Options that affect security: See Section 4.3.3, “Startup Options for mysqld Concerning Security.”

   SSL-related options: See Section 4.5.7.5, “4.5.7.5 SSL Command-Line Options.”

   Binary log control options: See Section 4.8.4, “The Binary Log.”

   Replication-related options: See Section 5.8, “Replication Startup Options.”

   Options specific to particular storage engines: See Section 8.1.1, “MyISAM Startup Options,” Section 8.4.3, “BDB Startup Options,” and Section 9.5, “InnoDB Startup Options.”

   --help, -?

     Display a short help message and exit. Before MySQL 4.1.1, --help displays the full help message. As of 4.1.1, it displays an abbreviated message only. Use both the --verbose and --help options to see the full message.

   --ansi

     Use standard SQL syntax instead of MySQL syntax. See Section 1.8.3, “Running MySQL in ANSI Mode.” For more precise control over the server SQL mode, use the --sql-mode option instead.

   --basedir=path, -b path

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

   --big-tables

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

   --bind-address=IP

     The IP address to bind to.

   --console

     Write the error log messages to stderr/stdout even if --log-error is specified. On Windows, mysqld will not close the console screen if this option is used.

   --character-sets-dir=path

     The directory where character sets are installed. See Section 4.7.1, “The Character Set Used for Data and Sorting.”

   --chroot=path

     Put the mysqld server in a closed environment during startup by using the chroot() system call. This is a recommended security measure as of MySQL 4.0. (MySQL 3.23 is not able to provide a chroot() jail that is 100% closed.) Note that use of this option somewhat limits LOAD DATA INFILE and SELECT ... INTO OUTFILE.

   --core-file

     Write a core file if mysqld dies. For some systems, you must also specify the --core-file-size option to mysqld_safe. See Section 4.1.3, “The mysqld_safe Server Startup Script.” Note that on some systems, such as Solaris, you will not get a core file if you are also using the --user option.

   --datadir=path, -h path

     The path to the data directory.

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

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

   --default-character-set=charset

     Use charset as the default character set. See Section 4.7.1, “The Character Set Used for Data and Sorting.”

   --default-collation=collation

     Use collation as the default collation. This option is available as of MySQL 4.1.1. See Section 4.7.1, “The Character Set Used for Data and Sorting.”

   --default-storage-engine=type

     This option is a synonym for --default-table-type. It is available as of MySQL 4.1.2.

   --default-table-type=type

     Set the default table type for tables. See Chapter 8, “MySQL Storage Engines and Table Types.”

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

     How the DELAYED KEYS option should be used. 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 DELAYED KEYS option. ALL delays key writes for all MyISAM tables. Available as of MySQL 4.0.3. See Section 6.5.2, “Tuning Server Parameters.” See Section 8.1.1, “MyISAM Startup Options.”

     Note: If you set this variable to ALL, you should not use MyISAM tables from within another program (such as from another MySQL server or with myisamchk) when the table is in use. Doing so will lead to index corruption.

   --delay-key-write-for-all-tables

     Old form of --delay-key-write=ALL for use prior to MySQL 4.0.3. As of 4.0.3, use --delay-key-write instead.

   --des-key-file=file_name

     Read the default keys used by DES_ENCRYPT() and DES_DECRYPT() from this file.

   --enable-named-pipe

     Enable support for named pipes. This option applies only on Windows NT, 2000, and XP systems, and can be used only with the mysqld-nt and mysqld-max-nt servers that support named pipe connections.

   --external-locking

     Enable system locking. Note that if you use this option on a system on which lockd does not fully work (as on Linux), you will easily get mysqld to deadlock. This option previously was named --enable-locking.

Note: If you use this option to enable updates to MyISAM tables from many MySQL processes, you have to ensure that these conditions are satisfied:

The easiest way to ensure this is to always use --external-locking together with --delay-key-write=OFF --query-cache-size=0.

(This is not done by default because in many setups it’s useful to have a mixture of the above options.)

   --exit-info[=flags], -T [flags]

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

   --flush

     Flush 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 synching to disk. See Section A.4.2, “What to Do If MySQL Keeps Crashing.”

   --init-file=file

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

   --language=lang_name, -L lang_name

     Client error messages in 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 4.7.2, “Setting the Error Message Language.”

   --log[=file], -l [file]

     Log connections and queries to this file. See Section 4.8.2, “The General Query Log.” If you don’t specify a filename, MySQL will use host_name.log as the filename.

   --log-bin=[file]

     The binary log file. Log all queries that change data to this file. Used for backup and replication. See Section 4.8.4, “The Binary Log.” If you don’t specify a filename, MySQL will use host_name-bin as the filename.

   --log-bin-index[=file]

     The index file for binary log filenames. See Section 4.8.4, “The Binary Log.” If you don’t specify a filename, MySQL will use host_name-bin.index as the filename.

   --log-error[=file]

     Log errors and startup messages to this file. See Section 4.8.1, “The Error Log.” If you don’t specify a filename, MySQL will use host_name.err as the filename.

   --log-isam[=file]

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

   --log-long-format

     Log some extra information to the log files (update log, binary update log, and slow queries log, whatever log has been activated). For example, username and timestamp are logged for queries. If you are using --log-slow-queries and --log-long-format, then queries that are not using indexes also are logged to the slow query log. Note that --log-long-format is deprecated as of MySQL version 4.1, when --log-short-format was introduced (the long log format is the default setting since version 4.1). Also note that starting with MySQL 4.1, the --log-queries-not-using-indexes option is available for the purpose of logging queries that do not use indexes to the slow query log.

   --log-queries-not-using-indexes

     If you are using this option with --log-slow-queries, then queries that are not using indexes also are logged to the slow query log. This option is available as of MySQL 4.1. See Section 4.8.5, ”The Slow Query Log.”

   --log-short-format

     Log less information to the log files (update log, binary update log, and slow queries log, whatever log has been activated). For example, username and timestamp are not logged for queries. This option was introduced in MySQL 4.1.

   --log-slow-queries[=file]

     Log all queries that have taken more than long_query_time seconds to execute to file. See Section 4.8.5, “The Slow Query Log.” Note that the default for the amount of information logged has changed in MySQL 4.1. See the --log-long-format and --log-short-format options for details.

   --log-update[=file]

     Log updates to file.# where # is a unique number if not given. See Section 4.8.3, “The Update Log.” The update log is deprecated and is removed in MySQL 5.0.0; you should use the binary log instead (--log-bin). See Section 4.8.4, “The Binary Log.” Starting from version 5.0.0, using --log-update will just turn on the binary log instead.

   --log-warnings, -W

     Print out warnings such as Aborted connection... to the error log. Enabling this option is recommended, for example, if you use replication (you will get more information about what is happening, such as messages about network failures and reconnections). This option is enabled by default as of MySQL 4.1.2; to disable it, use --skip-log-warnings. See Section A.2.10, “Communication Errors and Aborted Connections.”

