SYNOPSIS
mysqld [options]
DESCRIPTION
mysqld is the MySQL server. The following discussion covers these MySQL
server configuration topics:
o Startup options that the server supports
o Server system variables
o Server status variables
o How to set the server SQL mode
o 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 5.4.10, "SHOW ENGINES
Syntax".
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 (Server
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. 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.
+-------------------------------------+----------+-------------+------------+------------+
|Name | Cmd-line | Option file | Server Var | Status Var |
+-------------------------------------+----------+-------------+------------+------------+
|abort-slave-event-count | Y | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|back_log | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Com_replace | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_select | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_set_option | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|basedir | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_binlog_events | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_binlogs | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_charsets | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_collations | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_column_types | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_create_db | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_create_event | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_create_table | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_databases | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_engine_logs | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|bdb | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_engine_mutex | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_engine_status | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_errors | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_events | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_fields | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_grants | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_keys | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_master_status | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_new_master | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_open_tables | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: have_bdb | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_plugins | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_triggers | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_variables | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|bdb-home | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|Com_show_warnings | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_slave_start | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_slave_stop | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_stmt_close | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_stmt_execute | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_stmt_fetch | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_stmt_prepare | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_stmt_reset | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_stmt_send_long_data | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_truncate | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: bdb_home | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Com_unlock_tables | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_update | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_update_multi | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_xa_commit | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_xa_end | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_xa_prepare | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_xa_recover | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_xa_rollback | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_xa_start | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|completion-type | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|bdb-lock-detect | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|Compression | | | | Y |
|Created_tmp_disk_tables | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Created_tmp_files | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Created_tmp_tables | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|bdb-logdir | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|datadir | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|date_format | Y | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|datetime_format | Y | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|default-character-set | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|default-collation | Y | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|default-storage-engine | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|default-table-type | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|default-time-zone | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|default_week_format | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|defaults-extra-file | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: bdb_logdir | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|defaults-file | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|delay-key-write | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: | | | Y | |
|delay_key_write | | | | |
+-------------------------------------+----------+-------------+------------+------------+
|delay-key-write-for-all-tables | Y | | | |
+-------------------------------------+----------+-------------+------------+------------+
|Delayed_errors | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|delayed_insert_limit | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Delayed_insert_threads | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|delayed_insert_timeout | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|delayed_queue_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Delayed_writes | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|bdb-no-recover | Y | Y | | |
|engine_condition_pushdown | | | | |
+-------------------------------------+----------+-------------+------------+------------+
|error_count | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|exit-info | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|expire_logs_days | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Aborted_clients | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|bdb-no-sync | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|external-locking | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|flush | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Flush_commands | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|flush_time | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|foreign_key_checks | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|ft_boolean_syntax | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|ft_max_word_len | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|ft_min_word_len | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|ft_query_expansion_limit | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|ft_stopword_file | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|bdb-shared-data | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|gdb | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|group_concat_max_len | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Handler_commit | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Handler_delete | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Handler_discover | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Handler_prepare | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Handler_read_first | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Handler_read_key | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Handler_read_next | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Handler_update | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Handler_write | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|help | Y | | | |
+-------------------------------------+----------+-------------+------------+------------+
|identity | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|init-connect | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|bdb-tmpdir | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: init_connect | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|init-file | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: init_file | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|init-rpl-role | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|init-slave | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: init_slave | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_additional_mem_pool_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_autoextend_increment | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_buffer_pool_awe_mem_mb | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: bdb_tmpdir | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_buffer_pool_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_checksums | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_commit_concurrency | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_concurrency_tickets | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_data_file_path | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_data_home_dir | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_doublewrite | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_fast_shutdown | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_file_io_threads | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_log_arch_dir | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_log_archive | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_log_buffer_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_log_file_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_log_files_in_group | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|bdb_lock_max | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_log_group_home_dir | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_max_dirty_pages_pct | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_max_purge_lag | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_mirrored_log_groups | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_open_files | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_status_file | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_support_xa | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_sync_spin_loops | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_table_locks | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_thread_concurrency | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|bdb_log_buffer_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|innodb_thread_sleep_delay | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|insert_id | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|interactive_timeout | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|isam | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|join_buffer_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Key_blocks_not_flushed | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Key_blocks_unused | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Key_blocks_used | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|key_buffer_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Key_writes | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|language | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|large-pages | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|last_insert_id | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Last_query_cost | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|big-tables | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|license | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|local-infile | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: local_infile | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|log | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|log-bin | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|log-bin-index | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|log-bin-trust-function-creators | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: | | | Y | |
|log_bin_trust_function_creators | | | | |
+-------------------------------------+----------+-------------+------------+------------+
|log-bin-trust-routine-creators | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|log-error | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Aborted_connects | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: big_tables | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|log-isam | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|log-long-format | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|log-short-format | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|log-slave-updates | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|log-slow-admin-statements | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|log-slow-queries | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: log_slow_queries | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|log-tc | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: | | | Y | |
|low_priority_updates | | | | |
+-------------------------------------+----------+-------------+------------+------------+
|lower_case_table_names | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|master-connect-retry | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|master-host | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|master-info-file | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|master-password | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|binlog-do-db | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|master-port | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|master-retry-count | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|master-ssl | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|master-ssl-ca | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|master-ssl-capath | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|master-ssl-cert | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|master-ssl-cipher | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|master-ssl-key | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|master-user | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|max-binlog-dump-events | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|binlog-ignore-db | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|max_allowed_packet | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|max_binlog_cache_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|max_binlog_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|max_connect_errors | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|max_connections | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|max_delayed_threads | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|max_error_count | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|max_seeks_for_key | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|max_sort_length | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|max_sp_recursion_depth | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|max_tmp_tables | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Max_used_connections | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|max_user_connections | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|max_write_lock_count | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|binlog_cache_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|memlock | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: locked_in_memory | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|merge | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|multi_range_count | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|multi_read_range | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|myisam-recover | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|myisam_block_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|myisam_data_pointer_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|myisam_max_extra_sort_file_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|myisam_max_sort_file_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Binlog_cache_use | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|myisam_repair_threads | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|myisam_sort_buffer_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|myisam_stats_method | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|ndb-autoincrement-prefetch-sz | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|ndb-cache-check-time | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|ndb-connectstring | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|ndb-distribution | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|ndb-report-thresh-binlog-mem-usage10 | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|ndb_extra_logging | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|ndb_use_exact_count | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|ndbcluster | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|net_buffer_length | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|net_read_timeout | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|net_retry_count | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|bulk_insert_buffer_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|net_write_timeout | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|new | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|no-defaults | Y | | | |
+-------------------------------------+----------+-------------+------------+------------+
|Not_flushed_delayed_rows | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|old-passwords | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: old_passwords | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|old-style-user-limits | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Open_files | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|open_files_limit | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Open_streams | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Bytes_received | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Open_table_definitions | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Open_tables | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Opened_tables | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|optimizer_prune_level | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|optimizer_search_depth | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|pid-file | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|port | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Qcache_hits | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Qcache_inserts | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Qcache_lowmem_prunes | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Qcache_not_cached | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Qcache_queries_in_cache | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Qcache_total_blocks | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|query_alloc_block_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|query_cache_limit | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|character-set-client-handshake | Y | | | |
+-------------------------------------+----------+-------------+------------+------------+
|query_cache_min_res_unit | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|query_cache_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|query_cache_type | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|query_cache_wlock_invalidate | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|query_prealloc_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Questions | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|range_alloc_block_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|read_buffer_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|read_only | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|read_rnd_buffer_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|character-set-filesystem | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|record_buffer | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|relay-log | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|relay-log-index | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|relay-log-info-file | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|relay_log_purge | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|relay_log_space_limit | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|replicate-wild-do-table | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|replicate-wild-ignore-table | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|report-host | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|report-password | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|report-port | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|report-user | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|rpl-recovery-rank | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: rpl_recovery_rank | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: character_set_server | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Rpl_status | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|safe-mode | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|safe-show-database | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: safe_show_database | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|safe-user-create | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|safemalloc-mem-limit | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|secure-auth | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: secure_auth | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Select_full_join | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Select_full_range_join | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|character-sets-dir | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Select_range | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Select_range_check | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Select_scan | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|server-id | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: server_id | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|set-variable | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: external-locking | | | | |
+-------------------------------------+----------+-------------+------------+------------+
|skip-grant-tables | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|skip-host-cache | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|skip-innodb | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|skip-innodb-checksums | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|skip-innodb-doublewrite | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: innodb_doublewrite | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|skip-large-pages | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|character_set_connection | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: large-pages | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|skip-locking | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|skip-merge | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: merge | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|skip-name-resolve | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|skip-networking | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|skip-new | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|skip-show-database | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|skip-slave-start | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|skip-stack-trace | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|character_set_results | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|skip-symbolic-links | Y | | | |
+-------------------------------------+----------+-------------+------------+------------+
|skip-symlink | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|skip-sync-bdb-logs | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|skip-thread-priority | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|slave-load-tmpdir | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|slave-skip-errors | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|Slow_launch_threads | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|slow_launch_time | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Slow_queries | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|socket | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|sort_buffer_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Sort_merge_passes | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Sort_range | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Sort_rows | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|ansi | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|collation-server | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|Sort_scan | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|sporadic-binlog-dump-fail | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|sql-bin-update-same | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|sql-mode | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: sql_mode | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|sql_auto_is_null | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|sql_big_selects | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|sql_big_tables | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|sql_buffer_result | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|sql_log_bin | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: collation_server | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|sql_log_off | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|sql_log_update | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|sql_low_priority_updates | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|sql_max_join_size | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|sql_notes | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|ssl-ca | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|ssl-capath | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|ssl-cert | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|ssl-cipher | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|ssl-key | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|storage_engine | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|symbolic-links | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|sync-bdb-logs | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|sync-binlog | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|Com_alter_db | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: sync_binlog | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|sync-frm | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|- Variable: sync_frm | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|sysdate-is-now | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|table_cache | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|table_lock_wait_timeout | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Table_locks_immediate | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Table_locks_waited | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|table_open_cache | | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|table_type | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Com_alter_event | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|tc-heuristic-recover | Y | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Tc_log_max_pages_used | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Tc_log_page_size | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Tc_log_page_waits | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|temp-pool | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Threads_running | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|time_format | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|time_zone | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|timed_mutexes | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|timestamp | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|tmp_table_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|tmpdir | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|transaction-isolation | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|transaction_alloc_block_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Com_analyze | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|transaction_prealloc_size | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|tx_isolation | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|unique_checks | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|updatable_views_with_limit | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Uptime | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|user | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|verbose | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|version | Y | | | |
+-------------------------------------+----------+-------------+------------+------------+
|wait_timeout | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|warning_count | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Com_backup_table | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|warnings | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|with-debug | Y | Y | | |
+-------------------------------------+----------+-------------+------------+------------+
|Com_begin | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_change_db | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|auto-increment-increment | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Com_create_index | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_create_table | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_dealloc_sql | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|auto-increment-offset | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Com_delete | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_delete_multi | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_do | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_drop_db | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_drop_event | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_drop_function | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_drop_index | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_drop_table | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_drop_user | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_execute_sql | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|autocommit | | | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Com_flush | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_grant | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_ha_close | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_ha_open | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_ha_read | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_help | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_insert | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_insert_select | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_kill | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_load | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|automatic-sp-privileges | Y | Y | Y | |
+-------------------------------------+----------+-------------+------------+------------+
|Com_purge_before_date | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_rename_table | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
|Com_repair | | | | Y |
+-------------------------------------+----------+-------------+------------+------------+
COMMAND OPTIONS
When you start the mysqld server, you can specify program options using
any of the methods described in Section 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 3.2, "Using Option Files".
