5 Database Administration

This chapter covers topics that deal with administering a MySQL installation, such as configuring the server, managing user accounts, and performing backups.

5.1 The MySQL Server and Server Startup Scripts

The MySQL server, mysqld, is the main program that does most of the work in a MySQL installation. The server is accompanied by several related scripts that perform setup operations when you install MySQL or that are helper programs to assist you in starting and stopping the server.

This section provides an overview of the server and related programs, and information about server startup scripts. Information about configuring the server itself is given in section 5.2 Configuring the MySQL Server.

5.1.1 Overview of the Server-Side Scripts and Utilities

All MySQL programs take many different options. However, every MySQL program provides a --help option that you can use to get a description of the program's options. For example, try mysqld --help.

You can override default options for all standard programs by specifying options on the command line or in an option file. section 4.3 Specifying Program Options.

The following list briefly describes the MySQL server and server-related programs:

mysqld

The SQL daemon (that is, the MySQL server). To use client programs, this program must be running, because clients gain access to databases by connecting to the server. See section 5.2 Configuring the MySQL Server.

mysqld-max

A version of the server that includes additional features. See section 5.1.2 The mysqld-max Extended MySQL Server.

mysqld_safe

A server startup script. mysqld_safe attempts to start mysqld-max if it exists, and mysqld otherwise. See section 5.1.3 The mysqld_safe Server Startup Script.

mysql.server

A server startup script. This script is used on systems that use run directories containing scripts that start system services for particular run levels. It invokes mysqld_safe to start the MySQL server. See section 5.1.4 The mysql.server Server Startup Script.

mysqld_multi

A server startup script that can start or stop multiple servers installed on the system. See section 5.1.5 The mysqld_multi Program for Managing Multiple MySQL Servers.

mysql_install_db

This script creates the MySQL grant tables with default privileges. It is usually executed only once, when first installing MySQL on a system.

mysql_fix_privilege_tables

This script is used after an upgrade install operation, to update the grant tables with any changes that have been made in newer versions of MySQL.

There are several other programs that also are run on the server host:

myisamchk

A utility to describe, check, optimize, and repair MyISAM tables. myisamchk is described in section 5.7.2 Table Maintenance and Crash Recovery.

make_binary_distribution

This program makes a binary release of a compiled MySQL. This could be sent by FTP to `/pub/mysql/upload/' on ftp.mysql.com for the convenience of other MySQL users.

mysqlbug

The MySQL bug reporting script. It can be used to send a bug report to the MySQL mailing list. (You can also visit http://bugs.mysql.com/ to file a bug report online.)

5.1.2 The mysqld-max Extended MySQL Server

A MySQL-Max server is a version of the mysqld MySQL server that has been built to include additional features.

The distribution to use depends on your platform:

• For Windows, MySQL binary distributions include both the standard server (mysqld.exe) and the MySQL-Max server (mysqld-max.exe), so you need not get a special distribution. Just use a regular Windows distribution, available at http://dev.mysql.com/downloads/. See section 2.3 Installing MySQL on Windows.
• For Linux, if you install MySQL using RPM distributions, use the regular MySQL-server RPM first to install a standard server named mysqld. Then use the MySQL-Max RPM to install a server named mysqld-max. The MySQL-Max RPM presupposes that you have already installed the regular server RPM. See section 2.4 Installing MySQL on Linux for more information on the Linux RPM packages.
• All other MySQL-Max distributions contain a single server that is named mysqld but that has the additional features included.

You can find the MySQL-Max binaries on the MySQL AB Web site at http://dev.mysql.com/downloads/mysql-4.0.html.

MySQL AB builds the MySQL-Max servers by using the following configure options:

--with-server-suffix=-max

This option adds a -max suffix to the mysqld version string.

--with-innodb

This option enables support for the InnoDB storage engine. MySQL-Max servers always include InnoDB support, but this option actually is needed only for MySQL 3.23. From MySQL 4 on, InnoDB is included by default in binary distributions, so you do not need a MySQL-Max server to obtain InnoDB support.

--with-bdb

This option enables support for the Berkeley DB (BDB) storage engine.

CFLAGS=-DUSE_SYMDIR

This define enables symbolic link support for Windows.

MySQL-Max binary distributions are a convenience for those who wish to install precompiled programs. If you build MySQL using a source distribution, you can build your own Max-like server by enabling the same features at configuration time that the MySQL-Max binary distributions are built with.

MySQL-Max servers include the BerkeleyDB (BDB) storage engine whenever possible, but not all platforms support BDB. The following table shows which platforms allow MySQL-Max binaries to include BDB:

To find out which storage engines your server supports, issue the following statement:

mysql> SHOW ENGINES;

Before MySQL 4.1.2, SHOW ENGINES is unavailable. Use the following statement instead and check the value of the variable for the storage engine in which you are interested:

mysql> SHOW VARIABLES LIKE 'have_%';
+------------------+----------+
| Variable_name    | Value    |
+------------------+----------+
| have_bdb         | NO       |
| have_crypt       | YES      |
| have_innodb      | YES      |
| have_isam        | NO       |
| have_raid        | NO       |
| have_symlink     | DISABLED |
| have_openssl     | NO       |
| have_query_cache | YES      |
+------------------+----------+

The values in the second column indicate the server's level of support for each feature:

A value of NO means that the server was compiled without support for the feature, so it cannot be activated at runtime.