     This option was named --warnings before MySQL 4.0.

   --low-priority-updates

     Table-modifying operations (INSERT, REPLACE, DELETE, UPDATE) will have 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. See Section 6.3.2, “Table Locking Issues.”

   --memlock

     Lock the mysqld process in memory. This works on systems such as Solaris that support the mlockall() system call. This might help if you have a problem where the operating system is causing mysqld to swap on disk. Note that use of this option requires that you run the server as root, which normally is not a good idea for security reasons.

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

     Set the MyISAM storage engine recovery mode. The option value is any combination of the values of DEFAULT, BACKUP, FORCE, or QUICK. If you specify multiple values, separate them by commas. You can also use a value of "" to disable this option. If this option is used, mysqld will, when it opens a MyISAM table, check whether the table is marked as crashed or wasn’t closed properly. (The last option works only if you are running with --skip-external-locking.) If this is the case, mysqld will run a check on the table. If the table was corrupted, mysqld will attempt to repair it.

     The following options affect how the repair works:

     Before a table is automatically repaired, MySQL will add a note about this in 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 will force a repair of a table even if some rows would be deleted, but it will keep the old data file as a backup so that you can later examine what happened.

     This option is available as of MySQL 3.23.25.

   --new

     From version 4.0.12, the --new option can be used to make the server behave as 4.1 in certain respects, easing a 4.0 to 4.1 upgrade:

     This option can be used to help you see how your applications will behave in MySQL 4.1, without actually upgrading to 4.1.

   --pid-file=path

     The path to the process ID file used by mysqld_safe.

   --port=port_num, -P port_num

     The port number to use when listening for TCP/IP connections.

   --old-protocol, -o

     Use the 3.20 protocol for compatibility with some very old clients. See Section 2.5.6, “Upgrading from Version 3.20 to 3.21.”

   --one-thread

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

   --open-files-limit=count

     To change the number of file descriptors available to mysqld. If this is not set or set to 0, then mysqld will use this value to reserve file descriptors to use with setrlimit(). If this value is 0, then mysqld will reserve max_connections*5 or max_connections + table_cache*2 (whichever is larger) number of files. You should try increasing this if mysqld gives you the error “Too many open files.”

   --safe-mode

     Skip some optimization stages.

   --safe-show-database

     With this option, the SHOW DATABASES statement displays only the names of those databases for which the user has some kind of privilege. As of MySQL 4.0.2, this option is deprecated and doesn’t do anything (it is enabled by default), because there is now a SHOW DATABASES privilege that can be used to control access to database names on a per-account basis. See Section 4.4.3, “Privileges Provided by MySQL.”

   --safe-user-create

     If this is enabled, a user can’t create new users with the GRANT statement, if the user doesn’t have the INSERT privilege for the mysql.user table or any column in the table.

   --secure-auth

     Disallow authentication for accounts that have old (pre-4.1) passwords. This option is available as of MySQL 4.1.1.

   --skip-bdb

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

   --skip-concurrent-insert

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

   --skip-delay-key-write

     Ignore the DELAY_KEY_WRITE option for all tables. As of MySQL 4.0.3, you should use --delay-key-write=OFF instead. See Section 6.5.2, “Tuning Server Parameters.”

   --skip-external-locking

     Don’t use system locking. To use isamchk or myisamchk, you must shut down the server. See Section 1.2.3, “MySQL Stability.” In MySQL 3.23, you can use CHECK TABLE and REPAIR TABLE to check and repair MyISAM tables. This option previously was named --skip-locking.

   --skip-grant-tables

     This option causes the server not to use the privilege system at all. This gives everyone full access to all databases! (You can tell a running server to start using the grant tables again by executing a mysqladmin flush-privileges or mysqladmin reload command, or by issuing a FLUSH PRIVILEGES statement.)

   --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 6.5.5, “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-isam

     Disable the ISAM storage engine. As of MySQL 4.1, ISAM is disabled by default, so this option applies only if the server was configured with support for ISAM. This option was added in MySQL 4.1.1.

   --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 6.5.5, “How MySQL Uses DNS.”

   --skip-networking

     Don’t listen for TCP/IP connections at all. All interaction with mysqld must be made via named pipes (on Windows) or Unix socket files (on Unix). This option is highly recommended for systems where only local clients are allowed. See Section 6.5.5, “How MySQL Uses DNS.”

   --skip-new

     Don’t use new, possibly wrong routines.

   --skip-symlink

     This is the old form of --skip-symbolic-links, for use before MySQL 4.0.13.

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

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

     This option was added in MySQL 4.0.13.

   --skip-safemalloc

     If MySQL is configured with --with-debug=full, all MySQL programs check for memory overruns during each memory allocation and memory freeing operation. This checking is very slow, so for the server you can avoid it when you don’t need it by using the --skip-safemalloc option.

   --skip-show-database

     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.

   --skip-stack-trace

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

   --skip-thread-priority

     Disable using thread priorities for faster response time.

   --socket=path

     On Unix, this option specifies the Unix socket file to use for local connections. The default value is /tmp/mysql.sock. On Windows, the option specifies the pipe name to use for local connections that use a named pipe. The default value is MySQL.

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

     Set the SQL mode for MySQL. See Section 4.2.2, “The Server SQL Mode.” This option was added in 3.23.41.

   --temp-pool

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

   --transaction-isolation=level

     Sets the default transaction isolation level, which can be READ-UNCOMMITTED, READ-COMMITTED, REPEATABLE-READ, or SERIALIZABLE.

   --tmpdir=path, -t path

     The path of the directory to use for creating temporary files. It might be useful if your default /tmp directory resides on a partition that is too small to hold temporary tables. Starting from MySQL 4.1, 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. 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 will fail.

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

     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 will change its user ID during its startup sequence, causing it to run as that particular user rather than as root. See Section 4.3.1, “General Security Guidelines.”

     Starting from MySQL 3.23.56 and 4.0.12: To avoid a possible security hole where a user adds a --user=root option to some 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 datadir/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 will be 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.

   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 identifers in ANSI mode. With ANSI_QUOTES enabled, you cannot use double quotes to quote a literal string, because it will be interpreted as an identifier. (New in MySQL 4.0.0.)

   IGNORE_SPACE

     Allow spaces between a function name and the ‘(’ character. This forces all function names to be treated as reserved words. As a result, if you want to access any database, table, or column name that is a reserved word, you must quote it. For example, because there is a USER() function, the name of the user table in the mysql database and the User column in that table become reserved, so you must quote them:

SELECT "User" FROM mysql."user";

     (New in MySQL 4.0.0.)