mysqld reads options from the [mysqld] and [server] groups.
mysqld_safe reads options from the [mysqld], [server], [mysqld_safe],
and [safe_mysqld] groups. mysql.server reads options from the [mysqld]
and [mysql.server] groups.
An embedded MySQL server usually reads options from the [server],
[embedded], and [xxxxx_SERVER] groups, where xxxxx is the name of the
application into which the server is embedded.
mysqld accepts many command options. For a brief summary, execute
mysqld --help. To see the full list, use mysqld --verbose --help.
The following list shows some of the most common server options.
Additional options are described in other sections:
o Options that affect security: See Section 5.3, "Security-Related
mysqld Options".
o SSL-related options: See Section 7.7.3, "SSL Command Options".
o Binary log control options: See Section 10.3, "The Binary Log".
o Replication-related options: See Section 8, "Replication Startup
Options".
o Options specific to particular storage engines: See Section 1.1,
"MyISAM Startup Options", Section 5.3, "BDB Startup Options",
Section 2.4, "InnoDB Startup Options and System Variables", and
Section 6.5.1, "MySQL Cluster-Related Command Options for mysqld".
You can also set the values of server system variables by using variable names
as options, as described later in this section.
o --help, -?
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 9.3, "Running MySQL in ANSI Mode", and the section called "SQL
MODES".
o --basedir=path, -b path
The path to the MySQL installation directory. All paths are usually
resolved relative to this directory.
o big-tables
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.
o --bind-address=IP
The IP address to bind to.
o --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.
o --character-sets-dir=path
The directory where character sets are installed. See Section 9.1, "The
Character Set Used for Data and Sorting".
o --character-set-client-handshake
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.
o --character-set-filesystem=charset_name
The filesystem character set. This option sets the character_set_filesystem
system variable. It was added in MySQL 5.0.19.
o --character-set-server=charset_name, -C charset_name
Use charset_name as the default server character set. See Section 9.1, "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.
o --chroot=path
--log-error is specified. mysqld does not close the console window if this
option is used.
o --core-file
Write a core file if mysqld dies. For some systems, you must also specify
the --core-file-size option to mysqld_safe. See mysqld_safe(1). Note that
on some systems, such as Solaris, you do not get a core file if you are
also using the --user option.
o --datadir=path, -h path
The path to the data directory.
o --debug[=debug_options], -# [debug_options]
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 Section 1.2,
"Creating Trace Files".
o --default-character-set=charset_name (DEPRECATED)
Use charset_name as the default character set. This option is deprecated in
favor of --character-set-server. See Section 9.1, "The Character Set Used
for Data and Sorting".
o --default-collation=collation_name
Use collation_name as the default collation. This option is deprecated in
favor of --collation-server. See Section 9.1, "The Character Set Used for
Data and Sorting".
o --default-storage-engine=type
Set the default storage engine (table type) for tables. See Chapter 14,
Storage Engines and Table Types.
o --default-table-type=type
This option is a synonym for --default-storage-engine.
o --default-time-zone=timezone
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.
o --delay-key-write[={OFF|ON|ALL}]
Specify how to use delayed key writes. Delayed key writing causes key
o --enable-named-pipe
Enable support for named pipes. This option applies only on Windows NT,
2000, XP, and 2003 systems, and can be used only with the mysqld-nt and
mysqld-max-nt servers that support named-pipe connections.
o --exit-info[=flags], -T [flags]
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!
o --external-locking
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.
Note: If you use this option to enable updates to MyISAM tables from many
MySQL processes, you must ensure that the following conditions are
satisfied:
o You should not use the query cache for queries that use tables that are
updated by another process.
o You should not use --delay-key-write=ALL or DELAY_KEY_WRITE=1 on any
shared tables.
The easiest way to ensure this is to always use --external-locking together
with --delay-key-write=OFF and --query-cache-size=0. (This is not done by
default because in many setups it is useful to have a mixture of the
preceding options.)
o --flush
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 4.2, "What to Do If MySQL Keeps Crashing".
o --init-file=file_name
Read SQL statements from this file at startup. Each statement must be on a
single line and should not include comments.
o --innodb-safe-binlog
Adds consistency guarantees between the content of InnoDB tables and the
binary log. See Section 10.3, "The Binary Log". This option was removed in
MySQL 5.0.3, having been made obsolete by the introduction of XA
transaction support.
Some hardware/operating system architectures support memory pages greater
than the default (usually 4KB). The actual implementation of this support
depends on the underlying hardware and OS. Applications that perform a lot
of memory accesses may obtain performance improvements by using large pages
due to reduced Translation Lookaside Buffer (TLB) misses.
Currently, MySQL supports only the Linux implementation of large pages
support (which is called HugeTLB in Linux). We have plans to extend this
support to FreeBSD, Solaris and possibly other platforms.
Before large pages can be used on Linux, it is necessary to configure the
HugeTLB memory pool. For reference, consult the hugetlbpage.txt file in the
Linux kernel source.
This option is disabled by default. It was added in MySQL 5.0.3.
o --log[=file_name], -l [file_name]
Log connections and SQL statements received from clients to this file. See
Section 10.2, "The General Query Log". If you omit the filename, MySQL uses
host_name.log as the filename.
o --log-bin[=base_name]
Enable binary logging. The server logs all statements that change data to
the binary log, which is used for backup and replication. See Section 10.3,
"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 8.1, "Open Issues in MySQL", for the reason). Otherwise, MySQL uses
host_name-bin as the basename.
o --log-bin-index[=file_name]
The index file for binary log filenames. See Section 10.3, "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.
o --log-bin-trust-function-creators[={0|1}]
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 creation. See Section 5, "Binary Logging of Stored Routines
and Triggers".
This option was added in MySQL 5.0.16.
has no extension, the server adds an extension of .err.
o --log-isam[=file_name]
Log all MyISAM changes to this file (used only when debugging MyISAM).
o --log-long-format (DEPRECATED)
Log extra information to the update log, binary update log, and slow query
log, if they have been activated. For example, the username and timestamp
are logged for all queries. This option is deprecated, as it now represents
the default logging behavior. (See the description for --log-short-format.)
The --log-queries-not-using-indexes option is available for the purpose of
logging queries that do not use indexes to the slow query log.
o --log-queries-not-using-indexes
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 10.4, "The Slow
Query Log".
o --log-short-format
Log less information to the update log, binary update log, and slow query
log, if they have been activated. For example, the username and timestamp
are not logged for queries.
o --log-slow-admin-statements
Log slow administrative statements such as OPTIMIZE TABLE, ANALYZE TABLE,
and ALTER TABLE to the slow query log.
o --log-slow-queries[=file_name]
Log all queries that have taken more than long_query_time seconds to
execute to this file. See Section 10.4, "The Slow Query Log". See the
descriptions of the --log-long-format and --log-short-format options for
details.
o --log-tc=file_name
The name of the memory-mapped transaction coordinator log file (for XA
transactions that affect multiple storage engines when the binary log is
disabled). The default name is tc.log. The file is created under the data
directory if not given as a full pathname. Currently, this option is
unused. Added in MySQL 5.0.3.
o --log-tc-size=size
The size in bytes of the memory-mapped transaction coordinator log. The
default size is 24KB. Added in MySQL 5.0.3.
