBoth Yes
prepared_stmt_count   YesGlobalNo
protocol_version   YesGlobalNo
query_alloc_block_size Yes Yes YesBoth Yes
query_cache_limit Yes Yes YesGlobal Yes
query_cache_min_res_unit Yes Yes YesGlobal Yes
query_cache_size Yes Yes YesGlobal Yes
query_cache_type Yes Yes YesBoth Yes
query_cache_wlock_invalidate Yes Yes YesBoth Yes
query_prealloc_size Yes Yes YesBoth Yes
range_alloc_block_size Yes Yes YesBoth Yes
read_buffer_size Yes Yes YesBoth Yes
read_only Yes Yes YesGlobal Yes
read_rnd_buffer_size Yes Yes YesBoth Yes
relay_log_purge Yes Yes YesGlobal Yes
relay_log_space_limit Yes Yes YesGlobalNo
report-host Yes Yes  No
- Variable: report_host   YesGlobalNo
report-password Yes Yes  No
- Variable: report_password   YesGlobalNo
report-port Yes Yes  No
- Variable: report_port   YesGlobalNo
report-user Yes Yes  No
- Variable: report_user   YesGlobalNo
rpl_recovery_rank   YesGlobal Yes
secure-auth Yes Yes   Yes
- Variable: secure_auth   YesGlobal Yes
secure-file-priv Yes Yes  No
- Variable: secure_file_priv   YesGlobalNo
server-id Yes Yes   Yes
- Variable: server_id   YesGlobal Yes
shared_memory   YesGlobalNo
shared_memory_base_name   YesGlobalNo
skip-external-locking Yes Yes  No
- Variable: skip_external_locking   YesGlobalNo
skip-networking Yes Yes  No
- Variable: skip_networking   YesGlobalNo
skip-show-database Yes Yes  No
- Variable: skip_show_database   YesGlobalNo
slave-allow-batching Yes    Yes
- Variable: slave_allow_batching   YesGlobal Yes
slave_compressed_protocol Yes Yes YesGlobal Yes
slave_exec_mode   YesGlobal Yes
slave-load-tmpdir Yes Yes  No
- Variable: slave_load_tmpdir   YesGlobalNo
slave-net-timeout Yes Yes   Yes
- Variable: slave_net_timeout   YesGlobal Yes
slave-skip-errors Yes Yes  No
- Variable: slave_skip_errors   YesGlobalNo
slave_transaction_retries Yes Yes YesGlobal Yes
slow_launch_time Yes Yes YesGlobal Yes
slow-query-log Yes Yes   Yes
- Variable: slow_query_log   YesGlobal Yes
slow_query_log_file   YesGlobal Yes
socket Yes Yes YesGlobalNo
sort_buffer_size Yes Yes YesBoth Yes
sql_auto_is_null   YesSession Yes
sql_big_selects   YesSession Yes
sql_big_tables   YesSession Yes
sql_buffer_result   YesSession Yes
sql_log_bin   YesSession Yes
sql_log_off   YesSession Yes
sql_log_update   YesSession Yes
sql_low_priority_updates   YesBoth Yes
sql_max_join_size   YesBoth Yes
sql-mode Yes Yes   Yes
- Variable: sql_mode   YesBoth Yes
sql_notes   YesSession Yes
sql_quote_show_create   YesSession Yes
sql_safe_updates   YesSession Yes
sql_select_limit Yes Yes YesBoth Yes
sql_slave_skip_counter   YesGlobal Yes
sql_warnings   YesSession Yes
ssl-ca Yes Yes  No
- Variable: ssl_ca   YesGlobalNo
ssl-capath Yes Yes  No
- Variable: ssl_capath   YesGlobalNo
ssl-cert Yes Yes  No
- Variable: ssl_cert   YesGlobalNo
ssl-cipher Yes Yes  No
- Variable: ssl_cipher   YesGlobalNo
ssl-key Yes Yes  No
- Variable: ssl_key   YesGlobalNo
storage_engine   YesBoth Yes
sync-binlog Yes Yes   Yes
- Variable: sync_binlog   YesGlobal Yes
sync-frm Yes Yes   Yes
- Variable: sync_frm   YesGlobal Yes
system_time_zone   YesGlobalNo
table_cache Yes Yes YesGlobal Yes
table_definition_cache Yes Yes YesGlobal Yes
table_lock_wait_timeout Yes Yes YesGlobal Yes
table_open_cache  Yes YesGlobal Yes
table_type   YesBoth Yes
thread_cache_size Yes Yes YesGlobal Yes
thread_concurrency Yes Yes YesGlobalNo
thread_handling Yes Yes YesGlobalNo
thread_stack Yes Yes YesGlobalNo
timed_mutexes Yes Yes YesGlobal Yes
time_format Yes Yes YesBoth Yes
timestamp   YesSession Yes
time_zone Yes  YesBoth Yes
tmpdir Yes Yes YesGlobalNo
tmp_table_size Yes Yes YesBoth Yes
transaction_alloc_block_size Yes Yes YesBoth Yes
transaction_allow_batching   YesSession Yes
transaction_prealloc_size Yes Yes YesBoth Yes
tx_isolation   YesBoth Yes
unique_checks   YesSession Yes
updatable_views_with_limit Yes Yes YesBoth Yes
version Yes  YesGlobalNo
version_comment   YesGlobalNo
version_compile_machine   YesGlobalNo
version_compile_os   YesGlobalNo
wait_timeout Yes Yes YesBoth Yes
warning_count   YesSessionNo

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.

  • auto_increment_increment

    Option Sets Variable Yes, auto_increment_increment
    Variable Nameauto_increment_increment
    Variable ScopeBoth
    Dynamic Variable Yes
    Value Set
    Typenumeric
    Default1
    Range1-65535

    auto_increment_increment and auto_increment_offset are intended for use with master-to-master replication, and can be used to control the operation of AUTO_INCREMENT columns. Both variables have global and session values, and each can assume an integer value between 1 and 65,535 inclusive. Setting the value of either of these two variables to 0 causes its value to be set to 1 instead. Attempting to set the value of either of these two variables to an integer greater than 65,535 or less than 0 causes its value to be set to 65,535 instead. Attempting to set the value of auto_increment_increment or auto_increment_offset to a non-integer value gives rise to an error, and the actual value of the variable remains unchanged.

    Important

    auto_increment_increment and auto_increment_offset are not intended for use with MySQL Cluster replication. Attempting to set them in a Cluster replication scenario may give rise to unpredictable (and unrecoverable) errors. The use of these variables with Cluster replication is therefore not supported.

    These two variables affect AUTO_INCREMENT column behavior as follows:

    • auto_increment_increment controls the interval between successive column values. For example:

      mysql> SHOW VARIABLES LIKE 'auto_inc%';
      +--------------------------+-------+
      | Variable_name            | Value |
      +--------------------------+-------+
      | auto_increment_increment | 1     |
      | auto_increment_offset    | 1     |
      +--------------------------+-------+
      2 rows in set (0.00 sec)
      
      mysql> CREATE TABLE autoinc1
          -> (col INT NOT NULL AUTO_INCREMENT PRIMARY KEY);
        Query OK, 0 rows affected (0.04 sec)
      
      mysql> SET @@auto_increment_increment=10;
      Query OK, 0 rows affected (0.00 sec)
      
      mysql> SHOW VARIABLES LIKE 'auto_inc%';
      +--------------------------+-------+
      | Variable_name            | Value |
      +--------------------------+-------+
      | auto_increment_increment | 10    |
      | auto_increment_offset    | 1     |
      +--------------------------+-------+
      2 rows in set (0.01 sec)
      
      mysql> INSERT INTO autoinc1 VALUES (NULL), (NULL), (NULL), (NULL);
      Query OK, 4 rows affected (0.00 sec)
      Records: 4  Duplicates: 0  Warnings: 0
      
      mysql> SELECT col FROM autoinc1;
      +-----+
      | col |
      +-----+
      |   1 |
      |  11 |
      |  21 |
      |  31 |
      +-----+
      4 rows in set (0.00 sec)
      

      (Note how SHOW VARIABLES is used here to obtain the current values for these variables.)

    • auto_increment_offset determines the starting point for the AUTO_INCREMENT column value. Consider the following, assuming that these statements are executed during the same session as the example given in the description for auto_increment_increment:

      mysql> SET @@auto_increment_offset=5;
      Query OK, 0 rows affected (0.00 sec)
      
      mysql> SHOW VARIABLES LIKE 'auto_inc%';
      +--------------------------+-------+
      | Variable_name            | Value |
      +--------------------------+-------+
      | auto_increment_increment | 10    |
      | auto_increment_offset    | 5     |
      +--------------------------+-------+
      2 rows in set (0.00 sec)
      
      mysql> CREATE TABLE autoinc2
          -> (col INT NOT NULL AUTO_INCREMENT PRIMARY KEY);
      Query OK, 0 rows affected (0.06 sec)
      
      mysql> INSERT INTO autoinc2 VALUES (NULL), (NULL), (NULL), (NULL);
      Query OK, 4 rows affected (0.00 sec)
      Records: 4  Duplicates: 0  Warnings: 0
      
      mysql> SELECT col FROM autoinc2;
      +-----+
      | col |
      +-----+
      |   5 |
      |  15 |
      |  25 |
      |  35 |
      +-----+
      4 rows in set (0.02 sec)
      

      If the value of auto_increment_offset is greater than that of auto_increment_increment, the value of auto_increment_offset is ignored.