   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. (This is not a recommended practice, by the way.) For example, if you dump the table with mysqldump and then reload it, normally MySQL generates new sequence numbers when it encounters the 0 values, resulting in a table with different contents than the one that was dumped. Enabling NO_AUTO_VALUE_ON_ZERO before reloading the dump file solves this problem. As of MySQL 4.1.1, mysqldump automatically includes statements in the dump output to enable NO_AUTO_VALUE_ON_ZERO. (New in MySQL 4.1.1.)

   NO_DIR_IN_CREATE

     When creating a table, ignore all INDEX DIRECTORY and DATA DIRECTORY directives. This option is useful on slave replication servers. (New in MySQL 4.0.15.)

   NO_FIELD_OPTIONS

     Don’t print MySQL -specific column options in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode. (New in MySQL 4.1.1.)

   NO_KEY_OPTIONS

     Don’t print MySQL -specific index options in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode. (New in MySQL 4.1.1.)

   NO_TABLE_OPTIONS

     Don’t print MySQL -specific table options (such as ENGINE) in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode. (New in MySQL 4.1.1.)

   NO_UNSIGNED_SUBTRACTION

     In subtraction operations, don’t mark the result as UNSIGNED if one of the operands is unsigned. Note that this makes UNSIGNED BIGINT not 100% usable in all contexts. (New in MySQL 4.0.2.)

   ONLY_FULL_GROUP_BY

     Don’t allow queries that in the GROUP BY part refer to a not selected column. (New in MySQL 4.0.0.)

   PIPES_AS_CONCAT

     Treat || as a string concatenation operator (same as CONCAT()) rather than as a synonym for OR. (New in MySQL 4.0.0.)

   REAL_AS_FLOAT

     Treat REAL as a synonym for FLOAT rather than as a synonym for DOUBLE. (New in MySQL 4.0.0.)

   ANSI

     Equivalent to REAL_AS_FLOAT, PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, ONLY_FULL_GROUP_BY. 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.

   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.

   MYSQL40

     Equivalent to NO_FIELD_OPTIONS.

   ORACLE

     Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS.

   POSTGRESQL

     Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS.

   ansi_mode

     This is ON if mysqld was started with --ansi. See Section 1.8.3, “Running MySQL in ANSI Mode.” This variable was added in MySQL 3.23.6 and removed in 3.23.41. See the description for --sql-mode.

   back_log

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

     In other words, this value is the size of the listen queue for incoming TCP/IP connections. Your operating system has its own limit on the size of this queue. The manual page for the Unix listen() system call should have more details. Check your OS documentation for the maximum value for this variable. Attempting to set back_log higher than your operating system limit will be ineffective.

   basedir

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

   bdb_cache_size

     The size of the buffer that is allocated for caching indexes and rows for BDB tables. If you don’t use BDB tables, you should start mysqld with --skip-bdb to not waste memory for this cache. This variable was added in MySQL 3.23.14.

   bdb_home

     The base directory for BDB tables. This should be assigned the same value as the datadir variable. This variable was added in MySQL 3.23.14.

   bdb_log_buffer_size

     The size of the buffer that is allocated for caching indexes and rows for BDB tables. If you don’t use BDB tables, you should set this to 0 or start mysqld with --skip-bdb to not waste memory for this cache. This variable was added in MySQL 3.23.31.

   bdb_logdir

     The directory where the BDB storage engine writes its log files. This variable can be set with the --bdb-logdir option. This variable was added in MySQL 3.23.14.

   bdb_max_lock

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

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

     This variable was added in MySQL 3.23.29.

   bdb_shared_data

     This is ON if you are using --bdb-shared-data. This variable was added in MySQL 3.23.29.

   bdb_tmpdir

     The value of the --bdb-tmpdir option. This variable was added in MySQL 3.23.14.

   bdb_version

     The BDB storage engine version. This variable was added in MySQL 3.23.31.

   binlog_cache_size

     The size of the cache to hold the SQL statements for the binary log during a transaction. A binary log cache is allocated for each client if the server supports any transactional storage engines and, starting from MySQL 4.1.2, if the server has binary log enabled (--log-bin option). If you often use big, multiple-statement transactions, you can increase this 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. This variable was added in MySQL 3.23.29. See Section 4.8.4, “The Binary Log.”

   bulk_insert_buffer_size

     MyISAM uses a special tree-like cache to make bulk inserts faster for INSERT ... SELECT, INSERT ... VALUES (...), (...), ..., and LOAD DATA INFILE. This variable limits the size of the cache tree in bytes per thread. Setting it to 0 disables this optimization.

     Note: This cache is used only when adding data to a non-empty table. The default value is 8MB. This variable was added in MySQL 4.0.3. This variable previously was named myisam_bulk_insert_tree_size.

   character_set

     The default character set. This variable was added in MySQL 3.23.3, then removed in MySQL 4.1.1 and replaced by the various character_set_xxx variables.

   character_set_client

     The character set for statements that arrive from the client. This variable was added in MySQL 4.1.1.

   character_set_connection

     The character set used for literals that do not have a character set introducer, for some functions, and for number-to-string conversion. This variable was added in MySQL 4.1.1.

   character_set_database

     The character set used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as character_set_server. This variable was added in MySQL 4.1.1.

   character_set_results

     The character set used for returning query results to the client. This variable was added in MySQL 4.1.1.

   character_set_server

     The server default character set. This variable was added in MySQL 4.1.1.

   character_set_system

     The character set used by the server for storing identifiers. The value is always utf8. This variable was added in MySQL 4.1.1.

   character_sets

     The supported character sets. This variable was added in MySQL 3.23.15.

   collation_connection

     The collation of the connection character set. This variable was added in MySQL 4.1.1.

   collation_database

     The collation used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as collation_server. This variable was added in MySQL 4.1.1.

   collation_server

     The server default collation. This variable was added in MySQL 4.1.1.

   concurrent_inserts

     If ON (the default), MySQL allows INSERT and SELECT statements to run concurrently for MyISAM tables that have no free blocks in the middle. You can turn this option off by starting mysqld with --safe or --skip-new. This variable was added in MySQL 3.23.7.

   connect_timeout

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

   datadir

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

   default_week_format

     The default mode value to use for the WEEK() function. This variable is available as of MySQL 4.0.14.

   delay_key_write

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

     If DELAY_KEY_WRITE is enabled, this means that the key buffer for tables with this option are not flushed on every index update, but only when a table is closed. This will speed 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 4.2.1, “mysqld Command-Line Options,” and Section 8.1.1, “MyISAM Startup Options.”

     Note that --external-locking doesn’t offer any protection against index corruption for tables that use delayed key writes.

