Chapter 5. MySQL Server Administration

Chapter 5. MySQL Server Administration
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Table of Contents

5.1. The MySQL Server

5.1.1. Option and Variable Reference
5.1.2. Command Options
5.1.3. System Variables
5.1.4. Using System Variables
5.1.5. Status Variables
5.1.6. SQL Modes
5.1.7. Server-Side Help
5.1.8. Server Response to Signals
5.1.9. The Shutdown Process

5.2. MySQL Server Logs

5.2.1. Selecting General Query and Slow Query Log Output Destinations
5.2.2. The Error Log
5.2.3. The General Query Log
5.2.4. The Binary Log
5.2.5. The Slow Query Log
5.2.6. Server Log Maintenance

5.3. General Security Issues

5.3.1. General Security Guidelines
5.3.2. Making MySQL Secure Against Attackers
5.3.3. Security-Related mysqld Options
5.3.4. Security Issues with LOAD DATA LOCAL
5.3.5. How to Run MySQL as a Normal User

5.4. The MySQL Access Privilege System

5.4.1. What the Privilege System Does
5.4.2. How the Privilege System Works
5.4.3. Privileges Provided by MySQL
5.4.4. Connecting to the MySQL Server
5.4.5. Access Control, Stage 1: Connection Verification
5.4.6. Access Control, Stage 2: Request Verification
5.4.7. When Privilege Changes Take Effect
5.4.8. Causes of Access denied Errors
5.4.9. Password Hashing as of MySQL 4.1

5.5. MySQL User Account Management

5.5.1. MySQL Usernames and Passwords
5.5.2. Adding New User Accounts to MySQL
5.5.3. Removing User Accounts from MySQL
5.5.4. Limiting Account Resources
5.5.5. Assigning Account Passwords
5.5.6. Keeping Your Password Secure
5.5.7. Using Secure Connections

5.6. Backup and Recovery

5.6.1. Database Backups
5.6.2. Example Backup and Recovery Strategy
5.6.3. Point-in-Time Recovery
5.6.4. Table Maintenance and Crash Recovery

5.7. Running Multiple MySQL Servers on the Same Machine

5.7.1. Running Multiple Servers on Windows
5.7.2. Running Multiple Servers on Unix
5.7.3. Using Client Programs in a Multiple-Server Environment

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

Configuring the server
The server log files
Managing user accounts
Performing backups

5.1. The MySQL Server

5.1.1. Option and Variable Reference
5.1.2. Command Options
5.1.3. System Variables
5.1.4. Using System Variables
5.1.5. Status Variables
5.1.6. SQL Modes
5.1.7. Server-Side Help
5.1.8. Server Response to Signals
5.1.9. The Shutdown Process

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

Startup options that the server supports
Server system variables
Server status variables
How to set the server SQL mode
The server shutdown process

Note

Not all storage engines are supported by all MySQL server binaries and configurations. To find out how to determine which storage engines are supported by your MySQL server installation, see Section 11.5.4.14, “SHOW ENGINES Syntax”.

5.1.1. Option and Variable Reference

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

The table lists command line options (Cmd-line), options valid in configuration files (Option file), server system variables (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. For status variables, the scope of the variable is shown (Scope) as either global, session, or both. Please see the corresponding sections for details on setting and using the options and variables. Where appropriate, a direct link to further information on the item as available.

Note

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

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

5.1.2. Command Options

When you start the mysqld server, you can specify program options using any of the methods described in Section 4.2.2, “Specifying Program Options”. The most common methods are to provide options in an option file or on the command line. However, in most cases it is desirable to make sure that the server uses the same options each time it runs. The best way to ensure this is to list them in an option file. See Section 4.2.2.2, “Using Option Files”.

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

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

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

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

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

Options that affect security: See Section 5.3.3, “Security-Related mysqld Options”.
SSL-related options: See Section 5.5.7.3, “SSL Command Options”.
Binary log control options: See Section 5.2.4, “The Binary Log”.
Replication-related options: See Section 14.1.3, “Replication Options and Variables”.
Options specific to particular storage engines: See Section 12.4.1, “MyISAM Startup Options”, Section 12.5.4, “InnoDB Startup Options and System Variables”, and Section 15.6.5.1, “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.

--help, -?
Name help
Description Display help
Display a short help message and exit. Use both the --verbose and --help options to see the full message.
--abort-slave-event-count
Name abort-slave-event-count
Description Option used by mysql-test for debugging and testing of replication
Value Set
Type numeric
Default 0
Min Value 0
This option is used internally by the MySQL test suite for replication testing and debugging.
--allow-suspicious-udfs
Name allow-suspicious-udfs
Description Allows use of UDFs consisting of only one symbol xxx() without corresponding xxx_init() or xxx_deinit()
Value Set
Type boolean
Default FALSE
This option controls whether user-defined functions that have only an xxx symbol for the main function can be loaded. By default, the option is off and only UDFs that have at least one auxiliary symbol can be loaded; this prevents attempts at loading functions from shared object files other than those containing legitimate UDFs. See Section 27.3.4.6, “User-Defined Function Security Precautions”.
--ansi
Name ansi
Description Use ANSI SQL syntax instead of MySQL syntax
Use standard (ANSI) SQL syntax instead of MySQL syntax. For more precise control over the server SQL mode, use the --sql-mode option instead. See Section 1.8.3, “Running MySQL in ANSI Mode”, and Section 5.1.6, “SQL Modes”.

--basedir=path, -b path

Name basedir

Description Path to installation directory. All paths are usually resolved relative to this

Option Sets Variable Yes, basedir

Variable Name basedir

Variable Scope Global

Dynamic Variable no

Value Set

Type

filename

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

--big-tables

Name big-tables

Description Allow big result sets by saving all temporary sets on file

Option Sets Variable Yes, big_tables

Variable Name big-tables

Variable Scope Session

Dynamic Variable yes

Value Set

Type

boolean

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

--bind-address=IP
Name bind-address
Description IP address or hostname to bind to
Value Set
Type string
The IP address to bind to. Only one address can be selected. If this option is specified multiple times, the last address given is used.

--binlog-format={row|statement|mixed}

Name binlog-format

Description Specifies the format of the binary log

Version Introduced 5.1.5

Option Sets Variable Yes, binlog_format

Variable Name binlog_format

Variable Scope Both

Dynamic Variable no

Value Set

Type	enumeration
Default	`row`
Valid Values	`row`, `statement`, `mixed`

Specify whether to use row-based, statement-based, or mixed replication (statement-based is default). See Section 14.1.2, “Replication Formats”. This option was added in MySQL 5.1.5.

--binlog-row-event-max-size=N
Name binlog-row-event-max-size
Description Binary log max event size
Version Introduced 5.1.5
Value Set
Type numeric
Default 1024
Min Value 256
Specify the maximum size of a row-based binary log event, in bytes. Rows are grouped into events smaller than this size if possible. The value should be a multiple of 256. The default is 1024. See Section 14.1.2, “Replication Formats”. This option was added in MySQL 5.1.5.
--bootstrap
Name bootstrap
Description Used by mysql installation scripts
This option is used by the mysql_install_db script to create the MySQL privilege tables without having to start a full MySQL server.
This option is unavailable if MySQL was configured with the --disable-grant-options option. See Section 2.9.2, “Typical configure Options”.

--character-sets-dir=path

Name character-sets-dir

Description Directory where character sets are

Option Sets Variable Yes, character_sets_dir

Variable Name character-sets-dir

Variable Scope Global

Dynamic Variable no

Value Set

Type

filename

The directory where character sets are installed. See Section 8.2, “The Character Set Used for Data and Sorting”.

--character-set-client-handshake
Name character-set-client-handshake
Description Don't ignore client side character set value sent during handshake
Value Set
Type boolean
Default TRUE
Don't ignore character set information sent by the client. To ignore client information and use the default server character set, use --skip-character-set-client-handshake; this makes MySQL behave like MySQL 4.0.

--character-set-filesystem=charset_name

Name character-set-filesystem

Description Set the filesystem character set

Version Introduced 5.1.6

Option Sets Variable Yes, character_set_filesystem

Variable Name character_set_filesystem

Variable Scope Both

Dynamic Variable yes

Value Set

Type

string

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

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

Name character-set-server

Description Set the default collation (deprecated option, use instead). --default-collation=name

Option Sets Variable Yes, character_set_server

Variable Name character_set_server

Variable Scope Both

Dynamic Variable yes

Value Set

Type

string

Use charset_name as the default server character set. See Section 8.2, “The Character Set Used for Data and Sorting”. If you use this option to specify a non-default character set, you should also use --collation-server to specify the collation.

--chroot=path
Name chroot
Description Chroot mysqld daemon during startup
Value Set
Type filename
Put the mysqld server in a closed environment during startup by using the chroot() system call. This is a recommended security measure. Note that use of this option somewhat limits LOAD DATA INFILE and SELECT ... INTO OUTFILE.
--collation-server=collation_name
Name collation-server
Description Set the default collation
Option Sets Variable Yes, collation_server
Variable Name collation_server
Variable Scope Both
Dynamic Variable yes
Value Set
Type string
Use collation_name as the default server collation. See Section 8.2, “The Character Set Used for Data and Sorting”.
--console
Name console
Description Write error output on screen; do not remove the console window on Windows
Option Sets Variable Yes, console
Platform Specific windows
(Windows only.) Write error log messages to stderr and stdout even if --log-error is specified. mysqld does not close the console window if this option is used.
--core-file
Name core-file
Description Write core on errors
Value Set
Type boolean
Default TRUE
Write a core file if mysqld dies. For some systems, you must also specify the --core-file-size option to mysqld_safe. See Section 4.3.2, “mysqld_safe — MySQL Server Startup Script”. Note that on some systems, such as Solaris, you do not get a core file if you are also using the --user option.
--datadir=path, -h path
Name datadir
Description Path to the database root
Option Sets Variable Yes, datadir
Variable Name datadir
Variable Scope Global
Dynamic Variable no
Value Set
Type filename
The path to the data directory.
--debug[=debug_options], -# [debug_options]
Name debug
Description Output debug log
Value Set
Type string
Default 'd:t:o,/tmp/mysql.trace
If MySQL is configured with --with-debug, you can use this option to get a trace file of what mysqld is doing. The debug_options string often is 'd:t:o,file_name'. The default is 'd:t:i:o,mysqld.trace'. See MySQL Internals: Porting.
As of MySQL 5.1.12, using --with-debug to configure MySQL with debugging support enables you to use the --debug="d,parser_debug" option when you start the server. This causes the Bison parser that is used to process SQL statements to dump a parser trace to the server's standard error output. Typically, this output is written to the error log.
--default-character-set=charset_name (DEPRECATED)
Name default-character-set
Description Set the default character set
Option Sets Variable Yes, default-character-set
Deprecated 5.0
Value Set
Type string
Use charset_name as the default character set. This option is deprecated in favor of --character-set-server. See Section 8.2, “The Character Set Used for Data and Sorting”.
--default-collation=collation_name
Name default-collation
Description Set the default collation
Variable Name default-collation
Variable Scope
Dynamic Variable no
Deprecated 4.1.3
Value Set
Type string
Use collation_name as the default collation. This option is deprecated in favor of --collation-server. See Section 8.2, “The Character Set Used for Data and Sorting”.
--default-storage-engine=type
Name default-storage-engine
Description Set the default storage engine (table type) for tables
Set the default storage engine (table type) for tables. See Chapter 12, Storage Engines.
--default-table-type=type
Name default-table-type
Description This option is a synonym for --default-storage-engine
Deprecated 5.0, by default-storage-engine
Value Set
Type string
This option is a synonym for --default-storage-engine.
--default-time-zone=timezone
Name default-time-zone
Description Set the default time zone
Value Set
Type string
Set the default server time zone. This option sets the global time_zone system variable. If this option is not given, the default time zone is the same as the system time zone (given by the value of the system_time_zone system variable.

--delay-key-write[={OFF|ON|ALL}]

Name delay-key-write

Description Type of DELAY_KEY_WRITE

Option Sets Variable Yes, delay_key_write

Variable Name delay-key-write

Variable Scope Global

Dynamic Variable yes

Value Set

Type	enumeration
Default	`ON`
Valid Values	`ON`, `OFF`, `ALL`

Specify how to use delayed key writes. Delayed key writing causes key buffers not to be flushed between writes for MyISAM tables. OFF disables delayed key writes. ON enables delayed key writes for those tables that were created with the DELAY_KEY_WRITE option. ALL delays key writes for all MyISAM tables. See Section 6.5.2, “Tuning Server Parameters”, and Section 12.4.1, “MyISAM Startup Options”.

Note

If you set this variable to ALL, you should not use MyISAM tables from within another program (such as another MySQL server or myisamchk) when the tables are in use. Doing so leads to index corruption.

--des-key-file=file_name
Name des-key-file
Description Load keys for des_encrypt() and des_encrypt from given file
Option Sets Variable Yes, des-key-file
Variable Name des-key-file
Variable Scope Global
Dynamic Variable no
Read the default DES keys from this file. These keys are used by the DES_ENCRYPT() and DES_DECRYPT() functions.
--disconnect-slave-event-count
Name disconnect-slave-event-count
Description Option used by mysql-test for debugging and testing of replication
Option Sets Variable Yes, disconnect-slave-event-count
Value Set
Type numeric
Default 0
This option is used internally by the MySQL test suite for replication testing and debugging.
--enable-named-pipe
Name enable-named-pipe
Description Enable support for named pipes.
Platform Specific windows
Enable support for named pipes. This option applies only on Windows NT, 2000, XP, and 2003 systems. For MySQL 5.1.20 and earler, this option is available only when using the mysqld-nt and mysqld-debug servers that support named-pipe connections. For MySQL 5.1.21 and later, mysqld-nt is not available, but support is included in the standard mysqld and mysqld-debug servers.

--event-scheduler

Name event-scheduler

Description Enable/disable and start/stop the event scheduler. Note that this variable underwent significant changes in behavior and permitted values in MySQL 5.1.11 and 5.1.12

Version Introduced 5.1.6

Option Sets Variable Yes, event-scheduler

Variable Name event_scheduler

Variable Scope Global

Dynamic Variable no

Value Set

Type	enumeration
Default	`OFF`
Valid Values	`ON`, `OFF`, `DISABLED`

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

For detailed information, see The event-scheduler Option.

--exit-info[=flags], -T [flags]
Name exit-info
Description Used for debugging; Use at your own risk!
Value Set
Type numeric
This is a bit mask of different flags that you can use for debugging the mysqld server. Do not use this option unless you know exactly what it does!
--external-locking
Name external-locking
Description Use system (external) locking
Option Sets Variable Yes, external-locking
Disabled By skip-external-locking
Value Set
Type boolean
Default FALSE
Enable external locking (system locking), which is disabled by default as of MySQL 4.0. Note that if you use this option on a system on which lockd does not fully work (such as Linux), it is easy for mysqld to deadlock. This option previously was named --enable-locking.
For more information about external locking, including conditions under which it can and cannot be used, see Section 6.3.4, “External Locking”.
--flush
Name flush
Description Flush tables to disk between SQL commands
Variable Name flush
Variable Scope Global
Dynamic Variable yes
Value Set
Type boolean
Default OFF
Flush (synchronize) all changes to disk after each SQL statement. Normally, MySQL does a write of all changes to disk only after each SQL statement and lets the operating system handle the synchronizing to disk. See Section B.1.4.2, “What to Do If MySQL Keeps Crashing”.
--general-log[={0|1}]
Name general-log
Description Enable|disable general log
Version Introduced 5.1.12
Option Sets Variable Yes, general-log
Variable Name general_log
Variable Scope Global
Dynamic Variable no
Specify the initial general log state, if the --log or -l option is given. With no argument or an argument of 0, the --general-log option disables the log. If omitted or given with an argument of 1, the option enables the log. If --log or -l is not specified, --general-log has no effect. This option was added in MySQL 5.1.12.
--enable-pstack
Name enable-pstack
Description Print a symbolic stack trace on failure
Option Sets Variable Yes, enable-pstack
Value Set
Type boolean
Default FALSE
Print a symbolic stack trace on failure.
--gdb
Name gdb
Description Set up signals usable for debugging
Option Sets Variable Yes, gdb
Value Set
Type boolean
Default FALSE
Install an interrupt handler for SIGINT (needed to stop mysqld with ^C to set breakpoints) and disable stack tracing and core file handling. See MySQL Internals: Porting.
--init-file=file_name
Name init-file
Description Read SQL commands from this file at startup
Option Sets Variable Yes, init_file
Variable Name init_file
Variable Scope Global
Dynamic Variable no
Value Set
Type filename
Read SQL statements from this file at startup. Each statement must be on a single line and should not include comments.
This option is unavailable if MySQL was configured with the --disable-grant-options option. See Section 2.9.2, “Typical configure Options”.
--innodb-xxx
The InnoDB options are listed in Section 12.5.4, “InnoDB Startup Options and System Variables”.

--language=lang_name, -L lang_name

Name language

Description Client error messages in given language. May be given as a full path

Option Sets Variable Yes, language

Variable Name language

Variable Scope Global

Dynamic Variable no

Value Set

Type	filename
Default	`/usr/local/mysql/share/mysql/english/`

Return client error messages in the given language. lang_name can be given as the language name or as the full pathname to the directory where the language files are installed. See Section 8.3, “Setting the Error Message Language”.

--large-pages

Name large-pages

Description Enable support for large pages

Option Sets Variable Yes, large_pages

Variable Name large_pages

Variable Scope Global

Dynamic Variable no

Platform Specific linux

Value Set

Type	linux	boolean
Default	`FALSE`

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

Currently, MySQL supports only the Linux implementation of large pages support (which is called HugeTLB in Linux). We have plans to extend this support to FreeBSD, Solaris and possibly other platforms.

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

This option is disabled by default.

--log[=file_name], -l [file_name]
Name log
Description Log connections and queries to file
Option Sets Variable Yes, log
Variable Name log
Variable Scope Global
Dynamic Variable yes
Value Set
Type string
Default OFF
This option enables logging to the general query log, which contains entries that record client connections and SQL statements received from clients. The log output destination can be selected with the --log-output option as of MySQL 5.1.6. Before 5.1.6, logging occurs to the general query log file. If you omit the filename, MySQL uses host_name.log as the filename. See Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”, and Section 5.2.3, “The General Query Log”.
--log-bin[=base_name]
Name log-bin
Description Enables binary log
Value Set
Type filename
Enable binary logging. The server logs all statements that change data to the binary log, which is used for backup and replication. See Section 5.2.4, “The Binary Log”.
The option value, if given, is the basename for the log sequence. The server creates binary log files in sequence by adding a numeric suffix to the basename. It is recommended that you specify a basename (see Section B.1.8.1, “Open Issues in MySQL”, for the reason). Otherwise, MySQL uses host_name-bin as the basename.
--log-bin-index[=file_name]
Name log-bin-index
Description File that holds the names for last binary log files
Value Set
Type filename
The index file for binary log filenames. See Section 5.2.4, “The Binary Log”. If you omit the filename, and if you didn't specify one with --log-bin, MySQL uses host_name-bin.index as the filename.

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

Name log-bin-trust-function-creators

Description If equal to 0 (the default), then when --log-bin is used, creation of a stored function is allowed only to users having the SUPER privilege and only if the function created does not break binary logging

Option Sets Variable Yes, log_bin_trust_function_creators

Variable Name log_bin_trust_function_creators

Variable Scope Both

Dynamic Variable yes

Value Set

Type	boolean
Default	`FALSE`

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 18.4, “Binary Logging of Stored Routines and Triggers”.

--log-error[=file_name]
Name log-error
Description Error log file
Option Sets Variable Yes, log_error
Variable Name log-error
Variable Scope Global
Dynamic Variable yes
Value Set
Type filename
Log errors and startup messages to this file. See Section 5.2.2, “The Error Log”. If you omit the filename, MySQL uses host_name.err. If the filename has no extension, the server adds an extension of .err.
--log-isam[=file_name]
Name log-isam
Description Log all MyISAM changes to file
Value Set
Type filename
Log all MyISAM changes to this file (used only when debugging MyISAM).
--log-long-format (DEPRECATED)
Name log-long-format
Description Log some extra information to update log. Please note that this option is deprecated; see --log-short-format option
Deprecated 4.1
Log extra information to the binary log and slow query log, if they have been activated. For example, the username and timestamp are logged for all queries. This option is deprecated, as it now represents the default logging behavior. (See the description for --log-short-format.) The --log-queries-not-using-indexes option is available for the purpose of logging queries that do not use indexes to the slow query log.

--log-output[=value,...]

Name log-output

Description The destination for general query log and slow query log output. Syntax: log-output[=value[,value...]], where "value" could be TABLE, FILE, or NONE

Version Introduced 5.1.6

Option Sets Variable Yes, log_output

Variable Name log_output

Variable Scope Global

Dynamic Variable yes

Value Set

Type	enumeration
Default	`TABLE`
Valid Values	`TABLE`, `FILE`, `NONE`

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

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

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

--log-queries-not-using-indexes

Name log-queries-not-using-indexes

Description Log queries that are executed without benefit of any index to the slow query log if it is open

Version Introduced 5.1.11

Option Sets Variable Yes, log_queries_not_using_indexes

Variable Name log_queries_not_using_indexes

Variable Scope Global

Dynamic Variable no

Value Set

Type

boolean

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

--log-short-format
Name log-short-format
Description Don't log extra information to update and slow-query logs
Option Sets Variable Yes, log-short-format
Value Set
Type boolean
Default FALSE
Log less information to the binary log and slow query log, if they have been activated. For example, the username and timestamp are not logged for queries.

--log-slow-admin-statements

Name log-slow-admin-statements

Description Log slow OPTIMIZE, ANALYZE, ALTER and other administrative statements to the slow query log if it is open

Option Sets Variable Yes, log-slow-admin-statements

Value Set

Type	boolean
Default	`FALSE`

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

--log-slow-queries[=file_name]

Name log-slow-queries

Description Whether or not to log slow queries. Logging defaults to hostname-slow.log file. Must be enabled to activate other slow query log options

Option Sets Variable Yes, log-slow-queries

Variable Name log-slow-queries

Variable Scope Global

Dynamic Variable yes

Value Set

Type

boolean

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

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

--log-slow-slave-statements
Name log-slow-slave-statements
Description Cause slow statements as executed by the slave to be written to the slow query log
Version Introduced 5.1.21
Value Set
Type boolean
Default off
When the slow query log is enabled, this option enables logging for queries that have taken more than long_query_time seconds to execute on the slave.
This option was added in MySQL 5.1.21.

--log-tc=file_name

Name log-tc

Description Path to transaction coordinator log (used for transactions that affect more than one storage engine, when binary log is disabled)

Option Sets Variable Yes, log-tc

Value Set

Type	filename
Default	`tc.log`

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

--log-tc-size=size
Name log-tc-size
Description Size in KB of transaction coordinator log
Option Sets Variable Yes, log-tc-size
Value Set
Type numeric
Default 24576
Max Value 4294967295
The size in bytes of the memory-mapped transaction coordinator log. The default size is 24KB.

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

Name log-warnings

Description Log some not critical warnings to the log file

Option Sets Variable Yes, log-warnings

Variable Name log_warnings

Variable Scope Both

Dynamic Variable yes

Disabled By skip-log-warnings

Value Set

Type	numeric
Default	`1`

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

--low-priority-updates

Name low-priority-updates

Description INSERT/DELETE/UPDATE has lower priority than selects

Option Sets Variable Yes, low-priority-updates

Variable Name low_priority_updates

Variable Scope Both

Dynamic Variable yes

Value Set

Type	boolean
Default	`FALSE`

Give table-modifying operations (INSERT, REPLACE, DELETE, UPDATE) lower priority than selects. This can also be done via {INSERT | REPLACE | DELETE | UPDATE} LOW_PRIORITY ... to lower the priority of only one query, or by SET LOW_PRIORITY_UPDATES=1 to change the priority in one thread. This affects only storage engines that use only table-level locking (MyISAM, MEMORY, MERGE). See Section 6.3.2, “Table Locking Issues”.