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. See
Section 3.2, "Table Locking Issues".
o --memlock
Lock the mysqld process in memory. This works on systems such as Solaris
that support the mlockall() system call. This might help if you have a
problem where the operating system is causing mysqld to swap on disk. Note
that use of this option requires that you run the server as root, which is
normally not a good idea for security reasons. See Section 5.5, "How to Run
MySQL as a Normal User".
o --myisam-recover[=option[,option]...]]
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. You can also use a value
of "" to disable this option. If this option is used, 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:
+--------+----------------------------------------------+
|Option | Description |
+--------+----------------------------------------------+
|DEFAULT | The same as not giving any |
| | option to |
| | --myisam-recover. |
+--------+----------------------------------------------+
|BACKUP | If the data file was |
| | changed during recovery, |
| | save a backup of the |
| | tbl_name.MYD |
| | file |
| | as |
| | tbl_name-datetime.BAK. |
+--------+----------------------------------------------+
|FORCE | Run recovery even if we would lose more than |
| | one row from the |
| | .MYD file. |
+--------+----------------------------------------------+
|QUICK | Don'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
If the binary includes support for the NDB Cluster storage engine, this
option enables the engine, which is disabled by default. See Chapter 15,
MySQL Cluster.
o --old-passwords
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 6.9, "Password Hashing as of MySQL 4.1".
o --one-thread
Only use one thread (for debugging under Linux). This option is available
only if the server is built with debugging enabled. See Section 1,
"Debugging a MySQL Server".
o --open-files-limit=count
Change the number of file descriptors available to mysqld. If this option
is not set or is set to 0, mysqld uses the value to reserve file
descriptors with setrlimit(). If the value is 0, mysqld reserves
max_connectionsx5 or max_connections + table_open_cachex2 files (whichever
is larger). You should try increasing this value if mysqld gives you the
error Too many open files.
o --pid-file=path
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.
o --port=port_num, -P port_num
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.
o --port-open-timeout=num
On some systems, when the server is stopped, the TCP/IP port might not
become available immediately. If the server is restarted quickly afterward,
its attempt to reopen the port can fail. This option indicates how many
seconds the server should wait for the TCP/IP port to become free if it
cannot be opened. The default is not to wait. This option was added in
MySQL 5.0.19.
o --safe-mode
Skip some optimization stages.
o --safe-show-database (DEPRECATED)
Enable shared-memory connections by local clients. This option is available
only on Windows.
o --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.
o --skip-bdb
Disable the BDB storage engine. This saves memory and might speed up some
operations. Do not use this option if you require BDB tables.
o --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 3.3, "Concurrent Inserts".
o --skip-external-locking
Do not use external locking (system locking). With external locking
disabled, you must shut down the server to use myisamchk. (See Section 4.3,
"MySQL Stability".) To avoid this requirement, use the CHECK TABLE and
REPAIR TABLE statements to check and repair MyISAM tables.
External locking has been disabled by default since MySQL 4.0.
o --skip-grant-tables
This option causes the server not to use the privilege system at all, which
gives anyone with access to the server unrestricted access to all
databases. You can cause a running server to start using the grant tables
again by executing mysqladmin flush-privileges or mysqladmin reload command
from a system shell, or by issuing a MySQL FLUSH PRIVILEGES statement after
connecting to the server. This option also suppresses loading of
user-defined functions (UDFs).
o --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 5.6, "How MySQL Uses DNS".
o --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.
o --skip-ndbcluster
Disable the NDB Cluster storage engine. This is the default for binaries
that were built with NDB Cluster storage engine support; the server
allocates memory and other resources for this storage engine only if the
--ndbcluster option is given explicitly. See Section 4.3, "Quick Test Setup
of MySQL Cluster", for an example of usage.
o --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 5.6, "How MySQL Uses DNS".
o --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 7.7.3, "SSL Command Options".
o --standalone
Available on Windows NT-based systems only; instructs the MySQL server not
to run as a service.
o --symbolic-links, --skip-symbolic-links
Enable or disable symbolic link support. This option has different effects
on Windows and Unix:
o On Windows, enabling symbolic links allows you to establish a symbolic
link to a database directory by creating a db_name.sym file that
contains the path to the real directory. See Section 6.1.3, "Using
Symbolic Links for Databases on Windows".
o On Unix, enabling symbolic links means that you can link a MyISAM index
file or data file to another directory with the INDEX DIRECTORY or DATA
DIRECTORY options of the CREATE TABLE statement. If you delete or rename
the table, the files that its symbolic links point to also are deleted
or renamed. See Section 6.1.2, "Using Symbolic Links for Tables on
Unix".
o --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.
o --skip-show-database
Disable using thread priorities for faster response time.
o --socket=path
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).
o --sql-mode=value[,value[,value...]]
Set the SQL mode. See the section called "SQL MODES".
o --sysdate-is-now
As of MySQL 5.0.13, SYSDATE() by default returns the time at which it
executes, not the time at which the statement in which it occurs begins
executing. This differs from the behavior of NOW(). This option causes
SYSDATE() to be an alias for NOW(). For information about the implications
for binary logging and replication, see the description for SYSDATE() in
Section 5, "Date and Time Functions" and for SET TIMESTAMP in Section 5.3,
"SET Syntax".
This option was added in MySQL 5.0.20.
o --tc-heuristic-recover={COMMIT|ROLLBACK}
The type of decision to use in the heuristic recovery process. Currently,
this option is unused. Added in MySQL 5.0.3.
o --temp-pool
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.
o --transaction-isolation=level
Sets the default transaction isolation level. The level value can be
READ-UNCOMMITTED, READ-COMMITTED, REPEATABLE-READ, or SERIALIZABLE. See
Section 4.6, "SET TRANSACTION Syntax".
o --tmpdir=path, -t path
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
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 5.1, "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.
o --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.
It is also possible to set variables by using --set-variable=var_name=value or
-O var_name=value syntax. This syntax is deprecated.
You can change the values of most system variables for a running server with
the SET statement. See Section 5.3, "SET Syntax".
the section called "SYSTEM VARIABLES", provides a full description for all
variables, and additional information for setting them at server startup and
runtime. Section 5.2, "Tuning Server Parameters", includes information on
optimizing the server by tuning system variables.
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
mysqld --no-defaults --verbose --help
o To see the current values used by a running server, use the SHOW
VARIABLES statement.
This section provides a description of each system variable. Variables
with no version indicated are present in all MySQL 5.0 releases. For
historical information concerning their implementation, please see
MySQL 3.23, 4.0, 4.1 Reference Manual.
For additional system variable information, see these sections:
o the section called "USING SYSTEM VARIABLES", discusses the syntax
for setting and displaying system variable values.
o the section called "Dynamic System Variables", lists the variables
that can be set at runtime.
o Information on tuning sytem variables can be found in Section 5.2,
"Tuning Server Parameters".
o Section 2.4, "InnoDB Startup Options and System Variables", lists
InnoDB system variables.
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.
o auto_increment_increment
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 can be set
globally or locally, 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.
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.)
o 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;
+-----+
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 x 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 x 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
The auto_increment_increment variable was added in MySQL 5.0.2. Its
default value is 1. See Section 13, "Auto-Increment in Multiple-Master
Replication".
o > auto_increment_offset
This variable was introduced in MySQL 5.0.2. Its default value is 1.
For particulars, see the description for auto_increment_increment.
o back_log
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.
o basedir
The MySQL installation base directory. This variable can be set with
the --basedir option.
o bdb_cache_size
The size of the buffer that is allocated for caching indexes and
rows for BDB tables. If you don't use BDB tables, you should start
mysqld with --skip-bdb to not allocate memory for this cache.
o bdb_home
The base directory for BDB tables. This should be assigned the same
value as the datadir variable.
o bdb_log_buffer_size
The size of the buffer that is allocated for caching indexes and
rows for BDB tables. If you don't use BDB tables, you should set
this to 0 or start mysqld with --skip-bdb to not allocate memory for
this cache.
o bdb_logdir
This is ON if you are using --bdb-shared-data to start Berkeley DB
in multi-process mode. (Do not use DB_PRIVATE when initializing
Berkeley DB.)
o bdb_tmpdir
The BDB temporary file directory.
o binlog_cache_size
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 10.3, "The Binary Log".
o bulk_insert_buffer_size
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.
o character_set_client
The character set for statements that arrive from the client.
o character_set_connection
The character set used for literals that do not have a character set
introducer and for number-to-string conversion.
o character_set_database
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.
o character_set_filesystem
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
The character set used by the server for storing identifiers. The
value is always utf8.
o character_sets_dir
The directory where character sets are installed.
o collation_connection
The collation of the connection character set.
o collation_database
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.
o collation_server
The server's default collation.
o completion_type
The transaction completion type:
o If the value is 0 (the default), COMMIT and ROLLBACK are
unaffected.
o 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.)
o If the value is 2, COMMIT and ROLLBACK are equivalent to COMMIT
RELEASE and ROLLBACK RELEASE, respectively. (The server
disconnects after terminating the transaction.)