     This variable was added in MySQL 3.23.8.

   delayed_insert_limit

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

   delayed_insert_timeout

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

   delayed_queue_size

     How many rows to queue when handling INSERT DELAYED statements. If the queue becomes full, any client that issues an INSERT DELAYED statement will wait until there is room in the queue again.

   flush

     This is ON if you have started mysqld with the --flush option. This variable was added in MySQL 3.22.9.

   flush_time

     If this is set to a non-zero value, all tables will be closed every flush_time seconds to free up resources and sync unflushed data to disk. We recommend this option only on Windows 9x or Me, or on systems with minimal resources available. This variable was added in MySQL 3.22.18.

   ft_boolean_syntax

     The list of operators supported by boolean full-text searches performed using IN BOOLEAN MODE. This variable was added in MySQL 4.0.1.

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

   ft_max_word_len

     The maximum length of the word to be included in a FULLTEXT index. This variable was added in MySQL 4.0.0.

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

   ft_min_word_len

     The minimum length of the word to be included in a FULLTEXT index. This variable was added in MySQL 4.0.0.

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

   ft_query_expansion_limit

     The number of top matches to use for full-text searches performed using WITH QUERY EXPANSION. This variable was added in MySQL 4.1.1.

   ft_stopword_file

     The file from which to read the list of stopwords for full-text searches. All the words from the file are used; comments are not honored. By default, a built-in list of stopwords is used (as defined in the myisam/ft_static.c file). Setting this variable to the empty string (’’) disables stopword filtering. This variable was added in MySQL 4.0.10.

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

   group_concat_max_len

     The maximum allowed result length for the GROUP_CONCAT() function. This variable was added in MySQL 4.1.0.

   have_bdb

     YES if mysqld supports BDB tables. DISABLED if --skip-bdb is used. This variable was added in MySQL 3.23.30.

   have_innodb

     YES if mysqld supports InnoDB tables. DISABLED if --skip-innodb is used. This variable was added in MySQL 3.23.37.

   have_isam

     YES if mysqld supports ISAM tables. DISABLED if --skip-isam is used. This variable was added in MySQL 3.23.30.

   have_raid

     YES if mysqld supports the RAID option. This variable was added in MySQL 3.23.30.

   have_openssl

     YES if mysqld supports SSL (encryption) of the client/server protocol. This variable was added in MySQL 3.23.43.

   init_connect

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

     This variable was added in MySQL 4.1.2.

   init_file

     The name of the file specified with the --init-file option when you start the server. This is 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. This variable was added in MySQL 3.23.2.

   init_slave

     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. This variable was added in MySQL 4.1.2.

   innodb_xxx

     The InnoDB system variables are listed in Section, “InnoDB Startup Options Startup Options.”

   interactive_timeout

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

   join_buffer_size

     The size of the buffer that is used for full joins (joins that do not use indexes). The buffer is allocated one time for each full join between two tables. Increase this value to get a faster full join when adding indexes is not possible. (Normally the best way to get fast joins is to add indexes.)

   key_buffer_size

     Index blocks for MyISAM and ISAM 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.

     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.

     For even more speed when writing many rows at the same time, use LOCK TABLES.

     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.

     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_used status variable and the buffer block size. From MySQL 4.1.1 on, the buffer block size is available from the key_cache_block_size server variable. The fraction of the buffer in use is:

(Key_blocks_used * key_cache_block_size) / key_buffer_size

     Before MySQL 4.1.1, key cache blocks are 1024 bytes, so the fraction of the key buffer in use is:

(Key_blocks_used * 1024) / key_buffer_size

     See Section 6.4.6, “The MyISAM Key Cache.”

   key_cache_age_threshold

     This value controls the demotion of buffers from the hot sub-chain of a key cache to the warm sub-chain. Lower values cause demotion to happen more quickly. The minimum value is 100. The default value is 300. This variable was added in MySQL 4.1.1. See Section 6.4.6, “The MyISAM Key Cache.”

   key_cache_block_size

     The size in bytes of blocks in the key cache. The default value is 1024. This variable was added in MySQL 4.1.1. See Section 6.4.6, “The MyISAM Key Cache.”

   key_cache_division_limit

     The division point between the hot and warm sub-chains of the key cache buffer chain. The value is the percentage of the buffer chain to use for the warm sub-chain. Allowable values range from 1 to 100. The default value is 100. This variable was added in MySQL 4.1.1. See Section 6.4.6, “The MyISAM Key Cache.”

   language

     The language used for error messages.

   large_file_support

     Whether mysqld was compiled with options for large file support. This variable was added in MySQL 3.23.28.

   local_infile

     Whether LOCAL is supported for LOAD DATA INFILE statements. This variable was added in MySQL 4.0.3.

   locked_in_memory

     Whether mysqld was locked in memory with --memlock. This variable was added in MySQL 3.23.25.

   log

     Whether logging of all queries to the general query log is enabled. See Section 4.8.2, “The General Query Log.”

   log_bin

     Whether the binary log is enabled. This variable was added in MySQL 3.23.14. See Section 4.8.4, “The Binary Log.”

   log_slave_updates

     Whether updates received by a slave server from a master server should be logged to the slave’s own binary log. Binary logging must be enabled on the slave for this to have any effect. This variable was added in MySQL 3.23.17. See Section 5.8, “Replication Startup Options.”

   log_slow_queries

     Whether slow queries should be logged. “Slow” is determined by the value of the long_query_time variable. This variable was added in MySQL 4.0.2. See Section 4.8.5, “The Slow Query Log.”

   log_update

     Whether the update log is enabled. This variable was added in MySQL 3.22.18. Note that the binary log is preferable to the update log, which is unavailable as of MySQL 5.0. See Section 4.8.3, “The Update Log.”

   long_query_time

     If a query takes longer than this many seconds, the Slow_queries status variable is incremented. 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. See Section 4.8.5, “The Slow Query Log.”

   low_priority_updates

     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 variable previously was named sql_low_priority_updates. It was added in MySQL 3.22.5.

   lower_case_table_names

     If set to 1, table names are stored in lowercase on disk and table name comparisons are not case sensitive. This variable was added in MySQL 3.23.6. If set to 2 (new in 4.0.18), table names are stored as given but compared in lowercase. From MySQL 4.0.2, this option also applies to database names. From 4.1.1, it also applies to table aliases.

     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). New in 4.0.18: If this variable is 0 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

     The maximum size of one packet. The 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 big (possibly wrong) packets. You must increase this value if you are using big BLOB columns. It should be as big as the biggest BLOB you want to use. The protocol limit for max_allowed_packet is 16MB before MySQL 4.0 and 1GB thereafter.

   max_binlog_cache_size

     If a multiple-statement transaction requires more than this amount of memory, you will get the error Multi-statement transaction required more than ’max_binlog_cache_size’bytes of storage. This variable was added in MySQL 3.23.29.

   max_binlog_size

     If a write to the binary log exceeds the given value, rotate the binary logs. You cannot set this variable to more than 1GB or to less than 4096 bytes. (The minimum before MYSQL 4.0.14 is 1024 bytes.) The default value is 1GB. This variable was added in MySQL 3.23.33.