    Should one or both of these variables be changed and then new rows inserted into a table containing an AUTO_INCREMENT column, the results may seem counterintuitive because the series of AUTO_INCREMENT values is calculated without regard to any values already present in the column, and the next value inserted is the least value in the series that is greater than the maximum existing value in the AUTO_INCREMENT column. In other words, the series is calculated like so:

    auto_increment_offset + N × auto_increment_increment

    where N is a positive integer value in the series [1, 2, 3, ...]. For example:

    mysql> SHOW VARIABLES LIKE 'auto_inc%';
    +--------------------------+-------+
    | Variable_name            | Value |
    +--------------------------+-------+
    | auto_increment_increment | 10    |
    | auto_increment_offset    | 5     |
    +--------------------------+-------+
    2 rows in set (0.00 sec)
    
    mysql> SELECT col FROM autoinc1;
    +-----+
    | col |
    +-----+
    |   1 |
    |  11 |
    |  21 |
    |  31 |
    +-----+
    4 rows in set (0.00 sec)
    
    mysql> INSERT INTO autoinc1 VALUES (NULL), (NULL), (NULL), (NULL);
    Query OK, 4 rows affected (0.00 sec)
    Records: 4  Duplicates: 0  Warnings: 0
    
    mysql> SELECT col FROM autoinc1;
    +-----+
    | col |
    +-----+
    |   1 |
    |  11 |
    |  21 |
    |  31 |
    |  35 |
    |  45 |
    |  55 |
    |  65 |
    +-----+
    8 rows in set (0.00 sec)
    

    The values shown for auto_increment_increment and auto_increment_offset generate the series 5 + N × 10, that is, [5, 15, 25, 35, 45, ...]. The greatest value present in the col column prior to the INSERT is 31, and the next available value in the AUTO_INCREMENT series is 35, so the inserted values for col begin at that point and the results are as shown for the SELECT query.

    It is not possible to confine the effects of these two variables to a single table, and thus they do not take the place of the sequences offered by some other database management systems; these variables control the behavior of all AUTO_INCREMENT columns in all tables on the MySQL server. If the global value of either variable is set, its effects persist until the global value is changed or overridden by setting the session value, or until mysqld is restarted. If the local value is set, the new value affects AUTO_INCREMENT columns for all tables into which new rows are inserted by the current user for the duration of the session, unless the values are changed during that session.

    The default value of auto_increment_increment is 1. See Auto-Increment in Multiple-Master Replication.

    auto_increment_increment is supported for use with NDB tables beginning with MySQL 5.1.20. Previously, setting it when using MySQL Cluster tables or MySQL Cluster Replication produced unpredictable results.

  • auto_increment_offset

    Option Sets Variable Yes, auto_increment_offset
    Variable Nameauto_increment_offset
    Variable ScopeBoth
    Dynamic Variable Yes
    Value Set
    Typenumeric
    Default1
    Range1-65535

    This variable has a default value of 1. For particulars, see the description for auto_increment_increment.

    auto_increment_offset is supported for use with NDB tables beginning with MySQL 5.1.20. Previously, setting it when using MySQL Cluster tables or MySQL Cluster Replication produced unpredictable results.

  • automatic_sp_privileges

    Variable Nameautomatic_sp_privileges
    Variable ScopeGlobal
    Dynamic Variable Yes
    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.

  • back_log

    Option Sets Variable Yes, 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 Variable Yes, 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.

  • binlog_cache_size

    Option Sets Variable Yes, binlog_cache_size
    Variable Namebinlog_cache_size
    Variable ScopeGlobal
    Dynamic Variable Yes
    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 5.2.4, “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.

  • binlog_format

    Version Introduced5.1.5
    Option Sets Variable Yes, binlog_format
    Variable Namebinlog_format
    Variable ScopeBoth
    Dynamic Variable Yes
    Value Set
    Typeenumeration
    DefaultMIXED
    Valid ValuesROW, STATEMENT, MIXED

    The binary logging format, either STATEMENT, ROW, or MIXED. binlog_format is set by the --binlog-format option at startup, or by the binlog_format variable at runtime (you need the SUPER privilege to set this variable on a global scope). See Section 19.1.2, “Replication Formats”. The startup variable was added in MySQL 5.1.5, and the runtime variable in MySQL 5.1.8. MIXED was added in MySQL 5.1.8.

    STATEMENT was used by default prior to MySQL 5.1.12; beginning with MySQL 5.1.12, MIXED is the default. When MIXED is specified, statement-based replication is used, except for cases where only row-based replication is guaranteed to lead to proper results. For example, this is the case when statements contain user-defined functions (UDF) or the UUID() function. An exception to this rule is that MIXED always uses statement-based replication for stored functions and triggers.

    There are exceptions when you cannot switch the replication format at runtime:

    • From within a stored function or a trigger.

    • If NDB is enabled.

    • If the session is currently in row-based replication mode and has open temporary tables.

    Trying to switch the format in those cases results in an error.

    Before MySQL 5.1.8, switching to row-based replication format would implicitly set --log-bin-trust-function-creators=1 and --innodb_locks_unsafe_for_binlog. MySQL 5.1.8 and later no longer implicitly set these options when row-based replication is used.

  • bulk_insert_buffer_size

    Option Sets Variable Yes, bulk_insert_buffer_size
    Variable Namebulk_insert_buffer_size
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes
    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 Variable Yes
    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 Variable Yes
    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 Introduced5.1.6
    Option Sets Variable Yes, character_set_filesystem
    Variable Namecharacter_set_filesystem
    Variable ScopeBoth
    Dynamic Variable Yes
    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 5.1.6.

  • character_set_results

    Variable Namecharacter_set_results
    Variable ScopeBoth
    Dynamic Variable Yes
    Value Set
    Typestring

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

  • character_set_server

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

    The collation of the connection character set.

  • collation_database

    Variable Namecollation_database
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, collation_server
    Variable Namecollation_server
    Variable ScopeBoth
    Dynamic Variable Yes
    Value Set
    Typestring

    The server's default collation.

  • completion_type

    Option Sets Variable Yes, completion_type
    Variable Namecompetion_type
    Variable ScopeBoth
    Dynamic Variable Yes
    Value Set
    Typenumeric
    Default0
    Valid Values0, 1, 2

    The transaction completion type:

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

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

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

  • concurrent_insert

    Option Sets Variable Yes, concurrent_insert
    Variable Nameconcurrent_insert
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typenumeric
    Default1
    Valid Values0, 1, 2

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

    This variable can take three integer values:

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

    See also Section 7.3.3, “Concurrent Inserts”.

  • connect_timeout

    Option Sets Variable Yes, connect_timeout
    Variable Nameconnect_timeout
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set (<= 5.1.23)
    Typenumeric
    Default5
    Value Set (>= 5.1.23)
    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 5.1.23 and 5 seconds before that.

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

  • datadir

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

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

  • date_format

    This variable is unused.

  • datetime_format

    This variable is unused.

  • debug

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

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

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

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

    This variable was added in MySQL 5.1.7.

  • default_week_format

    Option Sets Variable Yes, default_week_format
    Variable Namedefault_week_format
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, delay_key_write
    Variable Namedelay-key-write
    Variable ScopeGlobal
    Dynamic Variable Yes
    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, “Command Options”, and Section 13.4.1, “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 Variable Yes, delayed_insert_limit
    Variable Namedelayed_insert_limit
    Variable ScopeGlobal
    Dynamic Variable Yes
    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 Variable Yes, delayed_insert_timeout
    Variable Namedelayed_insert_timeout
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typenumeric
    Default300

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

  • delayed_queue_size

    Option Sets Variable Yes, delayed_queue_size
    Variable Namedelayed_queue_size
    Variable ScopeGlobal
    Dynamic Variable Yes
    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

    Option Sets Variable Yes, div_precision_increment
    Variable Namediv_precision_increment
    Variable ScopeBoth
    Dynamic Variable Yes
    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 |
    +----------------+
    
  • event_scheduler

    Version Introduced5.1.6
    Option Sets Variable Yes, event-scheduler
    Variable Nameevent_scheduler
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typeenumeration
    DefaultOFF
    Valid ValuesON, OFF, DISABLED

    This variable indicates the status of the Event Scheduler; as of MySQL 5.1.12, possible values are ON, OFF, and DISABLED, with the default being OFF. This variable and its effects on the Event Scheduler's operation are discussed in greater detail in the Overview section of the Events chapter.