This variable was added in MySQL 5.0.3
o concurrent_insert
If ON (the default), MySQL allows INSERT and SELECT statements to
run concurrently for MyISAM tables that have no free blocks in the
middle. You can turn this option off by starting mysqld with --safe
or --skip-new.
In MySQL 5.0.6, this variable was changed to take three integer
values:
+------+-----------------------------+
| | by another thread |
| | the |
| | new row will be inserted |
| | at end of table. If |
| | table |
| | is not in use, MySQL does |
| | a normal read lock |
| | and |
| | inserts the new row into |
| | the hole. |
+------+-----------------------------+
See also Section 3.3, "Concurrent Inserts".
o connect_timeout
The number of seconds that the mysqld server waits for a connect
packet before responding with Bad handshake.
o datadir
The MySQL data directory. This variable can be set with the
--datadir option.
o date_format
This variable is not implemented.
o datetime_format
This variable is not implemented.
o default_week_format
The default mode value to use for the WEEK() function. See
Section 5, "Date and Time Functions".
o delay_key_write
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.
+-------+---------------------------------------+
|Option | Description |
+-------+---------------------------------------+
|OFF | DELAY_KEY_WRITE is |
| | ignored. |
+-------+---------------------------------------+
|ON | MySQL honors any |
| | DELAY_KEY_WRITE option |
| | specified in |
| | CREATE |
starting the server with the --myisam-recover option (for example,
--myisam-recover=BACKUP,FORCE). See the section called "COMMAND
OPTIONS", and Section 1.1, "MyISAM Startup Options".
Note that enabling external locking with --external-locking offers
no protection against index corruption for tables that use delayed
key writes.
o delayed_insert_limit
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.
o delayed_insert_timeout
How many seconds an INSERT DELAYED handler thread should wait for
INSERT statements before terminating.
o delayed_queue_size
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.
o div_precision_increment
This variable indicates the number of digits of precision by which
to increase the result of division operations performed with the /
operator. The default value is 4. The minimum and maximum values are
0 and 30, respectively. The following example illustrates the effect
of increasing the default value.
mysql> SELECT 1/7;
+--------+
| 1/7 |
+--------+
| 0.1429 |
+--------+
mysql> SET div_precision_increment = 12;
mysql> SELECT 1/7;
+----------------+
| 1/7 |
+----------------+
| 0.142857142857 |
+----------------+
This variable was added in MySQL 5.0.6.
o engine_condition_pushdown
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.
o flush
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 4.2, "What to Do If
MySQL Keeps Crashing". This variable is set to ON if you start
mysqld with the --flush option.
o flush_time
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.
o ft_boolean_syntax
The list of operators supported by boolean full-text searches
performed using IN BOOLEAN MODE. See Section 7.1, "Boolean Full-Text
Searches".
The default variable value is '+ -><()~*:""&|'. The rules for
changing the value are as follows:
o Operator function is determined by position within the string.
o The replacement value must be 14 characters.
o Each character must be an ASCII non-alphanumeric character.
o Either the first or second character must be a space.
o 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.
o Positions 10, 13, and 14 (which by default are set to `:', `&',
and `|') are reserved for future extensions.
o ft_max_word_len
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.
The file from which to read the list of stopwords for full-text
searches. All the words from the file are used; comments are not
honored. By default, a built-in list of stopwords is used (as
defined in the myisam/ft_static.c file). Setting this variable to
the empty string ('') disables stopword filtering.
Note: FULLTEXT indexes must be rebuilt after changing this variable
or the contents of the stopword file. Use REPAIR TABLE tbl_name
QUICK.
o group_concat_max_len
The maximum allowed result length for the GROUP_CONCAT() function.
The default is 1024.
o have_archive
YES if mysqld supports ARCHIVE tables, NO if not.
o have_bdb
YES if mysqld supports BDB tables. DISABLED if --skip-bdb is used.
o have_blackhole_engine
YES if mysqld supports BLACKHOLE tables, NO if not.
o 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.
o have_crypt
YES if the crypt() system call is available to the server, NO if
not. If not, the ENCRYPT() function cannot be used.
o have_csv
YES if mysqld supports ARCHIVE tables, NO if not.
o have_example_engine
YES if mysqld supports EXAMPLE tables, NO if not.
have_federated_engine
YES if mysqld supports FEDERATED tables, NO if not. This variable
was added in MySQL 5.0.3.
o have_geometry
o have_ndbcluster
YES if mysqld supports NDB Cluster tables. DISABLED if
--skip-ndbcluster is used.
o have_openssl
YES if mysqld supports SSL connections, NO if not.
o have_query_cache
YES if mysqld supports the query cache, NO if not.
o have_raid
In MySQL 5.0, this variable appears only for reasons of backward
compatibility. It is always NO because RAID tables are no longer
supported.
o have_rtree_keys
YES if RTREE indexes are available, NO if not. (These are used for
spatial indexes in MyISAM tables.)
o 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.
o init_connect
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
format of the string is the same as for the init_connect variable.
o innodb_xxx
InnoDB system variables are listed in Section 2.4, "InnoDB Startup
Options and System Variables".
o interactive_timeout
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.
o join_buffer_size
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.
o key_buffer_size
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. 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.
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 2.16, "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
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 4.6, "The MyISAM Key Cache".
o key_cache_age_threshold
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 4.6, "The MyISAM Key Cache".
o key_cache_block_size
The size in bytes of blocks in the key cache. The default value is
1024. See Section 4.6, "The MyISAM Key Cache".
o key_cache_division_limit
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 4.6, "The MyISAM Key Cache".
o language
The language used for error messages.
o large_file_support
Whether mysqld was compiled with options for large file support.
o large_pages
Whether large page support is enabled. This variable was added in
MySQL 5.0.3.
o license
The type of license the server has.
o local_infile
Whether LOCAL is supported for LOAD DATA INFILE statements. See
Section 5.4, "Security Issues with LOAD DATA LOCAL".
o locked_in_memory
Whether mysqld was locked in memory with --memlock.
o log
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. See
Section 5, "Binary Logging of Stored Routines and Triggers".
This variable was added in MySQL 5.0.16.
o log_bin_trust_routine_creators
This is the old name for log_bin_trust_function_creators. Before
MySQL 5.0.16, it also applies to stored procedures, not just stored
functions. As of 5.0.16, this variable is deprecated. It is
recognized for backward compatibility but its use results in a
warning.
This variable was added in MySQL 5.0.6.
o log_error
The location of the error log.
o log_queries_not_using_indexes
Whether queries that do not use indexes are logged to the slow query
log. See Section 10.4, "The Slow Query Log". This variable was added
in MySQL 5.0.23.
o 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 8, "Replication Startup Options".
o log_slow_queries
Whether slow queries should be logged. "Slow" is determined by the
value of the long_query_time variable. See Section 10.4, "The Slow
Query Log".
o log_warnings
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.
o long_query_time
o lower_case_file_system
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.
o lower_case_table_names
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 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.
o max_allowed_packet
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.
o max_binlog_cache_size
If a multiple-statement transaction requires more than this amount
of memory, the server generates a Multi-statement transaction
required more than 'max_binlog_cache_size' bytes of storage error.
o max_binlog_size
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
The number of simultaneous client connections allowed. Increasing
this value increases the number of file descriptors that mysqld
requires. See Section 4.8, "How MySQL Opens and Closes Tables", for
comments on file descriptor limits. See also Section 2.6, "Too many
connections".
o max_delayed_threads
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.
o max_error_count
The maximum number of error, warning, and note messages to be stored
for display by the SHOW ERRORS and SHOW WARNINGS statements.
o max_heap_table_size
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.
o max_insert_delayed_threads
This variable is a synonym for max_delayed_threads.
o max_join_size
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.
16,382. The allowable range of values is from 0 to 1 million. If the
value is set lower than the current number of prepared statements,
existing statements are not affected and can be used, but no new
statements can be prepared until the current number drops below the
limit. This variable was added in MySQL 5.0.21.
o max_relay_log_size
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 3,
"Replication Implementation Details".
o max_seeks_for_key
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 5.4.13, "SHOW INDEX Syntax"). By setting this
to a low value (say, 100), you can force MySQL to prefer indexes
instead of table scans.
o max_sort_length
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.
o max_sp_recursion_depth
The number of times that a stored procedure may call itself. The
default value for this option is 0, which completely disallows
recursion in stored procedures. The maximum value is 255.
This variable can be set globally and per session.
o max_tmp_tables
The maximum number of temporary tables a client can keep open at the
same time. (This option does not yet do anything.)
o max_user_connections
The maximum number of simultaneous connections allowed to any given
MySQL account. A value of 0 means "no limit."
The default pointer size in bytes, to be used by CREATE TABLE for
MyISAM tables when no MAX_ROWS option is specified. This variable
cannot be less than 2 or larger than 7. The default value is 6 (4
before MySQL 5.0.6). This variable was added in MySQL 4.1.2. See
Section 2.11, "The table is full".
o myisam_max_extra_sort_file_size (DEPRECATED)
If the temporary file used for fast MyISAM index creation would be
larger than using the key cache by the amount specified here, prefer
the key cache method. This is mainly used to force long character
keys in large tables to use the slower key cache method to create
the index. The value is given in bytes.