     Note if you are using transactions: A transaction is written in one chunk to the binary log, hence it is never split between several binary logs. Therefore, if you have big transactions, you might see binary logs bigger than max_binlog_size.

     If max_relay_log_size is 0, the value of max_binlog_size applies to relay logs as well. max_relay_log_size was added in MySQL 4.0.14.

   max_connect_errors

     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

     The number of simultaneous client connections allowed. 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. Also see Section A.2.6, “Too many connections.”

   max_delayed_threads

     Don’t 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 will be 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. This variable was added in MySQL 3.23.0.

   max_error_count

     The maximum number of error, warning, and note messages to be stored for display by SHOW ERRORS or SHOW WARNINGS. This variable was added in MySQL 4.1.0.

   max_heap_table_size

     This variable sets the maximum size to which MEMORY (HEAP) 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 TRUNCATE TABLE, or altered with ALTER TABLE. This variable was added in MySQL 3.23.0.

   max_insert_delayed_threads

     This variable is a synonym for max_delayed_threads. It was added in MySQL 4.0.19.

   max_join_size

     Don’t allow SELECT statements that probably will need to examine more than max_join_size row combinations or 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 SQL_BIG_SELECTS value to 0. If you set the SQL_BIG_SELECTS value again, the max_join_size variable is ignored.

     If a query result already is in the query cache, no result size check is performed, because the result has already 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_relay_log_size

     If a write by a replication slave to its relay log exceeds the given value, rotate the relay log. This variable enables you to put different size constraints on relay logs and binary logs. However, setting the variable to 0 makes MySQL use max_binlog_size for both binary logs and relay logs. You must set max_relay_log_size to between 4096 bytes and 1GB (inclusive), or to 0. The default value is 0. This variable was added in MySQL 4.0.14. See Section 5.3, “Replication Implementation Details.”

   max_seeks_for_key

     Limit the assumed maximum number of seeks when looking up rows based on a key. The MySQL optimizer will assume that no more than this number of key seeks will be required when searching for matching rows in a table by scanning a key, regardless of the actual cardinality of the key. By setting this to a low value (100?), you can force MySQL to prefer keys instead of table scans. This variable was added in MySQL 4.0.14.

   max_sort_length

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

   max_tmp_tables

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

   max_user_connections

     The maximum number of simultaneous connections allowed to any given MySQL account. A value of 0 means “no limit.” This variable was added in MySQL 3.23.34.

   max_write_lock_count

     After this many write locks, allow some read locks to run in between. This variable was added in MySQL 3.23.7.

   myisam_data_pointer_size

     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 8. The default value is 4. This variable was added in MySQL 4.1.2. See Section A.2.11, “The table is full.”

   myisam_max_extra_sort_file_size

     If the temporary file used for fast MyISAM index creation would be larger than using the key cache by the amount specified here, prefer the key cache method. This is mainly used to force long character keys in large tables to use the slower key cache method to create the index. This variable was added in MySQL 3.23.37. Note: The value is given in megabytes before 4.0.3 and in bytes thereafter.

   myisam_max_sort_file_size

     The maximum size of the temporary file 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 bigger than this value, the index will be created using the key cache instead, which is slower. This variable was added in MySQL 3.23.37. Note: The value is given in megabytes before 4.0.3 and in bytes thereafter.

   myisam_recover_options

     The value of the --myisam-recover option. This variable was added in MySQL 3.23.36.

   myisam_repair_threads

     If this value is greater than 1, MyISAM table indexes are created in parallel (each index in its own thread) during the Repair by sorting process. The default value is 1. Note: Multi-threaded repair is still alpha quality code. This variable was added in MySQL 4.0.13.

   myisam_sort_buffer_size

     The buffer that is allocated when sorting MyISAM indexes during a REPAIR TABLE or when creating indexes with CREATE INDEX or ALTER TABLE. This variable was added in MySQL 3.23.16.

   named_pipe

     On Windows, indicates whether the server supports connections over named pipes. This variable was added in MySQL 3.23.50.

   net_buffer_length

     The communication buffer is reset to this size between queries. This should not normally be changed, but if you have very little memory, you can set it to the expected length of SQL statements sent by clients. If statements exceed this length, the buffer is automatically enlarged, up to max_allowed_packet bytes.

   net_read_timeout

     The number of seconds to wait for more data from a connection before aborting the read. 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. This variable was added in MySQL 3.23.20.

   net_retry_count

     If a read on a communication port is interrupted, retry this many times before giving up. This value should be set quite high on FreeBSD because internal interrupts are sent to all threads. This variable was added in MySQL 3.23.7.

   net_write_timeout

     The number of seconds to wait for a block to be written to a connection before aborting the write. See also net_read_timeout. This variable was added in MySQL 3.23.20.

   open_files_limit

     The number of files that the operating system allows mysqld to open. This is the real value allowed by the system and might be different from the value you gave mysqld as a startup option. The value is 0 on systems where MySQL can’t change the number of open files. This variable was added in MySQL 3.23.20.

   pid_file

     The pathname of the process ID (PID) file. This variable can be set with the --pid-file option. This variable was added in MySQL 3.23.23.

   port

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

   protocol_version

     The version of the client/server protocol used by the MySQL server. This variable was added in MySQL 3.23.18.

   query_alloc_block_size

     The allocation size of memory blocks that are allocated for objects created during query parsing and execution. If you have problems with memory fragmentation, it might help to increase this a bit. This variable was added in MySQL 4.0.16.

   query_cache_limit

     Don’t cache results that are bigger than this. The default value is 1MB. This variable was added in MySQL 4.0.1.

   query_cache_min_res_unit

     The minimum size for blocks allocated by the query cache. The default value is 4KB. Tuning information for this variable is given in Section 4.10.3, “Query Cache Configuration.” This variable is present from MySQL 4.1.

   query_cache_size

     The amount of memory allocated for caching query results. The default value is 0, which disables the query cache. Note that this amount of memory will be allocated even if query_cache_type is set to 0. This variable was added in MySQL 4.0.1.

   query_cache_type

     Set 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.

     This variable was added in MySQL 4.0.3.

   query_cache_wlock_invalidate

     Normally, when one client acquires a WRITE lock on a MyISAM table, other clients are not blocked from issuing queries for 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. This variable was added in MySQL 4.0.19.

   query_prealloc_size

     The size of the persistent buffer used for query parsing and execution. This buffer is not freed between queries. 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.