    This variable was added in MySQL 5.1.6.

  • expire_logs_days

    Option Sets Variable Yes, expire_logs_days
    Variable Nameexpire_logs_days
    Variable ScopeGlobal
    Dynamic Variable Yes
    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 Variable Yes
    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 Variable Yes, flush_time
    Variable Nameflush_time
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typelinuxnumeric
    Default0 
    Min Value0 
    Value Set
    Typemacosxnumeric
    Default0 
    Min Value0 
    Value Set
    Typehpuxnumeric
    Default0 
    Min Value0 
    Value Set
    Typesolarisnumeric
    Default0 
    Min Value0 
    Value Set
    Typenetwarenumeric
    Default0 
    Min Value0 
    Value Set
    Typewindowsnumeric
    Default1800 
    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 Windows 9x or Me, or on systems with minimal resources.

  • ft_boolean_syntax

    Variable Nameft_boolean_syntax
    Variable ScopeGlobal
    Dynamic Variable Yes
    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 Variable Yes, 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 Variable Yes, 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 Variable Yes, 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 Variable Yes, ft_stopword_file
    Variable Nameft_stopword_file
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

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

    Note

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

  • general_log

    Version Introduced5.1.12
    Option Sets Variable Yes, general_log
    Variable Namegeneral_log
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typeboolean
    DefaultOFF

    Whether the general query log is enabled. The value can be 0 (or OFF) to disable the log or 1 (or ON) to enable the log. The default value depends on whether the --log option is given. The destination for log output is controlled by the log_output system variable; if that value is NONE, no log entries are written even if the log is enabled. The general_log variable was added in MySQL 5.1.12.

  • general_log_file

    Version Introduced5.1.12
    Variable Namegeneral_log_file
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typefilename
    Defaulthost_name.log

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

  • group_concat_max_len

    Option Sets Variable Yes, group_concat_max_len
    Variable Namegroup_concat_max_len
    Variable ScopeBoth
    Dynamic Variable Yes
    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. This variable was removed in MySQL 5.1.14.

  • have_blackhole_engine

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

  • have_compress

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

  • have_crypt

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

  • have_csv

    YES if mysqld supports ARCHIVE tables, NO if not.

  • have_dynamic_loading

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

  • have_example_engine

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

  • have_federated_engine

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

  • have_geometry

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

  • have_innodb

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

  • have_isam

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

  • have_merge_engine

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

  • have_openssl

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

  • have_partitioning

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

  • have_query_cache

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

  • have_row_based_replication

    Version Introduced5.1.5
    Variable Namehave_row_based_replication
    Variable ScopeGlobal
    Dynamic VariableNo
    Deprecated5.1.15
    Value Set
    Typeboolean

    YES if the server can perform replication using row-based binary logging. If the value is NO, the server can use only statement-based logging. See Section 19.1.2, “Replication Formats”. This variable was added in MySQL 5.1.5 and removed in 5.1.15.

  • have_raid

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

  • have_rtree_keys

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

  • have_ssl

    YES if mysqld supports SSL connections, NO if not. This variable was added in MySQL 5.1.17. Before that, use have_openssl.

  • have_symlink

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

  • hostname

    Version Introduced5.1.17
    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 5.1.17.

  • init_connect

    Option Sets Variable Yes, init_connect
    Variable Nameinit_connect
    Variable ScopeGlobal
    Dynamic Variable Yes
    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 Variable Yes, init_file
    Variable Nameinit_file
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename

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

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

  • init_slave

    Option Sets Variable Yes, init_slave
    Variable Nameinit_slave
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typestring

    This variable is similar to init_connect, but is a string to be executed by a slave server each time the SQL thread starts. The format of the string is the same as for the init_connect variable.

  • innodb_xxx

    InnoDB system variables are listed in Section 13.5.4, “InnoDB Startup Options and System Variables”.

  • interactive_timeout

    Option Sets Variable Yes, interactive_timeout
    Variable Nameinteractive_timeout
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, join_buffer_size
    Variable Namejoin_buffer_size
    Variable ScopeBoth
    Dynamic Variable Yes
    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. As of MySQL 5.1.23, 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).

  • keep_files_on_create

    Version Introduced5.1.21
    Option Sets Variable Yes, keep_files_on_create
    Variable Namekeep_files_on_create
    Variable ScopeBoth
    Dynamic Variable Yes
    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 5.1.23.

  • key_buffer_size

    Option Sets Variable Yes, key_buffer_size
    Variable Namekey_buffer_size
    Variable ScopeGlobal
    Dynamic Variable Yes
    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 5.1.23, values larger than 4GB are allowed for 64-bit platforms. The effective maximum size might be less, depending on your available physical RAM and per-process RAM limits imposed by your operating system or hardware platform. The value of this variable indicates the amount of memory requested. Internally, the server allocates as much memory as possible up to this amount, but the actual allocation might be less.

    Increase the value to get better index handling (for all reads and multiple writes) to as much as you can afford. Using a value that is 25% of total memory on a machine that mainly runs MySQL is quite common. However, if you make the value too large (for example, more than 50% of your total memory) your system might start to page and become extremely slow. MySQL relies on the operating system to perform 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 7.2.19, “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 12.5.4, “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 Variable Yes, key_cache_age_threshold
    Variable Namekey_cache_age_threshold
    Variable ScopeGlobal
    Dynamic Variable Yes
    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 Variable Yes, key_cache_block_size
    Variable Namekey_cache_block_size
    Variable ScopeGlobal
    Dynamic Variable Yes
    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 Variable Yes, key_cache_division_limit
    Variable Namekey_cache_division_limit
    Variable ScopeGlobal
    Dynamic Variable Yes
    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 Variable Yes, 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

    Option Sets Variable Yes, large_pages
    Variable Namelarge_pages
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform Specificlinux
    Value Set
    Typelinuxboolean
    DefaultFALSE 

    Whether large page support is enabled.

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

  • large_page_size

    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.

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

  • lc_time_names

    Version Introduced5.1.12
    Variable Namelc_time_names
    Variable ScopeBoth
    Dynamic Variable Yes
    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 5.1.12.

  • 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 Variable Yes

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

  • locked_in_memory

    Variable Namelocked_in_memory
    Variable ScopeGlobal
    Dynamic VariableNo

    Whether mysqld was locked in memory with --memlock.

  • log

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

  • log_bin

    Variable Namelog_bin
    Variable ScopeGlobal
    Dynamic VariableNo

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

  • log_bin_trust_function_creators

    Option Sets Variable Yes, log_bin_trust_function_creators
    Variable Namelog_bin_trust_function_creators
    Variable ScopeGlobal
    Dynamic Variable Yes
    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 23.4, “Binary Logging of Stored Routines and Triggers”.

  • log_error

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

    The location of the error log.

  • log_output

    Version Introduced5.1.6
    Option Sets Variable Yes, log_output
    Variable Namelog_output
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typeenumeration
    DefaultFILE
    Valid ValuesTABLE, FILE, NONE

    The destination for general query log and slow query log output. The value can be a comma-separated list of one or more of the words TABLE (log to tables), FILE (log to files), or NONE (do not log to tables or files). The default value is TABLE. NONE, if present, takes precedence over any other specifiers. If the value is NONE log entries are not written even if the logs are enabled. If the logs are not enabled, no logging occurs even if the value of log_output is not NONE. For more information, see Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”. This variable was added in MySQL 5.1.6.

  • log_queries_not_using_indexes

    Option Sets Variable Yes, log_queries_not_using_indexes
    Variable Namelog_queries_not_using_indexes
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typeboolean

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

  • log_slave_updates

    Whether updates received by a slave server from a master server should be logged to the slave's own binary log. Binary logging must be enabled on the slave for this variable to have any effect. See Section 19.1.3, “Replication Options and Variables”.

  • log_slow_queries

    Option Sets Variable Yes, log_slow_queries
    Variable Namelog_slow_queries
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typeboolean

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

  • log_warnings

    Option Sets Variable Yes, log-warnings
    Variable Namelog_warnings
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, long_query_time
    Variable Namelong_query_time
    Variable ScopeBoth
    Dynamic Variable Yes
    Value Set (>= 5.1.21)
    Typenumeric
    Default10
    Min Value0

    If a query takes longer than this many seconds, the server increments the Slow_queries status variable. If 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. Prior to MySQL 5.1.21, the minimum value is 1, and the value for this variable must be an integer. Beginning with MySQL 5.1.21, the minimum is 0, and a resolution of microseconds is supported when logging to a file. However, the microseconds part is ignored and only integer values are written when logging to tables. The default value is 10. See Section 5.2.5, “The Slow Query Log”.

  • low_priority_updates

    Option Sets Variable Yes, low_priority_updates
    Variable Namelow_priority_updates
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, 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 Variable Yes, 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 Variable Yes, max_allowed_packet
    Variable Namemax_allowed_packet
    Variable ScopeBoth
    Dynamic Variable Yes
    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_binlog_cache_size

    Option Sets Variable Yes, max_binlog_cache_size
    Variable Namemax_binlog_cache_size
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typenumeric
    Default4294967295
    Range4096-4294967295

    If a multiple-statement transaction requires more than this many bytes of memory, the server generates a Multi-statement transaction required more than 'max_binlog_cache_size' bytes of storage error. The minimum value is 4096, the maximum and default values are 4GB.