A value of DISABLED occurs either because the server was started with an option that disables the feature, or because not all options required to enable it were given. In the latter case, the host_name.err error log file should contain a reason indicating why the option is disabled.

One situation in which you might see DISABLED occurs with MySQL 3.23 when the InnoDB storage engine is compiled in. In MySQL 3.23, you must supply at least the innodb_data_file_path option at runtime to set up the InnoDB tablespace. Without this option, InnoDB disables itself. See section 15.3 InnoDB in MySQL 3.23. You can specify configuration options for the BDB storage engine, too, but BDB will not disable itself if you do not provide them. See section 14.4.3 BDB Startup Options.

You might also see DISABLED for the InnoDB, BDB, or ISAM storage engines if the server was compiled to support them, but was started with the --skip-innodb, --skip-bdb, or --skip-isam options at runtime.

As of Version 3.23, all MySQL servers support MyISAM tables, because MyISAM is the default storage engine.

5.1.3 The mysqld_safe Server Startup Script

mysqld_safe is the recommended way to start a mysqld server on Unix and NetWare. mysqld_safe adds some safety features such as restarting the server when an error occurs and logging runtime information to an error log file. NetWare-specific behaviors are listed later in this section.

Note: Before MySQL 4.0, mysqld_safe is named safe_mysqld. To preserve backward compatibility, MySQL binary distributions for some time will include safe_mysqld as a symbolic link to mysqld_safe.

By default, mysqld_safe tries to start an executable named mysqld-max if it exists, or mysqld otherwise. Be aware of the implications of this behavior:

• On Linux, the MySQL-Max RPM relies on this mysqld_safe behavior. The RPM installs an executable named mysqld-max, which causes mysqld_safe to automatically use that executable from that point on.
• If you install a MySQL-Max distribution that includes a server named mysqld-max, then upgrade later to a non-Max version of MySQL, mysqld_safe will still attempt to run the old mysqld-max server. If you perform such an upgrade, you should manually remove the old mysqld-max server to ensure that mysqld_safe runs the new mysqld server.

To override the default behavior and specify explicitly which server you want to run, specify a --mysqld or --mysqld-version option to mysqld_safe.

Many of the options to mysqld_safe are the same as the options to mysqld. See section 5.2.1 mysqld Command-Line Options.

All options specified to mysqld_safe on the command line are passed to mysqld. If you want to use any options that are specific to mysqld_safe and that mysqld doesn't support, do not specify them on the command line. Instead, list them in the [mysqld_safe] group of an option file. See section 4.3.2 Using Option Files.

mysqld_safe reads all options from the [mysqld], [server], and [mysqld_safe] sections in option files. For backward compatibility, it also reads [safe_mysqld] sections, although you should rename such sections to [mysqld_safe] when you begin using MySQL 4.0 or later.

mysqld_safe supports the following options:

--basedir=path

The path to the MySQL installation directory.

--core-file-size=size

The size of the core file mysqld should be able to create. The option value is passed to ulimit -c.

--datadir=path

The path to the data directory.

--defaults-extra-file=path

The name of an option file to be read in addition to the usual option files.

--defaults-file=path

The name of an option file to be read instead of the usual option files.

--err-log=path

The old form of the --log-error option, to be used before MySQL 4.0.

--ledir=path

The path to the directory containing the mysqld program. Use this option to explicitly indicate the location of the server.

--log-error=path

Write the error log to the given file. See section 5.9.1 The Error Log.

--mysqld=prog_name

The name of the server program (in the ledir directory) that you want to start. This option is needed if you use the MySQL binary distribution but have the data directory outside of the binary distribution.

--mysqld-version=suffix

This option is similar to the --mysqld option, but you specify only the suffix for the server program name. The basename is assumed to be mysqld. For example, if you use --mysqld-version=max, mysqld_safe will start the mysqld-max program in the ledir directory. If the argument to --mysqld-version is empty, mysqld_safe uses mysqld in the ledir directory.

--nice=priority

Use the nice program to set the server's scheduling priority to the given value. This option was added in MySQL 4.0.14.

--no-defaults

Do not read any option files.

--open-files-limit=count

The number of files mysqld should be able to open. The option value is passed to ulimit -n. Note that you need to start mysqld_safe as root for this to work properly!

--pid-file=path

The path to the process ID file.

--port=port_num

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

--socket=path

The Unix socket file to use for local connections.

--timezone=zone

Set the TZ time zone environment variable to the given option value. Consult your operating system documentation for legal time zone specification formats.

--user={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.)

The mysqld_safe script is written so that it normally can start a server that was installed from either a source or a binary distribution of MySQL, even though these types of distributions typically install the server in slightly different locations. (See section 2.1.5 Installation Layouts.) mysqld_safe expects one of the following conditions to be true:

• The server and databases can be found relative to the directory from which mysqld_safe is invoked. For binary distributions, mysqld_safe looks under its working directory for `bin' and `data' directories. For source distributions, it looks for `libexec' and `var' directories. This condition should be met if you execute mysqld_safe from your MySQL installation directory (for example, `/usr/local/mysql' for a binary distribution).
• If the server and databases cannot be found relative to the working directory, mysqld_safe attempts to locate them by absolute pathnames. Typical locations are `/usr/local/libexec' and `/usr/local/var'. The actual locations are determined from the values configured into the distribution at the time it was built. They should be correct if MySQL is installed in the location specified at configuration time.