Note: This variable was removed in MySQL 5.0.6.
o myisam_max_sort_file_size
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.
o myisam_recover_options
The value of the --myisam-recover option. See the section called
"COMMAND OPTIONS".
o myisam_repair_threads
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.
o myisam_sort_buffer_size
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.
o myisam_stats_method
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.
engine needs to send the range requests to all nodes, and sending
many of those requests at once reduces the communication costs
significantly. This variable was added in MySQL 5.0.3.
o named_pipe
(Windows only.) Indicates whether the server supports connections
over named pipes.
o ndb_autoincrement_prefetch_sz
Determines the probability of gaps in an autoincremented column. Set
to 1 to minimize this. Set to a high value for optimization -- makes
inserts faster, but decreases the likelihood that consecutive
autoincrement numbers will be used in a batch of inserts. Default
value: 32. Mimimum value: 1.
o ndb_cache_check_time
The number of milliseconds to wait before checking the NDB query
cache. Setting this to 0 (the default and minimum value) means that
the NDB query cache will be checked for validation on every query.
The recommended maximum value for this variable is 1000, which means
that the query cache is checked once per second. A larger value
means the NDB query cache is less often checked and invalidated due
to updates on a different mysqld. It is generally not desirable to
set this to a value greater than 2000.
o ndb_force_send
Forces sending of buffers to NDB immediately, without waiting for
other threads. Defaults to ON.
o ndb_index_stat_cache_entries
Sets the granularity of the statistics by determining the number of
starting and ending keys to store in the statistics memory cache.
Zero means no caching takes place; in this case, the data nodes are
always queries directly. Default value: 32.
o ndb_index_stat_enable
Use NDB index statistics in query optimization. Defaults to ON.
o ndb_index_stat_update_freq
How often to query data nodes instead of the statistics cache. For
example, a value of 20 (the default) means to direct every 20th
query to the data nodes.
o ndb_report_thresh_binlog_epoch_slip
will be sent to the cluster log.
o ndb_use_exact_count
Forces NDB to use a count of records during SELECT COUNT(*) query
planning to speed up this type of query. The default value is ON.
For faster queries overall, disable this feature by setting the
value of ndb_use_exact_count to OFF.
o ndb_use_transactions
You can disable NDB transaction support by setting this variable's
values to OFF (not recommended). The default is ON.
o net_buffer_length
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.
o net_read_timeout
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.
o net_retry_count
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.
o net_write_timeout
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.
o new
This variable was used in MySQL 4.0 to turn on some 4.1 behaviors,
o open_files_limit
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.
o optimizer_prune_level
Controls the heuristics applied during query optimization to prune
less-promising partial plans from the optimizer search space. A
value of 0 disables heuristics so that the optimizer performs an
exhaustive search. A value of 1 causes the optimizer to prune plans
based on the number of rows retrieved by intermediate plans. This
variable was added in MySQL 5.0.1.
o optimizer_search_depth
The maximum depth of search performed by the query optimizer. Values
larger than the number of relations in a query result in better
query plans, but take longer to generate an execution plan for a
query. Values smaller than the number of relations in a query return
an execution plan quicker, but the resulting plan may be far from
being optimal. If set to 0, the system automatically picks a
reasonable value. If set to the maximum number of tables used in a
query plus 2, the optimizer switches to the algorithm used in MySQL
5.0.0 (and previous versions) for performing searches. This variable
was added in MySQL 5.0.1.
o pid_file
The pathname of the process ID (PID) file. This variable can be set
with the --pid-file option.
o port
The number of the port on which the server listens for TCP/IP
connections. This variable can be set with the --port option.
o preload_buffer_size
The size of the buffer that is allocated when preloading indexes.
o prepared_stmt_count
The current number of prepared statements. (The maximum number of
statements is given by the max_prepared_stmt_count system variable.)
This variable was added in MySQL 5.0.21.
o protocol_version
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 12.3, "Query Cache Configuration".
o query_cache_size
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 12.3,
"Query Cache Configuration", for more information.
o query_cache_type
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:
+------------+----------------------------------------+
|Option | Description |
+------------+----------------------------------------+
|0 or OFF | Don'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 ON | Cache all query results except for |
| | those that begin with SELECT |
| | SQL_NO_CACHE. |
+------------+----------------------------------------+
|2 or DEMAND | Cache results only for queries that |
| | begin with SELECT |
| | SQL_CACHE. |
+------------+----------------------------------------+
This variable defaults to ON.
o query_cache_wlock_invalidate
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
The size of blocks that are allocated when doing range optimization.
o read_buffer_size
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.
o read_only
When the variable is set to ON for a replication slave server, it
causes the slave to allow no updates except from slave threads or
from users that have the SUPER privilege. This can be useful to
ensure that a slave server accepts updates only from its master
server and not from clients. As of MySQL 5.0.16, this variable does
not apply to TEMPORARY tables.
o read_rnd_buffer_size
When reading rows in sorted order following a key-sorting operation,
the rows are read through this buffer to avoid disk seeks. 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.
o relay_log_purge
Disables or enables automatic purging of relay log files as soon as
they are not needed any more. The default value is 1 (ON).
o rpl_recovery_rank
This variable is unused.
o secure_auth
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 2.3, "Client
does not support authentication protocol".
connections. This is useful when running multiple MySQL instances on
a single physical machine. The default name is MYSQL. The name is
case sensitive.
o skip_external_locking
This is OFF if mysqld uses external locking, ON if external locking
is disabled.
o 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.
o 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.
o slave_compressed_protocol
Whether to use compression of the slave/master protocol if both the
slave and the master support it.
o slave_load_tmpdir
The name of the directory where the slave creates temporary files
for replicating LOAD DATA INFILE statements.
o slave_net_timeout
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.
o slave_skip_errors
The replication errors that the slave should skip (ignore).
o slave_transaction_retries
increments the Slow_launch_threads status variable.
o socket
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).
o sort_buffer_size
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 4.4, "Where MySQL Stores Temporary Files".
o sql_mode
The current server SQL mode, which can be set dynamically. See the
section called "SQL MODES".
o sql_slave_skip_counter
The number of events from the master that a slave server should
skip. See Section 6.2.6, "SET GLOBAL SQL_SLAVE_SKIP_COUNTER Syntax".
o ssl_ca
The path to a file with a list of trusted SSL CAs. This variable was
added in MySQL 5.0.23.
o ssl_capath
The path to a directory that contains trusted SSL CA certificates in
PEM format. This variable was added in MySQL 5.0.23.
o ssl_cert
The name of the SSL certificate file to use for establishing a
secure connection. This variable was added in MySQL 5.0.23.
o ssl_cipher
A list of allowable ciphers to use for SSL encryption. The cipher
list has the same format as the openssl ciphers command. This
variable was added in MySQL 5.0.23.
o ssl_key
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 occasionaly as for any other file.
o sync_frm
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.
o system_time_zone
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 9.8, "MySQL
Server Time Zone Support".
o table_cache
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 the section called "STATUS
VARIABLES". If the value of Opened_tables is large and you don't do
FLUSH TABLES often (which just forces all tables to be closed and
reopened), then you should increase the value of the table_cache
variable. For more information about the table cache, see
Section 4.8, "How MySQL Opens and Closes Tables".
o table_lock_wait_timeout
Specifies a wait timeout for table-level locks, in seconds. The
default timeout is 50 seconds. The timeout is active only if the
connection has open cursors. This variable can also be set globally
at runtime (you need the SUPER privilege to do this). It's available
as of MySQL 5.0.10.
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 the section called "STATUS VARIABLES".
o thread_concurrency
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.
o thread_stack
The stack size for each thread. Many of the limits detected by the
crash-me test are dependent on this value. The default is large
enough for normal operation. See Section 1.4, "The MySQL Benchmark
Suite". The default is 192KB.
o time_format
This variable is not implemented.
o time_zone
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 9.8, "MySQL Server Time Zone
Support".
o timed_mutexes
This variable controls whether InnoDB mutexes are timed. If this
variable is set to 0 or OFF (the default), mutex timing is disabled.
If the variable is set to 1 or ON, mutex timing is enabled. With
timing enabled, the os_wait_times value in the output from SHOW
ENGINE INNODB MUTEX indicates the amount of time (in ms) spent in
operating system waits. Otherwise, the value is 0. This variable was
added in MySQL 5.0.3.
o tmp_table_size
The maximum size of 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.
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.
o transaction_alloc_block_size
The amount in bytes by which to increase a per-transaction memory
pool which needs memory. See the description of
transaction_prealloc_size.
o transaction_prealloc_size
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.
o tx_isolation
The default transaction isolation level. Defaults to
REPEATABLE-READ.
This variable is set by the SET TRANSACTION ISOLATION LEVEL
statement. See Section 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';
o updatable_views_with_limit
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:
The BDB storage engine version.
o 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.
o version_compile_machine
The type of machine or architecture on which MySQL was built.
o version_compile_os
The type of operating system on which MySQL was built.
o 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 connections, not to connections made via Unix socket
files, 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.
USING SYSTEM VARIABLES
The mysql server maintains many system variables that indicate how it
is configured. the section called "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:
o 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 3,
"Specifying Program Options".)
o The server also maintains a set of session variables for each client
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 the section called
"Dynamic System Variables". To change a system variable with SET, refer
to it as var_name, optionally preceded by a modifier:
o 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.
o 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.
o LOCAL and @@local. are synonyms for SESSION and @@session..
o 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;
used for new connections until the server restarts. (To make a global
system variable setting permanent, you should set it in an option
file.) The change is visible to any client that accesses that global
variable. However, the change affects the corresponding session
variable only for clients that connect after the change. The global
variable change does not affect the session variable for any client
that is currently connected (not even that of the client that issues
the SET GLOBAL statement).