--min-examined-row-limit=number

Name min-examined-row-limit

Description Queries examining fewer than this number of rows are not logged to slow query log

Version Introduced 5.1.21

Variable Name min_examined_row_limit

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`0`
Range	0-4294967295

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

This option was introduced in MySQL 5.1.21.

--max-binlog-dump-events
Name max-binlog-dump-events
Description Option used by mysql-test for debugging and testing of replication
Option Sets Variable Yes, max-binlog-dump-events
Value Set
Type numeric
Default 0
This option is used internally by the MySQL test suite for replication testing and debugging.
--memlock
Name memlock
Description Lock the mysqld process in memory
Option Sets Variable Yes, locked-in-memory
Variable Name memlock
Variable Scope Global
Dynamic Variable no
Value Set
Type boolean
Default FALSE
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 5.3.5, “How to Run MySQL as a Normal User”.

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

Name myisam-recover

Description Set the mode for automatic recovery

Value Set

Type	enumeration
Default	`OFF`
Valid Values	`DEFAULT`, `BACKUP`, `FORCE`, `QUICK`

Set the MyISAM storage engine recovery mode. The option value is any combination of the values of DEFAULT, BACKUP, FORCE, or QUICK. If you specify multiple values, separate them by commas. 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 BACKUP,FORCE. This forces a repair of a table even if some rows would be deleted, but it keeps the old data file as a backup so that you can later examine what happened.

See Section 12.4.1, “MyISAM Startup Options”.

--ndb-cluster-connection-pool=value
Name ndb-cluster-connection-pool
Description The number of connections to the cluster used by MySQL
Version Introduced 5.1.19-ndb-6.2.2
Value Set
Type numeric
Default 1
Range 1-63
MySQL Cluster 5.1 Carrier Grade EditionThe following information applies to users of MySQL Cluster 5.1 Carrier Grade Edition only. For more information about MySQL Cluster 5.1 Carrier Grade Edition, see Section 15.2, “MySQL Cluster 5.1 Carrier Grade Edition”.
This option controls how many connections are made to a MySQL Cluster by a MySQL server acting as a cluster SQL node. Normally, mysqld uses only a single connection to the cluster, and the usual way to scale out is by adding more SQL nodes (mysqld instances). However, by setting this option to a value greater than 1 (the default), it is possible to scale out by allowing multiple MySQL clients to leverage multiple connections made to the cluster by a single MySQL server. The maximum possible is 63.
Important
When this option is set to a value N, there must be at least N [mysqld] or [api] slots available for use; if there are fewer than this number, no MySQL clients are able to connect to the MySQL server.
This option was added in MySQL 5.1.19/NDB-6.2.2.
The following information applies to all MySQL Cluster users.
--ndb-connectstring=connect_string
Name ndb-connectstring
Description Indicates the management server that distributes the cluster configuration
Value Set
Type string
When using the NDB storage engine, it is possible to point out the management server that distributes the cluster configuration by setting the connect string option. See Section 15.4.4.2, “The Cluster Connectstring”, for syntax.

--ndbcluster

Name ndbcluster

Description Enable NDB Cluster (if this version of MySQL supports it)

Option Sets Variable Yes, ndbcluster

Variable Name ndbcluster

Variable Scope Both

Dynamic Variable yes

Value Set

Type	boolean
Default	`FALSE`

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.

--old-passwords

Name old-passwords

Description Use old password encryption method (needed for 4.0 and older clients)

Option Sets Variable Yes, old-passwords

Variable Name old_passwords

Variable Scope Both

Dynamic Variable yes

Value Set

Type	boolean
Default	`FALSE`

Force the server to generate short (pre-4.1) password hashes for new passwords. This is useful for compatibility when the server must support older client programs. See Section 5.4.9, “Password Hashing as of MySQL 4.1”.

--old-style-user-limits
Name old-style-user-limits
Description Enable old-style user limits (before 5.0.3, user resources were counted per each user+host vs. per account)
Value Set
Type boolean
Default FALSE
Enable old-style user limits. (Before MySQL 5.0.3, account resource limits were counted separately for each host from which a user connected rather than per account row in the user table.) See Section 5.5.4, “Limiting Account Resources”.
--one-thread
Name one-thread
Description Only use one thread (for debugging under Linux)
Only use one thread (for debugging under Linux). This option is available only if the server is built with debugging enabled. See MySQL Internals: Porting.
As of MySQL 5.1.17, this option is deprecated; use --thread_handling=one-thread instead.

--open-files-limit=count

Name open-files-limit

Description If this is not 0, then mysqld will use this value to reserve file descriptors to use with setrlimit()

Option Sets Variable Yes, open_files_limit

Variable Name open_files_limit

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`0`
Range	0-65535

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_connections×5 or max_connections + table_open_cache×2 files (whichever is larger). You should try increasing this value if mysqld gives you the error Too many open files.

--pid-file=path
Name pid-file
Description Pid file used by safe_mysqld
Option Sets Variable Yes, pid_file
Variable Name pid_file
Variable Scope Global
Dynamic Variable no
Value Set
Type filename
The pathname of the process ID file. This file is used by other programs such as mysqld_safe to determine the server's process ID.
--port=port_num, -P port_num
Name port
Description Port number to use for connection
Option Sets Variable Yes, port
Variable Name port
Variable Scope Global
Dynamic Variable no
Value Set
Type numeric
Default 3306
The port number to use when listening for TCP/IP connections. The port number must be 1024 or higher unless the server is started by the root system user.

--port-open-timeout=num

Name port-open-timeout

Description Maximum time in seconds to wait for the port to become free (Default: no wait)

Version Introduced 5.1.5

Option Sets Variable Yes, port-open-timeout

Value Set

Type	numeric
Default	`0`

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

--safe-mode
Name safe-mode
Description Skip some optimization stages (for testing)
Deprecated 5.0
Skip some optimization stages.

--safe-show-database (DEPRECATED)

Name safe-show-database

Description Deprecated option; use GRANT SHOW DATABASES instead

Option Sets Variable Yes, safe_show_database

Variable Name safe_show_database

Variable Scope Global

Dynamic Variable yes

Deprecated 4.0.2

Value Set

Type

boolean

See Section 5.4.3, “Privileges Provided by MySQL”.

--safe-user-create

Name safe-user-create

Description Don't allow new user creation by the user who has no write privileges to the mysql.user table

Option Sets Variable Yes, safe-user-create

Value Set

Type	boolean
Default	`FALSE`

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

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

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

--secure-auth

Name secure-auth

Description Disallow authentication for accounts that have old (pre-4.1) passwords

Option Sets Variable Yes, secure_auth

Variable Name secure_auth

Variable Scope Global

Dynamic Variable yes

Value Set

Type	boolean
Default	`FALSE`

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

--secure-file-priv=path

Name secure-file-priv

Description Limit LOAD_FILE(), LOAD DATA, and SELECT ... INTO OUTFILE to files in a single directory

Version Introduced 5.1.17

Option Sets Variable Yes, secure_file_priv

Variable Name secure_file_priv

Variable Scope Global

Dynamic Variable no

Value Set

Type

string

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

This option was added in MySQL 5.1.17.

--shared-memory
Name
Description
Enable shared-memory connections by local clients. This option is available only on Windows.
--shared-memory-base-name=name
Name
Description
The name of shared memory to use for shared-memory connections. This option is available only on Windows. The default name is MYSQL. The name is case sensitive.
--skip-concurrent-insert
Turn off the ability to select and insert at the same time on MyISAM tables. (This is to be used only if you think you have found a bug in this feature.) See Section 6.3.3, “Concurrent Inserts”.
--skip-external-locking
Do not use external locking (system locking). For more information about external locking, including conditions under which it can and cannot be used, see Section 6.3.4, “External Locking”.
External locking has been disabled by default since MySQL 4.0.
--skip-grant-tables
This option causes the server not to use the privilege system at all, which gives anyone with access to the server unrestricted access to all databases. You can cause a running server to start using the grant tables again by executing mysqladmin flush-privileges or mysqladmin reload command from a system shell, or by issuing a MySQL FLUSH PRIVILEGES statement after connecting to the server. This option also suppresses loading of plugins and user-defined functions (UDFs). Beginning with MySQL 5.1.17, it also suppresses loading of scheduled events (Bug#28607).
This option is unavailable if MySQL was configured with the --disable-grant-options option. See Section 2.9.2, “Typical configure Options”.
--skip-host-cache
Do not use the internal hostname cache for faster name-to-IP resolution. Instead, query the DNS server every time a client connects. See Section 6.5.9, “How MySQL Uses DNS”.
--skip-innodb
Disable the InnoDB storage engine. This saves memory and disk space and might speed up some operations. Do not use this option if you require InnoDB tables.
--skip-name-resolve
Do not resolve hostnames when checking client connections. Use only IP numbers. If you use this option, all Host column values in the grant tables must be IP numbers or localhost. See Section 6.5.9, “How MySQL Uses DNS”.
--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 15.4.3, “Quick Test Setup of MySQL Cluster”, for an example of usage.
--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 6.5.9, “How MySQL Uses DNS”.
--sporadic-binlog-dump-fail
Name sporadic-binlog-dump-fail
Description Option used by mysql-test for debugging and testing of replication
Option Sets Variable Yes, sporadic-binlog-dump-fail
Value Set
Type boolean
Default FALSE
This option is used internally by the MySQL test suite for replication testing and debugging.
--ssl*
Options that begin with --ssl specify whether to allow clients to connect via SSL and indicate where to find SSL keys and certificates. See Section 5.5.7.3, “SSL Command Options”.
--standalone
Name standalone
Description Instructs the MySQL server not to run as a service
Platform Specific windows
Available on Windows NT-based systems only; instructs the MySQL server not to run as a service.
--symbolic-links, --skip-symbolic-links
Name symbolic-links
Description Use symbolic links
Option Sets Variable Yes, symbolic-links
Enable or disable symbolic link support. This option has different effects on Windows and Unix:
- 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 6.6.1.3, “Using Symbolic Links for Databases on Windows”.
- 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 6.6.1.2, “Using Symbolic Links for Tables on Unix”.
--skip-safemalloc
Name skip-safemalloc
Description Don't check for memory overruns during each memory allocation
If MySQL is configured with --with-debug=full, all MySQL programs check for memory overruns during each memory allocation and memory freeing operation. This checking is very slow, so for the server you can avoid it when you don't need it by using the --skip-safemalloc option.
--skip-show-database
Name skip-show-database
Description Don't allow 'SHOW DATABASE' commands
Option Sets Variable Yes, skip_show_database
Variable Name skip_show_database
Variable Scope Global
Dynamic Variable yes
With this option, the SHOW DATABASES statement is allowed only to users who have the SHOW DATABASES privilege, and the statement displays all database names. Without this option, SHOW DATABASES is allowed to all users, but displays each database name only if the user has the SHOW DATABASES privilege or some privilege for the database. Note that any global privilege is considered a privilege for the database.
--skip-stack-trace
Name skip-stack-trace
Description Don't print a stack trace on failure
Don't write stack traces. This option is useful when you are running mysqld under a debugger. On some systems, you also must use this option to get a core file. See MySQL Internals: Porting.
--skip-thread-priority
Name skip-thread-priority
Description Don't give threads different priorities
Disable using thread priorities for faster response time.
--slow-query-log[={0|1}]
Name slow-query-log
Description Enable|disable slow query log
Version Introduced 5.1.12
Option Sets Variable Yes, slow-query-log
Value Set
Type boolean
Default FALSE
Specify the initial slow query log state, if the --log-slow-queries option is given. With no argument or an argument of 0, the --slow-query-log option disables the log. If omitted or given with an argument of 1, the option enables the log. If --log or -l is not specified, --slow-query-log has no effect. This option was added in MySQL 5.1.12.

--socket=path

Name socket

Description Socket file to use for connection

Option Sets Variable Yes, socket

Variable Name socket

Variable Scope Global

Dynamic Variable no

Value Set

Type	linux	filename
Default	`/tmp/mysql.sock`

Value Set

Type	hpux	filename
Default	`/tmp/mysql.sock`

Value Set

Type	solaris	filename
Default	`/tmp/mysql.sock`

Value Set

Type	macosx	filename
Default	`/tmp/mysql.sock`

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

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

Name sql-mode

Description Set the SQL server mode

Option Sets Variable Yes, sql_mode

Variable Name sql_mode

Variable Scope Both

Dynamic Variable yes

Value Set

Type	enumeration
Default	`OFF`
Valid Values	`ANSI`, `STRICT_TRANS_TABLES`, `TRADITIONAL`, `ERROR_FOR_DIVISION_BY_ZERO`, `ANSI_QUOTES`, `HIGH_NOT_PRECEDENCE`, `IGNORE_SPACE`, `NO_AUTO_CREATE_USER`, `ONLY_FULL_GROUP_BY`, `NO_AUTO_VALUE_ON_ZERO`, `NO_BACKSLASH_ESCAPES`, `NO_UNSIGNED_SUBTRACTION`, `OFF`

Set the SQL mode. See Section 5.1.6, “SQL Modes”.

--sysdate-is-now

Name sysdate-is-now

Description Non-default option to alias SYSDATE() to NOW() to make it safe-replicable

Version Introduced 5.1.8

Option Sets Variable Yes, sysdate-is-now

Value Set

Type	boolean
Default	`FALSE`

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 10.6, “Date and Time Functions” and for SET TIMESTAMP in Section 11.5.3, “SET Syntax”.

This option was added in MySQL 5.1.8.

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

Name tc-heuristic-recover

Description Decision to use in heuristic recover process. Possible values are COMMIT or ROLLBACK

Option Sets Variable Yes, tc-heuristic-recover

Value Set

Type	enumeration
Valid Values	`COMMIT`, `RECOVER`

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

--temp-pool

Name temp-pool

Description Using this option will cause most temporary files created to use a small set of names, rather than a unique name for each new file

Option Sets Variable Yes, temp-pool

Value Set

Type	boolean
Default	`TRUE`

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

--transaction-isolation=level
Name transaction-isolation
Description Default transaction isolation level
Value Set
Type enumeration
Valid Values READ-UNCOMMTTED, READ-COMMITTED, REPEATABLE-READ, SERIALIZABLE
Sets the default transaction isolation level. The level value can be READ-UNCOMMITTED, READ-COMMITTED, REPEATABLE-READ, or SERIALIZABLE. See Section 11.4.6, “SET TRANSACTION Syntax”.
--tmpdir=path, -t path
Name tmpdir
Description Path for temporary files
Option Sets Variable Yes, tmpdir
Variable Name tmpdir
Variable Scope Global
Dynamic Variable no
Value Set
Type filename
The path of the directory to use for creating temporary files. It might be useful if your default /tmp directory resides on a partition that is too small to hold temporary tables. This option accepts several paths that are used in round-robin fashion. Paths should be separated by colon characters (“:”) on Unix and semicolon characters (“;”) on Windows, NetWare, and OS/2. If the MySQL server is acting as a replication slave, you should not set --tmpdir to point to a directory on a memory-based filesystem or to a directory that is cleared when the server host restarts. For more information about the storage location of temporary files, see Section B.1.4.4, “Where MySQL Stores Temporary Files”. A replication slave needs some of its temporary files to survive a machine restart so that it can replicate temporary tables or LOAD DATA INFILE operations. If files in the temporary file directory are lost when the server restarts, replication fails.
--user={user_name|user_id}, -u {user_name|user_id}
Name user
Description Run mysqld daemon as user
Value Set
Type string
Run the mysqld server as the user having the name user_name or the numeric user ID user_id. (“User” in this context refers to a system login account, not a MySQL user listed in the grant tables.)
This option is mandatory when starting mysqld as root. The server changes its user ID during its startup sequence, causing it to run as that particular user rather than as root. See Section 5.3.1, “General Security Guidelines”.
To avoid a possible security hole where a user adds a --user=root option to a my.cnf file (thus causing the server to run as root), mysqld uses only the first --user option specified and produces a warning if there are multiple --user options. Options in /etc/my.cnf and $MYSQL_HOME/my.cnf are processed before command-line options, so it is recommended that you put a --user option in /etc/my.cnf and specify a value other than root. The option in /etc/my.cnf is found before any other --user options, which ensures that the server runs as a user other than root, and that a warning results if any other --user option is found.
--version, -V
Display version information and exit.

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

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

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

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 11.5.3, “SET Syntax”.

Section 5.1.3, “System Variables”, provides a full description for all variables, and additional information for setting them at server startup and runtime. Section 6.5.2, “Tuning Server Parameters”, includes information on optimizing the server by tuning system variables.

5.1.3. System Variables

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

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

To see the values that a server will use based on its compiled-in defaults and any option files that it reads, use this command:
```
mysqld --verbose --help
```
To see the values that a server will use based on its compiled-in defaults, ignoring the settings in any option files, use this command:
```
mysqld --no-defaults --verbose --help
```
To see the current values used by a running server, use the SHOW VARIABLES statement.

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

The following table lists all available system variables:

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

For additional system variable information, see these sections:

Section 5.1.4, “Using System Variables”, discusses the syntax for setting and displaying system variable values.
Section 5.1.4.2, “Dynamic System Variables”, lists the variables that can be set at runtime.
Information on tuning system variables can be found in Section 6.5.2, “Tuning Server Parameters”.
Section 12.5.4, “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.

auto_increment_increment

Name auto-increment-increment

Description Auto-increment columns are incremented by this value

Option Sets Variable Yes, auto_increment_increment

Variable Name auto_increment_increment

Variable Scope Both

Dynamic Variable no

Value Set

Type	numeric
Default	`1`
Range	1-65535

auto_increment_increment and auto_increment_offset are intended for use with master-to-master replication, and can be used to control the operation of AUTO_INCREMENT columns. Both variables 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.

Important

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

These two variables affect AUTO_INCREMENT column behavior as follows:

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

mysql> SHOW VARIABLES LIKE 'auto_inc%';
+--------------------------+-------+
| Variable_name            | Value |
+--------------------------+-------+
| auto_increment_increment | 1     |
| auto_increment_offset    | 1     |
+--------------------------+-------+
2 rows in set (0.00 sec)

mysql> CREATE TABLE autoinc1
    -> (col INT NOT NULL AUTO_INCREMENT PRIMARY KEY);
  Query OK, 0 rows affected (0.04 sec)

mysql> SET @@auto_increment_increment=10;
Query OK, 0 rows affected (0.00 sec)

mysql> SHOW VARIABLES LIKE 'auto_inc%';
+--------------------------+-------+
| Variable_name            | Value |
+--------------------------+-------+
| auto_increment_increment | 10    |
| auto_increment_offset    | 1     |
+--------------------------+-------+
2 rows in set (0.01 sec)

mysql> INSERT INTO autoinc1 VALUES (NULL), (NULL), (NULL), (NULL);
Query OK, 4 rows affected (0.00 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> SELECT col FROM autoinc1;
+-----+
| col |
+-----+
|   1 |
|  11 |
|  21 |
|  31 |
+-----+
4 rows in set (0.00 sec)

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

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

mysql> SET @@auto_increment_offset=5;
Query OK, 0 rows affected (0.00 sec)

mysql> SHOW VARIABLES LIKE 'auto_inc%';
+--------------------------+-------+
| Variable_name            | Value |
+--------------------------+-------+
| auto_increment_increment | 10    |
| auto_increment_offset    | 5     |
+--------------------------+-------+
2 rows in set (0.00 sec)

mysql> CREATE TABLE autoinc2
    -> (col INT NOT NULL AUTO_INCREMENT PRIMARY KEY);
Query OK, 0 rows affected (0.06 sec)

mysql> INSERT INTO autoinc2 VALUES (NULL), (NULL), (NULL), (NULL);
Query OK, 4 rows affected (0.00 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> SELECT col FROM autoinc2;
+-----+
| col |
+-----+
|   5 |
|  15 |
|  25 |
|  35 |
+-----+
4 rows in set (0.02 sec)

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

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

auto_increment_offset + N × auto_increment_increment

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

mysql> SHOW VARIABLES LIKE 'auto_inc%';
+--------------------------+-------+
| Variable_name            | Value |
+--------------------------+-------+
| auto_increment_increment | 10    |
| auto_increment_offset    | 5     |
+--------------------------+-------+
2 rows in set (0.00 sec)

mysql> SELECT col FROM autoinc1;
+-----+
| col |
+-----+
|   1 |
|  11 |
|  21 |
|  31 |
+-----+
4 rows in set (0.00 sec)

mysql> INSERT INTO autoinc1 VALUES (NULL), (NULL), (NULL), (NULL);
Query OK, 4 rows affected (0.00 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> SELECT col FROM autoinc1;
+-----+
| col |
+-----+
|   1 |
|  11 |
|  21 |
|  31 |
|  35 |
|  45 |
|  55 |
|  65 |
+-----+
8 rows in set (0.00 sec)

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

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

The default value of auto_increment_increment is 1. See replication-auto-increment.

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

auto_increment_offset

Name auto-increment-offset

Description Offset added to Auto-increment columns

Option Sets Variable Yes, auto_increment_offset

Variable Name auto_increment_offset

Variable Scope Both

Dynamic Variable no

Value Set

Type	numeric
Default	`1`
Range	1-65535

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

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

automatic_sp_privileges

Name automatic_sp_privileges

Description Creating and dropping stored procedures alters ACLs

Variable Name automatic_sp_privileges

Variable Scope Global

Dynamic Variable yes

Disabled By skip-automatic_sp_privileges

Value Set

Type	boolean
Default	`TRUE`

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

back_log

Name back_log

Description The number of outstanding connection requests MySQL can have

Option Sets Variable Yes, back_log

Variable Name back_log

Variable Scope Global

Dynamic Variable no

Value Set

Type	numeric
Default	`50`
Range	1-65535

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

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

basedir

Name basedir

Description Path to installation directory. All paths are usually resolved relative to this

Option Sets Variable Yes, basedir

Variable Name basedir

Variable Scope Global

Dynamic Variable no

Value Set

Type

filename

The MySQL installation base directory. This variable can be set with the --basedir option.

binlog_cache_size

Name binlog_cache_size

Description The size of the cache to hold the SQL statements for the binary log during a transaction

Option Sets Variable Yes, binlog_cache_size

Variable Name binlog_cache_size

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`32768`
Range	4096-4294967295

The size of the cache to hold the SQL statements for the binary log during a transaction. A binary log cache is allocated for each client if the server supports any transactional storage engines and if the server has the binary log enabled (--log-bin option). If you often use large, multiple-statement transactions, you can increase this cache size to get more performance. The Binlog_cache_use and Binlog_cache_disk_use status variables can be useful for tuning the size of this variable. See Section 5.2.4, “The Binary Log”.

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

binlog_format

Name binlog-format

Description Specifies the format of the binary log

Version Introduced 5.1.5

Option Sets Variable Yes, binlog_format

Variable Name binlog_format

Variable Scope Both

Dynamic Variable no

Value Set

Type	enumeration
Default	`row`
Valid Values	`row`, `statement`, `mixed`

The binary logging format, either STATEMENT, ROW, or MIXED. binlog_format is set by the --binlog-format option at startup, or by the binlog_format variable at runtime (you need the SUPER privilege to set this variable on a global scope). See Section 14.1.2, “Replication Formats”. The startup variable was added in MySQL 5.1.5, and the runtime variable in MySQL 5.1.8. MIXED was added in MySQL 5.1.8.

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

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

From within a stored function or a trigger.
If NDB is enabled.
If the session is currently in row-based replication mode and has open temporary tables.