Because mysqld_safe will try to find the server and databases relative to its own working directory, you can install a binary distribution of MySQL anywhere, as long as you run mysqld_safe from the MySQL installation directory:

shell> cd mysql_installation_directory
shell> bin/mysqld_safe &

If mysqld_safe fails, even when invoked from the MySQL installation directory, you can specify the --ledir and --datadir options to indicate the directories in which the server and databases are located on your system.

Normally, you should not edit the mysqld_safe script. Instead, configure mysqld_safe by using command-line options or options in the [mysqld_safe] section of a `my.cnf' option file. In rare cases, it might be necessary to edit mysqld_safe to get it to start the server properly. However, if you do this, your modified version of mysqld_safe might be overwritten if you upgrade MySQL in the future, so you should make a copy of your edited version that you can reinstall.

On NetWare, mysqld_safe is a NetWare Loadable Module (NLM) that is ported from the original Unix shell script. It does the following:

1. Runs a number of system and option checks.
2. Runs a check on MyISAM and ISAM tables.
3. Provides a screen presence for the MySQL server.
4. Starts mysqld, monitors it, and restarts it if it terminates in error.
5. Sends error messages from mysqld to the `host_name.err' file in the data directory.
6. Sends mysqld_safe screen output to the `host_name.safe' file in the data directory.

5.1.4 The mysql.server Server Startup Script

MySQL distributions on Unix include a script named mysql.server. It can be used on systems such as Linux and Solaris that use System V-style run directories to start and stop system services. It is also used by the Mac OS X Startup Item for MySQL.

mysql.server can be found in the `support-files' directory under your MySQL installation directory or in a MySQL source tree.

If you use the Linux server RPM package (MySQL-server-VERSION.rpm), the mysql.server script will already have been installed in the `/etc/init.d' directory with the name `mysql'. You need not install it manually. See section 2.4 Installing MySQL on Linux for more information on the Linux RPM packages.

Some vendors provide RPM packages that install a startup script under a different name such as mysqld.

If you install MySQL from a source distribution or using a binary distribution format that does not install mysql.server automatically, you can install it manually. Instructions are provided in section 2.9.2.2 Starting and Stopping MySQL Automatically.

mysql.server reads options from the [mysql.server] and [mysqld] sections of option files. (For backward compatibility, it also reads [mysql_server] sections, although you should rename such sections to [mysql.server] when you begin using MySQL 4.0 or later.)

5.1.5 The mysqld_multi Program for Managing Multiple MySQL Servers

mysqld_multi is meant for managing several mysqld processes that listen for connections on different Unix socket files and TCP/IP ports. It can start or stop servers, or report their current status.

The program searches for groups named [mysqld#] in `my.cnf' (or in the file named by the --config-file option). # can be any positive integer. This number is referred to in the following discussion as the option group number, or GNR. Group numbers distinguish option groups from one another and are used as arguments to mysqld_multi to specify which servers you want to start, stop, or obtain a status report for. Options listed in these groups are the same that you would use in the [mysqld] group used for starting mysqld. (See, for example, section 2.9.2.2 Starting and Stopping MySQL Automatically.) However, when using multiple servers it is necessary that each one use its own value for options such as the Unix socket file and TCP/IP port number. For more information on which options must be unique per server in a multiple-server environment, see section 5.10 Running Multiple MySQL Servers on the Same Machine.

To invoke mysqld_multi, use the following syntax:

shell> mysqld_multi [options] {start|stop|report} [GNR[,GNR]...]

start, stop, and report indicate which operation you want to perform. You can perform the designated operation on a single server or multiple servers, depending on the GNR list that follows the option name. If there is no list, mysqld_multi performs the operation for all servers in the option file.

Each GNR value represents an option group number or range of group numbers. The value should be the number at the end of the group name in the option file. For example, the GNR for a group named [mysqld17] is 17. To specify a range of numbers, separate the first and last numbers by a dash. The GNR value 10-13 represents groups [mysqld10] through [mysqld13]. Multiple groups or group ranges can be specified on the command line, separated by commas. There must be no whitespace characters (spaces or tabs) in the GNR list; anything after a whitespace character is ignored.

This command starts a single server using option group [mysqld17]:

shell> mysqld_multi start 17

This command stops several servers, using option groups [mysql8] and [mysqld10] through [mysqld13]:

shell> mysqld_multi stop 8,10-13

For an example of how you might set up an option file, use this command:

shell> mysqld_multi --example

mysqld_multi supports the following options:

--config-file=name

Specify the name of an alternative option file. This affects where mysqld_multi looks for [mysqld#] option groups. Without this option, all options are read from the usual `my.cnf' file. The option does not affect where mysqld_multi reads its own options, which are always taken from the [mysqld_multi] group in the usual `my.cnf' file.

--example

Display a sample option file.

--help

Display a help message and exit.

--log=name

Specify the name of the log file. If the file exists, log output is appended to it.

--mysqladmin=prog_name

The mysqladmin binary to be used to stop servers.

--mysqld=prog_name

The mysqld binary to be used. Note that you can specify mysqld_safe as the value for this option also. The options are passed to mysqld. Just make sure that you have the directory where mysqld is located in your PATH environment variable setting or fix mysqld_safe.

--no-log

Print log information to stdout rather than to the log file. By default, output goes to the log file.