To prevent incorrect usage, MySQL produces an error if you use SET
GLOBAL with a variable that can only be used with SET SESSION or if you
do not specify GLOBAL (or @@global.) when setting a global variable.
To set a SESSION variable to the GLOBAL value or a GLOBAL value to the
compiled-in MySQL default value, use the DEFAULT keyword. For example,
the following two statements are identical in setting the session value
of max_join_size to the global value:
SET max_join_size=DEFAULT;
SET @@session.max_join_size=@@global.max_join_size;
Not all system variables can be set to DEFAULT. In such cases, use of
DEFAULT results in an error.
You can refer to the values of specific global or sesson system
variables in expressions by using one of the @@-modifiers. For example,
you can retrieve values in a SELECT statement like this:
SELECT @@global.sql_mode, @@session.sql_mode, @@sql_mode;
When you refer to a system variable in an expression as @@var_name
(that is, when you do not specify @@global. or @@session.), MySQL
returns the session value if it exists and the global value otherwise.
(This differs from SET @@var_name = value, which always refers to the
session value.)
Note: Some 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 |
| character_set_database | latin1 |
| character_set_results | latin1 |
| character_set_server | latin1 |
| character_set_system | utf8 |
| character_sets_dir | /usr/share/mysql/charsets/ |
| collation_connection | latin1_swedish_ci |
| collation_database | latin1_swedish_ci |
| collation_server | latin1_swedish_ci |
| innodb_additional_mem_pool_size | 1048576 |
| innodb_autoextend_increment | 8 |
| innodb_buffer_pool_awe_mem_mb | 0 |
| innodb_buffer_pool_size | 8388608 |
| innodb_checksums | ON |
| innodb_commit_concurrency | 0 |
| innodb_concurrency_tickets | 500 |
| innodb_data_file_path | ibdata1:10M:autoextend |
| innodb_data_home_dir | |
| version | 5.0.19-Max |
| version_comment | MySQL Community Edition - Max (GPL) |
| version_compile_machine | i686 |
| version_compile_os | pc-linux-gnu |
| wait_timeout | 28800 |
+--------+--------------------------------------------------------------+
With a LIKE clause, the statement displays only those variables that
match the pattern. To obtain a specific variable name, use a LIKE
clause as shown:
SHOW VARIABLES LIKE 'max_join_size';
SHOW SESSION VARIABLES LIKE 'max_join_size';
To get a list of variables whose name match a pattern, use the `%'
wildcard character in a LIKE clause:
SHOW VARIABLES LIKE '%size%';
SHOW GLOBAL VARIABLES LIKE '%size%';
Wildcard characters can be used in any position within the pattern to
be matched. Strictly speaking, because `_' is a wildcard that matches
any single character, you should escape it as `\_' to match it
literally. In practice, this is rarely necessary.
For SHOW VARIABLES, if you specify neither GLOBAL nor SESSION, MySQL
returns SESSION values.
The reason for requiring the GLOBAL keyword when setting GLOBAL-only
variables but not when retrieving them is to prevent problems in the
future. If we were to remove a SESSION variable that has the same name
as a GLOBAL variable, a client with the SUPER privilege might
accidentally change the GLOBAL variable rather than just the SESSION
variable for its own connection. If we add a SESSION variable with the
same name as a GLOBAL variable, a client that intends to change the
MySQL 5.0 supports one structured variable type, which specifies
parameters governing the operation of key caches. A key cache
structured variable has these components:
o key_buffer_size
o key_cache_block_size
o key_cache_division_limit
o 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 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:
o 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.
o 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.
o 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.
o global, session, and local are not legal instance names. This avoids
a conflict with notation such as @@global.var_name for referring to
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.
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
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 Name | Value Type | Type |
+--------------------------------+----------------+------------------+
|character_set_server | string | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|slow_launch_time | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|sort_buffer_size | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|sql_auto_is_null | boolean | SESSION |
+--------------------------------+----------------+------------------+
|sql_big_selects | boolean | SESSION |
+--------------------------------+----------------+------------------+
|sql_big_tables | boolean | SESSION |
+--------------------------------+----------------+------------------+
|sql_buffer_result | boolean | SESSION |
+--------------------------------+----------------+------------------+
|sql_log_bin | boolean | SESSION |
+--------------------------------+----------------+------------------+
|sql_log_off | boolean | SESSION |
+--------------------------------+----------------+------------------+
|sql_log_update | boolean | SESSION |
+--------------------------------+----------------+------------------+
|sql_low_priority_updates | boolean | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|collation_connection | string | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|sql_max_join_size | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|sql_mode | enumeration | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|sql_notes | boolean | SESSION |
+--------------------------------+----------------+------------------+
|sql_quote_show_create | boolean | SESSION |
+--------------------------------+----------------+------------------+
|sql_safe_updates | boolean | SESSION |
+--------------------------------+----------------+------------------+
|sql_select_limit | numeric | SESSION |
+--------------------------------+----------------+------------------+
|sql_slave_skip_counter | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|updatable_views_with_limit | enumeration | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|sql_warnings | boolean | SESSION |
+--------------------------------+----------------+------------------+
|sync_binlog | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|timestamp | boolean | SESSION |
+--------------------------------+----------------+------------------+
|tmp_table_size | enumeration | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|transaction_alloc_block_size | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|transaction_prealloc_size | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|completion_type | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|tx_isolation | enumeration | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|unique_checks | boolean | SESSION |
+--------------------------------+----------------+------------------+
|wait_timeout | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|warning_count | numeric | SESSION |
+--------------------------------+----------------+------------------+
|concurrent_insert | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|connect_timeout | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|default_week_format | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|delay_key_write | OFF | ON | ALL | GLOBAL |
+--------------------------------+----------------+------------------+
|delayed_insert_limit | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|delayed_insert_timeout | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|autocommit | boolean | SESSION |
+--------------------------------+----------------+------------------+
|delayed_queue_size | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|div_precision_increment | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|engine_condition_pushdown | boolean | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|error_count | numeric | SESSION |
+--------------------------------+----------------+------------------+
|expire_logs_days | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|flush | boolean | GLOBAL |
+--------------------------------+----------------+------------------+
|flush_time | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|foreign_key_checks | boolean | SESSION |
+--------------------------------+----------------+------------------+
|ft_boolean_syntax | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|group_concat_max_len | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|innodb_support_xa | boolean | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|innodb_sync_spin_loops | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|innodb_table_locks | boolean | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|innodb_thread_concurrency | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|binlog_cache_size | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|innodb_thread_sleep_delay | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|insert_id | numeric | SESSION |
+--------------------------------+----------------+------------------+
|interactive_timeout | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|join_buffer_size | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|key_buffer_size | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|last_insert_id | numeric | SESSION |
+--------------------------------+----------------+------------------+
|local_infile | boolean | GLOBAL |
+--------------------------------+----------------+------------------+
|log_queries_not_using_indexes | boolean | GLOBAL |
+--------------------------------+----------------+------------------+
|log_warnings | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|long_query_time | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|bulk_insert_buffer_size | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|low_priority_updates | boolean | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|max_allowed_packet | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|max_binlog_cache_size | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|max_binlog_size | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|max_connect_errors | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|max_connections | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|max_delayed_threads | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|max_error_count | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|max_heap_table_size | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|max_insert_delayed_threads | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|max_user_connections | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|max_write_lock_count | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|multi_read_range | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|myisam_data_pointer_size | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|character_set_connection | string | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|log_bin_trust_function_creators | boolean | GLOBAL |
+--------------------------------+----------------+------------------+
|myisam_max_sort_file_size | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|myisam_repair_threads | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|myisam_sort_buffer_size | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|myisam_stats_method | enum | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|net_buffer_length | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|net_read_timeout | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|net_retry_count | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|net_write_timeout | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|old_passwords | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|character_set_filesystem | string | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|optimizer_prune_level | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|optimizer_search_depth | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|preload_buffer_size | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|query_alloc_block_size | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|query_cache_limit | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|query_cache_size | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|query_cache_type | enumeration | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|query_cache_wlock_invalidate | boolean | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|query_prealloc_size | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|range_alloc_block_size | numeric | GLOBAL | SESSION |
+--------------------------------+----------------+------------------+
|server_id | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|slave_compressed_protocol | boolean | GLOBAL |
+--------------------------------+----------------+------------------+
|slave_net_timeout | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
|slave_transaction_retries | numeric | GLOBAL |
+--------------------------------+----------------+------------------+
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 STATUS statement:
mysql> SHOW 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 |
+-----------------------------------+------------+
Many status variables are reset to 0 by the FLUSH STATUS statement.
The status variables have the following meanings. Variables with no
version indicated were already present prior to MySQL 5.0. For
information regarding their implementation history, see MySQL 3.23,
4.0, 4.1 Reference Manual.
o Aborted_clients
The number of connections that were aborted because the client died
without closing the connection properly. See Section 2.10,
"Communication Errors and Aborted Connections".
o Aborted_connects
The number of failed attempts to connect to the MySQL server. See
Section 2.10, "Communication Errors and Aborted Connections".
o Binlog_cache_disk_use
The number of transactions that used the temporary binary log cache
o 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 12.4,
"Query Cache Status and Maintenance".