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

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

bulk_insert_buffer_size

Name bulk_insert_buffer_size

Description Size of tree cache used in bulk insert optimization

Option Sets Variable Yes, bulk_insert_buffer_size

Variable Name bulk_insert_buffer_size

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`8388608`
Range	0-4294967295

MyISAM uses a special tree-like cache to make bulk inserts faster for INSERT ... SELECT, INSERT ... VALUES (...), (...), ..., and LOAD DATA INFILE when adding data to non-empty tables. This variable limits the size of the cache tree in bytes per thread. Setting it to 0 disables this optimization. The default value is 8MB.

character_set_client
Name character_set_client
Description Current client character set
Variable Name character_set_client
Variable Scope Both
Dynamic Variable yes
Value Set
Type string
The character set for statements that arrive from the client.
character_set_connection
Name character_set_connection
Description Current connection character set
Variable Name character_set_connection
Variable Scope Both
Dynamic Variable yes
Value Set
Type string
The character set used for literals that do not have a character set introducer and for number-to-string conversion.
character_set_database
Name character_set_database
Description The character set used by the default database
Variable Name character_set_database
Variable Scope Both
Dynamic Variable yes
Value Set
Type string
The character set used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as character_set_server.

character_set_filesystem

Name character-set-filesystem

Description Set the filesystem character set

Version Introduced 5.1.6

Option Sets Variable Yes, character_set_filesystem

Variable Name character_set_filesystem

Variable Scope Both

Dynamic Variable yes

Value Set

Type

string

The filesystem character set. This variable is used to interpret string literals that refer to filenames, such as in the LOAD DATA INFILE and SELECT ... INTO OUTFILE statements and the LOAD_FILE() function. Such filenames are converted from character_set_client to character_set_filesystem before the file opening attempt occurs. The default value is binary, which means that no conversion occurs. For systems on which multi-byte filenames are allowed, a different value may be more appropriate. For example, if the system represents filenames using UTF-8, set character_set_filesystem to 'utf8'. This variable was added in MySQL 5.1.6.

character_set_results
Name character_set_results
Description Current result character set
Variable Name character_set_results
Variable Scope Both
Dynamic Variable yes
Value Set
Type string
The character set used for returning query results to the client.

character_set_server

Name character-set-server

Description Set the default collation (deprecated option, use instead). --default-collation=name

Option Sets Variable Yes, character_set_server

Variable Name character_set_server

Variable Scope Both

Dynamic Variable yes

Value Set

Type

string

The server's default character set.

character_set_system
Name character_set_system
Description The character set used by the server for storing identifiers
Variable Name character_set_system
Variable Scope Global
Dynamic Variable yes
Value Set
Type string
The character set used by the server for storing identifiers. The value is always utf8.

character_sets_dir

Name character-sets-dir

Description Directory where character sets are

Option Sets Variable Yes, character_sets_dir

Variable Name character-sets-dir

Variable Scope Global

Dynamic Variable no

Value Set

Type

filename

The directory where character sets are installed.

collation_connection
Name collation_connection
Description The collation of the connection
Variable Name collation_connection
Variable Scope Both
Dynamic Variable yes
Value Set
Type string
The collation of the connection character set.
collation_database
Name collation_database
Description The collation used by the default database
Variable Name collation_database
Variable Scope Both
Dynamic Variable yes
Value Set
Type string
The collation used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as collation_server.
collation_server
Name collation-server
Description Set the default collation
Option Sets Variable Yes, collation_server
Variable Name collation_server
Variable Scope Both
Dynamic Variable yes
Value Set
Type string
The server's default collation.

completion_type

Name completion_type

Description Default completion type

Option Sets Variable Yes, completion_type

Variable Name competion_type

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`0`
Valid Values	`0`, `1`, `2`

The transaction completion type:

If the value is 0 (the default), COMMIT and ROLLBACK are unaffected.
If the value is 1, COMMIT and ROLLBACK are equivalent to COMMIT AND CHAIN and ROLLBACK AND CHAIN, respectively. (A new transaction starts immediately with the same isolation level as the just-terminated transaction.)
If the value is 2, COMMIT and ROLLBACK are equivalent to COMMIT RELEASE and ROLLBACK RELEASE, respectively. (The server disconnects after terminating the transaction.)

concurrent_insert

Name concurrent_insert

Description Use concurrent insert with MyISAM

Option Sets Variable Yes, concurrent_insert

Variable Name concurrent_insert

Variable Scope Global

Dynamic Variable yes

Value Set

Type	boolean
Default	`TRUE`

Value Set

Type	numeric
Default	`1`
Valid Values	`0`, `1`, `2`

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

This variable can take three integer values:

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

connect_timeout

Name connect_timeout

Description The number of seconds the mysqld server waits for a connect packet before responding with 'Bad handshake'

Option Sets Variable Yes, connect_timeout

Variable Name connect_timeout

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`5`
Min Value	`2`

Value Set

Type	numeric
Default	`10`

Value Set

Type	numeric
Default	`5`

Value Set

Type	numeric
Default	`10`

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

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

datadir
Name datadir
Description Path to the database root
Option Sets Variable Yes, datadir
Variable Name datadir
Variable Scope Global
Dynamic Variable no
Value Set
Type filename
The MySQL data directory. This variable can be set with the --datadir option.
date_format
This variable is not implemented.
datetime_format
Name datetime_format
Description The DATETIME/TIMESTAMP format (for future)
Option Sets Variable Yes, datetime_format
Variable Name datetime_format
Variable Scope Both
Dynamic Variable yes
Value Set
Type string
This variable is not implemented.

default_week_format

Name default_week_format

Description The default week format used by WEEK() functions

Option Sets Variable Yes, default_week_format

Variable Name default_week_format

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`0`
Range	0-7

The default mode value to use for the WEEK() function. See Section 10.6, “Date and Time Functions”.

delay_key_write

Name delay-key-write

Description Type of DELAY_KEY_WRITE

Option Sets Variable Yes, delay_key_write

Variable Name delay-key-write

Variable Scope Global

Dynamic Variable yes

Value Set

Type	enumeration
Default	`ON`
Valid Values	`ON`, `OFF`, `ALL`

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

Option	Description
`OFF`	`DELAY_KEY_WRITE` is ignored.
`ON`	MySQL honors any `DELAY_KEY_WRITE` option specified in `CREATE TABLE` statements. This is the default value.
`ALL`	All new opened tables are treated as if they were created with the `DELAY_KEY_WRITE` option enabled.

If DELAY_KEY_WRITE is enabled for a table, the key buffer is not flushed for the table on every index update, but only when the table is closed. This speeds up writes on keys a lot, but if you use this feature, you should add automatic checking of all MyISAM tables by starting the server with the --myisam-recover option (for example, --myisam-recover=BACKUP,FORCE). See Section 5.1.2, “Command Options”, and Section 12.4.1, “MyISAM Startup Options”.

Note that if you enable external locking with --external-locking, there is no protection against index corruption for tables that use delayed key writes.

delayed_insert_limit

Name delayed_insert_limit

Description After inserting delayed_insert_limit rows, the INSERT DELAYED handler will check if there are any SELECT statements pending. If so, it allows these to execute before continuing

Option Sets Variable Yes, delayed_insert_limit

Variable Name delayed_insert_limit

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`100`
Range	1-4294967295

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

delayed_insert_timeout

Name delayed_insert_timeout

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

Option Sets Variable Yes, delayed_insert_timeout

Variable Name delayed_insert_timeout

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`300`

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

delayed_queue_size

Name delayed_queue_size

Description What size queue (in rows) should be allocated for handling INSERT DELAYED

Option Sets Variable Yes, delayed_queue_size

Variable Name delayed_queue_size

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`1000`
Range	1-4294967295

This is a per-table limit on the number of rows to queue when handling INSERT DELAYED statements. If the queue becomes full, any client that issues an INSERT DELAYED statement waits until there is room in the queue again.

div_precision_increment

Name div_precision_increment

Description Scale of the result of '/' operator will be increased by this many digits

Version Introduced 5.1.6

Option Sets Variable Yes, div_precision_increment

Variable Name div_precision_increment

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`4`
Range	0-30

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

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

event_scheduler

Name event-scheduler

Description Enable/disable and start/stop the event scheduler. Note that this variable underwent significant changes in behavior and permitted values in MySQL 5.1.11 and 5.1.12

Version Introduced 5.1.6

Option Sets Variable Yes, event-scheduler

Variable Name event_scheduler

Variable Scope Global

Dynamic Variable no

Value Set

Type	enumeration
Default	`OFF`
Valid Values	`ON`, `OFF`, `DISABLED`

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

This variable was added in MySQL 5.1.6.

engine_condition_pushdown

Name engine_condition_pushdown

Description Push supported query conditions to the storage engine

Option Sets Variable Yes, engine_condition_pushdown

Variable Name engine_condition_pushdown

Variable Scope Both

Dynamic Variable yes

Value Set

Type	boolean
Default	`OFF`

This variable applies to NDB. By default it is 0 (OFF): If you execute a query such as SELECT * FROM t WHERE mycol = 42, where mycol is a non-indexed column, the query is executed as a full table scan on every NDB node. Each node sends every row to the MySQL server, which applies the WHERE condition. If engine_condition_pushdown is set to 1 (ON), the condition is “pushed down” to the storage engine and sent to the NDB nodes. Each node uses the condition to perform the scan, and only sends back to the MySQL server the rows that match the condition.

expire_logs_days

Name expire_logs_days

Description If non-zero, binary logs will be purged after expire_logs_days days; possible purges happen at startup and at binary log rotation

Option Sets Variable Yes, expire_logs_days

Variable Name expire_logs_days

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`0`
Range	0-99

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

flush
Name flush
Description Flush tables to disk between SQL commands
Variable Name flush
Variable Scope Global
Dynamic Variable yes
Value Set
Type boolean
Default OFF
If ON, the server flushes (synchronizes) all changes to disk after each SQL statement. Normally, MySQL does a write of all changes to disk only after each SQL statement and lets the operating system handle the synchronizing to disk. See Section B.1.4.2, “What to Do If MySQL Keeps Crashing”. This variable is set to ON if you start mysqld with the --flush option.

flush_time

Name flush_time

Description A dedicated thread is created to flush all tables at the given interval

Option Sets Variable Yes, flush_time

Variable Name flush_time

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`1800`
Min Value	`0`

If this is set to a non-zero value, all tables are closed every flush_time seconds to free up resources and synchronize unflushed data to disk. We recommend that this option be used only on Windows 9x or Me, or on systems with minimal resources.

ft_boolean_syntax

Name ft_boolean_syntax

Description List of operators for MATCH ... AGAINST ( ... IN BOOLEAN MODE)

Variable Name ft_boolean_syntax

Variable Scope Global

Dynamic Variable yes

Value Set

Type	string
Default	`+-><()~*:""&`

The list of operators supported by boolean full-text searches performed using IN BOOLEAN MODE. See Section 10.8.2, “Boolean Full-Text Searches”.

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

Operator function is determined by position within the string.
The replacement value must be 14 characters.
Each character must be an ASCII non-alphanumeric character.
Either the first or second character must be a space.
No duplicates are allowed except the phrase quoting operators in positions 11 and 12. These two characters are not required to be the same, but they are the only two that may be.
Positions 10, 13, and 14 (which by default are set to “:”, “&”, and “|”) are reserved for future extensions.

ft_max_word_len

Name ft_max_word_len

Description The maximum length of the word to be included in a FULLTEXT index. Note: FULLTEXT indexes must be rebuilt after changing this variable

Option Sets Variable Yes, ft_max_word_len

Variable Name ft_max_word_len

Variable Scope Global

Dynamic Variable no

Value Set

Type	numeric
Min Value	`10`

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

Note

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

ft_min_word_len

Name ft_min_word_len

Description The minimum length of the word to be included in a FULLTEXT index. Note: FULLTEXT indexes must be rebuilt after changing this variable

Option Sets Variable Yes, ft_min_word_len

Variable Name ft_min_word_len

Variable Scope Global

Dynamic Variable no

Value Set

Type	numeric
Default	`4`
Min Value	`1`

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

Note

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

ft_query_expansion_limit

Name ft_query_expansion_limit

Description Number of best matches to use for query expansion

Option Sets Variable Yes, ft_query_expansion_limit

Variable Name ft_query_expansion_limit

Variable Scope Global

Dynamic Variable no

Value Set

Type	numeric
Default	`20`
Range	0-1000

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

ft_stopword_file

Name ft_stopword_file

Description Use stopwords from this file instead of built-in list

Option Sets Variable Yes, ft_stopword_file

Variable Name ft_stopword_file

Variable Scope Global

Dynamic Variable no

Value Set

Type

filename

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

Note

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

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

general_log_file

Name general_log_file

Description Name of the general query log file

Version Introduced 5.1.12

Variable Name general_log_file

Variable Scope Global

Dynamic Variable no

Value Set

Type	filename
Default	`host_name.log`

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

group_concat_max_len

Name group_concat_max_len

Description The maximum length of the result of function group_concat

Option Sets Variable Yes, group_concat_max_len

Variable Name group_concat_max_len

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`1024`
Min Value	`4`

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

have_archive
YES if mysqld supports ARCHIVE tables, NO if not.
have_blackhole_engine
YES if mysqld supports BLACKHOLE tables, NO if not.
have_compress
YES if the zlib compression library is available to the server, NO if not. If not, the COMPRESS() and UNCOMPRESS() functions cannot be used.
have_crypt
YES if the crypt() system call is available to the server, NO if not. If not, the ENCRYPT() function cannot be used.
have_csv
YES if mysqld supports ARCHIVE tables, NO if not.
have_dynamic_loading
YES if mysqld supports dynamic loading of plugins, NO if not. This variable was added in MySQL 5.1.10.
have_example_engine
YES if mysqld supports EXAMPLE tables, NO if not.
have_federated_engine
YES if mysqld supports FEDERATED tables, NO if not.
have_geometry
YES if the server supports spatial data types, NO if not.
have_innodb
YES if mysqld supports InnoDB tables. DISABLED if --skip-innodb is used.
have_ndbcluster
YES if mysqld supports NDB Cluster tables. DISABLED if --skip-ndbcluster is used.
have_partitioning
YES if mysqld supports partitioning. Added in MySQL 5.1.1 as have_partition_engine and renamed to have_partioning in 5.1.6.
have_openssl
YES if mysqld supports SSL connections, NO if not. As of MySQL 5.1.17, this variable is an alias for have_ssl.
have_query_cache
YES if mysqld supports the query cache, NO if not.

have_row_based_replication

Name have_row_based_replication

Description Shows whether row-based replication is supported

Version Introduced 5.1.5

Variable Name have_row_based_replication

Variable Scope Global

Dynamic Variable no

Deprecated 5.1.15

Value Set

Type

boolean

YES if the server can perform replication using row-based binary logging. If the value is NO, the server can use only statement-based logging. See Section 14.1.2, “Replication Formats”. This variable was added in MySQL 5.1.5 and removed in 5.1.15.

have_rtree_keys
YES if RTREE indexes are available, NO if not. (These are used for spatial indexes in MyISAM tables.)
have_ssl
YES if mysqld supports SSL connections, NO if not. This variable was added in MySQL 5.1.17. Before that, use have_openssl.
have_symlink
YES if symbolic link support is enabled, NO if not. This is required on Unix for support of the DATA DIRECTORY and INDEX DIRECTORY table options, and on Windows for support of data directory symlinks.
hostname
Name hostname
Description The name of the server host
Version Introduced 5.1.17
Variable Name hostname
Variable Scope Global
Dynamic Variable no
Value Set
Type string
The server sets this variable to the server hostname at startup. This variable was added in MySQL 5.1.17.

init_connect

Name init_connect

Description Command(s) that are executed for each new connection

Option Sets Variable Yes, init_connect

Variable Name init_connect

Variable Scope Global

Dynamic Variable yes

Value Set

Type

string

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

SET GLOBAL init_connect='SET AUTOCOMMIT=0';

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

[mysqld]
init_connect='SET AUTOCOMMIT=0'

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

init_file
Name init-file
Description Read SQL commands from this file at startup
Option Sets Variable Yes, init_file
Variable Name init_file
Variable Scope Global
Dynamic Variable no
Value Set
Type filename
The name of the file specified with the --init-file option when you start the server. This should be a file containing SQL statements that you want the server to execute when it starts. Each statement must be on a single line and should not include comments.
Note that the --init-file option is unavailable if MySQL was configured with the --disable-grant-options option. See Section 2.9.2, “Typical configure Options”.

init_slave

Name init_slave

Description Command(s) that are executed when a slave connects to a master

Option Sets Variable Yes, init_slave

Variable Name init_slave

Variable Scope Global

Dynamic Variable yes

Value Set

Type

string

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

innodb_xxx
InnoDB system variables are listed in Section 12.5.4, “InnoDB Startup Options and System Variables”.

interactive_timeout

Name interactive_timeout

Description The number of seconds the server waits for activity on an interactive connection before closing it

Option Sets Variable Yes, interactive_timeout

Variable Name interactive_timeout

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`28800`
Min Value	`1`

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

join_buffer_size

Name join_buffer_size

Description The size of the buffer that is used for full joins

Option Sets Variable Yes, join_buffer_size

Variable Name join_buffer_size

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`131072`
Range	8200-4294967295

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

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

keep_files_on_create

Name keep_files_on_create

Description Do not overwrite existing .MYD/.MYI files in default database directory

Version Introduced 5.1.21

Option Sets Variable Yes, keep_files_on_create

Variable Name keep_files_on_create

Variable Scope Both

Dynamic Variable yes

Value Set

Type	boolean
Default	`OFF`

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

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

This variable was added in MySQL 5.1.23.

key_buffer_size

Name key_buffer_size

Description The size of the buffer used for index blocks for MyISAM tables

Option Sets Variable Yes, key_buffer_size

Variable Name key_buffer_size

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`131072`
Range	8-4294967295

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

The maximum allowable setting for key_buffer_size is 4GB on 32-bit platforms. As of MySQL 5.1.23, values larger than 4GB are allowed for 64-bit platforms. The effective maximum size might be less, depending on your available physical RAM and per-process RAM limits imposed by your operating system or hardware platform.

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 6.2.18, “Speed of INSERT Statements”.

You can check the performance of the key buffer by issuing a SHOW STATUS statement and examining the Key_read_requests, Key_reads, Key_write_requests, and Key_writes status variables. (See Section 11.5.4, “SHOW Syntax”.) The Key_reads/Key_read_requests ratio should normally be less than 0.01. The Key_writes/Key_write_requests ratio is usually near 1 if you are using mostly updates and deletes, but might be much smaller if you tend to do updates that affect many rows at the same time or if you are using the DELAY_KEY_WRITE table option.

The fraction of the key buffer in use can be determined using key_buffer_size in conjunction with the Key_blocks_unused status variable and the buffer block size, which is available from the key_cache_block_size system variable:

1 - ((Key_blocks_unused × key_cache_block_size) / key_buffer_size)

This value is an approximation because some space in the key buffer may be allocated internally for administrative structures.

It is possible to create multiple MyISAM key caches. The size limit of 4GB applies to each cache individually, not as a group. See Section 6.4.6, “The MyISAM Key Cache”.

key_cache_age_threshold

Name key_cache_age_threshold

Description This characterizes the number of hits a hot block has to be untouched until it is considered aged enough to be downgraded to a warm block. This specifies the percentage ratio of that number of hits to the total number of blocks in key cache

Option Sets Variable Yes, key_cache_age_threshold

Variable Name key_cache_age_threshold

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`300`
Range	100-4294967295

This value controls the demotion of buffers from the hot sub-chain of a key cache to the warm sub-chain. Lower values cause demotion to happen more quickly. The minimum value is 100. The default value is 300. See Section 6.4.6, “The MyISAM Key Cache”.

key_cache_block_size

Name key_cache_block_size

Description The default size of key cache blocks

Option Sets Variable Yes, key_cache_block_size

Variable Name key_cache_block_size

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`1024`
Range	512-16384

The size in bytes of blocks in the key cache. The default value is 1024. See Section 6.4.6, “The MyISAM Key Cache”.

key_cache_division_limit

Name key_cache_division_limit

Description The minimum percentage of warm blocks in key cache

Option Sets Variable Yes, key_cache_division_limit

Variable Name key_cache_division_limit

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`100`
Range	1-100

The division point between the hot and warm sub-chains of the key cache buffer chain. The value is the percentage of the buffer chain to use for the warm sub-chain. Allowable values range from 1 to 100. The default value is 100. See Section 6.4.6, “The MyISAM Key Cache”.

language

Name language

Description Client error messages in given language. May be given as a full path

Option Sets Variable Yes, language

Variable Name language

Variable Scope Global

Dynamic Variable no

Value Set

Type	filename
Default	`/usr/local/mysql/share/mysql/english/`

The language used for error messages.

large_files_support
Name large_files_support
Description Whether large files are supported
Variable Name large_files_support
Variable Scope Global
Dynamic Variable no
Whether mysqld was compiled with options for large file support.

large_pages

Name large-pages

Description Enable support for large pages

Option Sets Variable Yes, large_pages

Variable Name large_pages

Variable Scope Global

Dynamic Variable no

Platform Specific linux

Value Set

Type	linux	boolean
Default	`FALSE`

Whether large page support is enabled.

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

large_page_size
Name large_page_size
Description The size of memory pages when large page support is enabled
Variable Name large_page_size
Variable Scope Global
Dynamic Variable no
Value Set
Type linux numeric
Default 0
If large page support is enabled, this shows the size of memory pages. Currently, large memory pages are supported only on Linux; on other platforms, the value of this variable is always 0.
For more information, see the entry for the --large-pages server option.

lc_time_names

Name lc_time_names

Description The locale that controls the language used to display day and month names

Version Introduced 5.1.12

Variable Name lc_time_names

Variable Scope Both

Dynamic Variable yes

Value Set

Type

string

This variable specifies the locale that controls the language used to display day and month names and abbreviations. This variable affects the output from the DATE_FORMAT(), DAYNAME() and MONTHNAME() functions. Locale names are POSIX-style values such as 'ja_JP' or 'pt_BR'. The default value is 'en_US' regardless of your system's locale setting. For further information, see Section 8.10, “MySQL Server Locale Support”. This variable was added in MySQL 5.1.12.

license
Name license
Description Type of license for the server
Variable Name license
Variable Scope Global
Dynamic Variable no
Value Set
Type string
Default GPL
The type of license the server has.
local_infile
Name local_infile
Description Whether LOCAL is supported for LOAD DATA INFILE statements
Variable Name local_infile
Variable Scope Global
Dynamic Variable no
Whether LOCAL is supported for LOAD DATA INFILE statements. See Section 5.3.4, “Security Issues with LOAD DATA LOCAL”.
locked_in_memory
Name locked_in_memory
Description Whether mysqld is locked in memory
Variable Name locked_in_memory
Variable Scope Global
Dynamic Variable no
Whether mysqld was locked in memory with --memlock.
log
Name
Description
Whether logging of all statements to the general query log is enabled. See Section 5.2.3, “The General Query Log”.
log_bin
Name log_bin
Description Whether the binary log is enabled
Variable Name log_bin
Variable Scope Global
Dynamic Variable no
Whether the binary log is enabled. See Section 5.2.4, “The Binary Log”.

log_bin_trust_function_creators

Name log-bin-trust-function-creators

Option Sets Variable Yes, log_bin_trust_function_creators

Variable Name log_bin_trust_function_creators

Variable Scope Both

Dynamic Variable yes

Value Set

Type	boolean
Default	`FALSE`

This variable applies when binary logging is enabled. It controls whether stored function creators can be trusted not to create stored functions that will cause unsafe events to be written to the binary log. If set to 0 (the default), users are not allowed to create or alter stored routines 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 18.4, “Binary Logging of Stored Routines and Triggers”.

log_error
Name log-error
Description Error log file
Option Sets Variable Yes, log_error
Variable Name log-error
Variable Scope Global
Dynamic Variable yes
Value Set
Type filename
The location of the error log.

log_output

Name log-output

Description The destination for general query log and slow query log output. Syntax: log-output[=value[,value...]], where "value" could be TABLE, FILE, or NONE

Version Introduced 5.1.6

Option Sets Variable Yes, log_output

Variable Name log_output

Variable Scope Global

Dynamic Variable yes

Value Set

Type	enumeration
Default	`TABLE`
Valid Values	`TABLE`, `FILE`, `NONE`

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

log_queries_not_using_indexes

Name log-queries-not-using-indexes

Description Log queries that are executed without benefit of any index to the slow query log if it is open

Version Introduced 5.1.11

Option Sets Variable Yes, log_queries_not_using_indexes

Variable Name log_queries_not_using_indexes

Variable Scope Global

Dynamic Variable no

Value Set

Type

boolean

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

log_slave_updates
Name
Description
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 14.1.3, “Replication Options and Variables”.

log_slow_queries

Name log-slow-queries

Description Whether or not to log slow queries. Logging defaults to hostname-slow.log file. Must be enabled to activate other slow query log options

Option Sets Variable Yes, log-slow-queries

Variable Name log-slow-queries

Variable Scope Global

Dynamic Variable yes

Value Set

Type

boolean

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

log_warnings

Name log-warnings

Description Log some not critical warnings to the log file

Option Sets Variable Yes, log-warnings

Variable Name log_warnings

Variable Scope Both

Dynamic Variable yes

Disabled By skip-log-warnings

Value Set

Type	numeric
Default	`1`

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

long_query_time

Name long_query_time

Description Log all queries that have taken more than long_query_time seconds to execute to file

Option Sets Variable Yes, long_query_time

Variable Name long_query_time

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`10`
Min Value	`1`

Value Set

Type	numeric
Default	`10`
Min Value	`0`

Value Set

Type	numeric
Default	`10`
Min Value	`1`

Value Set

Type	numeric
Default	`10`
Min Value	`0`

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

low_priority_updates

Name low-priority-updates

Description INSERT/DELETE/UPDATE has lower priority than selects

Option Sets Variable Yes, low-priority-updates

Variable Name low_priority_updates

Variable Scope Both

Dynamic Variable yes

Value Set

Type	boolean
Default	`FALSE`

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

lower_case_file_system

Name lower_case_file_system

Description This variable describes the case sensitivity of filenames on the file system

Option Sets Variable Yes, lower_case_file_system

Variable Name lower_case_file_system

Variable Scope Global

Dynamic Variable no

Value Set

Type

boolean

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

lower_case_table_names

Name lower_case_table_names

Description If set to 1 table names are stored in lowercase on disk and table names will be case-insensitive. Should be set to 2 if you are using a case insensitive file system

Option Sets Variable Yes, lower_case_table_names

Variable Name lower_case_table_names

Variable Scope Global

Dynamic Variable no

Value Set

Type	numeric
Default	`0`
Range	0-2

If set to 1, table names are stored in lowercase on disk and table name comparisons are not case sensitive. If set to 2 table names are stored as given but compared in lowercase. This option also applies to database names and table aliases. See Section 7.2.2, “Identifier Case Sensitivity”.