--password=password

The password of the MySQL account to use when invoking mysqladmin. Note that the password value is not optional for this option, unlike for other MySQL programs.

--silent

Disable warnings. This option was added in MySQL 4.1.6.

--tcp-ip

Connect to each MySQL server via the TCP/IP port instead of the Unix socket file. (If a socket file is missing, the server might still be running, but accessible only via the TCP/IP port.) By default, connections are made using the Unix socket file. This option affects stop and report operations.

--user=user_name

The username of the MySQL account to use when invoking mysqladmin.

--verbose

Be more verbose. This option was added in MySQL 4.1.6.

--version

Display version information and exit.

Some notes about mysqld_multi:

• Make sure that the MySQL account used for stopping the mysqld servers (with the mysqladmin program) has the same username and password for each server. Also, make sure that the account has the SHUTDOWN privilege. If the servers that you want to manage have many different usernames or passwords for the administrative accounts, you might want to create an account on each server that has the same username and password. For example, you might set up a common multi_admin account by executing the following commands for each server:

  shell> mysql -u root -S /tmp/mysql.sock -proot_password
  mysql> GRANT SHUTDOWN ON *.*
      -> TO 'multi_admin'@'localhost' IDENTIFIED BY 'multipass';
  

  See section 5.5.2 How the Privilege System Works. You will have to do this for each mysqld server. Change the connection parameters appropriately when connecting to each one. Note that the host part of the account name must allow you to connect as multi_admin from the host where you want to run mysqld_multi.
• The --pid-file option is very important if you are using mysqld_safe to start mysqld (for example, --mysqld=mysqld_safe) Every mysqld should have its own process ID file. The advantage of using mysqld_safe instead of mysqld is that mysqld_safe ``guards'' its mysqld process and will restart it if the process terminates due to a signal sent using kill -9, or for other reasons, such as a segmentation fault. Please note that the mysqld_safe script might require that you start it from a certain place. This means that you might have to change location to a certain directory before running mysqld_multi. If you have problems starting, please see the mysqld_safe script. Check especially the lines:

  ----------------------------------------------------------------
  MY_PWD=`pwd`
  # Check if we are starting this relative (for the binary release)
  if test -d $MY_PWD/data/mysql -a -f ./share/mysql/english/errmsg.sys -a \
   -x ./bin/mysqld
  ----------------------------------------------------------------
  

  See section 5.1.3 The mysqld_safe Server Startup Script. The test performed by these lines should be successful, or you might encounter problems.
• The Unix socket file and the TCP/IP port number must be different for every mysqld.
• You might want to use the --user option for mysqld, but in order to do this you need to run the mysqld_multi script as the Unix root user. Having the option in the option file doesn't matter; you will just get a warning, if you are not the superuser and the mysqld processes are started under your own Unix account.
• Important: Make sure that the data directory is fully accessible to the Unix account that the specific mysqld process is started as. Do not use the Unix root account for this, unless you know what you are doing.
• Most important: Before using mysqld_multi be sure that you understand the meanings of the options that are passed to the mysqld servers and why you would want to have separate mysqld processes. Beware of the dangers of using multiple mysqld servers with the same data directory. Use separate data directories, unless you know what you are doing. Starting multiple servers with the same data directory will not give you extra performance in a threaded system. See section 5.10 Running Multiple MySQL Servers on the Same Machine.

The following example shows how you might set up an option file for use with mysqld_multi. The first and fifth [mysqld#] group were intentionally left out from the example to illustrate that you can have ``gaps'' in the option file. This gives you more flexibility. The order in which the mysqld programs are started or stopped depends on the order in which they appear in the option file.

# This file should probably be in your home dir (~/.my.cnf)
# or /etc/my.cnf
# Version 2.1 by Jani Tolonen

[mysqld_multi]
mysqld     = /usr/local/bin/mysqld_safe
mysqladmin = /usr/local/bin/mysqladmin
user       = multi_admin
password   = multipass

[mysqld2]
socket     = /tmp/mysql.sock2
port       = 3307
pid-file   = /usr/local/mysql/var2/hostname.pid2
datadir    = /usr/local/mysql/var2
language   = /usr/local/share/mysql/english
user       = john

[mysqld3]
socket     = /tmp/mysql.sock3
port       = 3308
pid-file   = /usr/local/mysql/var3/hostname.pid3
datadir    = /usr/local/mysql/var3
language   = /usr/local/share/mysql/swedish
user       = monty

[mysqld4]
socket     = /tmp/mysql.sock4
port       = 3309
pid-file   = /usr/local/mysql/var4/hostname.pid4
datadir    = /usr/local/mysql/var4
language   = /usr/local/share/mysql/estonia
user       = tonu

[mysqld6]
socket     = /tmp/mysql.sock6
port       = 3311
pid-file   = /usr/local/mysql/var6/hostname.pid6
datadir    = /usr/local/mysql/var6
language   = /usr/local/share/mysql/japanese
user       = jani

See section 4.3.2 Using Option Files.

5.2 Configuring the MySQL Server

This section discusses MySQL server configuration topics:

• Startup options that the server supports
• How to set the server SQL mode
• Server system variables
• Server status variables

5.2.1 mysqld Command-Line Options

When you start the mysqld server, you can specify program options using any of the methods described in section 4.3 Specifying Program Options. The most common methods are to provide options in an option file or on the command line. However, in most cases it is desirable to make sure that the server uses the same options each time it runs. The best way to ensure this is to list them in an option file. See section 4.3.2 Using Option Files.