All of the Com_stmt_xxx variables are increased even if a prepared
statement argument is unknown or an error occurred during execution.
In other words, their values correspond to the number of requests
issued, not to the number of requests successfully completed.
The Com_stmt_xxx status variables were added in 5.0.8:
o Com_stmt_prepare
o Com_stmt_execute
o Com_stmt_fetch
o Com_stmt_send_long_data
o Com_stmt_reset
o 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.
o Compression
Whether the client connection uses compression in the client/server
protocol. Added in MySQL 5.0.16.
o Connections
The number of connection attempts (successful or not) to the MySQL
server.
large, you may want to increase the tmp_table_size value to cause
temporary tables to be memory-based instead of disk-based.
o Delayed_errors
The number of rows written with INSERT DELAYED for which some error
occurred (probably duplicate key).
o Delayed_insert_threads
The number of INSERT DELAYED handler threads in use.
o Delayed_writes
The number of INSERT DELAYED rows written.
o Flush_commands
The number of executed FLUSH statements.
o Handler_commit
The number of internal COMMIT statements.
o Handler_delete
The number of times that rows have been deleted from tables.
o Handler_discover
The MySQL server can ask the NDB Cluster storage engine if it knows
about a table with a given name. This is called discovery.
Handler_discover indicates the number of times that tables have been
discovered via this mechanism.
o Handler_prepare
A counter for the prepare phase of two-phase commit operations.
Added in MySQL 5.0.3.
o 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.
o 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.
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.
o 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.
o Handler_rollback
The number of requests for a storage engine to perform a rollback
operation.
o Handler_savepoint
The number of requests for a storage engine to place a savepoint.
Added in MySQL 5.0.3.
o Handler_savepoint_rollback
The number of requests for a storage engine to roll back to a
savepoint. Added in MySQL 5.0.3.
o Handler_update
The number of requests to update a row in a table.
o Handler_write
The number of requests to insert a row in a table.
o Innodb_buffer_pool_pages_data
The number of pages containing data (dirty or clean). Added in MySQL
5.0.2.
o Innodb_buffer_pool_pages_dirty
The number of pages currently dirty. Added in MySQL 5.0.2.
o Innodb_buffer_pool_pages_flushed
The number of buffer pool page-flush requests. Added in MySQL 5.0.2.
o Innodb_buffer_pool_pages_free
The number of free pages. Added in MySQL 5.0.2.
o Innodb_buffer_pool_pages_total
The total size of buffer pool, in pages. Added in MySQL 5.0.2.
o Innodb_buffer_pool_read_ahead_rnd
The number of "random" read-aheads initiated by InnoDB. This happens
when a query scans a large portion of a table but in random order.
Added in MySQL 5.0.2.
o Innodb_buffer_pool_read_ahead_seq
The number of sequential read-aheads initiated by InnoDB. This
happens when InnoDB does a sequential full table scan. Added in
MySQL 5.0.2.
o Innodb_buffer_pool_read_requests
The number of logical read requests InnoDB has done. Added in MySQL
5.0.2.
o Innodb_buffer_pool_reads
The number of logical reads that InnoDB could not satisfy from the
buffer pool and had to do a single-page read. Added in MySQL 5.0.2.
o Innodb_buffer_pool_wait_free
Normally, writes to the InnoDB buffer pool happen in the background.
However, if it is necessary to read or create a page and no clean
pages are available, it is also necessary to wait for pages to be
flushed first. This counter counts instances of these waits. If the
buffer pool size has been set properly, this value should be small.
Added in MySQL 5.0.2.
o Innodb_buffer_pool_write_requests
The number writes done to the InnoDB buffer pool. Added in MySQL
5.0.2.
o Innodb_data_fsyncs
The number of fsync() operations so far. Added in MySQL 5.0.2.
o Innodb_data_pending_fsyncs
The current number of pending fsync() operations. Added in MySQL
5.0.2.
o Innodb_data_pending_reads
o Innodb_data_writes
The total number of data writes. Added in MySQL 5.0.2.
o Innodb_data_written
The amount of data written so far, in bytes. Added in MySQL 5.0.2.
o Innodb_dblwr_writes, Innodb_dblwr_pages_written
The number of doublewrite operations that have been performed and
the number of pages that have been written for this purpose. Added
in MySQL 5.0.2. See Section 2.14.1, "InnoDB Disk I/O".
o Innodb_log_waits
The number of times that the log buffer was too small and a wait was
required for it to be flushed before continuing. Added in MySQL
5.0.2.
o Innodb_log_write_requests
The number of log write requests. Added in MySQL 5.0.2.
o Innodb_log_writes
The number of physical writes to the log file. Added in MySQL 5.0.2.
o Innodb_os_log_fsyncs
The number of fsync() writes done to the log file. Added in MySQL
5.0.2.
o Innodb_os_log_pending_fsyncs
The number of pending log file fsync() operations. Added in MySQL
5.0.2.
o Innodb_os_log_pending_writes
The number of pending log file writes. Added in MySQL 5.0.2.
o Innodb_os_log_written
The number of bytes written to the log file. Added in MySQL 5.0.2.
o Innodb_page_size
The compiled-in InnoDB page size (default 16KB). Many values are
counted in pages; the page size allows them to be easily converted
to bytes. Added in MySQL 5.0.2.
The number of row locks currently being waited for. Added in MySQL
5.0.3.
o Innodb_row_lock_time
The total time spent in acquiring row locks, in milliseconds. Added
in MySQL 5.0.3.
o Innodb_row_lock_time_avg
The average time to acquire a row lock, in milliseconds. Added in
MySQL 5.0.3.
o Innodb_row_lock_time_max
The maximum time to acquire a row lock, in milliseconds. Added in
MySQL 5.0.3.
o Innodb_row_lock_waits
The number of times a row lock had to be waited for. Added in MySQL
5.0.3.
o Innodb_rows_deleted
The number of rows deleted from InnoDB tables. Added in MySQL 5.0.2.
o Innodb_rows_inserted
The number of rows inserted into InnoDB tables. Added in MySQL
5.0.2.
o Innodb_rows_read
The number of rows read from InnoDB tables. Added in MySQL 5.0.2.
o Innodb_rows_updated
The number of rows updated in InnoDB tables. Added in MySQL 5.0.2.
o Key_blocks_not_flushed
The number of key blocks in the key cache that have changed but have
not yet been flushed to disk.
o 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 the section called "SYSTEM VARIABLES".
o Key_blocks_used
o Key_write_requests
The number of requests to write a key block to the cache.
o Key_writes
The number of physical writes of a key block to disk.
o Last_query_cost
The total cost of the last compiled query as computed by the query
optimizer. This is useful for comparing the cost of different query
plans for the same query. The default value of 0 means that no query
has been compiled yet. This variable was added in MySQL 5.0.1, with
a default value of -1. In MySQL 5.0.7, the default was changed to 0;
also in version 5.0.7, the scope of Last_query_cost was changed to
session rather than global.
Prior to MySQL 5.0.16, this variable was not updated for queries
served from the query cache.
o Max_used_connections
The maximum number of connections that have been in use
simultaneously since the server started.
o Ndb_cluster_node_id
If the server is acting as a MySQL Cluster node, then the value of
this variable its node ID in the cluster.
If the server is not part of a MySQL Cluster, then the value of this
variable is 0.
o Ndb_config_from_host
If the server is part of a MySQL Cluster, the value of this variable
is the hostname or IP address of the Cluster management server from
which it gets its configuration data.
If the server is not part of a MySQL Cluster, then the value of this
variable is an empty string.
Prior to MySQL 5.0.23, this variable was named Ndb_connected_host.
o Ndb_config_from_port
If the server is part of a MySQL Cluster, the value of this variable
is the number of the port through which it is connected to the
CLuster management server from which it gets its configuration data.
The number of rows waiting to be written in INSERT DELAY queues.
o Open_files
The number of files that are open.
o Open_streams
The number of streams that are open (used mainly for logging).
o Open_tables
The number of tables that are open.
o Opened_tables
The number of tables that have been opened. If Opened_tables is big,
your table_cache value is probably too small.
o Qcache_free_blocks
The number of free memory blocks in the query cache.
o Qcache_free_memory
The amount of free memory for the query cache.
o Qcache_hits
The number of query cache hits.
o Qcache_inserts
The number of queries added to the query cache.
o Qcache_lowmem_prunes
The number of queries that were deleted from the query cache because
of low memory.
o Qcache_not_cached
The number of non-cached queries (not cacheable, or not cached due
to the query_cache_type setting).
o Qcache_queries_in_cache
The number of queries registered in the query cache.
o Qcache_total_blocks
indexes of your tables.
o Select_full_range_join
The number of joins that used a range search on a reference table.
o 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.
o 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.
o Select_scan
The number of joins that did a full scan of the first table.
o Slave_open_temp_tables
The number of temporary tables that the slave SQL thread currently
has open.
o Slave_running
This is ON if this server is a slave that is connected to a master.
o Slave_retried_transactions
The total number of times since startup that the replication slave
SQL thread has retried transactions. This variable was added in
version 5.0.4.
o Slow_launch_threads
The number of threads that have taken more than slow_launch_time
seconds to create.
o Slow_queries
The number of queries that have taken more than long_query_time
seconds. See Section 10.4, "The Slow Query Log".
o 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.