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

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

max_allowed_packet

Name max_allowed_packet

Description Max packetlength to send/receive from to server

Option Sets Variable Yes, max_allowed_packet

Variable Name max_allowed_packet

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`1048576`
Range	1024-1073741824

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

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

You must increase this value if you are using large BLOB columns or long strings. It should be as big as the largest BLOB you want to use. The protocol limit for max_allowed_packet is 1GB.

max_binlog_cache_size

Name max_binlog_cache_size

Description Can be used to restrict the total size used to cache a multi-transaction query

Option Sets Variable Yes, max_binlog_cache_size

Variable Name max_binlog_cache_size

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`4294967295`
Range	4096-4294967295

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

max_binlog_size

Name max_binlog_size

Description Binary log will be rotated automatically when the size exceeds this value

Option Sets Variable Yes, max_binlog_size

Variable Name max_binlog_size

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`1073741824`
Min Value	`4096`

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

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

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

max_connect_errors

Name max_connect_errors

Description If there is more than this number of interrupted connections from a host this host will be blocked from further connections

Option Sets Variable Yes, max_connect_errors

Variable Name max_connect_errors

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`10`
Range	1-4294967295

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

max_connections

Name max_connections

Description The number of simultaneous clients allowed

Option Sets Variable Yes, max_connections

Variable Name max_connections

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`100`

Value Set

Type	numeric
Default	`151`
Range	1-16384

Value Set

Type	numeric
Default	`151`
Range	1-100000

The number of simultaneous client connections allowed. By default, this is 150, beginning with MySQL 5.1.15. (Previously, the default was 100.) See Section B.1.2.7, “Too many connections”, for more information.

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

Increasing this value increases the number of file descriptors that mysqld requires. See Section 6.4.8, “How MySQL Opens and Closes Tables”, for comments on file descriptor limits.

max_delayed_threads

Name max_delayed_threads

Description Don't start more than this number of threads to handle INSERT DELAYED statements. If set to zero, which means INSERT DELAYED is not used

Option Sets Variable Yes, max_delayed_threads

Variable Name max_delayed_threads

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`20`
Range	0-16384

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

max_error_count

Name max_error_count

Description Max number of errors/warnings to store for a statement. --max_heap_table_size=# Don't allow creation of heap tables bigger than this

Option Sets Variable Yes, max_error_count

Variable Name max_error_count

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`64`
Range	0-65535

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

max_heap_table_size

Name max_heap_table_size

Description Don't allow creation of heap tables bigger than this

Option Sets Variable Yes, max_heap_table_size

Variable Name max_heap_table_size

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`16777216`
Range	16384-4294967295

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

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

max_insert_delayed_threads
Name max_insert_delayed_threads
Description This variable is a synonym for max_delayed_threads
Variable Name max_insert_delayed_threads
Variable Scope Both
Dynamic Variable yes
Value Set
Type numeric
This variable is a synonym for max_delayed_threads.

max_join_size

Name max_join_size

Description Joins that are probably going to read more than max_join_size records return an error

Option Sets Variable Yes, max_join_size

Variable Name max_join_size

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`4294967295`
Range	1-4294967295

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

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

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

This variable previously was named sql_max_join_size.

max_length_for_sort_data

Name max_length_for_sort_data

Description Max number of bytes in sorted records

Option Sets Variable Yes, max_length_for_sort_data

Variable Name max_length_for_sort_data

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`1024`
Range	4-8388608

The cutoff on the size of index values that determines which filesort algorithm to use. See Section 6.2.11, “ORDER BY Optimization”.

max_prepared_STATEMENT_count

Name	`max_prepared_STATEMENT_count`
Description	This variable limits the total number of prepared statements in the server
Version Introduced	5.1.10
Variable Name	`max_prepared_STATEMENT_count`
Variable Scope	Global
Dynamic Variable	no

This variable limits the total number of prepared statements in the server. It can be used in environments where there is the potential for denial-of-service attacks based on running the server out of memory by preparing huge numbers of statements. The default value is 16382. The allowable range of values is from 0 to 1 million. If the value is set lower than the current number of prepared statements, existing statements are not affected and can be used, but no new statements can be prepared until the current number drops below the limit. This variable was added in MySQL 5.1.10.

max_relay_log_size

Name max_relay_log_size

Description If non-zero: relay log will be rotated automatically when the size exceeds this value

Option Sets Variable Yes, max_relay_log_size

Variable Name max_relay_log_size

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`1024`
Range	0-1073741824

If a write by a replication slave to its relay log causes the current log file size to exceed the value of this variable, the slave rotates the relay logs (closes the current file and opens the next one). If max_relay_log_size is 0, the server uses max_binlog_size for both the binary log and the relay log. If max_relay_log_size is greater than 0, it constrains the size of the relay log, which enables you to have different sizes for the two logs. You must set max_relay_log_size to between 4096 bytes and 1GB (inclusive), or to 0. The default value is 0. See Section 14.4.1, “Replication Implementation Details”.

max_seeks_for_key

Name max_seeks_for_key

Description Limit assumed max number of seeks when looking up rows based on a key

Option Sets Variable Yes, max_seeks_for_key

Variable Name max_seeks_for_key

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`4294967295`
Range	1-4294967295

Limit the assumed maximum number of seeks when looking up rows based on a key. The MySQL optimizer assumes that no more than this number of key seeks are required when searching for matching rows in a table by scanning an index, regardless of the actual cardinality of the index (see Section 11.5.4.18, “SHOW INDEX Syntax”). By setting this to a low value (say, 100), you can force MySQL to prefer indexes instead of table scans.

max_sort_length

Name max_sort_length

Description The number of bytes to use when sorting BLOB or TEXT values

Option Sets Variable Yes, max_sort_length

Variable Name max_sort_length

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`1024`
Range	4-8388608

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

max_sp_recursion_depth

Name max_sp_recursion_depth

Description Maximum stored procedure recursion depth. (discussed with docs)

Option Sets Variable Yes, max_sp_recursion_depth

Variable Name max_sp_recursion_depth

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`0`
Max Value	`255`

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.

max_tmp_tables

Name max_tmp_tables

Description Maximum number of temporary tables a client can keep open at a time

Option Sets Variable Yes, max_tmp_tables

Variable Name max_tmp_tables

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`32`
Range	1-4294967295

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

max_user_connections

Name max_user_connections

Description The maximum number of active connections for a single user (0 = no limit)

Option Sets Variable Yes, max_user_connections

Variable Name max_user_connections

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Range	1-4294967295

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

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

max_write_lock_count

Name max_write_lock_count

Description After this many write locks, allow some read locks to run in between

Option Sets Variable Yes, max_write_lock_count

Variable Name max_write_lock_count

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`4294967295`
Range	1-4294967295

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

min_examined_row_limit

Name min-examined-row-limit

Description Queries examining fewer than this number of rows are not logged to slow query log

Version Introduced 5.1.21

Variable Name min_examined_row_limit

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`0`
Range	0-4294967295

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

multi_range_count

Name multi_range_count

Description The maximum number of ranges to send to a table handler at once during range selects

Option Sets Variable Yes, multi_range_count

Variable Name multi_range_count

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`256`
Range	1-4294967295

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

myisam_block_size

Name myisam_block_size

Description Block size to be used for MyISAM index pages

Option Sets Variable Yes, myisam_block_size

Variable Name myisam_block_size

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`1024`
Range	1024-16384

The block size to be used for MyISAM index pages.

myisam_data_pointer_size

Name myisam_data_pointer_size

Description Default pointer size to be used for MyISAM tables

Option Sets Variable Yes, myisam_data_pointer_size

Variable Name myisam_data_pointer_size

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`4`
Range	2-8

Value Set

Type	numeric
Default	`6`
Range	2-7

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

myisam_max_extra_sort_file_size (DEPRECATED)

Name myisam_max_extra_sort_file_size

Description Deprecated option

Command Line Format --myisam_max_extra_sort_file_size=#

Config File Format myisam_max_extra_sort_file_size

Option Sets Variable Yes, myisam_max_extra_sort_file_size

Variable Name myisam_max_extra_sort_file_size

Variable Scope Global

Dynamic Variable no

Deprecated 5.0.6

Value Set

Type	numeric
Default	`2147483648`

Note

This variable is not supported in MySQL 5.1. See MySQL 5.0 Reference Manual for more information.

myisam_max_sort_file_size

Name myisam_max_sort_file_size

Description Don't use the fast sort index method to created index if the temporary file would get bigger than this

Option Sets Variable Yes, myisam_max_sort_file_size

Variable Name myisam_max_sort_file_size

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`2147483648`

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

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

myisam_recover_options
Name myisam_recover_options
Description The value of the --myisam-recover option
Variable Name myisam_recover_options
Variable Scope
Dynamic Variable no
The value of the --myisam-recover option. See Section 5.1.2, “Command Options”.

myisam_repair_threads

Name myisam_repair_threads

Description Number of threads to use when repairing MyISAM tables. The value of 1 disables parallel repair

Option Sets Variable Yes, myisam_repair_threads

Variable Name myisam_repair_threads

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`1`
Range	1-4294967295

If this value is greater than 1, MyISAM table indexes are created in parallel (each index in its own thread) during the Repair by sorting process. The default value is 1.

Note

Multi-threaded repair is still beta-quality code.

myisam_sort_buffer_size

Name myisam_sort_buffer_size

Description The buffer that is allocated when sorting the index when doing a REPAIR or when creating indexes with CREATE INDEX or ALTER TABLE

Option Sets Variable Yes, myisam_sort_buffer_size

Variable Name myisam_sort_buffer_size

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`8388608`
Range	4-4294967295

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

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

myisam_stats_method

Name myisam_stats_method

Description Specifies how MyISAM index statistics collection code should treat NULLs

Option Sets Variable Yes, myisam_stats_method

Variable Name myisam_stats_method

Variable Scope Both

Dynamic Variable yes

Value Set

Type	enumeration
Default	`nulls_unequal`

Value Set

Type	enumeration
Valid Values	`nulls_equal`, `nulls_unequal`

How the server treats NULL values when collecting statistics about the distribution of index values for MyISAM tables. This variable has two possible values, nulls_equal and nulls_unequal. For nulls_equal, all NULL index values are considered equal and form a single value group that has a size equal to the number of NULL values. For nulls_unequal, NULL values are considered unequal, and each NULL forms a distinct value group of size 1.

The method that is used for generating table statistics influences how the optimizer chooses indexes for query execution, as described in Section 6.4.7, “MyISAM Index Statistics Collection”.

myisam_use_mmap

Name myisam_use_mmap

Description Use memory mapping for reading and writing MyISAM tables

Version Introduced 5.1.4

Option Sets Variable Yes, myisam_use_mmap

Variable Name myisam_use_mmap

Variable Scope Global

Dynamic Variable no

Value Set

Type	boolean
Default	`FALSE`

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

multi_read_range

Name multi_read_range

Description Specifies the maximum number of ranges to send to a storage engine during range selects

Option Sets Variable Yes, multi_read_range

Variable Name multi_read_range

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`256`

Specifies the maximum number of ranges to send to a storage engine during range selects. The default value is 256. Sending multiple ranges to an engine is a feature that can improve the performance of certain selects dramatically, particularly for NDBCLUSTER. This engine needs to send the range requests to all nodes, and sending many of those requests at once reduces the communication costs significantly.

named_pipe
Name named_pipe
Description Indicates whether the server supports connections over named pipes
Variable Name named_pipe
Variable Scope
Dynamic Variable no
Platform Specific windows
(Windows only.) Indicates whether the server supports connections over named pipes.

ndb_autoincrement_prefetch_sz

Name ndb_autoincrement_prefetch_sz

Description NDB Auto-increment prefetch size

Option Sets Variable Yes, ndb_autoincrement_prefetch_sz

Variable Name ndb_autoincrement_prefetch_sz

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`32`
Range	1-256

Value Set

Type	numeric
Default	`1`
Range	1-256

Value Set

Type	numeric
Default	`32`
Range	1-256

Value Set

Type	numeric
Default	`1`
Range	1-256

Value Set

Type	numeric
Default	`32`
Range	1-256

Value Set

Type	numeric
Default	`1`
Range	1-256

Value Set

Type	numeric
Default	`32`
Range	1-256

Value Set

Type	numeric
Default	`1`
Range	1-256

Value Set

Type	numeric
Default	`32`
Range	1-256

Value Set

Type	numeric
Default	`1`
Range	1-256

Determines the probability of gaps in an autoincremented column. Set it to 1 to minimize this. Setting it 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. Minimum value: 1.

Beginning with MySQL 5.1.23-ndb-6.2.10, MySQL 5.1.23-ndb-6.3.7, and MySQL 5.1.23, this variable affects the number of AUTO_INCREMENT IDs that are fetched between statements only. Within a statement, at least 32 IDs are now obtained at a time. The default value for ndb_autoincrement_prefetch_sz is now 1, to increase the speed of statements inserting single rows. (Bug#31956)

ndb_cache_check_time

Name ndb_cache_check_time

Description The number of milliseconds to wait before checking the NDB query cache

Option Sets Variable Yes, ndb_cache_check_time

Variable Name ndb_cache_check_time

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`0`

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.

ndb_extra_logging

Name ndb_extra_logging

Description This variable can be set to a non-zero value to enable extra NDB logging

Version Introduced 5.1.6

Variable Name ndb_extra_logging

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`0`

This variable can be set to a non-zero value to enable extra NDB logging for debugging or troubleshooting purposes. The default value is 0.

This variable was added in MySQL 5.1.6.

ndb_force_send

Name ndb_force_send

Description Forces sending of buffers to NDB immediately, without waiting for other threads

Option Sets Variable Yes, ndb_force_send

Variable Name ndb_force_send

Variable Scope Both

Dynamic Variable yes

Value Set

Type	boolean
Default	`TRUE`

Forces sending of buffers to NDB immediately, without waiting for other threads. Defaults to ON.

ndb_index_stat_cache_entries
Name ndb_index_stat_cache_entries
Description Sets the granularity of the statistics by determining the number of starting and ending keys
Value Set
Type numeric
Default 32
Range 0-4294967295
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 queried directly. Default value: 32.
ndb_index_stat_enable
Name ndb_index_stat_enable
Description Use NDB index statistics in query optimization
Value Set
Type boolean
Default ON
Use NDB index statistics in query optimization. Defaults to ON.
ndb_index_stat_update_freq
Name ndb_index_stat_update_freq
Description How often to query data nodes instead of the statistics cache
Value Set
Type numeric
Default 20
Range 0-4294967295
How often to query data nodes instead of the statistics cache. For example, a value of 20 (the default) means to direct every 20^th query to the data nodes.

ndb_optimized_node_selection

Name ndb_optimized_node_selection

Description Determines how an SQL node chooses a cluster data node to use as transaction coordinator

Value Set

Type	boolean
Default	`ON`

Value Set

Type	numeric
Default	`1`
Range	0-3

Causes an SQL node to use a data node on the same host machine as transaction coordinator. Enabled by default. Set to 0 or OFF to disable, in which case the SQL node uses each data node in the cluster in succession. When this option is disabled, or if there is no data node process running on the same host as the SQL node, the SQL node attempts to use a given data node 8 times before proceeding to the next one.

MySQL Cluster 5.1 Carrier Grade EditionThe following information applies to users of MySQL Cluster 5.1 Carrier Grade Edition only. For more information about MySQL Cluster 5.1 Carrier Grade Edition, see Section 15.2, “MySQL Cluster 5.1 Carrier Grade Edition”.

In MySQL 5.1.22-ndb-6.3.4 and later MySQL Cluster 5.1 Carrier Grade Edition 6.3.x releases, this option takes one of the integer values 0, 1, 2, or 3, with 1 being the default. These values affect node selection as follows:

0: Each data node is employed as the transaction coordinator 8 times before the SQL node proceeds to the next data node. (This is the same behavior as caused by setting this option to 0 or OFF in previous MySQL versions.)
1: If a data node process is running on the the same host as the SQL node, this data node is used as the transaction coordinator. (This is the same behavior as caused by setting this option to 1 or ON in previous MySQL versions.)
2: The SQL node follows the same behavior as if this option had been set to 1; however, the setting is global.
3: The data node housing the cluster partition accessed by the first statement of a given transaction is used as the transaction coordinator for the entire transaction. This is effective only if the first statement of the transaction accesses no more than one cluster partition; otherwise, the SQL node reverts to the round-robin behavior seen when this option is set to 0.

Important

In MySQL 5.1.22-ndb-6.3.4 and later MySQL Cluster 5.1 Carrier Grade Edition 6.3.x versions, it is no longer possible to --ndb_optimized_node_selection to ON or OFF; attempting to do so causes mysqld to abort with an error.

The following information applies to all MySQL Cluster users.

ndb_report_thresh_binlog_epoch_slip
Name ndb_report_thresh_binlog_epoch_slip
Description This is a threshold on the number of epochs to be behind before reporting binlog status
Value Set
Type numeric
Default 3
Range 0-256
This is a threshold on the number of epochs to be behind before reporting binlog status. For example, a value of 3 (the default) means that if the difference between which epoch has been received from the storage nodes and which epoch has been applied to the binlog is 3 or more, a status message will be sent to the cluster log.
ndb_report_thresh_binlog_mem_usage
Name ndb_report_thresh_binlog_mem_usage
Description This is a threshold on the percentage of free memory remaining before reporting binlog status
Value Set
Type numeric
Default 10
Range 0-10
This is a threshold on the percentage of free memory remaining before reporting binlog status. For example, a value of 10 (the default) means that if the amount of available memory for receiving binlog data from the data nodes falls below 10%, a status message will be sent to the cluster log.
ndb_use_copying_alter_table
Name ndb_use_copying_alter_table
Description Use copying ALTER TABLE operations in MySQL Cluster
Version Introduced 5.1.12
Variable Name ndb_use_copying_alter_table
Variable Scope Both
Dynamic Variable no
Forces NDB to use copying of tables in the event of problems with online ALTER TABLE operations. The default value is OFF.
This variable was added in MySQL 5.1.12.
ndb_use_exact_count
Name ndb_use_exact_count
Description NDB Use Exact Count
Variable Name ndb_use_exact_count
Variable Scope Both
Dynamic Variable yes
Value Set
Type boolean
Default OFF
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.
ndb_use_transactions
Name ndb_use_transactions
Description Forces NDB to use a count of records during SELECT COUNT(*) query planning to speed up this type of query
Value Set
Type boolean
Default ON
You can disable NDB transaction support by setting this variable's values to OFF (not recommended). The default is ON.

ndb_wait_connected

Name ndb_wait_connected

Description Time (in seconds) for the MySQL server to wait for connection to cluster management and data nodes before accepting MySQL client connections.

Version Introduced 5.1.16-ndb-6.2.0

Option Sets Variable Yes, ndb_wait_connected

Variable Name ndb_wait_connected

Variable Scope

Dynamic Variable no

Value Set

Type	numeric
Default	`0`

MySQL Cluster 5.1 Carrier Grade Edition This variable is available in MySQL Cluster 5.1 Carrier Grade Edition only. For more information about MySQL Cluster 5.1 Carrier Grade Edition, see Section 15.2, “MySQL Cluster 5.1 Carrier Grade Edition”.