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

mysqld accepts many command-line options. For a list, execute mysqld --help. Before MySQL 4.1.1, --help prints the full help message. As of 4.1.1, it prints a brief message; to see the full list, use mysqld --verbose --help.

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

• Options that affect security: See section 5.4.3 Startup Options for mysqld Concerning Security.
• SSL-related options: See section 5.6.7.5 SSL Command-Line Options.
• Binary log control options: See section 5.9.4 The Binary Log.
• Replication-related options: See section 6.8 Replication Startup Options.
• Options specific to particular storage engines: See section 14.1.1 MyISAM Startup Options, section 14.4.3 BDB Startup Options, section 15.5 InnoDB Startup Options.

You can also set the value of a server system variable by using the variable name as an option, as described later in this section.

--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 1.5.3 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 5.8.1 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.

--character-set-server=charset

Use charset as the default server character set. This option is available as of MySQL 4.1.3. See section 5.8.1 The Character Set Used for Data and Sorting.

--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 5.1.3 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.

--collation-server=collation

Use collation as the default server collation. This option is available as of MySQL 4.1.3. See section 5.8.1 The Character Set Used for Data and Sorting.

--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'. See section E.1.2 Creating Trace Files.

--default-character-set=charset

Use charset as the default character set. This option is deprecated in favor of --character-set-server as of MySQL 4.1.3. See section 5.8.1 The Character Set Used for Data and Sorting.

--default-collation=collation

Use collation as the default collation. This option is deprecated in favor of --collation-server as of MySQL 4.1.3. See section 5.8.1 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 section 14 MySQL Storage Engines and Table Types.

--default-time-zone=type

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 will be the same as the system time zone (given by the value of the system_time_zone system variable. This option is available as of MySQL 4.1.3.

--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 7.5.2 Tuning Server Parameters. See section 14.1.1 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, XP, and 2003 systems, and can be used only with the mysqld-nt and mysqld-max-nt servers that support named pipe connections.

--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!

--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:

• You should not use the query cache for queries that use tables that are updated by another process.
• You should not use --delay-key-write=ALL or DELAY_KEY_WRITE=1 on any shared tables.

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

--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.

--innodb-safe-binlog

Adds consistency guarantees between the content of InnoDB tables and the binary log. See section 5.9.4 The Binary Log.

--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 5.8.2 Setting the Error Message Language.

--log[=file], -l [file]

Log connections and queries to this file. See section 5.9.2 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 5.9.4 The Binary Log. If you don't specify a filename, MySQL will use host_name-bin as the log file basename.

--log-bin-index[=file]

The index file for binary log filenames. See section 5.9.4 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 5.9.1 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, 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 5.9.5 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 this file. See section 5.9.5 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 5.9.3 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 5.9.4 The Binary Log. Starting from version 5.0.0, using --log-update will just turn on the binary log instead (see section D.1.4 Changes in release 5.0.0 (22 Dec 2003: Alpha)).

--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 4.0.19 and 4.1.2; to disable it, use --skip-log-warnings. As of MySQL 4.0.21 and 4.1.3, aborted connections are not logged to the error log unless the value is greater than 1. 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 7.3.2 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 is normally 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, open 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:

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 will 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 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.

--ndb-connectstring=connect_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 16.3.4.2 The MySQL Cluster connectstring for syntax.

--ndbcluster

If the binary includes support for the NDB Cluster storage engine (from version 4.1.3, the MySQL-Max binaries are built with NDB Cluster enabled) the default disabling of support for the NDB Cluster storage engine can be overruled by using this option. Using the NDB Cluster storage engine is necessary for using MySQL Cluster. See section 16 MySQL Cluster.

--new

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:

• Hexadecimal strings such as 0xFF are treated as strings by default rather than as numbers. (Works in 4.0.12 and up.)
• TIMESTAMP is returned as a string with the format 'YYYY-MM-DD HH:MM:SS'. (Works in 4.0.13 and up.) See section 11 Column Types.

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 2.10.6 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. See section E.1 Debugging a MySQL Server.

--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 5.5.3 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.

--shared-memory

Enable shared-memory connections by local clients. This option is available only on Windows. It was added in MySQL 4.1.0.

--shared-memory-base-name=name

The name to use for shared-memory connections. This option is available only on Windows. It was added in MySQL 4.1.0.

--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 7.5.2 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 7.5.6 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 7.5.6 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, this means that the system will only allocate memory and other resources for this storage engine if it is explicitly enabled.

--skip-networking

Don't listen for TCP/IP connections at all. All interaction with mysqld must be made via named pipes or shared memory (on Windows) or Unix socket files (on Unix). This option is highly recommended for systems where only local clients are allowed. See section 7.5.6 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:

• On Windows, enabling symbolic links allows you to establish a symbolic link to a database directory by creating a directory.sym file that contains the path to the real directory. See section 7.6.1.3 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 13.2.6 CREATE TABLE Syntax.

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. See section E.1 Debugging a MySQL Server.

--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 5.2.2 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. See section 13.4.6 SET TRANSACTION Syntax.

--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 5.4.1 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.

As of MySQL 4.0, 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 setting a variable to a value, MySQL might automatically correct it to stay within a given range, or adjust the value to the closest allowable value if only certain values are allowed.