Variables used for SSL connections.
o Table_locks_immediate
The number of times that a table lock was acquired immediately.
o Table_locks_waited
The number of times that a table lock could not be acquired
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.
o Tc_log_max_pages_used
For the memory-mapped implementation of the log that is used by
mysqld when it acts as the transaction coordinator for recovery of
internal XA transactions, this variable indicates the largest number
of pages used for the log since the server started. If the product
of Tc_log_max_pages_used and Tc_log_page_size is always
significantly less than the log size, the size is larger than
necessary and can be reduced. (The size is set by the --log-tc-size
option. Currently, this variable is unused: It is unneeded for
binary log-based recovery, and the memory-mapped recovery log method
is not used unless the number of storage engines capable of
two-phase commit is greater than one. (InnoDB is the only applicable
engine.) Added in MySQL 5.0.3.
o Tc_log_page_size
The page size used for the memory-mapped implementation of the XA
recovery log. The default value is determined using getpagesize().
Currently, this variable is unused for the same reasons as described
for Tc_log_max_pages_used. Added in MySQL 5.0.3.
o Tc_log_page_waits
For the memory-mapped implementation of the recovery log, this
variable increments each time the server was not able to commit a
transaction and had to wait for a free page in the log. If this
value is large, you might want to increase the log size (with the
--log-tc-size option). For binary log-based recovery, this variable
increments each time the binary log cannot be closed because there
are two-phase commits in progress. (The close operation waits until
all such transactions are finished.) Added in MySQL 5.0.3.
o Threads_cached
The number of threads in the thread cache.
o Threads_connected
The number of seconds that the server has been up.
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.
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. 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="") if you
want to clear it explicitly.
You can change the SQL mode at runtime by using a SET [GLOBAL|SESSION]
sql_mode='modes' statement to set the sql_mode system value. Setting
the GLOBAL variable requires the SUPER privilege and affects the
operation of all clients that connect from that time on. Setting the
SESSION variable affects only the current client. Any client can change
its own session sql_mode value at any time.
You can retrieve the current global or session sql_mode value with the
following statements:
SELECT @@global.sql_mode;
SELECT @@session.sql_mode;
The most important sql_mode values are probably these:
o ANSI
Change syntax and behavior to be more conformant to standard SQL.
o STRICT_TRANS_TABLES
If a value could not be inserted as given into a transactional
table, abort the statement. For a non-transactional table, abort the
statement if the value occurs in a single-row statement or the first
row of a multiple-row statement. More detail is given later in this
section. (Implemented in MySQL 5.0.2)
o 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
Don't do full checking of dates. Check only that the month is in the
range from 1 to 12 and the day is in the range from 1 to 31. This is
very convenient for Web applications where you obtain year, month,
and day in three different fields and you want to store exactly what
the user inserted (without date validation). This mode applies to
DATE and DATETIME columns. It does not apply TIMESTAMP columns,
which always require a valid date.
This mode is implemented in MySQL 5.0.2. Before 5.0.2, this was the
default MySQL date-handling mode. As of 5.0.2, the server requires
that month and day values be legal, and not merely in the range 1 to
12 and 1 to 31, respectively. With strict mode disabled, invalid
dates such as '2004-04-31' are converted to '0000-00-00' and a
warning is generated. With strict mode enabled, invalid dates
generate an error. To allow such dates, enable ALLOW_INVALID_DATES.
o 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.
o ERROR_FOR_DIVISION_BY_ZERO
Produce an error in strict mode (otherwise a warning) when a
division by zero (or MOD(X,0)) occurs during an INSERT or UPDATE. If
this mode is not enabled, MySQL instead returns NULL for divisions
by zero. For INSERT IGNORE or UPDATE IGNORE, MySQL generates a
warning for divisions by zero, but the result of the operation is
NULL. (Implemented in MySQL 5.0.2)
o HIGH_NOT_PRECEDENCE
From MySQL 5.0.2 on, the precedence of the NOT operator is such that
expressions such as NOT a BETWEEN b AND c are parsed as NOT (a
BETWEEN b AND c). Before MySQL 5.0.2, the expression is parsed as
(NOT a) BETWEEN b AND c. The old higher-precedence behavior can be
obtained by enabling the HIGH_NOT_PRECEDENCE SQL mode. (Added in
MySQL 5.0.2)
mysql> SET sql_mode = '';
mysql> SELECT NOT 1 BETWEEN -5 AND 5;
-> 0
mysql> SET sql_mode = 'HIGH_NOT_PRECEDENCE';
mysql> SELECT NOT 1 BETWEEN -5 AND 5;
-> 1
o IGNORE_SPACE
Allow spaces between a function name and the `(' character. This
Prevent GRANT from automatically creating new users if it would
otherwise do so, unless a non-empty password also is specified.
(Added in MySQL 5.0.2)
o 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.
o NO_BACKSLASH_ESCAPES
Disable the use of the backslash character (`\') as an escape
character within strings. With this mode enabled, backslash becomes
an ordinary character like any other. (Implemented in MySQL 5.0.1)
o NO_DIR_IN_CREATE
When creating a table, ignore all INDEX DIRECTORY and DATA DIRECTORY
directives. This option is useful on slave replication servers.
o NO_ENGINE_SUBSTITUTION
Prevents automatic substitution of the default storage engine when a
statement such as CREATE TABLE specifies a storage engine that is
disabled or not compiled in. (Implemented in MySQL 5.0.8)
o 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.
o 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.
o NO_TABLE_OPTIONS
Do not print MySQL-specific table options (such as ENGINE) in the
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 8, "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 |
+-------------------------+
o NO_ZERO_DATE
In strict mode, don't allow '0000-00-00' as a valid date. You can
still insert zero dates with the IGNORE option. When not in strict
mode, the date is accepted but a warning is generated. (Added in
MySQL 5.0.2)
o NO_ZERO_IN_DATE
In strict mode, don't accept dates where the month or day part is 0.
If used with the IGNORE option, MySQL inserts a '0000-00-00' date
for any such date. When not in strict mode, the date is accepted but
a warning is generated. (Added in MySQL 5.0.2)
o 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
Treat REAL as a synonym for FLOAT. By default, MySQL treats REAL as
a synonym for DOUBLE.
o STRICT_ALL_TABLES
Enable strict mode for all storage engines. Invalid data values are
rejected. Additional detail follows. (Added in MySQL 5.0.2)
o STRICT_TRANS_TABLES
Enable strict mode for transactional storage engines, and when
possible for non-transactional storage engines. Additional details
follow. (Implemented in MySQL 5.0.2)
Strict mode controls how MySQL handles input values that are invalid or
missing. A value can be invalid for several reasons. For example, it
might have the wrong data type for the column, or it might be out of
range. A value is missing when a new row to be inserted does not
contain a value for a column that has no explicit DEFAULT clause in its
definition.
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:
o 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.
o 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 1.4, "Data Type Default Values".
Strict mode disallows invalid date values such as '2004-04-31'. It does
not disallow dates with zero parts such as '2004-04-00' or "zero"
dates. To disallow these as well, enable the NO_ZERO_IN_DATE and
recent version of MySQL. For older versions, a combination mode does
not include individual mode values that are not available except in
newer versions.
o ANSI
Equivalent to REAL_AS_FLOAT, PIPES_AS_CONCAT, ANSI_QUOTES,
IGNORE_SPACE. Before MySQL 5.0.3, ANSI also includes
ONLY_FULL_GROUP_BY. See Section 9.3, "Running MySQL in ANSI Mode".
o DB2
Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE,
NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS.
o MAXDB
Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE,
NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS,
NO_AUTO_CREATE_USER.
o MSSQL
Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE,
NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS.
o MYSQL323
Equivalent to NO_FIELD_OPTIONS, HIGH_NOT_PRECEDENCE.
o MYSQL40
Equivalent to NO_FIELD_OPTIONS, HIGH_NOT_PRECEDENCE.
o ORACLE
Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE,
NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS,
NO_AUTO_CREATE_USER.
o POSTGRESQL
Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE,
NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS.
o 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.
THE SHUTDOWN PROCESS
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 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
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 BitKeeper 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.
COPYRIGHT
Copyright 1997-2006 MySQL AB
This documentation is NOT distributed under a GPL license. Use of this
documentation is subject to the following terms: You may create a
printed copy of this documentation solely for your own personal use.
Conversion to other formats is allowed as long as the actual content is
not altered or edited in any way. You shall not publish or distribute
this documentation in any form or on any media, except if you
distribute the documentation in a manner similar to how MySQL
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SEE ALSO
msql2mysql(1), myisam_ftdump(1), myisamchk(1), myisamlog(1),
myisampack(1), mysql(1), mysql.server(1), mysql_config(1),
mysql_explain_log(1), mysql_fix_privilege_tables(1), mysql_upgrade(1),
mysql_zap(1), mysqlaccess(1), mysqladmin(1), mysqlbinlog(1),
mysqlcheck(1), mysqld(1), mysqld_multi(1), mysqld_safe(1),
mysqldump(1), mysqlhotcopy(1), mysqlimport(1), mysqlmanager(1),
mysqlmanager(8), mysqlshow(1), perror(1), replace(1), safe_mysqld(1)
Man(1) output converted with
man2html
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