  • max_binlog_size

    Option Sets Variable Yes, max_binlog_size
    Variable Namemax_binlog_size
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typenumeric
    Default1073741824
    Min Value4096

    If a write to the binary log causes the current log file size to exceed the value of this variable, the server rotates the binary logs (closes the current file and opens the next one). You cannot set this variable to more than 1GB or to less than 4096 bytes. The default value is 1GB.

    A transaction is written in one chunk to the binary log, so it is never split between several binary logs. Therefore, if you have big transactions, you might see binary logs larger than max_binlog_size.

    If max_relay_log_size is 0, the value of max_binlog_size applies to relay logs as well.

  • max_connect_errors

    Option Sets Variable Yes, max_connect_errors
    Variable Namemax_connect_errors
    Variable ScopeGlobal
    Dynamic Variable Yes
    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 Variable Yes, max_connections
    Variable Namemax_connections
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set (<= 5.1.14)
    Typenumeric
    Default100
    Value Set (>= 5.1.15)
    Typenumeric
    Default151
    Range1-16384
    Value Set (>= 5.1.17)
    Typenumeric
    Default151
    Range1-100000

    The number of simultaneous client connections allowed. By default, this is 151, beginning with MySQL 5.1.15. (Previously, the default was 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 Variable Yes, max_delayed_threads
    Variable Namemax_delayed_threads
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, max_error_count
    Variable Namemax_error_count
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, max_heap_table_size
    Variable Namemax_heap_table_size
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes
    Value Set
    Typenumeric

    This variable is a synonym for max_delayed_threads.

  • max_join_size

    Option Sets Variable Yes, max_join_size
    Variable Namemax_join_size
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, max_length_for_sort_data
    Variable Namemax_length_for_sort_data
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Introduced5.1.10
    Command Line Format
    --max_prepared_stmt_count=#5.0.21
    Config File Format
    max_prepared_stmt_count5.0.21
    Option Sets Variable Yes, max_prepared_stmt_count
    Variable Namemax_prepared_stmt_count
    Variable ScopeGlobal
    Dynamic Variable Yes
    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 5.1.10.

  • max_relay_log_size

    Option Sets Variable Yes, max_relay_log_size
    Variable Namemax_relay_log_size
    Variable ScopeGlobal
    Dynamic Variable Yes
    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 19.4.1, “Replication Implementation Details”.

  • max_seeks_for_key

    Option Sets Variable Yes, max_seeks_for_key
    Variable Namemax_seeks_for_key
    Variable ScopeBoth
    Dynamic Variable Yes
    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 12.5.4.18, “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 Variable Yes, max_sort_length
    Variable Namemax_sort_length
    Variable ScopeBoth
    Dynamic Variable Yes
    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

    Option Sets Variable Yes, max_sp_recursion_depth
    Variable Namemax_sp_recursion_depth
    Variable ScopeBoth
    Dynamic Variable Yes
    Value Set
    Typenumeric
    Default0
    Max Value255

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

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

  • max_tmp_tables

    Option Sets Variable Yes, max_tmp_tables
    Variable Namemax_tmp_tables
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, max_user_connections
    Variable Namemax_user_connections
    Variable ScopeBoth
    Dynamic Variable Yes
    Value Set
    Typenumeric
    Range1-4294967295

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

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

  • max_write_lock_count

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

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

  • min_examined_row_limit

    Version Introduced5.1.21
    Variable Namemin_examined_row_limit
    Variable ScopeBoth
    Dynamic Variable Yes
    Value Set
    Typenumeric
    Default0
    Range0-4294967295

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

  • myisam_block_size

    Option Sets Variable Yes, myisam_block_size
    Variable Namemyisam_block_size
    Variable ScopeBoth
    Dynamic Variable Yes
    Value Set
    Typenumeric
    Default1024
    Range1024-16384

    The block size to be used for MyISAM index pages.

  • myisam_data_pointer_size

    Option Sets Variable Yes, myisam_data_pointer_size
    Variable Namemyisam_data_pointer_size
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typenumeric
    Default6
    Range2-7

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

  • myisam_max_sort_file_size

    Option Sets Variable Yes, myisam_max_sort_file_size
    Variable Namemyisam_max_sort_file_size
    Variable ScopeGlobal
    Dynamic Variable Yes
    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, “Command Options”.

  • myisam_repair_threads

    Option Sets Variable Yes, myisam_repair_threads
    Variable Namemyisam_repair_threads
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, myisam_sort_buffer_size
    Variable Namemyisam_sort_buffer_size
    Variable ScopeBoth
    Dynamic Variable Yes
    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. As of MySQL 5.1.23, values larger than 4GB are allowed for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB with a warning).

  • myisam_stats_method

    Option Sets Variable Yes, myisam_stats_method
    Variable Namemyisam_stats_method
    Variable ScopeBoth
    Dynamic Variable Yes
    Value Set
    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.

  • myisam_use_mmap

    Version Introduced5.1.4
    Option Sets Variable Yes, myisam_use_mmap
    Variable Namemyisam_use_mmap
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typeboolean
    DefaultFALSE

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

  • 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 Variable Yes, net_buffer_length
    Variable Namenet_buffer_length
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, net_read_timeout
    Variable Namenet_read_timeout
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, net_retry_count
    Variable Namenet_retry_count
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, net_write_timeout
    Variable Namenet_write_timeout
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, new
    Variable Namenew
    Variable ScopeBoth
    Dynamic Variable Yes
    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 5.1, its value is always OFF.

  • old

    Version Introduced5.1.18
    Variable Nameold
    Variable ScopeGlobal
    Dynamic VariableNo

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

    Currently, when old is enabled, it changes the default scope of index hints to that used prior to MySQL 5.1.17. That is, index hints with no FOR clause apply only to how indexes are used for row retrieval and not to resolution of ORDER BY or GROUP BY clauses. (See Section 12.2.7.2, “Index Hint Syntax”.) Take care about enabling this in a replication setup. With statement-based binary logging, having different modes for the master and slaves might lead to replication errors.

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

  • old_passwords

    Option Sets Variable Yes, old_passwords
    Variable Nameold_passwords
    Variable ScopeBoth
    Dynamic Variable Yes
    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 12.5.3, “SET Syntax”.

  • open_files_limit

    Option Sets Variable Yes, 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

    Option Sets Variable Yes, optimizer_prune_level
    Variable Nameoptimizer_prune_level
    Variable ScopeBoth
    Dynamic Variable Yes
    Value Set
    Typeboolean
    Default1

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

  • optimizer_search_depth

    Option Sets Variable Yes, optimizer_search_depth
    Variable Nameoptimizer_search_depth
    Variable ScopeBoth
    Dynamic Variable Yes
    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.

  • pid_file

    Option Sets Variable Yes, 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 Introduced5.1.2
    Option Sets Variable Yes, plugin_dir
    Variable Nameplugin_dir
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename
    Default/usr/local/mysql/lib/mysql

    The pathname of the plugins directory. This variable was added in MySQL 5.1.2.

  • port

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

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

  • 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 5.1.10. In MySQL 5.1.14, 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 Variable Yes, query_alloc_block_size
    Variable Namequery_alloc_block_size
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, query_cache_limit
    Variable Namequery_cache_limit
    Variable ScopeGlobal
    Dynamic Variable Yes
    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 Variable Yes, query_cache_min_res_unit
    Variable Namequery_cache_min_res_unit
    Variable ScopeGlobal
    Dynamic Variable Yes
    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 Variable Yes, query_cache_size
    Variable Namequery_cache_size
    Variable ScopeGlobal
    Dynamic Variable Yes
    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 Variable Yes, query_cache_type
    Variable Namequery_cache_type
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, query_cache_wlock_invalidate
    Variable Namequery_cache_wlock_invalidate
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, query_prealloc_size
    Variable Namequery_prealloc_size
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, range_alloc_block_size
    Variable Namerange_alloc_block_size
    Variable ScopeBoth
    Dynamic Variable Yes
    Value Set
    Typenumeric
    Default4096
    Max Value4294967295

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

  • read_buffer_size

    Option Sets Variable Yes, read_buffer_size
    Variable Nameread_buffer_size
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, read_only
    Variable Nameread_only
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typenumeric
    Default0

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

    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.

    As of MySQL 5.1.15, the following conditions apply:

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

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

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

  • read_rnd_buffer_size

    Option Sets Variable Yes, read_rnd_buffer_size
    Variable Nameread_rnd_buffer_size
    Variable ScopeBoth
    Dynamic Variable Yes
    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.