This variable can be used to cause the MySQL server to wait a given period of time for connections to MySQL Cluster management and data nodes to be established before accepting MySQL client connections. The time is specified in seconds. The default value is 0.

net_buffer_length

Name net_buffer_length

Description Buffer length for TCP/IP and socket communication

Option Sets Variable Yes, net_buffer_length

Variable Name net_buffer_length

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`16384`
Range	1024-1048576

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

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

net_read_timeout

Name net_read_timeout

Description Number of seconds to wait for more data from a connection before aborting the read

Option Sets Variable Yes, net_read_timeout

Variable Name net_read_timeout

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`30`
Min Value	`1`

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

net_retry_count

Name net_retry_count

Description If a read on a communication port is interrupted, retry this many times before giving up

Option Sets Variable Yes, net_retry_count

Variable Name net_retry_count

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`10`
Range	1-4294967295

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

net_write_timeout

Name net_write_timeout

Description Number of seconds to wait for a block to be written to a connection before aborting the write

Option Sets Variable Yes, net_write_timeout

Variable Name net_write_timeout

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`60`
Min Value	`1`

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

new
Name new
Description Use very new, possibly 'unsafe' functions
Option Sets Variable Yes, new
Variable Name new
Variable Scope Both
Dynamic Variable yes
Disabled By skip-new
Value Set
Type boolean
Default FALSE
This variable was used in MySQL 4.0 to turn on some 4.1 behaviors, and is retained for backward compatibility. In MySQL 5.1, its value is always OFF.
old
Name old
Description Cause the server to revert to certain behaviors present in older versions
Version Introduced 5.1.18
Variable Name old
Variable Scope Global
Dynamic Variable no
old is a compatibility variable. It is disabled by default, but can be enabled at startup to revert the server to behaviors present in older versions.
Currently, when old is enabled, it changes the default scope of index hints to that used prior to MySQL 5.1.17. That is, index hints with no FOR clause apply only to how indexes are used for row retrieval and not to resolution of ORDER BY or GROUP BY clauses. (See Section 11.2.7.2, “Index Hint Syntax”.) Take care about enabling this in a replication setup. With statement-based binary logging, having different modes for the master and slaves might lead to replication errors.
This variable was added as old_mode in MySQL 5.1.17 and renamed to old in MySQL 5.1.18.

old_passwords

Name old-passwords

Description Use old password encryption method (needed for 4.0 and older clients)

Option Sets Variable Yes, old-passwords

Variable Name old_passwords

Variable Scope Both

Dynamic Variable yes

Value Set

Type	boolean
Default	`FALSE`

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

one_shot
This is not a variable, but it can be used when setting some variables. It is described in Section 11.5.3, “SET Syntax”.

open_files_limit

Name open-files-limit

Description If this is not 0, then mysqld will use this value to reserve file descriptors to use with setrlimit()

Option Sets Variable Yes, open_files_limit

Variable Name open_files_limit

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`0`
Range	0-65535

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

optimizer_prune_level

Name optimizer_prune_level

Description Controls the heuristic(s) applied during query optimization to prune less-promising partial plans from the optimizer search space

Option Sets Variable Yes, optimizer_prune_level

Variable Name optimizer_prune_level

Variable Scope Both

Dynamic Variable yes

Value Set

Type	boolean
Default	`1`

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

optimizer_search_depth

Name optimizer_search_depth

Description Maximum depth of search performed by the query optimizer

Option Sets Variable Yes, optimizer_search_depth

Variable Name optimizer_search_depth

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`62`

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

pid_file
Name pid-file
Description Pid file used by safe_mysqld
Option Sets Variable Yes, pid_file
Variable Name pid_file
Variable Scope Global
Dynamic Variable no
Value Set
Type filename
The pathname of the process ID (PID) file. This variable can be set with the --pid-file option.

plugin_dir

Name plugin_dir

Description Directory for plugins

Version Introduced 5.1.2

Option Sets Variable Yes, plugin_dir

Variable Name plugin_dir

Variable Scope Global

Dynamic Variable no

Value Set

Type	filename
Default	`/usr/local/mysql/lib/mysql`

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

port
Name port
Description Port number to use for connection
Option Sets Variable Yes, port
Variable Name port
Variable Scope Global
Dynamic Variable no
Value Set
Type numeric
Default 3306
The number of the port on which the server listens for TCP/IP connections. This variable can be set with the --port option.

preload_buffer_size

Name preload_buffer_size

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

Option Sets Variable Yes, preload_buffer_size

Variable Name preload_buffer_size

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`32768`
Range	1024-1073741824

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

prepared_STATEMENT_count
Name
Description
The current number of prepared statements. (The maximum number of statements is given by the max_prepared_STATEMENT_count system variable.) This variable was added in MySQL 5.1.10. In MySQL 5.1.14, it was converted to the global Prepared_STATEMENT_count status variable.
protocol_version
Name protocol_version
Description The version of the client/server protocol used by the MySQL server
Variable Name protocol_version
Variable Scope Global
Dynamic Variable no
Value Set
Type numeric
The version of the client/server protocol used by the MySQL server.

query_alloc_block_size

Name query_alloc_block_size

Description Allocation block size for query parsing and execution

Option Sets Variable Yes, query_alloc_block_size

Variable Name query_alloc_block_size

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`8192`
Range	1024-4294967295

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

query_cache_limit

Name query_cache_limit

Description Don't cache results that are bigger than this

Option Sets Variable Yes, query_cache_limit

Variable Name query_cache_limit

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`1048576`
Min Value	`0`

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

query_cache_min_res_unit

Name query_cache_min_res_unit

Description Minimal size of unit in which space for results is allocated (last unit will be trimmed after writing all result data)

Option Sets Variable Yes, query_cache_min_res_unit

Variable Name query_cache_min_res_unit

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`1024`
Min Value	`0`

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 6.5.4.3, “Query Cache Configuration”.

query_cache_size

Name query_cache_size

Description The memory allocated to store results from old queries

Option Sets Variable Yes, query_cache_size

Variable Name query_cache_size

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`0`

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 6.5.4.3, “Query Cache Configuration”, for more information.

query_cache_type

Name query_cache_type

Description Query cache type

Option Sets Variable Yes, query_cache_type

Variable Name query_cache_type

Variable Scope Both

Dynamic Variable yes

Value Set

Type	enumeration
Default	`1`
Valid Values	`0`, `1`, `2`

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

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.

query_cache_wlock_invalidate

Name query_cache_wlock_invalidate

Description Invalidate queries in query cache on LOCK for write

Option Sets Variable Yes, query_cache_wlock_invalidate

Variable Name query_cache_wlock_invalidate

Variable Scope Both

Dynamic Variable yes

Value Set

Type	boolean
Default	`FALSE`

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

query_prealloc_size

Name query_prealloc_size

Description Persistent buffer for query parsing and execution

Option Sets Variable Yes, query_prealloc_size

Variable Name query_prealloc_size

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`8192`
Range	8192-4294967295

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

range_alloc_block_size

Name range_alloc_block_size

Description Allocation block size for storing ranges during optimization

Option Sets Variable Yes, range_alloc_block_size

Variable Name range_alloc_block_size

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`2048`
Max Value	`4294967295`

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

read_buffer_size

Name read_buffer_size

Description Each thread that does a sequential scan allocates a buffer of this size for each table it scans

Option Sets Variable Yes, read_buffer_size

Variable Name read_buffer_size

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`131072`
Range	8200-2147479552

Each thread that does a sequential scan allocates a buffer of this size (in bytes) for each table it scans. If you do many sequential scans, you might want to increase this value, which defaults to 131072.

The maximum allowable setting for read_buffer_size is 2GB.

read_buffer_size and read_rnd_buffer_size are not specific to any storage engine and apply in a general manner for optimization. See Section 6.5.7, “How MySQL Uses Memory”, for example.

read_only
Name read_only
Description Make all non-temporary tables read-only
Option Sets Variable Yes, read_only
Variable Name read_only
Variable Scope Global
Dynamic Variable yes
Value Set
Type numeric
Default 0
This variable is off by default. When it is enabled, the server allows no updates except from users that have the SUPER privilege or (on a slave server) from updates performed by slave threads. On a slave server, this can be useful to ensure that the slave accepts updates only from its master server and not from clients. This variable does not apply to TEMPORARY tables.
read_only exists only as a GLOBAL variable, so changes to its value require the SUPER privilege. Changes to read_only on a master server are not replicated to slave servers. The value can be set on a slave server independent of the setting on the master.
As of MySQL 5.1.15, the following conditions apply:
- If you attempt to enable read_only while you have any explicit locks (acquired with LOCK TABLES) or have a pending transaction, an error occurs.
- If you attempt to enable read_only while other clients hold explicit table locks or have pending transactions, the attempt blocks until the locks are released and the transactions end. While the attempt to enable read_only is pending, requests by other clients for table locks or to begin transactions also block until read_only has been set.
- read_only can be enabled while you hold a global read lock (acquired with FLUSH TABLES WITH READ LOCK) because that does not involve table locks.

read_rnd_buffer_size

Name read_rnd_buffer_size

Description When reading rows in sorted order after a sort, the rows are read through this buffer to avoid a disk seeks. If not set, then it's set to the value of record_buffer

Option Sets Variable Yes, read_rnd_buffer_size

Variable Name read_rnd_buffer_size

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`262144`
Range	8200-4294967295

When reading rows in sorted order following a key-sorting operation, the rows are read through this buffer to avoid disk seeks. See Section 6.2.11, “ORDER BY Optimization”. Setting the variable to a large value can improve ORDER BY performance by a lot. However, this is a buffer allocated for each client, so you should not set the global variable to a large value. Instead, change the session variable only from within those clients that need to run large queries.

The maximum allowable setting for read_rnd_buffer_size is 2GB.

read_buffer_size and read_rnd_buffer_size are not specific to any storage engine and apply in a general manner for optimization. See Section 6.5.7, “How MySQL Uses Memory”, for example.

relay_log_purge

Name relay_log_purge

Description Determines whether relay logs are purged

Option Sets Variable Yes, relay_log_purge

Variable Name relay_log_purge

Variable Scope Global

Dynamic Variable yes

Value Set

Type	boolean
Default	`TRUE`

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

rpl_recovery_rank
This variable is unused.

secure_auth

Name secure-auth

Description Disallow authentication for accounts that have old (pre-4.1) passwords

Option Sets Variable Yes, secure_auth

Variable Name secure_auth

Variable Scope Global

Dynamic Variable yes

Value Set

Type	boolean
Default	`FALSE`

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

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

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

secure_file_priv

Name secure-file-priv

Description Limit LOAD_FILE(), LOAD DATA, and SELECT ... INTO OUTFILE to files in a single directory

Version Introduced 5.1.17

Option Sets Variable Yes, secure_file_priv

Variable Name secure_file_priv

Variable Scope Global

Dynamic Variable no

Value Set

Type

string

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

This variable was added in MySQL 5.1.17.

server_id

Name server-id

Description Uniquely identifies the server instance in the community of replication partners

Option Sets Variable Yes, server_id

Variable Name server_id

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`0`

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

shared_memory
Name shared_memory
Description Whether the server allows shared-memory connections
Variable Name shared_memory
Variable Scope
Dynamic Variable no
Platform Specific windows
(Windows only.) Whether the server allows shared-memory connections.
shared_memory_base_name
Name shared_memory_base_name
Description The name of shared memory to use for shared-memory connections
Variable Name shared_memory_base_name
Variable Scope
Dynamic Variable no
Platform Specific windows
(Windows only.) The name of shared memory to use for shared-memory connections. This is useful when running multiple MySQL instances on a single physical machine. The default name is MYSQL. The name is case sensitive.
skip_external_locking
This is OFF if mysqld uses external locking, ON if external locking is disabled.
skip_networking
This is ON if the server allows only local (non-TCP/IP) connections. On Unix, local connections use a Unix socket file. On Windows, local connections use a named pipe or shared memory. On NetWare, only TCP/IP connections are supported, so do not set this variable to ON. This variable can be set to ON with the --skip-networking option.
skip_show_database
This prevents people from using the SHOW DATABASES statement if they do not have the SHOW DATABASES privilege. This can improve security if you have concerns about users being able to see databases belonging to other users. Its effect depends on the SHOW DATABASES privilege: If the variable value is ON, the SHOW DATABASES statement is allowed only to users who have the SHOW DATABASES privilege, and the statement displays all database names. If the value is OFF, SHOW DATABASES is allowed to all users, but displays the names of only those databases for which the user has the SHOW DATABASES or other privilege.

slave_compressed_protocol

Name slave_compressed_protocol

Description Use compression on master/slave protocol

Option Sets Variable Yes, slave_compressed_protocol

Variable Name slave_compressed_protocol

Variable Scope Global

Dynamic Variable yes

Value Set

Type	boolean
Default	`FALSE`

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

slave_load_tmpdir

Name slave-load-tmpdir

Description The location where the slave should put its temporary files when replicating a LOAD DATA INFILE command

Option Sets Variable Yes, slave_load_tmpdir

Variable Name slave_load_tmpdir

Variable Scope Global

Dynamic Variable no

Value Set

Type	filename
Default	`/tmp`

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

slave_net_timeout

Name slave-net-timeout

Description Number of seconds to wait for more data from a master/slave connection before aborting the read

Option Sets Variable Yes, slave_net_timeout

Variable Name slave_net_timeout

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`3600`
Min Value	`1`

The number of seconds to wait for more data from a master/slave connection before aborting the read. This timeout applies only to TCP/IP connections, not to connections made via Unix socket files, named pipes, or shared memory.

slave_skip_errors

Name	`slave-skip-errors`
Description	Tells the slave thread to continue replication when a query returns an error from the provided list
Option Sets Variable	Yes, `slave_skip_errors`
Variable Name	`slave_skip_errors`
Variable Scope	Global
Dynamic Variable	yes

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

slave_transaction_retries

Name slave_transaction_retries

Description Number of times the slave SQL thread will retry a transaction in case it failed with a deadlock or elapsed lock wait timeout, before giving up and stopping

Option Sets Variable Yes, slave_transaction_retries

Variable Name slave_transaction_retries

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`10`
Min Value	`0`

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

slow_launch_time

Name slow_launch_time

Description If creating the thread takes longer than this value (in seconds), the Slow_launch_threads counter will be incremented

Option Sets Variable Yes, slow_launch_time

Variable Name slow_launch_time

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`2`

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

slow_query_log
Name slow_query_log
Description Whether the slow query log is enabled
Version Introduced 5.1.12
Variable Name slow_query_log
Variable Scope Global
Dynamic Variable no
Whether the slow query log is enabled. The value can be 0 (or OFF) to disable the log or 1 (or ON) to enable the log. The default value depends on whether the --log-slow-queries option is given. The destination for log output is controlled by the log_output system variable; if that value is NONE, no log entries are written even if the log is enabled. The slow_query_log variable was added in MySQL 5.1.12.
slow_query_log_file
Name slow_query_log_file
Description Name of the slow query log file
Version Introduced 5.1.12
Variable Name slow_query_log_file
Variable Scope Global
Dynamic Variable no
Value Set
Type filename
The name of the slow query log file. The default value is host_name-slow.log, but the initial value can be changed with the --log-slow-queries option. This variable was added in MySQL 5.1.12.

socket

Name socket

Description Socket file to use for connection

Option Sets Variable Yes, socket

Variable Name socket

Variable Scope Global

Dynamic Variable no

Value Set

Type	linux	filename
Default	`/tmp/mysql.sock`

Value Set

Type	hpux	filename
Default	`/tmp/mysql.sock`

Value Set

Type	solaris	filename
Default	`/tmp/mysql.sock`

Value Set

Type	macosx	filename
Default	`/tmp/mysql.sock`

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

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

sort_buffer_size

Name sort_buffer_size

Description Each thread that needs to do a sort allocates a buffer of this size

Option Sets Variable Yes, sort_buffer_size

Variable Name sort_buffer_size

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`2097144`
Max Value	`4294967295`

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

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

sql_mode

Name sql-mode

Description Set the SQL server mode

Option Sets Variable Yes, sql_mode

Variable Name sql_mode

Variable Scope Both

Dynamic Variable yes

Value Set

Type	enumeration
Default	`OFF`
Valid Values	`ANSI`, `STRICT_TRANS_TABLES`, `TRADITIONAL`, `ERROR_FOR_DIVISION_BY_ZERO`, `ANSI_QUOTES`, `HIGH_NOT_PRECEDENCE`, `IGNORE_SPACE`, `NO_AUTO_CREATE_USER`, `ONLY_FULL_GROUP_BY`, `NO_AUTO_VALUE_ON_ZERO`, `NO_BACKSLASH_ESCAPES`, `NO_UNSIGNED_SUBTRACTION`, `OFF`

The current server SQL mode, which can be set dynamically. See Section 5.1.6, “SQL Modes”.

sql_slave_skip_counter

Name sql_slave_skip_counter

Description The number of events from the master that a slave server should skip

Variable Name sql_slave_skip_counter

Variable Scope Global

Dynamic Variable yes

Value Set

Type

numeric

The number of events from the master that a slave server should skip. See Section 11.6.2.6, “SET GLOBAL SQL_SLAVE_SKIP_COUNTER Syntax”.

ssl_ca

Name ssl-ca

Description CA file in PEM format (check OpenSSL docs, implies --ssl)

Version Introduced 5.1.11

Option Sets Variable Yes, ssl_ca

Variable Name ssl_ca

Variable Scope Global

Dynamic Variable no

Value Set

Type

filename

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

ssl_capath

Name ssl-capath

Description CA directory (check OpenSSL docs, implies --ssl)

Version Introduced 5.1.11

Option Sets Variable Yes, ssl_capath

Variable Name ssl_capath

Variable Scope Global

Dynamic Variable no

Value Set

Type

filename

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

ssl_cert

Name ssl-cert

Description X509 cert in PEM format (implies --ssl)

Version Introduced 5.1.11

Option Sets Variable Yes, ssl_cert

Variable Name ssl_cert

Variable Scope Global

Dynamic Variable no

Value Set

Type

filename

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

ssl_cipher

Name ssl-cipher

Description SSL cipher to use (implies --ssl)

Version Introduced 5.1.11

Option Sets Variable Yes, ssl_cipher

Variable Name ssl_cipher

Variable Scope Global

Dynamic Variable no

Value Set

Type

filename

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

ssl_key
Name ssl-key
Description X509 key in PEM format (implies --ssl)
Option Sets Variable Yes, ssl_key
Variable Name ssl_key
Variable Scope Global
Dynamic Variable no
Value Set
Type string
The name of the SSL key file to use for establishing a secure connection. This variable was added in MySQL 5.1.11.
storage_engine
Name storage_engine
Description The default storage engine
Variable Name storage_engine
Variable Scope Both
Dynamic Variable yes
Value Set
Type enumeration
The default storage engine (table type). To set the storage engine at server startup, use the --default-storage-engine option. See Section 5.1.2, “Command Options”.

sync_binlog

Name sync-binlog

Description Synchronously flush binary log to disk after every #th event

Option Sets Variable Yes, sync_binlog

Variable Name sync_binlog

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`0`
Range	0-4294967295

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

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

sync_frm
Name sync-frm
Description Sync .frm to disk on create. Enabled by default
Option Sets Variable Yes, sync_frm
Variable Name sync_frm
Variable Scope Global
Dynamic Variable yes
Value Set
Type boolean
Default TRUE
If this variable is set to 1, when any non-temporary table is created its .frm file is synchronized to disk (using fdatasync()). This is slower but safer in case of a crash. The default is 1.
system_time_zone
Name system_time_zone
Description The server system time zone
Variable Name system_time_zone
Variable Scope Global
Dynamic Variable yes
Value Set
Type string
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 8.9, “MySQL Server Time Zone Support”.

table_cache

Name table_cache

Description Deprecated; use --table_open_cache instead

Option Sets Variable Yes, table_cache

Variable Name table_cache

Variable Scope Global

Dynamic Variable yes

Deprecated 5.1.3, by table_open_cache

Value Set

Type	numeric
Default	`64`
Range	1-524288

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

table_definition_cache

Name table_definition_cache

Description The number of table definitions that can be stored in the definition cache.

Version Introduced 5.1.3

Variable Name table_definition_cache

Variable Scope Global

Dynamic Variable no

Value Set

Type	numeric
Default	`128`
Range	1-524288

The number of table definitions that can be stored in the definition cache. If you use a large number of tables, you can create a large table definition cache to speed up opening of tables. The table definition cache takes less space and does not use file descriptors, unlike the normal table cache. This variable was added in MySQL 5.1.3.

table_lock_wait_timeout

Name table_lock_wait_timeout

Description Timeout in seconds to wait for a table level lock before returning an error. Used only if the connection has active cursors

Option Sets Variable Yes, table_lock_wait_timeout

Variable Name table_lock_wait_timeout

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`50`
Range	1-1073741824

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

table_open_cache

Name table_open_cache

Description The number of open tables for all threads

Version Introduced 5.1.3

Variable Name table_open_cache

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`64`
Range	1-524288

The number of open tables for all threads. Increasing this value increases the number of file descriptors that mysqld requires. You can check whether you need to increase the table cache by checking the Opened_tables status variable. See Section 5.1.5, “Status Variables”. If the value of Opened_tables is large and you don't do FLUSH TABLES often (which just forces all tables to be closed and reopened), then you should increase the value of the table_open_cache variable. For more information about the table cache, see Section 6.4.8, “How MySQL Opens and Closes Tables”. Before MySQL 5.1.3, this variable is called table_cache.

table_type
Name table_type
Description A synonym for storage_engine
Variable Name table_type
Variable Scope Both
Dynamic Variable yes
Value Set
Type enumeration
This variable is a synonym for storage_engine. In MySQL 5.1, storage_engine is the preferred name. In MySQL 6.0, table_type will be removed.

thread_cache_size

Name thread_cache_size

Description How many threads we should keep in a cache for reuse

Option Sets Variable Yes, thread_cache_size

Variable Name thread_cache_size

Variable Scope Global

Dynamic Variable yes

Value Set

Type	numeric
Default	`0`
Range	0-16384

How many threads the server should cache for reuse. When a client disconnects, the client's threads are put in the cache if there are fewer than thread_cache_size threads there. Requests for threads are satisfied by reusing threads taken from the cache if possible, and only when the cache is empty is a new thread created. This variable can be increased to improve performance if you have a lot of new connections. (Normally, this doesn't provide a notable performance improvement if you have a good thread implementation.) By examining the difference between the Connections and Threads_created status variables, you can see how efficient the thread cache is. For details, see Section 5.1.5, “Status Variables”.

thread_concurrency

Name thread_concurrency

Description Permits the application to give the threads system a hint for the desired number of threads that should be run at the same time

Option Sets Variable Yes, thread_concurrency

Variable Name thread_concurrency

Variable Scope Global

Dynamic Variable no

Value Set

Type	numeric
Default	`10`
Range	1-512

On Solaris, mysqld calls thr_setconcurrency() with this value. This function enables applications to give the threads system a hint about the desired number of threads that should be run at the same time.

thread_handling

Name thread_handling

Description The thread-handling model

Version Introduced 5.1.17

Option Sets Variable Yes, thread_handling

Variable Name thread_handling

Variable Scope Both

Dynamic Variable no

Value Set

Type	numeric
Default	`196608`

Value Set

Type	enumeration
Valid Values	`no-threads`, `one-thread-per-connection`

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

thread_stack

Name thread_stack

Description The stack size for each thread

Option Sets Variable Yes, thread_stack

Variable Name thread_stack

Variable Scope Global

Dynamic Variable no

Value Set

Type	numeric
Default	`196608`
Range	131072-4294967295

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 6.1.4, “The MySQL Benchmark Suite”. The default is 192KB.

time_format
This variable is not implemented.
time_zone
Name time_zone
Description The current time zone.
Variable Name time_zone
Variable Scope Both
Dynamic Variable yes
Value Set
Type string
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 8.9, “MySQL Server Time Zone Support”.

timed_mutexes

Name timed_mutexes

Description Specify whether to time mutexes (only InnoDB mutexes are currently supported)

Option Sets Variable Yes, timed_mutexes

Variable Name timed_mutexes

Variable Scope Global

Dynamic Variable yes

Value Set

Type	boolean
Default	`OFF`

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

tmp_table_size

Name tmp_table_size

Description If an in-memory temporary table exceeds this size, MySQL will automatically convert it to an on-disk MyISAM table

Option Sets Variable Yes, tmp_table_size

Variable Name tmp_table_size

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`33554432`
Range	1024-4294967295

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

tmpdir
Name tmpdir
Description Path for temporary files
Option Sets Variable Yes, tmpdir
Variable Name tmpdir
Variable Scope Global
Dynamic Variable no
Value Set
Type filename
The directory used for temporary files and temporary tables. This variable can be set to a list of several paths that are used in round-robin fashion. Paths should be separated by colon characters (“:”) on Unix and semicolon characters (“;”) on Windows, NetWare, and OS/2.
The multiple-directory feature can be used to spread the load between several physical disks. If the MySQL server is acting as a replication slave, you should not set tmpdir to point to a directory on a memory-based filesystem or to a directory that is cleared when the server host restarts. A replication slave needs some of its temporary files to survive a machine restart so that it can replicate temporary tables or LOAD DATA INFILE operations. If files in the temporary file directory are lost when the server restarts, replication fails. However, if you are using MySQL 4.0.0 or later, you can set the slave's temporary directory using the slave_load_tmpdir variable. In that case, the slave won't use the general tmpdir value and you can set tmpdir to a non-permanent location.

transaction_alloc_block_size

Name transaction_alloc_block_size

Description Allocation block size for transactions to be stored in binary log

Option Sets Variable Yes, transaction_alloc_block_size

Variable Name transaction_alloc_block_size

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`8192`
Range	1024-4294967295

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

transaction_prealloc_size

Name transaction_prealloc_size

Description Persistent buffer for transactions to be stored in binary log

Option Sets Variable Yes, transaction_prealloc_size

Variable Name transaction_prealloc_size

Variable Scope Both

Dynamic Variable yes

Value Set

Type	numeric
Default	`4096`

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

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

tx_isolation

Name tx_isolation

Description The default transaction isolation level

Variable Name tx_isolation

Variable Scope Both

Dynamic Variable yes

Value Set

Type	enumeration
Default	`REPEATABLE-READ`
Valid Values	`READ-UNCOMMITTED`, `READ-COMMITTED`, `REPEATABLE-READ`, `SERIALIZABLE`

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

This variable is set by the SET TRANSACTION ISOLATION LEVEL statement. See Section 11.4.6, “SET TRANSACTION Syntax”. If you set tx_isolation directly to an isolation level name that contains a space, the name should be enclosed within quotes, with the space replaced by a dash. For example:

SET tx_isolation = 'READ-COMMITTED';

updatable_views_with_limit

Name updatable_views_with_limit

Description This variable controls whether updates to a view can be made when the view does not contain all columns of the primary key

Option Sets Variable Yes, updatable_views_with_limit

Variable Name updatable_views_with_limit

Variable Scope Both

Dynamic Variable yes

Value Set

Type	boolean
Default	`1`

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

The variable can have two values:

1 or YES: Issue a warning only (not an error message). This is the default value.
0 or NO: Prohibit the update.

version
The version number for the server.
version_comment
The configure script has a --with-comment option that allows a comment to be specified when building MySQL. This variable contains the value of that comment.
version_compile_machine
The type of machine or architecture on which MySQL was built.
version_compile_os
Name version_compile_os
Description The type of operating system on which MySQL was built
Variable Name version_compile_os
Variable Scope Global
Dynamic Variable yes
Value Set
Type string
The type of operating system on which MySQL was built.
wait_timeout
The number of seconds the server waits for activity on a non-interactive connection before closing it. This timeout applies only to TCP/IP and Unix socket file connections, not to connections made via named pipes, or shared memory.
On thread startup, the session wait_timeout value is initialized from the global wait_timeout value or from the global interactive_timeout value, depending on the type of client (as defined by the CLIENT_INTERACTIVE connect option to mysql_real_connect()). See also interactive_timeout.