It is also possible to set variables by using --set-variable=var_name=value or -O var_name=value syntax. However, this syntax is deprecated as of MySQL 4.0.

You can find a full description for all variables in section 5.2.3 Server System Variables. The section on tuning server parameters includes information on how to optimize them. See section 7.5.2 Tuning Server Parameters.

You can change the values of most system variables for a running server with the SET statement. See section 13.5.3 SET Syntax.

If you want to restrict the maximum value that a startup option can be set to with SET, you can define this by using the --maximum-var_name command-line option.

5.2.2 The Server SQL Mode

The MySQL server can operate in different SQL modes, and (as of MySQL 4.1) can apply these modes differentially for different clients. This allows an application to tailor server operation to its own requirements.

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

You can set the default SQL mode by starting mysqld with the --sql-mode="modes" option. The value also can be empty (--sql-mode="") if you want to reset it.

Beginning with MySQL 4.1, you can also change the SQL mode after startup time by setting the sql_mode variable with a SET [SESSION|GLOBAL] sql_mode='modes' statement. 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 session sql_mode value.

modes is a list of different modes separated by comma (`,') characters. You can retrieve the current mode by issuing a SELECT @@sql_mode statement. The default value is empty (no modes set).

The most important sql_mode values are probably these:

ANSI

Change syntax and behavior to be more conformant to standard SQL. (New in MySQL 4.1.1)

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. (New in MySQL 5.0.2)

TRADITIONAL

Make MySQL behave like a ``traditional'' SQL database system. A simple description of this mode is ``give an error instead of a warning'' when inserting an incorrect value into a column. Note: The INSERT/UPDATE will abort 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 will not be rolled back, resulting in a ``partially-done'' update. (New in MySQL 5.0.2)

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

The following list describes all the supported modes:

ALLOW_INVALID_DATES

Don't do full checking of dates in strict mode. Check only that the month is in the range from 1 to 12 and the day is in the range from 1 to 31. This is very convenient for Web applications where you obtain year, month, and day in three different fields and you want to store exactly what the user inserted (without date validation). This mode applies to DATE and DATETIME columns. It does not apply TIMESTAMP columns, which always require a valid date. This mode is new in MySQL 5.0.2. Before 5.0.2, this was the default MySQL date-handling mode. As of 5.0.2, enabling strict mode causes the server to require that month and day values be legal, not just in the range from 1 to 12 and 1 to 31. For example, '2004-04-31' is legal with strict mode disabled, but illegal with strict mode enabled. To allow such dates in strict mode, enable ALLOW_INVALID_DATES as well.

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)

ERROR_FOR_DIVISION_BY_ZERO

Produce an error in strict mode (otherwise a warning) when we encounter a division by zero (or MOD(X,0)) during an INSERT/ UPDATE. If this mode is not given, MySQL instead returns NULL for divisions by zero. If used with IGNORE, MySQL generates a warning for divisions by zero, but the result of the operation is NULL. (New in MySQL 5.0.2)

HIGH_NOT_PRECEDENCE

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

mysql> SET sql_mode = '';
mysql> SELECT NOT 1 BETWEEN -5 AND 5;
        -> 0
mysql> SET sql_mode = 'broken_not';
mysql> SELECT NOT 1 BETWEEN -5 AND 5;
        -> 1

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_CREATE_USER

Prevent GRANT from automatically creating new users if it would otherwise do so, unless a password also is specified. (New in MySQL 5.0.2)

NO_AUTO_VALUE_ON_ZERO

NO_AUTO_VALUE_ON_ZERO affects handling of AUTO_INCREMENT columns. Normally, you generate the next sequence number for the column by inserting either NULL or 0 into it. NO_AUTO_VALUE_ON_ZERO suppresses this behavior for 0 so that only NULL generates the next sequence number. (New in MySQL 4.1.1) 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, MySQL normally 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 a statement in the dump output to enable NO_AUTO_VALUE_ON_ZERO.

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. See section 12.7 Cast Functions and Operators. (New in MySQL 4.0.2)

NO_ZERO_DATE

Don't allow '0000-00-00' as a valid date. You can still insert zero dates with the IGNORE option. (New in MySQL 5.0.2)

NO_ZERO_IN_DATE

Don't accept dates where the month or day part is 0. If used with the IGNORE option, we insert a '0000-00-00' date for any such date. (New in MySQL 5.0.2)

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)

STRICT_ALL_TABLES

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

STRICT_TRANS_TABLES

Enable strict mode for transactional storage engines, and when possible for non-transactional storage engines. Additional detail follows. (New in MySQL 5.0.2)

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

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

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

• For STRICT_ALL_TABLES, MySQL returns an error and ignores the rest of the rows. However, in this case, the earlier rows will already 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 13.2.6 CREATE TABLE Syntax.

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 13.5.4.20 SHOW WARNINGS Syntax.

The following special modes are provided as shorthand for combinations of mode values from the preceding list. All are available as of MySQL 4.1.1, except TRADITIONAL (5.0.2).

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

ANSI

Equivalent to REAL_AS_FLOAT, PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, ONLY_FULL_GROUP_BY. See section 1.5.3 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.

5.2.3 Server System Variables

The server maintains many system variables that indicate how it is configured. All of them have default values. They can be set at server startup using options on the command line or in option files. Most of them can be set at runtime using the SET statement.

Beginning with MySQL 4.0.3, the mysqld server maintains two kinds of variables. Global variables affect the overall operation of the server. Session variables affect its operation for individual client connections.