  • relay_log_purge

    Option Sets Variable Yes, relay_log_purge
    Variable Namerelay_log_purge
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typeboolean
    DefaultTRUE

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

  • relay_log_space_limit

    Option Sets Variable Yes, relay_log_space_limit
    Variable Namerelay_log_space_limit
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typenumeric
    Default0

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

  • report_host

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

  • report_password

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

  • report_port

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

  • report_user

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

  • rpl_recovery_rank

    This variable is unused.

  • secure_auth

    Option Sets Variable Yes, secure_auth
    Variable Namesecure_auth
    Variable ScopeGlobal
    Dynamic Variable Yes
    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 Introduced5.1.17
    Option Sets Variable Yes, 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 5.1.17.

  • server_id

    Option Sets Variable Yes, server_id
    Variable Nameserver_id
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typenumeric
    Default0

    The server ID. This value is set by the --server-id option. It is used for replication to enable master and slave servers to identify themselves uniquely.

  • 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.

  • slave_compressed_protocol

    Option Sets Variable Yes, slave_compressed_protocol
    Variable Nameslave_compressed_protocol
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typeboolean
    DefaultFALSE

    Whether to use compression of the slave/master protocol if both the slave and the master support it.

  • slave_exec_mode

    Version Introduced5.1.24
    Variable Nameslave_exec_mode
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typeenumeration
    DefaultSTRICT
    Valid ValuesIDEMPOTENT, STRICT

    Controls whether IDEMPOTENT or STRICT mode is used in replication conflict resolution and error checking. IDEMPOTENT mode causes suppression of some errors, including duplicate-key and no-key-found errors. Beginning with MySQL 5.1.23-ndb-6.2.14 and MySQL 5.1.24, this mode should be employed in multi-master replication, circular replication, and some other special replication scenarios. STRICT mode is the default, and is suitable for most other cases.

  • slave_load_tmpdir

    Option Sets Variable Yes, slave_load_tmpdir
    Variable Nameslave_load_tmpdir
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typefilename
    Default/tmp

    The name of the directory where the slave creates temporary files for replicating LOAD DATA INFILE statements.

  • slave_net_timeout

    Option Sets Variable Yes, slave_net_timeout
    Variable Nameslave_net_timeout
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typenumeric
    Default3600
    Min Value1

    The number of seconds to wait for more data from a master/slave 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.

  • slave_skip_errors

    Option Sets Variable Yes, slave_skip_errors
    Variable Nameslave_skip_errors
    Variable ScopeGlobal
    Dynamic VariableNo

    Normally, replication stops when an error occurs on the slave. This gives you the opportunity to resolve the inconsistency in the data manually. This variable tells the slave SQL thread to continue replication when a statement returns any of the errors listed in the variable value.

  • slave_transaction_retries

    Option Sets Variable Yes, slave_transaction_retries
    Variable Nameslave_transaction_retries
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typenumeric
    Default10
    Min Value0

    If a replication slave SQL thread fails to execute a transaction because of an InnoDB deadlock or exceeded InnoDB's innodb_lock_wait_timeout or NDBCLUSTER's TransactionDeadlockDetectionTimeout or TransactionInactiveTimeout, it automatically retries slave_transaction_retries times before stopping with an error. The default value is 10.

  • slow_launch_time

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

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

  • slow_query_log

    Whether the slow query log is enabled. The value can be 0 (or OFF) to disable the log or 1 (or ON) to enable the log. The default value depends on whether the --log-slow-queries option is given. The destination for log output is controlled by the log_output system variable; if that value is NONE, no log entries are written even if the log is enabled. The slow_query_log variable was added in MySQL 5.1.12.

  • slow_query_log_file

    Version Introduced5.1.12
    Variable Nameslow_query_log_file
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typefilename

    The name of the slow query log file. The default value is host_name-slow.log, but the initial value can be changed with the --log-slow-queries option. This variable was added in MySQL 5.1.12.

  • socket

    Option Sets Variable Yes, socket
    Variable Namesocket
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typelinuxfilename
    Default/tmp/mysql.sock 
    Value Set
    Typehpuxfilename
    Default/tmp/mysql.sock 
    Value Set
    Typesolarisfilename
    Default/tmp/mysql.sock 
    Value Set
    Typemacosxfilename
    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 Variable Yes, sort_buffer_size
    Variable Namesort_buffer_size
    Variable ScopeBoth
    Dynamic Variable Yes
    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. As of MySQL 5.1.23, values larger than 4GB are allowed for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB with a warning).

  • sql_mode

    Option Sets Variable Yes, sql_mode
    Variable Namesql_mode
    Variable ScopeBoth
    Dynamic Variable Yes
    Value Set
    Typeenumeration
    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, “SQL Modes”.

  • sql_slave_skip_counter

    Variable Namesql_slave_skip_counter
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typenumeric

    The number of events from the master that a slave server should skip. See Section 12.6.2.6, “SET GLOBAL SQL_SLAVE_SKIP_COUNTER Syntax”.

  • ssl_ca

    Version Introduced5.1.11
    Option Sets Variable Yes, 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 5.1.11.

  • ssl_capath

    Version Introduced5.1.11
    Option Sets Variable Yes, 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 5.1.11.

  • ssl_cert

    Version Introduced5.1.11
    Option Sets Variable Yes, 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 5.1.11.

  • ssl_cipher

    Version Introduced5.1.11
    Option Sets Variable Yes, 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 5.1.11.

  • ssl_key

    Version Introduced5.1.11
    Option Sets Variable Yes, 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 5.1.11.

  • storage_engine

    Variable Namestorage_engine
    Variable ScopeBoth
    Dynamic Variable Yes
    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, “Command Options”.

  • sync_binlog

    Option Sets Variable Yes, sync_binlog
    Variable Namesync_binlog
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typenumeric
    Default0
    Range0-4294967295

    If the value of this variable is positive, the MySQL server synchronizes its binary log to disk (using fdatasync()) after every sync_binlog writes to the binary log. Note that there is one write to the binary log per statement if autocommit is enabled, and one write per transaction otherwise. The default value is 0, which does no synchronizing to disk. A value of 1 is the safest choice, because in the event of a crash you lose at most one statement or transaction from the binary log. However, it is also the slowest choice (unless the disk has a battery-backed cache, which makes synchronization very fast).

    If the value of sync_binlog is 0 (the default), no extra flushing is done. The server relies on the operating system to flush the file contents occasionally as for any other file.

  • sync_frm

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

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

  • table_definition_cache

    Version Introduced5.1.3
    Option Sets Variable Yes, table_definition_cache
    Variable Nametable_definition_cache
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set (<= 5.1.25)
    Typenumeric
    Default128
    Range1-524288
    Value Set (>= 5.1.25)
    Typenumeric
    Default256
    Range256-524288

    The number of table definitions that can be stored in the definition cache. If you use a large number of tables, you can create a large table definition cache to speed up opening of tables. The table definition cache takes less space and does not use file descriptors, unlike the normal table cache. This variable was added in MySQL 5.1.3. The minimum and default values are 1 and 128 before MySQL 5.1.25. The minimum and default are both 256 as of MySQL 5.1.25.

  • table_lock_wait_timeout

    Option Sets Variable Yes, table_lock_wait_timeout
    Variable Nametable_lock_wait_timeout
    Variable ScopeGlobal
    Dynamic Variable Yes
    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).

  • table_open_cache

    Version Introduced5.1.3
    Variable Nametable_open_cache
    Variable ScopeGlobal
    Dynamic Variable Yes
    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, “Status Variables”. If the value of Opened_tables is large and you don't do FLUSH TABLES often (which just forces all tables to be closed and reopened), then you should increase the value of the table_open_cache variable. For more information about the table cache, see Section 7.4.8, “How MySQL Opens and Closes Tables”. Before MySQL 5.1.3, this variable is called table_cache.

  • table_type

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

    This variable is a synonym for storage_engine. In MySQL 5.1, storage_engine is the preferred name. In MySQL 6.0, table_type will be removed.

  • thread_cache_size

    Option Sets Variable Yes, thread_cache_size
    Variable Namethread_cache_size
    Variable ScopeGlobal
    Dynamic Variable Yes
    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, “Status Variables”.

  • thread_concurrency

    Option Sets Variable Yes, 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.

  • thread_handling

    Version Introduced5.1.17
    Option Sets Variable Yes, thread_handling
    Variable Namethread_handling
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typeenumeration
    Valid Valuesno-threads, one-thread-per-connection

    The thread-handling model. The allowable values are one-thread (the server uses one thread) and one-thread-per-connection (the server uses one thread to handle each client connection). one-thread is useful for debugging under Linux; see MySQL Internals: Porting. This variable was added in MySQL 5.1.17

  • thread_stack

    Option Sets Variable Yes, 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 Variable Yes
    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

    Option Sets Variable Yes, timed_mutexes
    Variable Nametimed_mutexes
    Variable ScopeGlobal
    Dynamic Variable Yes
    Value Set
    Typeboolean
    DefaultOFF

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

  • tmp_table_size

    Option Sets Variable Yes, tmp_table_size
    Variable Nametmp_table_size
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, 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 Variable Yes, transaction_alloc_block_size
    Variable Nametransaction_alloc_block_size
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes, transaction_prealloc_size
    Variable Nametransaction_prealloc_size
    Variable ScopeBoth
    Dynamic Variable Yes
    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 Variable Yes
    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

    Option Sets Variable Yes, updatable_views_with_limit
    Variable Nameupdatable_views_with_limit
    Variable ScopeBoth
    Dynamic Variable Yes
    Value Set
    Typeboolean
    Default1

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

    The variable can have two values:

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

    • 0 or NO: Prohibit the update.