     This variable was added in MySQL 4.0.16.

   range_alloc_block_size

     The size of blocks that are allocated when doing range optimization. This variable was added in MySQL 4.0.16.

   read_buffer_size

     Each thread that does a sequential scan allocates a buffer of this size for each table it scans. If you do many sequential scans, you might want to increase this value. This variable was added in MySQL 4.0.3. Previously, it was named record_buffer.

   read_only

     When the variable is set to ON for a replication slave server, it causes the slave to allow no updates except from slave threads or from users with the SUPER privilege. This can be useful to ensure that a slave server accepts no updates from clients. This variable was added in MySQL 4.0.14.

   read_rnd_buffer_size

     When reading rows in sorted order after a sort, the rows are read through this buffer to avoid disk seeks. Setting the variable to a large value can improve ORDER BY performance by a lot. However, this is a buffer allocated for each client, so you should not set the global variable to a large value. Instead, change the session variable only from within those clients that need to run large queries. This variable was added in MySQL 4.0.3. Previously, it was named record_rnd_buffer.

   safe_show_database

     Don’t show databases for which the user has no database or table privileges. This can improve security if you’re concerned about people being able to see what databases other users have. See also skip_show_database.

     This variable was removed in MySQL 4.0.5. Instead, use the SHOW DATABASES privilege to control access by MySQL accounts to database names.

   secure_auth

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

     You should enable this option if you want to prevent all usage of passwords in old format (and hence insecure communication over the network). This variable was added in MySQL 4.1.1.

     Server startup will fail with an error if this option is enabled and the privilege tables are in pre-4.1 format.

     When used as a client-side option, the client refuses to connect to a server if the server requires a password in old format for the client account.

   server_id

     The value of the --server-id option. It is used for master and slave replication servers. This variable was added in MySQL 3.23.26.

   skip_external_locking

     This is OFF if mysqld uses external locking. This variable was added in MySQL 4.0.3. Previously, it was named skip_locking.

   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. On NetWare, only TCP/IP connections are supported, so do not set this variable to ON. This variable was added in MySQL 3.22.23.

   skip_show_database

     This prevents people from using the SHOW DATABASES statement if they don’t have the SHOW DATABASES privilege. This can improve security if you’re concerned about people being able to see what databases other users have. See also safe_show_database. This variable was added in MySQL 3.23.4. As of MySQL 4.0.2, its effect also 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 each database name only if the user has the SHOW DATABASES privilege or some privilege for the database.

   slave_net_timeout

     The number of seconds to wait for more data from a master/slave connection before aborting the read. This variable was added in MySQL 3.23.40.

   slow_launch_time

     If creating a thread takes longer than this many seconds, the server increments the Slow_launch_threads status variable. This variable was added in MySQL 3.23.15.

   socket

     On Unix, this is the Unix socket file used for local client connections. On Windows, this is the name of the named pipe used for local client connections.

   sort_buffer_size

     Each thread that needs to do a sort allocates a buffer of this size. Increase this value for faster ORDER BY or GROUP BY operations. See Section A.4.4, “Where MySQL Stores Temporary Files.”

   sql_mode

     The current server SQL mode. This variable was added in MySQL 3.23.41. See Section 4.2.2, “The Server SQL Mode.”

   storage_engine

     This variable is a synonym for table_type. It was added in MySQL 4.1.2.

   table_cache

     The number of open tables for all threads. Increasing this value increases the number of file descriptors that mysqld requires. You can check whether you need to increase the table cache by checking the Opened_tables status variable. See Section 4.2.4, “Server Status Variables.” If the value of Opened_tables is large and you don’t do FLUSH TABLES a lot (which just forces all tables to be closed and reopened), then you should increase the value of the table_cache variable.

     For more information about the table cache, see Section 6.4.8, “6.4.8 How MySQL Opens and Closes Tables.”

   table_type

     The default table type (storage engine). To set the table type at server startup, use the --default-table-type option. This variable was added in MySQL 3.23.0. See Section 4.2.1, “mysqld Command-Line Options.”

   thread_cache_size

     How many threads the server should cache for reuse. When a client disconnects, the client’s threads are put in the cache if there aren’t already 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 give a notable performance improvement if you have a good thread implementation.) By examining the difference between the Connections and Threads_created status variables (see Section 4.2.4, “4.2.4 Server Status Variables,” for details) you can see how efficient the thread cache is. This variable was added in MySQL 3.23.16.

   thread_concurrency

     On Solaris, mysqld calls thr_setconcurrency() with this value. This function allows applications to give the threads system a hint about the desired number of threads that should be run at the same time. This variable was added in MySQL 3.23.7.

   thread_stack

     The stack size for each thread. Many of the limits detected by the crash-me test are dependent on this value. The default is large enough for normal operation. See Section 6.1.4, “The MySQL Benchmark Suite.”

   timezone

     The time zone for the server. This is set from the TZ environment variable when mysqld is started. The time zone also can be set by giving a --timezone argument to mysqld_safe. This variable was added in MySQL 3.23.15. See Section A.4.6, “Time Zone Problems.”

   tmp_table_size

     If an in-memory temporary table exceeds this size, MySQL automatically converts it to an on-disk MyISAM table. Increase the value of tmp_table_size if you do many advanced GROUP BY queries and you have lots of memory.

   tmpdir

     The directory used for temporary files and temporary tables. Starting from MySQL 4.1, 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.

     This 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 will fail.

     This variable was added in MySQL 3.22.4.

   transaction_alloc_block_size

     The allocation size of memory blocks that are allocated for storing queries that are part of a transaction to be stored in the binary log when doing a commit. This variable was added in MySQL 4.0.16.

   transaction_prealloc_size

     The size of the persistent buffer for transaction_alloc_blocks that is not freed between queries. By making this big enough to fit all queries in a common transaction, you can avoid a lot of malloc() calls. This variable was added in MySQL 4.0.16.

   tx_isolation

     The default transaction isolation level. This variable was added in MySQL 4.0.3.

   version

     The version number for the server.

   wait_timeout

     The number of seconds the server waits for activity on a non-interactive connection before closing it.

     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.

   Aborted_clients

     The number of connections that were aborted because the client died without closing the connection properly. See Section A.2.10, “Communication Errors and Aborted Connections.”

   Aborted_connects

     The number of tries to connect to the MySQL server that failed. See Section A.2.10, “Communication Errors and Aborted Connections.”

   Binlog_cache_use

     The number of transactions that used the temporary binary log cache. This variable was added in MySQL 4.1.2.

   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. This variable was added in MySQL 4.1.2.

   Bytes_received

     The number of bytes received from all clients. This variable was added in MySQL 3.23.7.

   Bytes_sent

     The number of bytes sent to all clients. This variable was added in MySQL 3.23.7.

   Com_xxx

     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.

   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. This variable was added in MySQL 3.23.24.

   Created_tmp_files

     How many temporary files mysqld has created. This variable was added in MySQL 3.23.28.