When the server starts, it initializes all global variables to their default values. These defaults can be changed by options specified in option files or on the command line. After the server starts, those global variables that are dynamic can be changed by connecting to the server and issuing a SET GLOBAL var_name statement. To change a global variable, you must have the SUPER privilege.

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 those session variables that are dynamic, the client can change them by issuing a SET SESSION var_name statement. Setting a session variable requires no special privilege, but a client can change only its own session variables, not those of any other client.

A change to a global variable is visible to any client that accesses that global variable. However, it affects the corresponding session variable that is initialized from the global variable only for clients that connect after the change. It does not affect the session variable for any client that is already connected (not even that of the client that issues the SET GLOBAL statement).

When setting a variable using a startup option, variable values can be given with a suffix of K, M, or G to indicate kilobytes, megabytes, or gigabytes, respectively. For example, the following command starts the server with a key buffer size of 16 megabytes:

mysqld --key_buffer_size=16M

Before MySQL 4.0, use this syntax instead:

mysqld --set-variable=key_buffer_size=16M

The lettercase of suffix letters does not matter; 16M and 16m are equivalent.

At runtime, use the SET statement to set system variables. In this context, suffix letters cannot be used, but the value can take the form of an expression:

mysql> SET sort_buffer_size = 10 * 1024 * 1024;

To specify explicitly whether to set the global or session variable, use the GLOBAL or SESSION options:

mysql> SET GLOBAL sort_buffer_size = 10 * 1024 * 1024;
mysql> SET SESSION sort_buffer_size = 10 * 1024 * 1024;

Without either option, the statement sets the session variable.

The variables that can be set at runtime are listed in section 5.2.3.1 Dynamic System Variables.

If you want to restrict the maximum value to which a system variable can be set with the SET statement, you can specify this maximum by using an option of the form --maximum-var_name 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. This feature is available as of MySQL 4.0.2.

You can view system variables and their values by using the SHOW VARIABLES statement. See section 9.4 System Variables for more information.

mysql> SHOW VARIABLES;
+---------------------------------+------------------------------+
| Variable_name                   | Value                        |
+---------------------------------+------------------------------|
| back_log                        | 50                           |
| basedir                         | /usr/local/mysql             |
| bdb_cache_size                  | 8388572                      |
| bdb_home                        | /usr/local/mysql             |
| bdb_log_buffer_size             | 32768                        |
| bdb_logdir                      |                              |
| bdb_max_lock                    | 10000                        |
| bdb_shared_data                 | OFF                          |
| bdb_tmpdir                      | /tmp/                        |
| bdb_version                     | Sleepycat Software: ...      |
| binlog_cache_size               | 32768                        |
| bulk_insert_buffer_size         | 8388608                      |
| character_set                   | latin1                       |
| character_sets                  | latin1 big5 czech euc_kr     |
| concurrent_insert               | ON                           |
| connect_timeout                 | 5                            |
| convert_character_set           |                              |
| datadir                         | /usr/local/mysql/data/       |
| default_week_format             | 0                            |
| delay_key_write                 | ON                           |
| delayed_insert_limit            | 100                          |
| delayed_insert_timeout          | 300                          |
| delayed_queue_size              | 1000                         |
| flush                           | OFF                          |
| flush_time                      | 0                            |
| ft_boolean_syntax               | + -><()~*:""&|               |
| ft_max_word_len                 | 84                           |
| ft_min_word_len                 | 4                            |
| ft_query_expansion_limit        | 20                           |
| ft_stopword_file                | (built-in)                   |
| have_bdb                        | YES                          |
| have_innodb                     | YES                          |
| have_isam                       | YES                          |
| have_openssl                    | YES                          |
| have_query_cache                | YES                          |
| have_raid                       | NO                           |
| have_symlink                    | DISABLED                     |
| init_file                       |                              |
| innodb_additional_mem_pool_size | 1048576                      |
| innodb_buffer_pool_size         | 8388608                      |
| innodb_data_file_path           | ibdata1:10M:autoextend       |
| innodb_data_home_dir            |                              |
| innodb_fast_shutdown            | ON                           |
| innodb_file_io_threads          | 4                            |
| innodb_flush_log_at_trx_commit  | 1                            |
| innodb_flush_method             |                              |
| innodb_force_recovery           | 0                            |
| innodb_lock_wait_timeout        | 50                           |
| innodb_log_arch_dir             |                              |
| innodb_log_archive              | OFF                          |
| innodb_log_buffer_size          | 1048576                      |
| innodb_log_file_size            | 5242880                      |
| innodb_log_files_in_group       | 2                            |
| innodb_log_group_home_dir       | ./                           |
| innodb_mirrored_log_groups      | 1                            |
| innodb_thread_concurrency       | 8                            |
| interactive_timeout             | 28800                        |
| join_buffer_size                | 131072                       |
| key_buffer_size                 | 16773120                     |
| key_cache_age_threshold         | 300                          |
| key_cache_block_size            | 1024                         |
| key_cache_division_limit        | 100                          |
| language                        | /usr/local/mysql/share/...   |
| large_files_support             | ON                           |
| local_infile                    | ON                           |
| locked_in_memory                | OFF                          |
| log                             | OFF                          |
| log_bin                         | OFF                          |
| log_slave_updates               | OFF                          |
| log_slow_queries                | OFF                          |
| log_update                      | OFF                          |
| log_warnings                    | 1                            |
| long_query_time                 | 10                           |
| low_priority_updates            | OFF                          |
| lower_case_table_names          | 0                            |
| max_allowed_packet              | 1047552                      |
| max_binlog_cache_size           | 4294967295                   |
| max_binlog_size                 | 1073741824                   |
| max_connect_errors              | 10                           |
| max_connections                 | 100                          |
| max_delayed_threads             | 20                           |
| max_error_count                 | 64                           |
| max_heap_table_size             | 16777216                     |
| max_join_size                   | 4294967295                   |
| max_relay_log_size              | 0                            |
| max_sort_length                 | 1024                         |
| max_tmp_tables                  | 32                           |
| max_user_connections            | 0                            |
| max_write_lock_count            | 4294967295                   |
| myisam_max_extra_sort_file_size | 268435456                    |
| myisam_max_sort_file_size       | 2147483647                   |
| myisam_recover_options          | force                        |
| myisam_repair_threads           | 1                            |
| myisam_sort_buffer_size         | 8388608                      |
| net_buffer_length               | 16384                        |
| net_read_timeout                | 30                           |
| net_retry_count                 | 10                           |
| net_write_timeout               | 60                           |
| open_files_limit                | 1024                         |
| pid_file                        | /usr/local/mysql/name.pid    |
| port                            | 3306                         |
| protocol_version                | 10                           |
| query_cache_limit               | 1048576                      |
| query_cache_size                | 0                            |
| query_cache_type                | ON                           |
| read_buffer_size                | 131072                       |
| read_rnd_buffer_size            | 262144                       |
| rpl_recovery_rank               | 0                            |
| server_id                       | 0                            |
| skip_external_locking           | ON                           |
| skip_networking                 | OFF                          |
| skip_show_database              | OFF                          |
| slave_net_timeout               | 3600                         |
| slow_launch_time                | 2                            |
| socket                          | /tmp/mysql.sock              |
| sort_buffer_size                | 2097116                      |
| sql_mode                        |                              |
| table_cache                     | 64                           |
| table_type                      | MYISAM                       |
| thread_cache_size               | 3                            |
| thread_stack                    | 131072                       |
| timezone                        | EEST                         |
| tmp_table_size                  | 33554432                     |
| tmpdir                          | /tmp/:/mnt/hd2/tmp/          |
| tx_isolation                    | READ-COMMITTED               |
| version                         | 4.0.4-beta                   |
| wait_timeout                    | 28800                        |
+---------------------------------+------------------------------+