  • version

    The version number for the server.

  • version_comment

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

  • version_compile_machine

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

  • version_compile_os

    Variable Nameversion_compile_os
    Variable ScopeGlobal
    Dynamic VariableNo
    Value Set
    Typestring

    The type of operating system on which MySQL was built.

  • wait_timeout

    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:

NameCmd-LineOption fileSystem VarDynamic
autocommit   Yes Yes
big-tables Yes Yes  
- Variable: big_tables   Yes Yes
error_count   YesNo
foreign_key_checks   Yes Yes
identity   Yes Yes
insert_id   Yes Yes
last_insert_id   Yes Yes
ndb_table_no_logging   Yes Yes
ndb_table_temporary   Yes Yes
sql_auto_is_null   Yes Yes
sql_big_selects   Yes Yes
sql_big_tables   Yes Yes
sql_buffer_result   Yes Yes
sql_log_bin   Yes Yes
sql_log_off   Yes Yes
sql_log_update   Yes Yes
sql_notes   Yes Yes
sql_quote_show_create   Yes Yes
sql_safe_updates   Yes Yes
sql_warnings   Yes Yes
timestamp   Yes Yes
transaction_allow_batching   Yes Yes
unique_checks   Yes Yes
warning_count   YesNo
  • AUTOCOMMIT = {0 | 1}

    Set the autocommit mode. If set to 1, all changes to a table take effect immediately. If set to 0 you have to 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 = {0 | 1}

    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 12.5.4.15, “SHOW ERRORS Syntax”.

  • FOREIGN_KEY_CHECKS = {0 | 1}

    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 13.5.6.4, “FOREIGN KEY Constraints”.

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

    Note

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

  • IDENTITY = value

    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 = value

    Set 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 = value

    Set 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.

  • SQL_AUTO_IS_NULL = {0 | 1}

    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 = {0 | 1}

    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 = {0 | 1}

    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 = {0 | 1}

    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 = {0 | 1}

    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 = {0 | 1}

    This variable is deprecated, and is mapped to SQL_LOG_BIN.

  • SQL_NOTES = {0 | 1}

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

  • SQL_QUOTE_SHOW_CREATE = {0 | 1}

    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 12.5.4.9, “SHOW CREATE TABLE Syntax”, and Section 12.5.4.6, “SHOW CREATE DATABASE Syntax”.

  • SQL_SAFE_UPDATES = {0 | 1}

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

  • SQL_SELECT_LIMIT = {value | DEFAULT}

    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.

  • SQL_WARNINGS = {0 | 1}

    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 = {0 | 1}

    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 12.5.4.32, “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, “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 @@[email protected]@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                         | /home/mysql/                      |
| binlog_cache_size               | 32768                             |
| bulk_insert_buffer_size         | 8388608                           |
| character_set_client            | latin1                            |
| character_set_connection        | latin1                            |
| character_set_database          | latin1                            |
| character_set_results           | latin1                            |
| character_set_server            | latin1                            |
| character_set_system            | utf8                              |
| character_sets_dir              | /home/mysql/share/mysql/charsets/ |
| collation_connection            | latin1_swedish_ci                 |
| collation_database              | latin1_swedish_ci                 |
| collation_server                | latin1_swedish_ci                 |
...
| innodb_additional_mem_pool_size | 1048576                           |
| innodb_autoextend_increment     | 8                                 |
| innodb_buffer_pool_size         | 8388608                           |
| innodb_checksums                | ON                                |
| innodb_commit_concurrency       | 0                                 |
| innodb_concurrency_tickets      | 500                               |
| innodb_data_file_path           | ibdata1:10M:autoextend            |
| innodb_data_home_dir            |                                   |
...
| version                         | 5.1.6-alpha-log                   |
| version_comment                 | Source distribution               |
| version_compile_machine         | i686                              |
| version_compile_os              | suse-linux                        |
| wait_timeout                    | 28800                             |
+---------------------------------+-----------------------------------+

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

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

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

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

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

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

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

5.1.5.1. 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 5.1 supports one structured variable type, which specifies parameters governing the operation of key caches. A key cache structured variable has these components:

  • key_buffer_size

  • key_cache_block_size

  • key_cache_division_limit

  • key_cache_age_threshold

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 12.5.3, “SET Syntax”, 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
binlog_formatenumerationGLOBAL | SESSION
bulk_insert_buffer_sizenumericGLOBAL | SESSION
character_set_clientstringGLOBAL | SESSION
character_set_connectionstringGLOBAL | SESSION
character_set_databasestringGLOBAL | SESSION
character_set_filesystemstringGLOBAL | SESSION
character_set_resultsstringGLOBAL | SESSION
character_set_serverstringGLOBAL | SESSION
collation_connectionstringGLOBAL | SESSION
collation_databasestringGLOBAL | SESSION
collation_serverstringGLOBAL | SESSION
completion_typenumericGLOBAL | SESSION
concurrent_insertbooleanGLOBAL
connect_timeoutnumericGLOBAL
date_formatstringGLOBAL | SESSION
datetime_formatstringGLOBAL | SESSION
debugstringGLOBAL | SESSION
default_week_formatnumericGLOBAL | SESSION
delayed_insert_limitnumericGLOBAL
delayed_insert_timeoutnumericGLOBAL
delayed_queue_sizenumericGLOBAL
delay_key_writeenumerationGLOBAL
div_precision_incrementnumericGLOBAL | SESSION
engine_condition_pushdownbooleanGLOBAL | SESSION
event-schedulerenumerationGLOBAL
expire_logs_daysnumericGLOBAL
flushbooleanGLOBAL
flush_timenumericGLOBAL
foreign_key_checksbooleanSESSION
ft_boolean_syntaxstringGLOBAL
general_logbooleanGLOBAL
general_log_filefilenameGLOBAL
group_concat_max_lennumericGLOBAL | SESSION
identitynumericSESSION
init_connectstringGLOBAL
init_slavestringGLOBAL
innodb_autoextend_incrementnumericGLOBAL
innodb_commit_concurrencynumericGLOBAL
innodb_concurrency_ticketsnumericGLOBAL
innodb_fast_shutdownbooleanGLOBAL
innodb_flush_log_at_trx_commitnumericGLOBAL
innodb_max_dirty_pages_pctnumericGLOBAL
innodb_max_purge_lagnumericGLOBAL
innodb_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
logstringGLOBAL
log_bin_trust_function_creatorsbooleanGLOBAL
log_bin_trust_routine_creatorsbooleanGLOBAL
log_outputenumerationGLOBAL
log_queries_not_using_indexesbooleanGLOBAL
log_slow_queriesbooleanGLOBAL
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
min_examined_row_limitnumericGLOBAL | SESSION
multi_range_countnumericGLOBAL | SESSION
myisam_block_sizenumericGLOBAL | SESSION
myisam_data_pointer_sizenumericGLOBAL
myisam_max_sort_file_sizenumericGLOBAL
myisam_repair_threadsnumericGLOBAL | SESSION
myisam_sort_buffer_sizenumericGLOBAL | SESSION
myisam_stats_methodenumerationGLOBAL | SESSION
myisam_use_mmapbooleanGLOBAL
ndb_autoincrement_prefetch_sznumericGLOBAL | SESSION
ndb_cache_check_timenumericGLOBAL
ndbclusterbooleanGLOBAL | SESSION
ndb_extra_loggingnumericGLOBAL
ndb_force_sendbooleanGLOBAL | SESSION
ndb_log_update_as_writebooleanGLOBAL
ndb_log_updated_onlybooleanGLOBAL
ndb_optimization_delaynumericGLOBAL
ndb_table_no_loggingbooleanSESSION
ndb_table_temporarybooleanSESSION
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
plugin_innodb_autoextend_incrementnumericGLOBAL | SESSION
plugin_innodb_checksumsbooleanGLOBAL | SESSION
plugin_innodb_commit_concurrencynumericGLOBAL
plugin_innodb_concurrency_ticketsnumericGLOBAL
plugin_innodb_flush_log_at_trx_commitnumericGLOBAL
plugin_innodb_max_dirty_pages_pctnumericGLOBAL
plugin_innodb_max_purge_lagnumericGLOBAL
plugin_innodb_support_xabooleanGLOBAL | SESSION
plugin_innodb_sync_spin_loopsnumericGLOBAL
plugin_innodb_table_locksbooleanGLOBAL | SESSION
plugin_innodb_thread_concurrencynumericGLOBAL
plugin_innodb_thread_sleep_delaynumericGLOBAL
preload_buffer_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
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_allow_batchingbooleanGLOBAL
slave_compressed_protocolbooleanGLOBAL
slave_exec_modeenumerationGLOBAL
slave_net_timeoutnumericGLOBAL
slave_transaction_retriesnumericGLOBAL
slow_launch_timenumericGLOBAL
slow_query_logbooleanGLOBAL
slow_query_log_filefilenameGLOBAL
sort_buffer_sizenumericGLOBAL | SESSION
sql_auto_is_nullbooleanSESSION
sql_big_selectsbooleanSESSION
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_modeenumerationGLOBAL | 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_definition_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_allow_batchingbooleanSESSION
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. 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 12.5.4.27, “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_repreparenumericGLOBAL | 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-connection-poolnumericGLOBAL
Ndb_cluster_node_idnumericGLOBAL | SESSION
Ndb_config_from_hostnumericGLOBAL | SESSION
Ndb_config_from_portnumericGLOBAL | SESSION
Ndb_conflict_fn_maxnumericGLOBAL | SESSION
Ndb_conflict_fn_oldnumericGLOBAL | SESSION
ndb_execute_countnumericGLOBAL
Ndb_number_of_data_nodesnumericGLOBAL | SESSION
Not_flushed_delayed_rowsnumericGLOBAL | SESSION
Opened_filesnumericGLOBAL
Opened_tablesnumericGLOBAL | SESSION
Open_filesnumericGLOBAL | SESSION
Open_streamsnumericGLOBAL | SESSION
Open_table_definitionsnumericGLOBAL | 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_heartbeat_period GLOBAL
Slave_open_temp_tablesnumericGLOBAL | SESSION
Slave_received_heartbeats GLOBAL
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
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