   Created_tmp_tables

     The number of in-memory temporary tables created automatically by the server while executing statements. If Created_tmp_disk_tables is big, 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. This variable was added in MySQL 4.0.2.

   Handler_delete

     The number of times a row was deleted from a table.

   Handler_read_first

     The number of times the first entry was read from an index. If this 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 is high, it is a good indication that your queries and tables are properly indexed.

   Handler_read_next

     The number of requests to read the next row in key order. This will be 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. This variable was added in MySQL 3.23.6.

   Handler_read_rnd

     The number of requests to read a row based on a fixed position. This will be 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 whole 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 will be 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 internal ROLLBACK statements. This variable was added in MySQL 4.0.2.

   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.

   Key_blocks_used

     The number of used 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 4.2.3, “Server System Variables.”

   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 big, 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.

   Max_used_connections

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

   Not_flushed_delayed_rows

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

   Not_flushed_key_blocks

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

   Open_files

     The number of files that are open.

   Open_streams

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

   Open_tables

     The number of tables that are open.

   Opened_tables

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

   Qcache_free_blocks

     The number of free memory blocks in query cache.

   Qcache_free_memory

     The amount of free memory for query cache.

   Qcache_hits

     The number of cache hits.

   Qcache_inserts

     The number of queries added to the cache.

   Qcache_lowmem_prunes

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

   Qcache_not_cached

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

   Qcache_queries_in_cache

     The number of queries registered in the cache.

   Qcache_total_blocks

     The total number of blocks in the query cache.

   Questions

     The number of queries that have been sent to the server.

   Rpl_status

     The status of failsafe replication (not yet implemented).

   Select_full_join

     The number of joins that do not use indexes. If this value is not 0, you should carefully check the indexes of your tables. This variable was added in MySQL 3.23.25.

   Select_full_range_join

     The number of joins that used a range search on a reference table. This variable was added in MySQL 3.23.25.

   Select_range

     The number of joins that used ranges on the first table. (It’s normally not critical even if this is big.) This variable was added in MySQL 3.23.25.

   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.) This variable was added in MySQL 3.23.25.

   Select_scan

     The number of joins that did a full scan of the first table. This variable was added in MySQL 3.23.25.

   Slave_open_temp_tables

     The number of temporary tables currently open by the slave SQL thread. This variable was added in MySQL 3.23.29.

   Slave_running

     This is ON if the server is a slave that is connected to a master. This variable was added in MySQL 3.23.16.

   Slow_launch_threads

     The number of threads that have taken more than slow_launch_time seconds to create. This variable was added in MySQL 3.23.15.

   Slow_queries

     The number of queries that have taken more than long_query_time seconds. See Section 4.8.5, “The Slow Query Log.”

   Sort_merge_passes

     The number of merge passes 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. This variable was added in MySQL 3.23.28.

   Sort_range

     The number of sorts that were done with ranges. This variable was added in MySQL 3.23.25.

   Sort_rows

     The number of sorted rows. This variable was added in MySQL 3.23.25.

   Sort_scan

     The number of sorts that were done by scanning the table. This variable was added in MySQL 3.23.25.

   Ssl_xxx

     Variables used for SSL connections. These variables were added in MySQL 4.0.0.

   Table_locks_immediate

     The number of times that a table lock was acquired immediately. This variable was added as of MySQL 3.23.33.

   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. This variable was added as of MySQL 3.23.33.

   Threads_cached

     The number of threads in the thread cache. This variable was added in MySQL 3.23.17.

   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 hit rate can be calculated as Threads_created/Connections. This variable was added in MySQL 3.23.31.

   Threads_running

     The number of threads that are not sleeping.

   Uptime

     The number of seconds the server has been up.

   Do not ever give anyone (except MySQL root accounts) access to the user table in the mysql database! This is critical. The encrypted password is the real password in MySQL. Anyone who knows the password that is listed in the user table and has access to the host listed for the account can easily log in as that user.

   Learn the MySQL access privilege system. The GRANT and REVOKE statements are used for controlling access to MySQL. Do not grant any more privileges than necessary. Never grant privileges to all hosts.

     Checklist:

   Do not store any plain-text passwords in your database. If your computer becomes compromised, the intruder can take the full list of passwords and use them. Instead, use MD5(), SHA1(), or some other one-way hashing function.

   Do not choose passwords from dictionaries. There are special programs to break them. Even passwords like “xfish98” are very bad. Much better is “duag98” which contains the same word “fish” but typed one key to the left on a standard QWERTY keyboard. Another method is to use “Mhall” which is taken from the first characters of each word in the sentence “Mary had a little lamb.” This is easy to remember and type, but difficult to guess for someone who does not know it.

   Invest in a firewall. This protects you from at least 50% of all types of exploits in any software. Put MySQL behind the firewall or in a demilitarized zone (DMZ).

     Checklist:

   Do not trust any data entered by users of your applications. They can try to trick your code by entering special or escaped character sequences in Web forms, URLs, or whatever application you have built. Be sure that your application remains secure if a user enters something like “; DROP DATABASE mysql;”. This is an extreme example, but large security leaks and data loss might occur as a result of hackers using similar techniques, if you do not prepare for them.

     A common mistake is to protect only string data values. Remember to check numeric data as well. If an application generates a query such as SELECT * FROM table WHERE ID=234 when a user enters the value 234, the user can enter the value 234 OR 1=1 to cause the application to generate the query SELECT * FROM table WHERE ID=234 OR 1=1. As a result, the server retrieves every record in the table. This exposes every record and causes excessive server load. The simplest way to protect from this type of attack is to use apostrophes around the numeric constants: SELECT * FROM table WHERE ID=’234’. If the user enters extra information, it all becomes part of the string. In numeric context, MySQL automatically converts this string to a number and strips any trailing non-numeric characters from it.

     Sometimes people think that if a database contains only publicly available data, it need not be protected. This is incorrect. Even if it is allowable to display any record in the database, you should still protect against denial of service attacks (for example, those that are based on the technique in the preceding paragraph that causes the server to waste resources). Otherwise, your server becomes unresponsive to legitimate users.

     Checklist:

   Many application programming interfaces provide a means of escaping special characters in data values. Properly used, this prevents application users from entering values that cause the application to generate statements that have a different effect than you intend:

     Other programming interfaces might have similar capabilities.

   Do not transmit plain (unencrypted) data over the Internet. This information is accessible to everyone who has the time and ability to intercept it and use it for their own purposes. Instead, use an encrypted protocol such as SSL or SSH. MySQL supports internal SSL connections as of Version 4.0.0. SSH port-forwarding can be used to create an encrypted (and compressed) tunnel for the communication.

   Learn to use the tcpdump and strings utilities. For most cases, you can check whether MySQL data streams are unencrypted by issuing a command like the following:

shell> tcpdump -l -i eth0 -w - src or dst port 3306 | strings

     (This works under Linux and should work with small modifications under other systems.) Warning: If you do not see plaintext data, this doesn’t always mean that the information actually is encrypted. If you need high security, you should consult with a security expert.

   Use passwords for all MySQL users. A client program does not necessarily know the identity of the person running it. It is common for client/server applications that the user can specify any username to the client program. For example, anyone can use the mysql program to connect as any other person simply by invoking it as mysql -u other_user db_name if other_user has no password. If all users have a password, connecting using another user’s account becomes much more difficult.

     To change the password for a user, use the SET PASSWORD statement. It is also possible to update the user table in the mysql database directly. For example, to change the password of all MySQL accounts that have a username of root, do this:

shell> mysql -u root
mysql> UPDATE mysql.user SET Password=PASSWORD('newpwd')
    -> WHERE User='root';
mysql> FLUSH PRIVILEGES;

   Don't run the MySQL server as the Unix root user. This is very dangerous, because any user with the FILE privilege will be able to create files as root (for example, ~root/.bashrc). To prevent this, mysqld refuses to run as root unless that is specified explicitly using a --user=root option.

     mysqld can be run as an ordinary unprivileged user instead. You can also create a separate Unix account named mysql to make everything even more secure. Use the account only for administering MySQL. To start mysqld as another Unix user, add a user option that specifies the username to the [mysqld] group of the /etc/my.cnf option file or the my.cnf option file in the server’s data directory. For example:

[mysqld]
user=mysql

     This causes the server to start as the designated user whether you start it manually or by using mysqld_safe or mysql.server. For more details, see Section A.3.2, “How to Run MySQL as a Normal User.”

     Running mysql as a Unix user other than root does not mean that you need to change the root username in the user table. Usernames for MySQL accounts have nothing to do with usernames for Unix accounts.

   Don’t allow the use of symlinks to tables. (This can be disabled with the --skip- symbolic-links option.) This is especially important if you run mysqld as root, because anyone that has write access to the server’s data directory then could delete any file in the system! See Section 6.6.1.2, “Using Symbolic Links for Tables on Unix.”

   Make sure that the only Unix user with read or write privileges in the database directories is the user that mysqld runs as.

   Don’t grant the PROCESS or SUPER privilege to non-administrative users. The output of mysqladmin processlist shows the text of the currently executing queries, so any user who is allowed to execute that command might be able to see if another user issues an UPDATE user SET password=PASSWORD(’not_secure’) query.

     mysqld reserves an extra connection for users who have the SUPER privilege (PROCESS before MySQL 4.0.2), so that a MySQL root user can log in and check server activity even if all normal connections are in use.

     The SUPER privilege can be used to terminate client connections, change server operation by changing the value of system variables, and control replication servers.

   Don’t grant the FILE privilege to non-administrative users. Any user that has this privilege can write a file anywhere in the filesystem with the privileges of the mysqld daemon! To make this a bit safer, files generated with SELECT ... INTO OUTFILE will not overwrite existing files and are writable by everyone.

     The FILE privilege may also be used to read any file that is world-readable or accessible to the Unix user that the server runs as. With this privilege, you can read any file into a database table. This could be abused, for example, by using LOAD DATA to load /etc/passwd into a table, which then can be displayed with SELECT.

   If you don’t trust your DNS, you should use IP numbers rather than hostnames in the grant tables. In any case, you should be very careful about creating grant table entries using hostname values that contain wildcards!

   If you want to restrict the number of connections allowed to a single account, you can do so by setting the max_user_connections variable in mysqld. The GRANT statement also supports resource control options for limiting the extent of server use allowed to an account.

   --local-infile[={0|1}]

     If you start the server with --local-infile=0, clients cannot use LOCAL in LOAD DATA statements. See Section 4.3.4, “Security Issues with LOAD DATA LOCAL.”

   --safe-show-database

     With this option, the SHOW DATABASES statement displays the names of only those databases for which the user has some kind of privilege. As of MySQL 4.0.2, this option is deprecated and doesn’t do anything (it is enabled by default), because there is now a SHOW DATABASES privilege that can be used to control access to database names on a per-account basis.

   --safe-user-create

     If this is enabled, a user cannot create new users with the GRANT statement unless the user has the INSERT privilege for the mysql.user table. If you want a user to have the ability to create new users with those privileges that the user has right to grant, you should grant the user the following privilege:

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

     This will ensure that the user can’t change any privilege columns directly, but has to use the GRANT statement to give privileges to other users.

   --secure-auth

     Disallow authentication for accounts that have old (pre-4.1) passwords. This option is available as of MySQL 4.1.1.

   --skip-grant-tables

     This option causes the server not to use the privilege system at all. This gives everyone full access to all databases! (You can tell a running server to start using the grant tables again by executing a mysqladmin flush-privileges or mysqladmin reload command, or by issuing a FLUSH PRIVILEGES statement.)

   --skip-name-resolve

     Hostnames are not resolved. All Host column values in the grant tables must be IP numbers or localhost.

   --skip-networking

     Don’t allow TCP/IP connections over the network. All connections to mysqld must be made via Unix socket files. This option is unsuitable when using a MySQL version prior to 3.23.27 with the MIT-pthreads package, because Unix socket files were not supported by MIT-pthreads at that time.

   --skip-show-database

     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.

   The transfer of the file from the client host to the server host is initiated by the MySQL server. In theory, a patched server could be built that would tell the client program to transfer a file of the server’s choosing rather than the file named by the client in the LOAD DATA statement. Such a server could access any file on the client host to which the client user has read access.

   In a Web environment where the clients are connecting from a Web server, a user could use LOAD DATA LOCAL to read any files that the Web server process has read access to (assuming that a user could run any command against the SQL server). In this environment, the client with respect to the MySQL server actually is the Web server, not the program being run by the user connecting to the Web server.

   By default, all MySQL clients and libraries in binary distributions are compiled with the --enable-local-infile option, to be compatible with MySQL 3.23.48 and before.

   If you build MySQL from source but don’t use the --enable-local-infile option to configure, LOAD DATA LOCAL cannot be used by any client unless it is written explicitly to invoke mysql_options(... MYSQL_OPT_LOCAL_INFILE, 0).

   You can disable all LOAD DATA LOCAL commands from the server side by starting mysqld with the --local-infile=0 option.

   For the mysql command-line client, LOAD DATA LOCAL can be enabled by specifying the --local-infile[=1] option, or disabled with the --local-infile=0 option. Similarly, for mysqlimport, the --local or -L option enables local data file loading. In any case, successful use of a local loading operation requires that the server is enabled to allow it.

   If LOAD DATA LOCAL INFILE is disabled, either in the server or the client, a client that attempts to issue such a statement receives the following error message:

ERROR 1148: The used command is not allowed with this MySQL version