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

5.1.4. Using System Variables

5.1.4.1. Structured System Variables
5.1.4.2. Dynamic System Variables

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

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

When the server starts, it initializes all global variables to their default values. These defaults can be changed by options specified on the command line or in an option file. (See Section 4.2.2, “Specifying Program Options”.)
The server also maintains a set of session variables for each client that connects. The client's session variables are initialized at connect time using the current values of the corresponding global variables. For example, the client's SQL mode is controlled by the session sql_mode value, which is initialized when the client connects to the value of the global sql_mode value.

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

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

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

[mysqld]
query_cache_size=16M
max_allowed_packet=1G

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

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

Many system variables are dynamic and can be changed while the server runs by using the SET statement. For a list, see Section 5.1.4.2, “Dynamic System Variables”. To change a system variable with SET, refer to it as var_name, optionally preceded by a modifier:

To indicate explicitly that a variable is a global variable, precede its name by GLOBAL or @@global.. The SUPER privilege is required to set global variables.
To indicate explicitly that a variable is a session variable, precede its name by SESSION, @@session., or @@. Setting a session variable requires no special privilege, but a client can change only its own session variables, not those of any other client.
LOCAL and @@local. are synonyms for SESSION and @@session..
If no modifier is present, SET changes the session variable.

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

Examples:

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

When you assign a value to a system variable with SET, you cannot use suffix letters in the value (as can be done with startup options). However, the value can take the form of an expression:

SET sort_buffer_size = 10 * 1024 * 1024;

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

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

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

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

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

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

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

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

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

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

Note

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

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

mysql> SHOW VARIABLES;
+---------------------------------+-----------------------------------+
| Variable_name                   | Value                             |
+---------------------------------+-----------------------------------+
| auto_increment_increment        | 1                                 |
| auto_increment_offset           | 1                                 |
| automatic_sp_privileges         | ON                                |
| back_log                        | 50                                |
| basedir                         | /home/mysql/                      |
| binlog_cache_size               | 32768                             |
| bulk_insert_buffer_size         | 8388608                           |
| character_set_client            | latin1                            |
| character_set_connection        | latin1                            |
| character_set_database          | latin1                            |
| character_set_results           | latin1                            |
| character_set_server            | latin1                            |
| character_set_system            | utf8                              |
| character_sets_dir              | /home/mysql/share/mysql/charsets/ |
| collation_connection            | latin1_swedish_ci                 |
| collation_database              | latin1_swedish_ci                 |
| collation_server                | latin1_swedish_ci                 |
...
| innodb_additional_mem_pool_size | 1048576                           |
| innodb_autoextend_increment     | 8                                 |
| innodb_buffer_pool_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                         | 5.1.6-alpha-log                   |
| version_comment                 | Source distribution               |
| version_compile_machine         | i686                              |
| version_compile_os              | suse-linux                        |
| wait_timeout                    | 28800                             |
+---------------------------------+-----------------------------------+

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

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

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

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

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

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

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

5.1.4.1. Structured System Variables

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

Its value is a structure with components that specify server parameters considered to be closely related.
There might be several instances of a given type of structured variable. Each one has a different name and refers to a different resource maintained by the server.

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

key_buffer_size
key_cache_block_size
key_cache_division_limit
key_cache_age_threshold

This section describes the syntax for referring to structured variables. Key cache variables are used for syntax examples, but specific details about how key caches operate are found elsewhere, in Section 6.4.6, “The MyISAM Key Cache”.

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

hot_cache.key_buffer_size
hot_cache.key_cache_block_size
cold_cache.key_cache_block_size

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

Structured variable instances and components follow these naming rules:

For a given type of structured variable, each instance must have a name that is unique within variables of that type. However, instance names need not be unique across structured variable types. For example, each structured variable has an instance named default, so default is not unique across variable types.
The names of the components of each structured variable type must be unique across all system variable names. If this were not true (that is, if two different types of structured variables could share component member names), it would not be clear which default structured variable to use for references to member names that are not qualified by an instance name.
If a structured variable instance name is not legal as an unquoted identifier, refer to it as a quoted identifier using backticks. For example, hot-cache is not legal, but `hot-cache` is.
global, session, and local are not legal instance names. This avoids a conflict with notation such as @@global.var_name for referring to non-structured system variables.

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

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

shell> mysqld --hot_cache.key_buffer_size=64K

In an option file, use this syntax:

[mysqld]
hot_cache.key_buffer_size=64K

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

Suppose that you start the server as follows:

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

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

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

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

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

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

To retrieve the cache size, do this:

mysql> SELECT @@global.hot_cache.key_buffer_size;

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

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

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

5.1.4.2. Dynamic System Variables

Many server system variables are dynamic and can be set at runtime using SET GLOBAL or SET SESSION. You can also obtain their values using SELECT. See Section 5.1.4, “Using System Variables”.

The following table shows the full list of all dynamic system variables. The last column indicates for each variable whether GLOBAL or SESSION (or both) apply. The table also lists session options that can be set with the SET statement. Section 11.5.3, “SET Syntax”, discusses these options.

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

Variable Name	Variable Type	Variable Scope
`autocommit`	boolean	`SESSION`
`automatic_sp_privileges`	boolean	`GLOBAL`
`big_tables`	boolean	`SESSION`
`binlog_cache_size`	numeric	`GLOBAL`
`bulk_insert_buffer_size`	numeric	`GLOBAL` \| `SESSION`
`character_set_filesystem`	string	`GLOBAL` \| `SESSION`
`character_set_server`	string	`GLOBAL` \| `SESSION`
`character_set_client`	string	`GLOBAL` \| `SESSION`
`character_set_connection`	string	`GLOBAL` \| `SESSION`
`character_set_database`	string	`GLOBAL` \| `SESSION`
`character_set_results`	string	`GLOBAL` \| `SESSION`
`character_set_system`	string	`GLOBAL`
`collation_server`	string	`GLOBAL` \| `SESSION`
`collation_connection`	string	`GLOBAL` \| `SESSION`
`collation_database`	string	`GLOBAL` \| `SESSION`
`completion_type`	numeric	`GLOBAL` \| `SESSION`
`concurrent_insert`	boolean	`GLOBAL`
`connect_timeout`	numeric	`GLOBAL`
`date_format`	string	`GLOBAL` \| `SESSION`
`datetime_format`	string	`GLOBAL` \| `SESSION`
`default_week_format`	numeric	`GLOBAL` \| `SESSION`
`delay_key_write`	enumeration	`GLOBAL`
`delayed_insert_limit`	numeric	`GLOBAL`
`delayed_insert_timeout`	numeric	`GLOBAL`
`delayed_queue_size`	numeric	`GLOBAL`
`div_precision_increment`	numeric	`GLOBAL` \| `SESSION`
`engine_condition_pushdown`	boolean	`GLOBAL` \| `SESSION`
`expire_logs_days`	numeric	`GLOBAL`
`flush`	boolean	`GLOBAL`
`flush_time`	numeric	`GLOBAL`
`foreign_key_checks`	boolean	`SESSION`
`ft_boolean_syntax`	string	`GLOBAL`
`group_concat_max_len`	numeric	`GLOBAL` \| `SESSION`
`identity`	numeric	`SESSION`
`init_connect`	string	`GLOBAL`
`init_slave`	string	`GLOBAL`
`innodb_autoextend_increment`	numeric	`GLOBAL`
`innodb_autoinc_lock_mode`	numeric	`GLOBAL`
`innodb_checksums`	boolean	`GLOBAL`
`innodb_commit_concurrency`	numeric	`GLOBAL`
`innodb_concurrency_tickets`	numeric	`GLOBAL`
`innodb_fast_shutdown`	boolean	`GLOBAL`
`innodb_flush_log_at_trx_commit`	numeric	`GLOBAL`
`innodb_max_dirty_pages_pct`	numeric	`GLOBAL`
`innodb_max_purge_lag`	numeric	`GLOBAL`
`innodb_support_xa`	boolean	`GLOBAL` \| `SESSION`
`innodb_sync_spin_loops`	numeric	`GLOBAL`
`innodb_table_locks`	boolean	`GLOBAL` \| `SESSION`
`innodb_thread_concurrency`	numeric	`GLOBAL`
`innodb_thread_sleep_delay`	numeric	`GLOBAL`
`insert_id`	numeric	`SESSION`
`interactive_timeout`	numeric	`GLOBAL` \| `SESSION`
`join_buffer_size`	numeric	`GLOBAL` \| `SESSION`
`keep_files_on_create`	boolean	`GLOBAL` \| `SESSION`
`key_buffer_size`	numeric	`GLOBAL`
`key_cache_age_threshold`	numeric	`GLOBAL`
`key_cache_block_size`	numeric	`GLOBAL`
`key_cache_division_limit`	numeric	`GLOBAL`
`last_insert_id`	numeric	`SESSION`
`lc_time_names`	string	`GLOBAL` \| `SESSION`
`log`	string	`GLOBAL`
`log_bin_trust_function_creators`	boolean	`GLOBAL` \| `SESSION`
`log_bin_trust_routine_creators`	boolean	`GLOBAL`
`log_error`	filename	`GLOBAL`
`log_output`	enumeration	`GLOBAL`
`log-slow-queries`	boolean	`GLOBAL`
`log-warnings`	numeric	`GLOBAL` \| `SESSION`
`long_query_time`	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` \| `SESSION`
`max_error_count`	numeric	`GLOBAL` \| `SESSION`
`max_heap_table_size`	numeric	`GLOBAL` \| `SESSION`
`max_insert_delayed_threads`	numeric	`GLOBAL` \| `SESSION`
`max_join_size`	numeric	`GLOBAL` \| `SESSION`
`max_length_for_sort_data`	numeric	`GLOBAL` \| `SESSION`
`max_prepared_stmt_count`	numeric	`GLOBAL`
`max_relay_log_size`	numeric	`GLOBAL`
`max_seeks_for_key`	numeric	`GLOBAL` \| `SESSION`
`max_sort_length`	numeric	`GLOBAL` \| `SESSION`
`max_sp_recursion_depth`	numeric	`GLOBAL` \| `SESSION`
`max_tmp_tables`	numeric	`GLOBAL` \| `SESSION`
`max_user_connections`	numeric	`GLOBAL` \| `SESSION`
`max_write_lock_count`	numeric	`GLOBAL`
`min_examined_row_limit`	numeric	`GLOBAL` \| `SESSION`
`multi_range_count`	numeric	`GLOBAL` \| `SESSION`
`multi_read_range`	numeric	`GLOBAL` \| `SESSION`
`myisam_block_size`	numeric	`GLOBAL` \| `SESSION`
`myisam_data_pointer_size`	numeric	`GLOBAL`
`myisam_max_sort_file_size`	numeric	`GLOBAL`
`myisam_repair_threads`	numeric	`GLOBAL` \| `SESSION`
`myisam_sort_buffer_size`	numeric	`GLOBAL` \| `SESSION`
`myisam_stats_method`	enumeration	`GLOBAL` \| `SESSION`
`ndb_autoincrement_prefetch_sz`	numeric	`GLOBAL` \| `SESSION`
`ndb_cache_check_time`	numeric	`GLOBAL`
`ndb_extra_logging`	numeric	`GLOBAL`
`ndb_force_send`	boolean	`GLOBAL` \| `SESSION`
`ndb_log_update_as_write`	boolean	`GLOBAL`
`ndb_log_updated_only`	boolean	`GLOBAL`
`ndb_optimization_delay`	numeric	`GLOBAL`
`ndb_use_exact_count`	boolean	`GLOBAL` \| `SESSION`
`ndbcluster`	boolean	`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`
`new`	boolean	`GLOBAL` \| `SESSION`
`old-passwords`	boolean	`GLOBAL` \| `SESSION`
`open_files_limit`	numeric	`GLOBAL`
`optimizer_prune_level`	boolean	`GLOBAL` \| `SESSION`
`optimizer_search_depth`	numeric	`GLOBAL` \| `SESSION`
`plugin_innodb_autoextend_increment`	numeric	`GLOBAL` \| `SESSION`
`plugin_innodb_checksums`	boolean	`GLOBAL` \| `SESSION`
`plugin_innodb_commit_concurrency`	numeric	`GLOBAL`
`plugin_innodb_concurrency_tickets`	numeric	`GLOBAL`
`plugin_innodb_flush_log_at_trx_commit`	numeric	`GLOBAL`
`plugin_innodb_max_dirty_pages_pct`	numeric	`GLOBAL`
`plugin_innodb_max_purge_lag`	numeric	`GLOBAL`
`plugin_innodb_support_xa`	boolean	`GLOBAL` \| `SESSION`
`innodb_sync_spin_loops`	numeric	`GLOBAL`
`plugin_innodb_table_locks`	boolean	`GLOBAL` \| `SESSION`
`plugin_innodb_thread_concurrency`	numeric	`GLOBAL`
`plugin_innodb_thread_sleep_delay`	numeric	`GLOBAL`
`preload_buffer_size`	numeric	`GLOBAL` \| `SESSION`
`query_alloc_block_size`	numeric	`GLOBAL` \| `SESSION`
`query_cache_limit`	numeric	`GLOBAL`
`query_cache_min_res_unit`	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`
`read_buffer_size`	numeric	`GLOBAL` \| `SESSION`
`read_only`	numeric	`GLOBAL`
`read_rnd_buffer_size`	numeric	`GLOBAL` \| `SESSION`
`relay_log_purge`	boolean	`GLOBAL`
`relay_log_space_limit`	numeric	`GLOBAL`
`rpl_recovery_rank`	numeric	`GLOBAL`
`secure_auth`	boolean	`GLOBAL`
`server_id`	numeric	`GLOBAL`
`skip_networking`		`GLOBAL`
`skip_show_database`		`GLOBAL`
`slave_allow_batching`	boolean	`GLOBAL`
`slave_net_timeout`	numeric	`GLOBAL`
`slave_skip_errors`		`GLOBAL`
`slave_compressed_protocol`	boolean	`GLOBAL`
`slave_transaction_retries`	numeric	`GLOBAL`
`slow_launch_time`	numeric	`GLOBAL`
`sort_buffer_size`	numeric	`GLOBAL` \| `SESSION`
`sql_mode`	enumeration	`GLOBAL` \| `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`
`sql_max_join_size`	numeric	`GLOBAL` \| `SESSION`
`sql_notes`	boolean	`SESSION`
`sql_quote_show_create`	boolean	`SESSION`
`sql_safe_updates`	boolean	`SESSION`
`sql_select_limit`	numeric	`GLOBAL` \| `SESSION`
`sql_slave_skip_counter`	numeric	`GLOBAL`
`sql_warnings`	boolean	`SESSION`
`storage_engine`	enumeration	`GLOBAL` \| `SESSION`
`sync_binlog`	numeric	`GLOBAL`
`sync_frm`	boolean	`GLOBAL`
`system_time_zone`	string	`GLOBAL`
`table_cache`	numeric	`GLOBAL`
`table_lock_wait_timeout`	numeric	`GLOBAL`
`table_open_cache`	numeric	`GLOBAL`
`table_type`	enumeration	`GLOBAL` \| `SESSION`
`thread_cache_size`	numeric	`GLOBAL`
`time_format`	string	`GLOBAL` \| `SESSION`
`time_zone`	string	`GLOBAL` \| `SESSION`
`timed_mutexes`	boolean	`GLOBAL`
`timestamp`	string	`SESSION`
`tmp_table_size`	numeric	`GLOBAL` \| `SESSION`
`transaction_alloc_block_size`	numeric	`GLOBAL` \| `SESSION`
`transaction_allow_batching`	boolean	`SESSION`
`transaction_prealloc_size`	numeric	`GLOBAL` \| `SESSION`
`tx_isolation`	enumeration	`GLOBAL` \| `SESSION`
`unique_checks`	boolean	`SESSION`
`updatable_views_with_limit`	boolean	`GLOBAL` \| `SESSION`
`version_compile_os`	string	`GLOBAL`
`wait_timeout`	numeric	`GLOBAL` \| `SESSION`

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

5.1.5. Status Variables

The server maintains many status variables that provide information about its operation. You can view these variables and their values by using the SHOW [GLOBAL] STATUS statement. The optional GLOBAL keyword aggregates the values over all connections.

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

The following table lists all available server status variables:

Variable Name	Variable Type	Variable Scope
`Aborted_clients`	numeric	`GLOBAL` \| `SESSION`
`Aborted_connects`	numeric	`GLOBAL` \| `SESSION`
`Binlog_cache_disk_use`	numeric	`GLOBAL` \| `SESSION`
`Binlog_cache_use`	numeric	`GLOBAL` \| `SESSION`
`Bytes_received`	numeric	`GLOBAL` \| `SESSION`
`Bytes_sent`	numeric	`GLOBAL` \| `SESSION`
`Com_admin_commands`	numeric	`GLOBAL` \| `SESSION`
`Com_alter_db`	numeric	`GLOBAL` \| `SESSION`
`Com_alter_event`	numeric	`GLOBAL` \| `SESSION`
`Com_alter_table`	numeric	`GLOBAL` \| `SESSION`
`Com_analyze`	numeric	`GLOBAL` \| `SESSION`
`Com_backup_table`	numeric	`GLOBAL` \| `SESSION`
`Com_begin`	numeric	`GLOBAL` \| `SESSION`
`Com_call_procedure`	numeric	`GLOBAL` \| `SESSION`
`Com_change_db`	numeric	`GLOBAL` \| `SESSION`
`Com_change_master`	numeric	`GLOBAL` \| `SESSION`
`Com_check`	numeric	`GLOBAL` \| `SESSION`
`Com_checksum`	numeric	`GLOBAL` \| `SESSION`
`Com_commit`	numeric	`GLOBAL` \| `SESSION`
`Com_create_db`	numeric	`GLOBAL` \| `SESSION`
`Com_create_event`	numeric	`GLOBAL` \| `SESSION`
`Com_create_function`	numeric	`GLOBAL` \| `SESSION`
`Com_create_index`	numeric	`GLOBAL` \| `SESSION`
`Com_create_table`	numeric	`GLOBAL` \| `SESSION`
`Com_create_user`	numeric	`GLOBAL` \| `SESSION`
`Com_dealloc_sql`	numeric	`GLOBAL` \| `SESSION`
`Com_delete`	numeric	`GLOBAL` \| `SESSION`
`Com_delete_multi`	numeric	`GLOBAL` \| `SESSION`
`Com_do`	numeric	`GLOBAL` \| `SESSION`
`Com_drop_db`	numeric	`GLOBAL` \| `SESSION`
`Com_drop_event`	numeric	`GLOBAL` \| `SESSION`
`Com_drop_function`	numeric	`GLOBAL` \| `SESSION`
`Com_drop_index`	numeric	`GLOBAL` \| `SESSION`
`Com_drop_table`	numeric	`GLOBAL` \| `SESSION`
`Com_drop_user`	numeric	`GLOBAL` \| `SESSION`
`Com_execute_sql`	numeric	`GLOBAL` \| `SESSION`
`Com_flush`	numeric	`GLOBAL` \| `SESSION`
`Com_grant`	numeric	`GLOBAL` \| `SESSION`
`Com_ha_close`	numeric	`GLOBAL` \| `SESSION`
`Com_ha_open`	numeric	`GLOBAL` \| `SESSION`
`Com_ha_read`	numeric	`GLOBAL` \| `SESSION`
`Com_help`	numeric	`GLOBAL` \| `SESSION`
`Com_insert`	numeric	`GLOBAL` \| `SESSION`
`Com_insert_select`	numeric	`GLOBAL` \| `SESSION`
`Com_kill`	numeric	`GLOBAL` \| `SESSION`
`Com_load`	numeric	`GLOBAL` \| `SESSION`
`Com_lock_tables`	numeric	`GLOBAL` \| `SESSION`
`Com_optimize`	numeric	`GLOBAL` \| `SESSION`
`Com_preload_keys`	numeric	`GLOBAL` \| `SESSION`
`Com_prepare_sql`	numeric	`GLOBAL` \| `SESSION`
`Com_purge`	numeric	`GLOBAL` \| `SESSION`
`Com_purge_before_date`	numeric	`GLOBAL` \| `SESSION`
`Com_rename_table`	numeric	`GLOBAL` \| `SESSION`
`Com_repair`	numeric	`GLOBAL` \| `SESSION`
`Com_replace`	numeric	`GLOBAL` \| `SESSION`
`Com_replace_select`	numeric	`GLOBAL` \| `SESSION`
`Com_reset`	numeric	`GLOBAL` \| `SESSION`
`Com_restore_table`	numeric	`GLOBAL` \| `SESSION`
`Com_revoke`	numeric	`GLOBAL` \| `SESSION`
`Com_revoke_all`	numeric	`GLOBAL` \| `SESSION`
`Com_rollback`	numeric	`GLOBAL` \| `SESSION`
`Com_savepoint`	numeric	`GLOBAL` \| `SESSION`
`Com_select`	numeric	`GLOBAL` \| `SESSION`
`Com_set_option`	numeric	`GLOBAL` \| `SESSION`
`Com_show_binlog_events`	numeric	`GLOBAL` \| `SESSION`
`Com_show_binlogs`	numeric	`GLOBAL` \| `SESSION`
`Com_show_charsets`	numeric	`GLOBAL` \| `SESSION`
`Com_show_collations`	numeric	`GLOBAL` \| `SESSION`
`Com_show_column_types`	numeric	`GLOBAL` \| `SESSION`
`Com_show_create_db`	numeric	`GLOBAL` \| `SESSION`
`Com_show_create_event`	numeric	`GLOBAL` \| `SESSION`
`Com_show_create_table`	numeric	`GLOBAL` \| `SESSION`
`Com_show_databases`	numeric	`GLOBAL` \| `SESSION`
`Com_show_engine_logs`	numeric	`GLOBAL` \| `SESSION`
`Com_show_engine_mutex`	numeric	`GLOBAL` \| `SESSION`
`Com_show_engine_status`	numeric	`GLOBAL` \| `SESSION`
`Com_show_errors`	numeric	`GLOBAL` \| `SESSION`
`Com_show_events`	numeric	`GLOBAL` \| `SESSION`
`Com_show_fields`	numeric	`GLOBAL` \| `SESSION`
`Com_show_grants`	numeric	`GLOBAL` \| `SESSION`
`Com_show_innodb_status`	numeric	`GLOBAL` \| `SESSION`
`Com_show_keys`	numeric	`GLOBAL` \| `SESSION`
`Com_show_logs`	numeric	`GLOBAL` \| `SESSION`
`Com_show_master_status`	numeric	`GLOBAL` \| `SESSION`
`Com_show_ndb_status`	numeric	`GLOBAL` \| `SESSION`
`Com_show_new_master`	numeric	`GLOBAL` \| `SESSION`
`Com_show_open_tables`	numeric	`GLOBAL` \| `SESSION`
`Com_show_plugins`	numeric	`GLOBAL` \| `SESSION`
`Com_show_privileges`	numeric	`GLOBAL` \| `SESSION`
`Com_show_processlist`	numeric	`GLOBAL` \| `SESSION`
`Com_show_slave_hosts`	numeric	`GLOBAL` \| `SESSION`
`Com_show_slave_status`	numeric	`GLOBAL` \| `SESSION`
`Com_show_status`	numeric	`GLOBAL` \| `SESSION`
`Com_show_storage_engines`	numeric	`GLOBAL` \| `SESSION`
`Com_show_tables`	numeric	`GLOBAL` \| `SESSION`
`Com_show_triggers`	numeric	`GLOBAL` \| `SESSION`
`Com_show_variables`	numeric	`GLOBAL` \| `SESSION`
`Com_show_warnings`	numeric	`GLOBAL` \| `SESSION`
`Com_slave_start`	numeric	`GLOBAL` \| `SESSION`
`Com_slave_stop`	numeric	`GLOBAL` \| `SESSION`
`Com_stmt_close`	numeric	`GLOBAL` \| `SESSION`
`Com_stmt_execute`	numeric	`GLOBAL` \| `SESSION`
`Com_stmt_fetch`	numeric	`GLOBAL` \| `SESSION`
`Com_stmt_prepare`	numeric	`GLOBAL` \| `SESSION`
`Com_stmt_reset`	numeric	`GLOBAL` \| `SESSION`
`Com_stmt_send_long_data`	numeric	`GLOBAL` \| `SESSION`
`Com_truncate`	numeric	`GLOBAL` \| `SESSION`
`Com_unlock_tables`	numeric	`GLOBAL` \| `SESSION`
`Com_update`	numeric	`GLOBAL` \| `SESSION`
`Com_update_multi`	numeric	`GLOBAL` \| `SESSION`
`Com_xa_commit`	numeric	`GLOBAL` \| `SESSION`
`Com_xa_end`	numeric	`GLOBAL` \| `SESSION`
`Com_xa_prepare`	numeric	`GLOBAL` \| `SESSION`
`Com_xa_recover`	numeric	`GLOBAL` \| `SESSION`
`Com_xa_rollback`	numeric	`GLOBAL` \| `SESSION`
`Com_xa_start`	numeric	`GLOBAL` \| `SESSION`
`Compression`	numeric	`GLOBAL` \| `SESSION`
`Connections`	numeric	`GLOBAL` \| `SESSION`
`Created_tmp_disk_tables`	numeric	`GLOBAL` \| `SESSION`
`Created_tmp_files`	numeric	`GLOBAL` \| `SESSION`
`Created_tmp_tables`	numeric	`GLOBAL` \| `SESSION`
`Delayed_errors`	numeric	`GLOBAL` \| `SESSION`
`Delayed_insert_threads`	numeric	`GLOBAL` \| `SESSION`
`Delayed_writes`	numeric	`GLOBAL` \| `SESSION`
`Flush_commands`	numeric	`GLOBAL` \| `SESSION`
`Handler_commit`	numeric	`GLOBAL` \| `SESSION`
`Handler_delete`	numeric	`GLOBAL` \| `SESSION`
`Handler_discover`	numeric	`GLOBAL` \| `SESSION`
`Handler_prepare`	numeric	`GLOBAL` \| `SESSION`
`Handler_read_first`	numeric	`GLOBAL` \| `SESSION`
`Handler_read_key`	numeric	`GLOBAL` \| `SESSION`
`Handler_read_next`	numeric	`GLOBAL` \| `SESSION`
`Handler_read_prev`	numeric	`GLOBAL` \| `SESSION`
`Handler_read_rnd`	numeric	`GLOBAL` \| `SESSION`
`Handler_read_rnd_next`	numeric	`GLOBAL` \| `SESSION`
`Handler_rollback`	numeric	`GLOBAL` \| `SESSION`
`Handler_savepoint`	numeric	`GLOBAL` \| `SESSION`
`Handler_savepoint_rollback`	numeric	`GLOBAL` \| `SESSION`
`Handler_update`	numeric	`GLOBAL` \| `SESSION`
`Handler_write`	numeric	`GLOBAL` \| `SESSION`
`Innodb_buffer_pool_pages_data`	numeric	`GLOBAL` \| `SESSION`
`Innodb_buffer_pool_pages_dirty`	numeric	`GLOBAL` \| `SESSION`
`Innodb_buffer_pool_pages_flushed`	numeric	`GLOBAL` \| `SESSION`
`Innodb_buffer_pool_pages_free`	numeric	`GLOBAL` \| `SESSION`
`Innodb_buffer_pool_pages_latched`	numeric	`GLOBAL` \| `SESSION`
`Innodb_buffer_pool_pages_misc`	numeric	`GLOBAL` \| `SESSION`
`Innodb_buffer_pool_pages_total`	numeric	`GLOBAL` \| `SESSION`
`Innodb_buffer_pool_read_ahead_rnd`	numeric	`GLOBAL` \| `SESSION`
`Innodb_buffer_pool_read_ahead_seq`	numeric	`GLOBAL` \| `SESSION`
`Innodb_buffer_pool_read_requests`	numeric	`GLOBAL` \| `SESSION`
`Innodb_buffer_pool_reads`	numeric	`GLOBAL` \| `SESSION`
`Innodb_buffer_pool_wait_free`	numeric	`GLOBAL` \| `SESSION`
`Innodb_buffer_pool_write_requests`	numeric	`GLOBAL` \| `SESSION`
`Innodb_data_fsyncs`	numeric	`GLOBAL` \| `SESSION`
`Innodb_data_pending_fsyncs`	numeric	`GLOBAL` \| `SESSION`
`Innodb_data_pending_reads`	numeric	`GLOBAL` \| `SESSION`
`Innodb_data_pending_writes`	numeric	`GLOBAL` \| `SESSION`
`Innodb_data_read`	numeric	`GLOBAL` \| `SESSION`
`Innodb_data_reads`	numeric	`GLOBAL` \| `SESSION`
`Innodb_data_writes`	numeric	`GLOBAL` \| `SESSION`
`Innodb_data_written`	numeric	`GLOBAL` \| `SESSION`
`Innodb_dblwr_pages_written`	numeric	`GLOBAL` \| `SESSION`
`Innodb_dblwr_writes`	numeric	`GLOBAL` \| `SESSION`
`Innodb_log_waits`	numeric	`GLOBAL` \| `SESSION`
`Innodb_log_write_requests`	numeric	`GLOBAL` \| `SESSION`
`Innodb_log_writes`	numeric	`GLOBAL` \| `SESSION`
`Innodb_os_log_fsyncs`	numeric	`GLOBAL` \| `SESSION`
`Innodb_os_log_pending_fsyncs`	numeric	`GLOBAL` \| `SESSION`
`Innodb_os_log_pending_writes`	numeric	`GLOBAL` \| `SESSION`
`Innodb_os_log_written`	numeric	`GLOBAL` \| `SESSION`
`Innodb_page_size`	numeric	`GLOBAL` \| `SESSION`
`Innodb_pages_created`	numeric	`GLOBAL` \| `SESSION`
`Innodb_pages_read`	numeric	`GLOBAL` \| `SESSION`
`Innodb_pages_written`	numeric	`GLOBAL` \| `SESSION`
`Innodb_row_lock_current_waits`	numeric	`GLOBAL` \| `SESSION`
`Innodb_row_lock_time`	numeric	`GLOBAL` \| `SESSION`
`Innodb_row_lock_time_avg`	numeric	`GLOBAL` \| `SESSION`
`Innodb_row_lock_time_max`	numeric	`GLOBAL` \| `SESSION`
`Innodb_row_lock_waits`	numeric	`GLOBAL` \| `SESSION`
`Innodb_rows_deleted`	numeric	`GLOBAL` \| `SESSION`
`Innodb_rows_inserted`	numeric	`GLOBAL` \| `SESSION`
`Innodb_rows_read`	numeric	`GLOBAL` \| `SESSION`
`Innodb_rows_updated`	numeric	`GLOBAL` \| `SESSION`
`Key_blocks_not_flushed`	numeric	`GLOBAL` \| `SESSION`
`Key_blocks_unused`	numeric	`GLOBAL` \| `SESSION`
`Key_blocks_used`	numeric	`GLOBAL` \| `SESSION`
`Key_read_requests`	numeric	`GLOBAL` \| `SESSION`
`Key_reads`	numeric	`GLOBAL` \| `SESSION`
`Key_write_requests`	numeric	`GLOBAL` \| `SESSION`
`Key_writes`	numeric	`GLOBAL` \| `SESSION`
`Last_query_cost`	numeric	`GLOBAL` \| `SESSION`
`Max_used_connections`	numeric	`GLOBAL` \| `SESSION`
`Ndb_cluster_node_id`	numeric	`GLOBAL` \| `SESSION`
`Ndb_config_from_host`	numeric	`GLOBAL` \| `SESSION`
`Ndb_config_from_port`	numeric	`GLOBAL` \| `SESSION`
`Ndb_conflict_fn_max`	numeric	`GLOBAL` \| `SESSION`
`Ndb_conflict_fn_old`	numeric	`GLOBAL` \| `SESSION`
`ndb_execute_count`	numeric	`GLOBAL`
`Ndb_number_of_data_nodes`	numeric	`GLOBAL` \| `SESSION`
`Not_flushed_delayed_rows`	numeric	`GLOBAL` \| `SESSION`
`Open_files`	numeric	`GLOBAL` \| `SESSION`
`Open_streams`	numeric	`GLOBAL` \| `SESSION`
`Open_table_definitions`	numeric	`GLOBAL` \| `SESSION`
`Open_tables`	numeric	`GLOBAL` \| `SESSION`
`Opened_tables`	numeric	`GLOBAL` \| `SESSION`
`prepared_stmt_count`	numeric	`GLOBAL` \| `SESSION`
`Qcache_free_blocks`	numeric	`GLOBAL` \| `SESSION`
`Qcache_free_memory`	numeric	`GLOBAL` \| `SESSION`
`Qcache_hits`	numeric	`GLOBAL` \| `SESSION`
`Qcache_inserts`	numeric	`GLOBAL` \| `SESSION`
`Qcache_lowmem_prunes`	numeric	`GLOBAL` \| `SESSION`
`Qcache_not_cached`	numeric	`GLOBAL` \| `SESSION`
`Qcache_queries_in_cache`	numeric	`GLOBAL` \| `SESSION`
`Qcache_total_blocks`	numeric	`GLOBAL` \| `SESSION`
`Questions`	numeric	`GLOBAL` \| `SESSION`
`Relay_Log_Space`	numeric	`GLOBAL` \| `SESSION`
`Rpl_status`		`GLOBAL` \| `SESSION`
`Select_full_join`	numeric	`GLOBAL` \| `SESSION`
`Select_full_range_join`	numeric	`GLOBAL` \| `SESSION`
`Select_range`	numeric	`GLOBAL` \| `SESSION`
`Select_range_check`	numeric	`GLOBAL` \| `SESSION`
`Select_scan`	numeric	`GLOBAL` \| `SESSION`
`Slave_heartbeat_period`		`GLOBAL`
`Slave_open_temp_tables`	numeric	`GLOBAL` \| `SESSION`
`Slave_received_heartbeats`		`GLOBAL`
`Slave_retried_transactions`	numeric	`GLOBAL` \| `SESSION`
`Slave_running`	boolean	`GLOBAL` \| `SESSION`
`Slow_launch_threads`	numeric	`GLOBAL` \| `SESSION`
`Slow_queries`	numeric	`GLOBAL` \| `SESSION`
`Sort_merge_passes`	numeric	`GLOBAL` \| `SESSION`
`Sort_range`	numeric	`GLOBAL` \| `SESSION`
`Sort_rows`	numeric	`GLOBAL` \| `SESSION`
`Sort_scan`	numeric	`GLOBAL` \| `SESSION`
`Table_locks_immediate`	numeric	`GLOBAL` \| `SESSION`
`Table_locks_waited`	numeric	`GLOBAL` \| `SESSION`
`Tc_log_max_pages_used`	numeric	`GLOBAL` \| `SESSION`
`Tc_log_page_size`	numeric	`GLOBAL` \| `SESSION`
`Tc_log_page_waits`	numeric	`GLOBAL` \| `SESSION`
`Threads_cached`	numeric	`GLOBAL` \| `SESSION`
`Threads_connected`	numeric	`GLOBAL` \| `SESSION`
`Threads_created`	numeric	`GLOBAL` \| `SESSION`
`Threads_running`	numeric	`GLOBAL` \| `SESSION`
`Uptime`	numeric	`GLOBAL` \| `SESSION`

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

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

The status variables have the following meanings. Variables with no version indicated were already present prior to MySQL 5.1. For information regarding their implementation history, see MySQL 5.0 Reference Manual.

Aborted_clients
The number of connections that were aborted because the client died without closing the connection properly. See Section B.1.2.11, “Communication Errors and Aborted Connections”.
Aborted_connects
The number of failed attempts to connect to the MySQL server. See Section B.1.2.11, “Communication Errors and Aborted Connections”.
Binlog_cache_disk_use
The number of transactions that used the temporary binary log cache but that exceeded the value of binlog_cache_size and used a temporary file to store statements from the transaction.
Binlog_cache_use
The number of transactions that used the temporary binary log cache.
Bytes_received
The number of bytes received from all clients.
Bytes_sent
The number of bytes sent to all clients.
Com_xxx
The Com_xxx statement counter variables indicate the number of times each xxx statement has been executed. There is one status variable for each type of statement. For example, Com_delete and Com_insert count DELETE and INSERT statements, respectively. However, if a query result is returned from query cache, the server increments the Qcache_hits status variable, not Com_select. See Section 6.5.4.4, “Query Cache Status and Maintenance”.
All of the Com_STATEMENT_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_STATEMENT_xxx status variables are as follows:
- Com_STATEMENT_prepare
- Com_STATEMENT_execute
- Com_STATEMENT_fetch
- Com_STATEMENT_send_long_data
- Com_STATEMENT_reset
- Com_STATEMENT_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_STATEMENT_prepare(), mysql_STATEMENT_execute(), and so forth are executed. However, Com_STATEMENT_prepare, Com_STATEMENT_execute and Com_STATEMENT_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_STATEMENT_fetch stands for the total number of network round-trips issued when fetching from cursors.
Compression
Whether the client connection uses compression in the client/server protocol. Added in MySQL 5.1.2.
Connections
The number of connection attempts (successful or not) to the MySQL server.
Created_tmp_disk_tables
The number of temporary tables on disk created automatically by the server while executing statements.
Created_tmp_files
How many temporary files mysqld has created.
Created_tmp_tables
The number of in-memory temporary tables created automatically by the server while executing statements. If Created_tmp_disk_tables is large, you may want to increase the tmp_table_size value to cause temporary tables to be memory-based instead of disk-based.
Delayed_errors
The number of rows written with INSERT DELAYED for which some error occurred (probably duplicate key).
Delayed_insert_threads
The number of INSERT DELAYED handler threads in use.
Delayed_writes
The number of INSERT DELAYED rows written.
Flush_commands
The number of executed FLUSH statements.
Handler_commit
The number of internal COMMIT statements.
Handler_delete
The number of times that rows have been deleted from tables.
Handler_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.
Handler_prepare
A counter for the prepare phase of two-phase commit operations.
Handler_read_first
The number of times the first entry was read from an index. If this value is high, it suggests that the server is doing a lot of full index scans; for example, SELECT col1 FROM foo, assuming that col1 is indexed.
Handler_read_key
The number of requests to read a row based on a key. If this value is high, it is a good indication that your tables are properly indexed for your queries.
Handler_read_next
The number of requests to read the next row in key order. This value is incremented if you are querying an index column with a range constraint or if you are doing an index scan.
Handler_read_prev
The number of requests to read the previous row in key order. This read method is mainly used to optimize ORDER BY ... DESC.
Handler_read_rnd
The number of requests to read a row based on a fixed position. This value is high if you are doing a lot of queries that require sorting of the result. You probably have a lot of queries that require MySQL to scan entire tables or you have joins that don't use keys properly.
Handler_read_rnd_next
The number of requests to read the next row in the data file. This value is high if you are doing a lot of table scans. Generally this suggests that your tables are not properly indexed or that your queries are not written to take advantage of the indexes you have.
Handler_rollback
The number of requests for a storage engine to perform a rollback operation.
Handler_savepoint
The number of requests for a storage engine to place a savepoint.
Handler_savepoint_rollback
The number of requests for a storage engine to roll back to a savepoint.
Handler_update
The number of requests to update a row in a table.
Handler_write
The number of requests to insert a row in a table.
Innodb_buffer_pool_pages_data
The number of pages containing data (dirty or clean).
Innodb_buffer_pool_pages_dirty
The number of pages currently dirty.
Innodb_buffer_pool_pages_flushed
The number of buffer pool page-flush requests.
Innodb_buffer_pool_pages_free
The number of free pages.
Innodb_buffer_pool_pages_latched
The number of latched pages in InnoDB buffer pool. These are pages currently being read or written or that cannot be flushed or removed for some other reason.
Innodb_buffer_pool_pages_misc
The number of pages that are busy because they have been allocated for administrative overhead such as row locks or the adaptive hash index. This value can also be calculated as Innodb_buffer_pool_pages_total – Innodb_buffer_pool_pages_free – Innodb_buffer_pool_pages_data.
Innodb_buffer_pool_pages_total
The total size of the buffer pool, in pages.
Innodb_buffer_pool_read_ahead_rnd
The number of “random” read-aheads initiated by InnoDB. This happens when a query scans a large portion of a table but in random order.
Innodb_buffer_pool_read_ahead_seq
The number of sequential read-aheads initiated by InnoDB. This happens when InnoDB does a sequential full table scan.
Innodb_buffer_pool_read_requests
The number of logical read requests InnoDB has done.
Innodb_buffer_pool_reads
The number of logical reads that InnoDB could not satisfy from the buffer pool and had to do a single-page read.
Innodb_buffer_pool_wait_free
Normally, writes to the InnoDB buffer pool happen in the background. However, if it is necessary to read or create a page and no clean pages are available, it is also necessary to wait for pages to be flushed first. This counter counts instances of these waits. If the buffer pool size has been set properly, this value should be small.
Innodb_buffer_pool_write_requests
The number writes done to the InnoDB buffer pool.
Innodb_data_fsyncs
The number of fsync() operations so far.
Innodb_data_pending_fsyncs
The current number of pending fsync() operations.
Innodb_data_pending_reads
The current number of pending reads.
Innodb_data_pending_writes
The current number of pending writes.
Innodb_data_read
The amount of data read so far, in bytes.
Innodb_data_reads
The total number of data reads.
Innodb_data_writes
The total number of data writes.
Innodb_data_written
The amount of data written so far, in bytes.
Innodb_dblwr_writes, 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. See Section 12.5.14.1, “InnoDB Disk I/O”.
Innodb_log_waits
The number of times that the log buffer was too small and a wait was required for it to be flushed before continuing.
Innodb_log_write_requests
The number of log write requests.
Innodb_log_writes
The number of physical writes to the log file.
Innodb_os_log_fsyncs
The number of fsync() writes done to the log file.
Innodb_os_log_pending_fsyncs
The number of pending log file fsync() operations.
Innodb_os_log_pending_writes
The number of pending log file writes.
Innodb_os_log_written
The number of bytes written to the log file.
Innodb_page_size
The compiled-in InnoDB page size (default 16KB). Many values are counted in pages; the page size allows them to be easily converted to bytes.
Innodb_pages_created
The number of pages created.
Innodb_pages_read
The number of pages read.
Innodb_pages_written
The number of pages written.
Innodb_row_lock_current_waits
The number of row locks currently being waited for.
Innodb_row_lock_time
The total time spent in acquiring row locks, in milliseconds.
Innodb_row_lock_time_avg
The average time to acquire a row lock, in milliseconds.
Innodb_row_lock_time_max
The maximum time to acquire a row lock, in milliseconds.
Innodb_row_lock_waits
The number of times a row lock had to be waited for.
Innodb_rows_deleted
The number of rows deleted from InnoDB tables.
Innodb_rows_inserted
The number of rows inserted into InnoDB tables.
Innodb_rows_read
The number of rows read from InnoDB tables.
Innodb_rows_updated
The number of rows updated in InnoDB tables.
Key_blocks_not_flushed
The number of key blocks in the key cache that have changed but have not yet been flushed to disk.
Key_blocks_unused
The number of unused blocks in the key cache. You can use this value to determine how much of the key cache is in use; see the discussion of key_buffer_size in Section 5.1.3, “System Variables”.
Key_blocks_used
The number of used blocks in the key cache. This value is a high-water mark that indicates the maximum number of blocks that have ever been in use at one time.
Key_read_requests
The number of requests to read a key block from the cache.
Key_reads
The number of physical reads of a key block from disk. If Key_reads is large, then your key_buffer_size value is probably too small. The cache miss rate can be calculated as Key_reads/Key_read_requests.
Key_write_requests
The number of requests to write a key block to the cache.
Key_writes
The number of physical writes of a key block to disk.
Last_query_cost
The total cost of the last compiled query as computed by the query optimizer. This is useful for comparing the cost of different query plans for the same query. The default value of 0 means that no query has been compiled yet. The default value is 0. Last_query_cost has session scope.
The Last_query_cost value can be computed accurately only for simple “flat” queries, not complex queries such as those with subqueries or UNION. For the latter, the value is set to 0.
Max_used_connections
The maximum number of connections that have been in use simultaneously since the server started.
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.
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 5.1.12, this variable was named Ndb_connected_host.
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.
If the server is not part of a MySQL Cluster, then the value of this variable is 0.
Prior to MySQL 5.1.12, this variable was named Ndb_connected_port.
Ndb_number_of_data_nodes
If the server is part of a MySQL Cluster, the value of this variable is the number of data nodes in the cluster.
If the server is not part of a MySQL Cluster, then the value of this variable is 0.
Prior to MySQL 5.1.12, this variable was named Ndb_number_of_storage_nodes.
Not_flushed_delayed_rows
The number of rows waiting to be written in INSERT DELAY queues.
Open_files
The number of files that are open.
Open_streams
The number of streams that are open (used mainly for logging).
Open_table_definitions
The number of cached .frm files. This variable was added in MySQL 5.1.3.
Open_tables
The number of tables that are open.
Opened_tables
The number of tables that have been opened. If Opened_tables is big, your table_open_cache value is probably too small.
Prepared_STATEMENT_count
The current number of prepared statements. (The maximum number of statements is given by the max_prepared_STATEMENT_count system variable.) This variable was added in MySQL 5.1.14.
Qcache_free_blocks
The number of free memory blocks in the query cache.
Qcache_free_memory
The amount of free memory for the query cache.
Qcache_hits
The number of query cache hits.
Qcache_inserts
The number of queries added to the query cache.
Qcache_lowmem_prunes
The number of queries that were deleted from the query cache because of low memory.
Qcache_not_cached
The number of non-cached queries (not cacheable, or not cached due to the query_cache_type setting).
Qcache_queries_in_cache
The number of queries registered in the query cache.
Qcache_total_blocks
The total number of blocks in the query cache.
Questions
The number of statements that clients have sent to the server.
Rpl_status
The status of fail-safe replication (not yet implemented).
Select_full_join
The number of joins that perform table scans because they do not use indexes. If this value is not 0, you should carefully check the indexes of your tables.
Select_full_range_join
The number of joins that used a range search on a reference table.
Select_range
The number of joins that used ranges on the first table. This is normally not a critical issue even if the value is quite large.
Select_range_check
The number of joins without keys that check for key usage after each row. If this is not 0, you should carefully check the indexes of your tables.
Select_scan
The number of joins that did a full scan of the first table.
MySQL Cluster 5.1 Carrier Grade EditionThe following information applies to users of MySQL Cluster 5.1 Carrier Grade Edition only. For more information about MySQL Cluster 5.1 Carrier Grade Edition, see Section 15.2, “MySQL Cluster 5.1 Carrier Grade Edition”.
Slave_heartbeat_period
Shows the replication heartbeat interval (in seconds) on a replication slave.
This variable was added in MySQL 5.1.22-ndb-6.3.4.
The following information applies to all MySQL users.
Slave_open_temp_tables
The number of temporary tables that the slave SQL thread currently has open.
MySQL Cluster 5.1 Carrier Grade EditionThe following information applies to users of MySQL Cluster 5.1 Carrier Grade Edition only. For more information about MySQL Cluster 5.1 Carrier Grade Edition, see Section 15.2, “MySQL Cluster 5.1 Carrier Grade Edition”.
Slave_received_heartbeats
This counter increments with each replication heartbeat received by a replication slave since the last time that the slave was restarted or reset, or a CHANGE MASTER statement was issued.
This variable was added in MySQL 5.1.22-ndb-6.3.4.
The following information applies to all MySQL users.
Slave_retried_transactions
The total number of times since startup that the replication slave SQL thread has retried transactions.
Slave_running
This is ON if this server is a slave that is connected to a master.
Slow_launch_threads
The number of threads that have taken more than slow_launch_time seconds to create.
Slow_queries
The number of queries that have taken more than long_query_time seconds. See Section 5.2.5, “The Slow Query Log”.
Sort_merge_passes
The number of merge passes that the sort algorithm has had to do. If this value is large, you should consider increasing the value of the sort_buffer_size system variable.
Sort_range
The number of sorts that were done using ranges.
Sort_rows
The number of sorted rows.
Sort_scan
The number of sorts that were done by scanning the table.
Ssl_xxx
Variables used for SSL connections.
Table_locks_immediate
The number of times that a table lock was acquired immediately.
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.
Tc_log_max_pages_used
For the memory-mapped implementation of the log that is used by mysqld when it acts as the transaction coordinator for recovery of internal XA transactions, this variable indicates the largest number of pages used for the log since the server started. If the product of Tc_log_max_pages_used and Tc_log_page_size is always significantly less than the log size, the size is larger than necessary and can be reduced. (The size is set by the --log-tc-size option. Currently, this variable is unused: It is unneeded for binary log-based recovery, and the memory-mapped recovery log method is not used unless the number of storage engines capable of two-phase commit is greater than one. (InnoDB is the only applicable engine.)
Tc_log_page_size
The page size used for the memory-mapped implementation of the XA recovery log. The default value is determined using getpagesize(). Currently, this variable is unused for the same reasons as described for Tc_log_max_pages_used.
Tc_log_page_waits
For the memory-mapped implementation of the recovery log, this variable increments each time the server was not able to commit a transaction and had to wait for a free page in the log. If this value is large, you might want to increase the log size (with the --log-tc-size option). For binary log-based recovery, this variable increments each time the binary log cannot be closed because there are two-phase commits in progress. (The close operation waits until all such transactions are finished.)
Threads_cached
The number of threads in the thread cache.
Threads_connected
The number of currently open connections.
Threads_created
The number of threads created to handle connections. If Threads_created is big, you may want to increase the thread_cache_size value. The cache miss rate can be calculated as Threads_created/Connections.
Threads_running
The number of threads that are not sleeping.
Uptime
The number of seconds that the server has been up.

5.1.6. SQL Modes

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

For answers to some questions that are often asked about server SQL modes in MySQL, see Section A.3, “MySQL 5.1 FAQ — Server SQL Mode”.

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

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

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

Important

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

See Section 16.5, “Restrictions and Limitations on Partitioning”, for more information.

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

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

The most important sql_mode values are probably these:

ANSI
This mode changes syntax and behavior to conform more closely to standard SQL.
STRICT_TRANS_TABLES
If a value could not be inserted as given into a transactional table, abort the statement. For a non-transactional table, abort the statement if the value occurs in a single-row statement or the first row of a multiple-row statement. More detail is given later in this section.
TRADITIONAL
Make MySQL behave like a “traditional” SQL database system. A simple description of this mode is “give an error instead of a warning” when inserting an incorrect value into a column.
Note
The INSERT/UPDATE aborts as soon as the error is noticed. This may not be what you want if you are using a non-transactional storage engine, because data changes made prior to the error may not be rolled back, resulting in a “partially done” update.

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

The following list describes all supported modes:

ALLOW_INVALID_DATES
Don't do full checking of dates. Check only that the month is in the range from 1 to 12 and the day is in the range from 1 to 31. This is very convenient for Web applications where you obtain year, month, and day in three different fields and you want to store exactly what the user inserted (without date validation). This mode applies to DATE and DATETIME columns. It does not apply TIMESTAMP columns, which always require a valid date.
The server requires that month and day values be legal, and not merely in the range 1 to 12 and 1 to 31, respectively. With strict mode disabled, invalid dates such as '2004-04-31' are converted to '0000-00-00' and a warning is generated. With strict mode enabled, invalid dates generate an error. To allow such dates, enable ALLOW_INVALID_DATES.
ANSI_QUOTES
Treat “"” as an identifier quote character (like the “`” quote character) and not as a string quote character. You can still use “`” to quote identifiers with this mode enabled. With ANSI_QUOTES enabled, you cannot use double quotes to quote literal strings, because it is interpreted as an identifier.
ERROR_FOR_DIVISION_BY_ZERO
Produce an error in strict mode (otherwise a warning) when a division by zero (or MOD(X,0)) occurs during an INSERT or UPDATE. If this mode is not enabled, MySQL instead returns NULL for divisions by zero. For INSERT IGNORE or UPDATE IGNORE, MySQL generates a warning for divisions by zero, but the result of the operation is NULL.
HIGH_NOT_PRECEDENCE
The precedence of the NOT operator is such that expressions such as NOT a BETWEEN b AND c are parsed as NOT (a BETWEEN b AND c). In some older versions of MySQL, the expression was parsed as (NOT a) BETWEEN b AND c. The old higher-precedence behavior can be obtained by enabling the HIGH_NOT_PRECEDENCE SQL mode.
```
mysql> SET sql_mode = '';
mysql> SELECT NOT 1 BETWEEN -5 AND 5;
        -> 0
mysql> SET sql_mode = 'HIGH_NOT_PRECEDENCE';
mysql> SELECT NOT 1 BETWEEN -5 AND 5;
        -> 1
```
IGNORE_SPACE
Allow spaces between a function name and the “(” character. This causes built-in function names to be treated as reserved words. As a result, identifiers that are the same as function names must be quoted as described in Section 7.2, “Schema Object Names”. For example, because there is a COUNT() function, the use of count as a table name in the following statement causes an error:
```
mysql> CREATE TABLE count (i INT);
ERROR 1064 (42000): You have an error in your SQL syntax
```
The table name should be quoted:
```
mysql> CREATE TABLE `count` (i INT);
Query OK, 0 rows affected (0.00 sec)
```
The IGNORE_SPACE SQL mode applies to built-in functions, not to user-defined functions or stored functions. It is always allowable to have spaces after a UDF or stored function name, regardless of whether IGNORE_SPACE is enabled.
For further discussion of IGNORE_SPACE, see Section 7.2.4, “Function Name Parsing and Resolution”.
NO_AUTO_CREATE_USER
Prevent the GRANT statement from automatically creating new users if it would otherwise do so, unless a non-empty password also is specified.
NO_AUTO_VALUE_ON_ZERO
NO_AUTO_VALUE_ON_ZERO affects handling of AUTO_INCREMENT columns. Normally, you generate the next sequence number for the column by inserting either NULL or 0 into it. NO_AUTO_VALUE_ON_ZERO suppresses this behavior for 0 so that only NULL generates the next sequence number.
This mode can be useful if 0 has been stored in a table's AUTO_INCREMENT column. (Storing 0 is not a recommended practice, by the way.) For example, if you dump the table with mysqldump and then reload it, MySQL normally generates new sequence numbers when it encounters the 0 values, resulting in a table with contents different from the one that was dumped. Enabling NO_AUTO_VALUE_ON_ZERO before reloading the dump file solves this problem. mysqldump now automatically includes in its output a statement that enables NO_AUTO_VALUE_ON_ZERO, to avoid this problem.
NO_BACKSLASH_ESCAPES
Disable the use of the backslash character (“\”) as an escape character within strings. With this mode enabled, backslash becomes an ordinary character like any other.
NO_DIR_IN_CREATE
When creating a table, ignore all INDEX DIRECTORY and DATA DIRECTORY directives. This option is useful on slave replication servers.
NO_ENGINE_SUBSTITUTION
Control automatic substitution of the default storage engine when a statement such as CREATE TABLE or ALTER TABLE specifies a storage engine that is disabled or not compiled in.
Up through MySQL 5.1.11, with NO_ENGINE_SUBSTITUTION disabled, the default engine is used and a warning occurs if the desired engine is known but disabled or not compiled in. If the desired engine is invalid (not a known engine name), an error occurs and the table is not created or altered.
With NO_ENGINE_SUBSTITUTION enabled, an error occurs and the table is not created or altered if the desired engine is unavailable for any reason (whether disabled or invalid).
As of MySQL 5.1.12, storage engines can be pluggable at runtime, so the distinction between disabled and invalid no longer applies. All unavailable engines are treated the same way:
With NO_ENGINE_SUBSTITUTION disabled, for CREATE TABLE the default engine is used and a warning occurs if the desired engine is unavailable. For ALTER TABLE, a warning occurs and the table is not altered.
With NO_ENGINE_SUBSTITUTION enabled, an error occurs and the table is not created or altered if the desired engine is unavailable.
NO_FIELD_OPTIONS
Do not print MySQL-specific column options in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode.
NO_KEY_OPTIONS
Do not print MySQL-specific index options in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode.
NO_TABLE_OPTIONS
Do not print MySQL-specific table options (such as ENGINE) in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode.

NO_UNSIGNED_SUBTRACTION

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

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

mysql> SET SQL_MODE='NO_UNSIGNED_SUBTRACTION';
mysql> CREATE TABLE t2 SELECT c1 - 1 AS c2 FROM test;
mysql> DESCRIBE t2;
+-------+------------+------+-----+---------+-------+
| Field | Type       | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| c2    | bigint(21) |      |     | 0       |       |
+-------+------------+------+-----+---------+-------+

Note that this means that BIGINT UNSIGNED is not 100% usable in all contexts. See Section 10.9, “Cast Functions and Operators”.

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

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

NO_ZERO_DATE
In strict mode, don't allow '0000-00-00' as a valid date. You can still insert zero dates with the IGNORE option. When not in strict mode, the date is accepted but a warning is generated.
NO_ZERO_IN_DATE
In strict mode, 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.
ONLY_FULL_GROUP_BY
Do not allow queries for which the SELECT list refers to non-aggregated columns that are not named in the GROUP BY clause. The following query is invalid with this mode enabled because address is not named in the GROUP BY clause:
```
SELECT name, address, MAX(age) FROM t GROUP BY name;
```
As of MySQL 5.1.11, this mode also restricts references to non-aggregated columns in the HAVING clause that are not named in the GROUP BY clause.
PIPES_AS_CONCAT
Treat || as a string concatenation operator (same as CONCAT()) rather than as a synonym for OR.
REAL_AS_FLOAT
Treat REAL as a synonym for FLOAT. By default, MySQL treats REAL as a synonym for DOUBLE.
STRICT_ALL_TABLES
Enable strict mode for all storage engines. Invalid data values are rejected. Additional detail follows.
STRICT_TRANS_TABLES
Enable strict mode for transactional storage engines, and when possible for non-transactional storage engines. Additional details follow.

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

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

For non-transactional tables, the behavior is the same for either mode, if the bad value occurs in the first row to be inserted or updated. The statement is aborted and the table remains unchanged. If the statement inserts or modifies multiple rows and the bad value occurs in the second or later row, the result depends on which strict option is enabled:

For STRICT_ALL_TABLES, MySQL returns an error and ignores the rest of the rows. However, in this case, the earlier rows still have been inserted or updated. This means that you might get a partial update, which might not be what you want. To avoid this, it's best to use single-row statements because these can be aborted without changing the table.
For STRICT_TRANS_TABLES, MySQL converts an invalid value to the closest valid value for the column and insert the adjusted value. If a value is missing, MySQL inserts the implicit default value for the column data type. In either case, MySQL generates a warning rather than an error and continues processing the statement. Implicit defaults are described in Section 9.1.4, “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 NO_ZERO_DATE SQL modes in addition to strict mode.

If you are not using strict mode (that is, neither STRICT_TRANS_TABLES nor STRICT_ALL_TABLES is enabled), MySQL inserts adjusted values for invalid or missing values and produces warnings. In strict mode, you can produce this behavior by using INSERT IGNORE or UPDATE IGNORE. See Section 11.5.4.32, “SHOW WARNINGS Syntax”.

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

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

ANSI
Equivalent to REAL_AS_FLOAT, PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE.
As of MySQL 5.1.18, ANSI mode also causes the server to return an error for queries where a set function S with an outer reference S(outer_ref) cannot be aggregated in the outer query against which the outer reference has been resolved. This is such a query:
```
SELECT * FROM t1 WHERE t1.a IN (SELECT MAX(t1.b) FROM t2 WHERE ...);
```
Here, MAX(t1.b) cannot aggregated in the outer query because it appears in the WHERE clause of that query. Standard SQL requires an error in this situation. If ANSI mode is not enabled, the server treats S(outer_ref) in such queries the same way that it would interpret S(const), as was always done prior to 5.1.18.
See Section 1.8.3, “Running MySQL in ANSI Mode”.
DB2
Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS.
MAXDB
Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS, NO_AUTO_CREATE_USER.
MSSQL
Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS.
MYSQL323
Equivalent to NO_FIELD_OPTIONS, HIGH_NOT_PRECEDENCE.
MYSQL40
Equivalent to NO_FIELD_OPTIONS, HIGH_NOT_PRECEDENCE.
ORACLE
Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS, NO_AUTO_CREATE_USER.
POSTGRESQL
Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS.
TRADITIONAL
Equivalent to STRICT_TRANS_TABLES, STRICT_ALL_TABLES, NO_ZERO_IN_DATE, NO_ZERO_DATE, ERROR_FOR_DIVISION_BY_ZERO, NO_AUTO_CREATE_USER.

5.1.7. Server-Side Help

MySQL Server supports a HELP statement that returns online information from the MySQL Reference manual (see Section 11.3.2, “HELP Syntax”). The proper operation of this statement requires that the help tables in the mysql database be initialized with help topic information, which is done by processing the contents of the fill_help_tables.sql script.

For a MySQL binary distribution on Unix, help table setup occurs when you run mysql_install_db. For an RPM distribution on Linux or binary distribution on Windows, help table setup occurs as part of the MySQL installation process.

For a MySQL source distribution, you can find the fill_help_tables.sql file in the scripts directory. To load the file manually, make sure that you have initialized the mysql database by running mysql_install_db, and then process the file with the mysql client as follows:

shell> mysql -u root mysql < fill_help_tables.sql

If you are working with 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.

5.1.8. Server Response to Signals

On Unix, signals can be sent to processes. mysqld responds to signals sent to it as follows:

SIGTERM causes the server to shut down.

SIGHUP causes the server to reload the grant tables and flush the logs (like FLUSH PRIVILEGES and FLUSH LOGS). It also writes a status report to the error log that has this format:

Status information:

Current dir: /var/mysql/data/
Running threads: 0  Stack size: 196608
Current locks:

Key caches:
default
Buffer_size:       8388600
Block_size:           1024
Division_limit:        100
Age_limit:             300
blocks used:             0
not flushed:             0
w_requests:              0
writes:                  0
r_requests:              0
reads:                   0

handler status:
read_key:            0
read_next:           0
read_rnd             0
read_first:          1
write:               0
delete               0
update:              0

Table status:
Opened tables:          5
Open tables:            0
Open files:             7
Open streams:           0

Alarm status:
Active alarms:   1
Max used alarms: 2
Next alarm time: 67

On some Mac OS X 10.3 versions, mysqld ignores SIGHUP and SIGQUIT.

5.1.9. The Shutdown Process

The server shutdown process takes place as follows:

The shutdown process is initiated.
Server shutdown can be initiated several ways. For example, a user with the SHUTDOWN privilege can execute a mysqladmin shutdown command. mysqladmin can be used on any platform supported by MySQL. Other operating system-specific shutdown initiation methods are possible as well: The server shuts down on Unix when it receives a SIGTERM signal. A server running as a service on Windows shuts down when the services manager tells it to.
The server creates a shutdown thread if necessary.
Depending on how shutdown was initiated, the server might create a thread to handle the shutdown process. If shutdown was requested by a client, a shutdown thread is created. If shutdown is the result of receiving a SIGTERM signal, the signal thread might handle shutdown itself, or it might create a separate thread to do so. If the server tries to create a shutdown thread and cannot (for example, if memory is exhausted), it issues a diagnostic message that appears in the error log:
```
Error: Can't create thread to kill server
```
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.
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 11.5.5.3, “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.
Storage engines are shut down or closed.
At this stage, the table cache is flushed and all open tables are closed.
Each storage engine performs any actions necessary for tables that it manages. For example, MyISAM flushes any pending index writes for a table. InnoDB flushes its buffer pool to disk, unless innodb_fast_shutdown is 2, writes the current LSN to the tablespace, and terminates its own internal threads.
The server exits.

5.2. MySQL Server Logs

5.2.1. Selecting General Query and Slow Query Log Output Destinations
5.2.2. The Error Log
5.2.3. The General Query Log
5.2.4. The Binary Log
5.2.5. The Slow Query Log
5.2.6. Server Log Maintenance

MySQL has several different logs that can help you find out what is going on inside mysqld:

Log Type	Information Written to Log
The error log	Problems encountered starting, running, or stopping mysqld
The general query log	Established client connections and statements received from clients
The binary log	All statements that change data (also used for replication)
The slow query log	All queries that took more than `long_query_time` seconds to execute or didn't use indexes

By default, all log files are created in the mysqld data directory. You can force mysqld to close and reopen the log files (or in some cases switch to a new log) by flushing the logs. Log flushing occurs when you issue a FLUSH LOGS statement or execute mysqladmin flush-logs or mysqladmin refresh. See Section 11.5.5.2, “FLUSH Syntax”, and Section 4.5.2, “mysqladmin — Client for Administering a MySQL Server”.

If you are using MySQL replication capabilities, slave replication servers maintain additional log files called relay logs. Chapter 14, Replication, discusses relay log contents and configuration.

MySQL Enterprise The MySQL Enterprise Monitor provides a number of advisors specifically related to the various log files. For more information see http://www.mysql.com/products/enterprise/advisors.html.

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

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

5.2.1. Selecting General Query and Slow Query Log Output Destinations

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

Note

For new installations of MySQL 5.1.6 or higher, the log tables are created during the installation procedure along with the other system tables. If you upgrade MySQL from a release older than 5.1.6 to MySQL 5.1.6 or higher, you must upgrade the system tables after upgrading to make sure that the log tables exist. See Section 4.4.7, “mysql_upgrade — Check Tables for MySQL Upgrade”.

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

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

If --log-output is given with a value, the value can be a comma-separated list of one or more of the words TABLE (log to tables), FILE (log to files), or NONE (do not log to tables or files). NONE, if present, takes precedence over any other specifiers.
If --log-output is omitted or given without a value, the effect is the same as --log-output=FILE. That is, the file destination is selected. (For MySQL 5.1.6 through 5.1.20, the default is the table destination.)
If --log-output option also sets the value of the global log_output system variable, which can be modified at runtime to change the logging destination for the server while it executes.

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

Examples:

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

Several system variables are associated with log tables and files:

The global general_log and slow_query_log variables indicate whether the general query log and slow query log are enabled (ON) or disabled (OFF). You can set these variables at runtime to control whether the logs are enabled.
The global general_log_file and slow_query_log_file variables indicate the names of the general query log and slow query log files. You can set these variables at runtime to change the names of the log files. (If the --log and --log-slow-queries options were not given, the variable values are set to the default log filenames.)
The session sql_log_off variable can be set to ON or OFF to disable or enable general query logging for the current connection.

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

Log entries have a standard format. To display the current structure of the log tables, use these statements:
```
SHOW CREATE TABLE mysql.general_log;
SHOW CREATE TABLE mysql.slow_log;
```
Log contents are accessible via SQL statements. This enables the use of queries that select only those log entries that satisfy specific criteria. For example, to select log contents associated with a particular client (which can be useful for identifying problematic queries from that client), it is easier to do this using a log table than a log file.
Logs are accessible remotely through any client that can connect to the server and issue queries (if the client has the appropriate log table privileges). It's not necessary to log in to the server host and directly access the filesystem.

The log table implementation has the following characteristics:

In general, the primary purpose of log tables is to provide an interface for users to observe the runtime execution of the server, not to interfere with its runtime execution.
CREATE TABLE, ALTER TABLE, and DROP TABLE are valid operations on a log table. For ALTER TABLE and DROP TABLE, the log table cannot be in use and must be disabled, as described later.
By default, the log tables use the CSV storage engine that writes data in comma-separated values format. For users who have access to the .CSV files that contain log table data, the files are easy to import into other programs such as spreadsheets that can process CSV input.
Beginning with MySQL 5.1.12, the log tables can be altered to use the MyISAM storage engine. You

Name	`ansi`
Description	Use ANSI SQL syntax instead of MySQL syntax

Name	`bootstrap`
Description	Used by mysql installation scripts

Name	`console`
Description	Write error output on screen; do not remove the console window on Windows
Option Sets Variable	Yes, `console`
Platform Specific	windows

Name	`default-storage-engine`
Description	Set the default storage engine (table type) for tables

Name	`des-key-file`
Description	Load keys for des_encrypt() and des_encrypt from given file
Option Sets Variable	Yes, `des-key-file`
Variable Name	`des-key-file`
Variable Scope	Global
Dynamic Variable	no

Name	`enable-named-pipe`
Description	Enable support for named pipes.
Platform Specific	windows

Name	`general-log`
Description	Enable\|disable general log
Version Introduced	5.1.12
Option Sets Variable	Yes, `general-log`
Variable Name	`general_log`
Variable Scope	Global
Dynamic Variable	no

Name	`log-long-format`
Description	Log some extra information to update log. Please note that this option is deprecated; see --log-short-format option
Deprecated	4.1

Name	`one-thread`
Description	Only use one thread (for debugging under Linux)

Name	`safe-mode`
Description	Skip some optimization stages (for testing)
Deprecated	5.0

Name	`standalone`
Description	Instructs the MySQL server not to run as a service
Platform Specific	windows

Name	`symbolic-links`
Description	Use symbolic links
Option Sets Variable	Yes, `symbolic-links`

Name	`skip-safemalloc`
Description	Don't check for memory overruns during each memory allocation

Name	`skip-show-database`
Description	Don't allow 'SHOW DATABASE' commands
Option Sets Variable	Yes, `skip_show_database`
Variable Name	`skip_show_database`
Variable Scope	Global
Dynamic Variable	yes

Name	`skip-stack-trace`
Description	Don't print a stack trace on failure

Name	`skip-thread-priority`
Description	Don't give threads different priorities

Name	`large_files_support`
Description	Whether large files are supported
Variable Name	`large_files_support`
Variable Scope	Global
Dynamic Variable	no

Name	`local_infile`
Description	Whether LOCAL is supported for LOAD DATA INFILE statements
Variable Name	`local_infile`
Variable Scope	Global
Dynamic Variable	no

Name	`locked_in_memory`
Description	Whether mysqld is locked in memory
Variable Name	`locked_in_memory`
Variable Scope	Global
Dynamic Variable	no

Name	`log_bin`
Description	Whether the binary log is enabled
Variable Name	`log_bin`
Variable Scope	Global
Dynamic Variable	no

Name	`myisam_recover_options`
Description	The value of the --myisam-recover option
Variable Name	`myisam_recover_options`
Variable Scope
Dynamic Variable	no

Name	`named_pipe`
Description	Indicates whether the server supports connections over named pipes
Variable Name	`named_pipe`
Variable Scope
Dynamic Variable	no
Platform Specific	windows

Name	`ndb_use_copying_alter_table`
Description	Use copying ALTER TABLE operations in MySQL Cluster
Version Introduced	5.1.12
Variable Name	`ndb_use_copying_alter_table`
Variable Scope	Both
Dynamic Variable	no

Name	`old`
Description	Cause the server to revert to certain behaviors present in older versions
Version Introduced	5.1.18
Variable Name	`old`
Variable Scope	Global
Dynamic Variable	no

Name	`shared_memory`
Description	Whether the server allows shared-memory connections
Variable Name	`shared_memory`
Variable Scope
Dynamic Variable	no
Platform Specific	windows

Name	`shared_memory_base_name`
Description	The name of shared memory to use for shared-memory connections
Variable Name	`shared_memory_base_name`
Variable Scope
Dynamic Variable	no
Platform Specific	windows

Name	`slow_query_log`
Description	Whether the slow query log is enabled
Version Introduced	5.1.12
Variable Name	`slow_query_log`
Variable Scope	Global
Dynamic Variable	no