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 5.1. For information regarding their implementation history, see MySQL 5.0 Reference Manual.

  • 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 are as follows:

    • Com_stmt_prepare

    • Com_stmt_execute

    • Com_stmt_fetch

    • Com_stmt_send_long_data

    • Com_stmt_reset

    • Com_stmt_close

    Those variables stand for prepared statement commands. Their names refer to the COM_xxx command set used in the network layer. In other words, their values increase whenever prepared statement API calls such as mysql_stmt_prepare(), mysql_stmt_execute(), and so forth are executed. However, Com_stmt_prepare, Com_stmt_execute and Com_stmt_close also increase for PREPARE, EXECUTE, or DEALLOCATE PREPARE, respectively. Additionally, the values of the older (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.

    Com_stmt_reprepare indicated the number of times statements were automatically reprepared by the server after metadata changes to tables or views referred to by the statement. This variable was added in MySQL 5.1.25. A reprepare operation increments Com_stmt_reprepare is incremented, and also Com_stmt_prepare.

  • Compression

    Whether the client connection uses compression in the client/server protocol. Added in MySQL 5.1.2.

  • 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.

  • 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.

  • Handler_savepoint_rollback

    The number of requests for a storage engine to roll back to a savepoint.

  • Handler_update

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

  • Handler_write

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

  • Innodb_buffer_pool_pages_data

    The number of pages containing data (dirty or clean).

  • Innodb_buffer_pool_pages_dirty

    The number of pages currently dirty.

  • Innodb_buffer_pool_pages_flushed

    The number of buffer pool page-flush requests.

  • Innodb_buffer_pool_pages_free

    The number of free pages.

  • Innodb_buffer_pool_pages_latched

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

  • Innodb_buffer_pool_pages_misc

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

  • Innodb_buffer_pool_pages_total

    The total size of the buffer pool, in pages.

  • Innodb_buffer_pool_read_ahead_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.

  • 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.

  • Innodb_buffer_pool_read_requests

    The number of logical read requests InnoDB has done.

  • Innodb_buffer_pool_reads

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

  • Innodb_buffer_pool_wait_free

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

  • Innodb_buffer_pool_write_requests

    The number writes done to the InnoDB buffer pool.

  • Innodb_data_fsyncs

    The number of fsync() operations so far.

  • Innodb_data_pending_fsyncs

    The current number of pending fsync() operations.

  • Innodb_data_pending_reads

    The current number of pending reads.

  • Innodb_data_pending_writes

    The current number of pending writes.

  • Innodb_data_read

    The amount of data read so far, in bytes.

  • Innodb_data_reads

    The total number of data reads.

  • Innodb_data_writes

    The total number of data writes.

  • Innodb_data_written

    The amount of data written so far, in bytes.

  • Innodb_dblwr_writes

    The number of doublewrite operations that have been performed. See Section 13.5.14.1, “InnoDB Disk I/O”.

  • Innodb_dblwr_pages_written

    The number of pages that have been written for doublewrite operations. See Section 13.5.14.1, “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.

  • Innodb_log_write_requests

    The number of log write requests.

  • Innodb_log_writes

    The number of physical writes to the log file.

  • Innodb_os_log_fsyncs

    The number of fsync() writes done to the log file.

  • Innodb_os_log_pending_fsyncs

    The number of pending log file fsync() operations.

  • Innodb_os_log_pending_writes

    The number of pending log file writes.

  • Innodb_os_log_written

    The number of bytes written to the log file.

  • Innodb_page_size

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

  • Innodb_pages_created

    The number of pages created.

  • Innodb_pages_read

    The number of pages read.

  • Innodb_pages_written

    The number of pages written.

  • Innodb_row_lock_current_waits

    The number of row locks currently being waited for.

  • Innodb_row_lock_time

    The total time spent in acquiring row locks, in milliseconds.

  • Innodb_row_lock_time_avg

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

  • Innodb_row_lock_time_max

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

  • Innodb_row_lock_waits

    The number of times a row lock had to be waited for.

  • Innodb_rows_deleted

    The number of rows deleted from InnoDB tables.

  • Innodb_rows_inserted

    The number of rows inserted into InnoDB tables.

  • Innodb_rows_read

    The number of rows read from InnoDB tables.

  • Innodb_rows_updated

    The number of rows updated in InnoDB tables.

  • 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, “System Variables”.

  • Key_blocks_used

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

  • Key_read_requests

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

  • Key_reads

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

  • Key_write_requests

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

  • Key_writes

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

  • Last_query_cost

    The total cost of the last compiled query as computed by the query optimizer. This is useful for comparing the cost of different query plans for the same query. The default value of 0 means that no query has been compiled yet. The default value is 0. Last_query_cost has session scope.

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

  • Max_used_connections

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

  • Not_flushed_delayed_rows

    The number of rows waiting to be written in INSERT 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_table_definitions

    The number of cached .frm files. This variable was added in MySQL 5.1.3.

  • Open_tables

    The number of tables that are open.

  • Opened_files

    The number of files that have been opened with my_open() (a mysys library function). Parts of the server that open files without using this function do not increment the count. This variable was added in MySQL 5.1.21.

  • Opened_tables

    The number of tables that have been opened. If Opened_tables is big, your table_open_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 5.1.14.

  • 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.

  • 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 5.2.5, “The Slow Query Log”.

  • Sort_merge_passes

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

  • Sort_range

    The number of sorts that were done using ranges.

  • Sort_rows

    The number of sorted rows.

  • Sort_scan

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

  • Ssl_xxx

    Variables used for SSL connections.

  • Table_locks_immediate

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

  • Table_locks_waited

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

  • Tc_log_max_pages_used

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

  • Tc_log_page_size

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

  • Tc_log_page_waits

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

  • Threads_cached

    The number of threads in the thread cache.

  • Threads_connected

    The number of currently open connections.

  • Threads_created

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

  • Threads_running

    The number of threads that are not sleeping.

  • Uptime

    The number of seconds that the server has been up.

5.1.7. 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 5.1 FAQ — Server SQL Mode”.

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

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

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

Important

SQL mode and user-defined partitioning.  Changing the server SQL mode after creating and inserting data into partitioned tables can cause major changes in the behavior of such tables, and could lead to loss or corruption of data. It is strongly recommended that you never change the SQL mode once you have created tables employing user-defined partitioning.

See Section 21.5, “Restrictions and Limitations on Partitioning”, for more information.

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

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

The most important sql_mode values are probably these:

  • ANSI

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

  • STRICT_TRANS_TABLES

    If a value could not be inserted as given into a transactional table, abort the statement. For a 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.

  • 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.

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.

    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.

  • HIGH_NOT_PRECEDENCE

    The precedence of the NOT operator is such that expressions such as NOT a BETWEEN b AND c are parsed as NOT (a BETWEEN b AND c). In some older versions of MySQL, the expression was parsed as (NOT a) BETWEEN b AND c. The old higher-precedence behavior can be obtained by enabling the HIGH_NOT_PRECEDENCE SQL mode.

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

    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 8.2.4, “Function Name Parsing and Resolution”.