Most system variables are described here. Variables with no version indicated have been present since at least MySQL 3.22. InnoDB system variables are listed at section 15.5 InnoDB Startup Options.

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

Information on tuning these variables can be found in section 7.5.2 Tuning Server Parameters.

ansi_mode

This is ON if mysqld was started with --ansi. See section 1.5.3 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

See the description for version_bdb.

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 5.9.4 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 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 and removed in MySQL 4.1.1. (Use SHOW CHARACTER SET for a list of character sets.)

character_sets_dir

The directory where character sets are installed. This variable was added in MySQL 4.1.2.

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_insert

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

convert_character_set

The current character set mapping that was set by SET CHARACTER SET. This variable was removed in MySQL 4.1.

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.

Option	Description
OFF	DELAYED_KEY_WRITE is ignored.
ON	MySQL honors the DELAY_KEY_WRITE option for CREATE TABLE. 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, 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 5.2.1 mysqld Command-Line Options and section 14.1.1 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

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 will wait until there is room in the queue again.

expire_logs_days

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. This variable was added in MySQL 4.1.0.

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. See section 12.6.1 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

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_archive

YES if mysqld supports ARCHIVE tables, NO if not. This variable was added in MySQL 4.1.3.

have_bdb

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

have_compress

Whether the zlib compression library is available to the server. If not, the COMPRESS() and UNCOMPRESS() functions cannot be used. This variable was added in MySQL 4.1.1.

have_crypt

Whether the crypt() system call is available to the server. If not, the CRYPT() function cannot be used. This variable was added in MySQL 4.0.10.

have_csv

YES if mysqld supports ARCHIVE tables, NO if not. This variable was added in MySQL 4.1.4.

have_example_engine

YES if mysqld supports EXAMPLE tables, NO if not. This variable was added in MySQL 4.1.4.

have_geometry

Whether the server supports spatial data types. This variable was added in MySQL 4.1.3.

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_ndbcluster

YES if mysqld supports NDB Cluster tables. DISABLED if --skip-ndbcluster is used. This variable was added in MySQL 4.1.2.

have_openssl

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

have_query_cache

YES if mysqld supports the query cache. This variable was added in MySQL 4.0.2.

have_raid

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

have_rtree_keys

Whether RTREE indexes are available. (These are used for spatial indexed in MyISAM tables.) This variable was added in MySQL 4.1.3.

have_symlink

Whether symbolic link support is enabled. This is required on Unix for support of the DATA DIRECTORY and INDEX DIRECTORY table options. This variable was added in MySQL 4.0.0.

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'

Note that the content of init_connect is not executed for users having the SUPER privilege; this is in case that content has been wrongly set (contains a wrong query, for example with a syntax error), thus making all connections fail. Not executing it for SUPER users enables those to open a connection and fix init_connect. 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 at section 15.5 InnoDB 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). 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.

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