  • NO_AUTO_CREATE_USER

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

  • NO_AUTO_VALUE_ON_ZERO

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

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

  • NO_BACKSLASH_ESCAPES

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

  • NO_DIR_IN_CREATE

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

  • NO_ENGINE_SUBSTITUTION

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

    Up through MySQL 5.1.11, 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).

    As of MySQL 5.1.12, storage engines can be pluggable at runtime, so the distinction between disabled and invalid no longer applies. All unavailable engines are treated the same way:

    With NO_ENGINE_SUBSTITUTION disabled, for CREATE TABLE the default engine is used and a warning occurs if the desired engine is unavailable. For ALTER TABLE, a warning occurs and the table is not altered.

    With NO_ENGINE_SUBSTITUTION enabled, an error occurs and the table is not created or altered if the desired engine is unavailable.

  • NO_FIELD_OPTIONS

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

  • NO_KEY_OPTIONS

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

  • NO_TABLE_OPTIONS

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

  • NO_UNSIGNED_SUBTRACTION

    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.

  • 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.

  • 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 5.1.11, this mode also restricts references to non-aggregated columns in the HAVING clause that are not named in the GROUP BY clause.

  • PAD_CHAR_TO_FULL_LENGTH

    By default, trailing spaces are trimmed from CHAR column values on retrieval. If PAD_CHAR_TO_FULL_LENGTH is enabled, trimming does not occur and retrieved CHAR values are padded to their full length. This mode does not apply to VARCHAR columns, for which trailing spaces are retained on retrieval. This mode was added in MySQL 5.1.20.

    mysql> CREATE TABLE t1 (c1 CHAR(10));
    Query OK, 0 rows affected (0.37 sec)
    
    mysql> INSERT INTO t1 (c1) VALUES('xy');
    Query OK, 1 row affected (0.01 sec)
    
    mysql> SET sql_mode = '';
    Query OK, 0 rows affected (0.00 sec)
    
    mysql> SELECT c1, CHAR_LENGTH(c1) FROM t1;
    +------+-----------------+
    | c1   | CHAR_LENGTH(c1) |
    +------+-----------------+
    | xy   |               2 | 
    +------+-----------------+
    1 row in set (0.00 sec)
    
    mysql> SET sql_mode = 'PAD_CHAR_TO_FULL_LENGTH';
    Query OK, 0 rows affected (0.00 sec)
    
    mysql> SELECT c1, CHAR_LENGTH(c1) FROM t1;
    +------------+-----------------+
    | c1         | CHAR_LENGTH(c1) |
    +------------+-----------------+
    | xy         |              10 | 
    +------------+-----------------+
    1 row in set (0.00 sec)
    
  • PIPES_AS_CONCAT

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

  • REAL_AS_FLOAT

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

  • STRICT_ALL_TABLES

    Enable strict mode for all storage engines. Invalid data values are rejected. Additional detail follows.

  • STRICT_TRANS_TABLES

    Enable strict mode for transactional storage engines, and when possible for non-transactional storage engines. Additional details follow.

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

For transactional tables, an error occurs for invalid or missing values in a statement when either of the STRICT_ALL_TABLES or STRICT_TRANS_TABLES modes are enabled. The statement is aborted and rolled back.

For 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 12.5.4.32, “SHOW WARNINGS Syntax”.

The following special modes are provided as shorthand for combinations of mode values from the preceding list.

The descriptions include all mode values that are available in the most recent version of MySQL. For older versions, a combination mode does not include individual mode values that are not available except in newer versions.

  • ANSI

    Equivalent to REAL_AS_FLOAT, PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE.

    As of MySQL 5.1.18, 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 5.1.18.

    See Section 1.8.3, “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 12.5.5.3, “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, 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 12.5.5.2, “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 19, 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.

As of MySQL 5.1.6, the server can write general query and slow query entries to log tables, log files, or both. For details, see Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”.

As of MySQL 5.1.12, additional runtime control of the general query and slow query logs is available: You can enable or disable logging, or change the name of the log file. See Section 5.2.3, “The General Query Log”, and Section 5.2.5, “The Slow Query Log”.

5.2.1. Selecting General Query and Slow Query Log Output Destinations

As of MySQL 5.1.6, the server provides flexible control over the destination for log output. Log entries can be written to log files to the general_log and slow_log tables in the mysql database. If logging is enabled, either or both destinations can be selected. (Before MySQL 5.1.6, the server uses only log files as the destination for general query log and slow query log entries, if those logs are enabled.)

Note

For new installations of MySQL 5.1.6 or higher, the log tables are created during the installation procedure along with the other system tables. If you upgrade MySQL from a release older than 5.1.6 to MySQL 5.1.6 or higher, you must upgrade the system tables after upgrading to make sure that the log tables exist. See Section 4.4.8, “mysql_upgrade — Check Tables for MySQL Upgrade”.

Currently, logging to tables incurs significantly more server overhead than logging to files. If you enable the general log or slow query log and require highest performance, you should log to files and not to tables.

The --log-output option specifies the destination for log output, if logging is enabled, but the option does not in itself enable the logs. The syntax for this option is --log-output[=value,...]:

  • If --log-output is given with a value, the value can be a comma-separated list of one or more of the words TABLE (log to tables), FILE (log to files), or NONE (do not log to tables or files). NONE, if present, takes precedence over any other specifiers.

  • If --log-output is omitted or given without a value, the effect is the same as --log-output=FILE. That is, the file destination is selected. (For MySQL 5.1.6 through 5.1.20, the default is the table destination.)

  • If --log-output option also sets the value of the global log_output system variable, which can be modified at runtime to change the logging destination for the server while it executes.

The --log[=file_name] option, if given, enables logging to the general query log for the selected log destinations. Similarly, the --log-slow-queries[=file_name] option, if given, enables logging to the slow query log for the selected destinations. If you specify either option, the server opens the corresponding log file and writes startup messages to it. However, logging of queries to the file does not occur unless the FILE log destination is selected.

Examples:

  • To write general query log entries to the log table and the log file, use --log-output=TABLE,FILE to select both log destinations and the --log option to enable the general query log.

  • To write general and slow query log entries only to the log tables, use --log-output=TABLE to select tables as the log destination and the --log and --log-slow-queries options to enable both logs.

  • To write slow query log entries only to the log file, use --log-output=FILE to select files as the log destination and the --log-slow-queries option to enable the slow query log. (In this case, because the default log destination is FILE, you could omit the --log-output option.)

Several system variables are associated with log tables and files:

  • The global general_log and slow_query_log variables indicate whether the general query log and slow query log are enabled (ON) or disabled (OFF). You can set these variables at runtime to control whether the logs are enabled.

  • The global general_log_file and slow_query_log_file variables indicate the names of the general query log and slow query log files. You can set these variables at runtime to change the names of the log files. (If the --log and --log-slow-queries options were not given, the initial variable values are the default log filenames.)

  • The session sql_log_off variable can be set to ON or OFF to disable or enable general query logging for the current connection.

The use of tables for log output offers the following benefits:

  • Log entries have a standard format. To display the current structure of the log tables, use these statements:

    SHOW CREATE TABLE mysql.general_log;
    SHOW CREATE TABLE mysql.slow_log;
    
  • Log contents are accessible via SQL statements. This enables the use of queries that select only those log entries that satisfy specific criteria. For example, to select log contents associated with a particular client (which can be useful for identifying problematic queries from that client), it is easier to do this using a log table than a log file.

  • Logs are accessible remotely through any client that can connect to the server and issue queries (if the client has the appropriate log table privileges). It's not necessary to log in to the server host and directly access the filesystem.

The log table implementation has the following characteristics:

  • In general, the primary purpose of log tables is to provide an interface for users to observe the runtime execution of the server, not to interfere with its runtime execution.

  • CREATE TABLE, ALTER TABLE, and DROP TABLE are valid operations on a log table. For ALTER TABLE and DROP TABLE, the log table cannot be in use and must be disabled, as described later.

  • By default, the log tables use the CSV storage engine that writes data in comma-separated values format. For users who have access to the .CSV files that contain log table data, the files are easy to import into other programs such as spreadsheets that can process CSV input.

    Beginning with MySQL 5.1.12, the log tables can be altered to use the MyISAM storage engine. You cannot use ALTER TABLE to alter a log table that is in use. The log must be disabled first. No engines other than CSV or MyISAM are legal for the log tables.

  • To disable logging so that you can alter (or drop) a log table, you can use the following strategy. The example uses the general query log; the procedure for the slow query log is similar but uses the slow_log table and slow_query_log system variable.

    SET @old_log_state = @@global.general_log;
    SET GLOBAL general_log = 'OFF';
    ALTER TABLE mysql.general_log ENGINE = MyISAM;
    SET GLOBAL general_log = @old_log_state;
    
  • TRUNCATE TABLE is a valid operation on a log table. It can be used to expire log entries.

  • As of MySQL 5.1.13, RENAME TABLE is a valid operation on a log table. You can atomically rename a log table (to perform log rotation, for example) using the following strategy: