This chapter covers topics that deal with administering a MySQL installation, such as configuring the server, managing user accounts, and performing backups.
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.
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
mysqld-max
mysqld-max Extended MySQL Server.
mysqld_safe
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
mysqld_safe to start the MySQL server.
See section 5.1.4 The mysql.server Server Startup Script.
mysqld_multi
mysqld_multi Program for Managing Multiple MySQL Servers.
mysql_install_db
mysql_fix_privilege_tables
There are several other programs that also are run on the server host:
myisamchk
MyISAM tables.
myisamchk is described in
section 5.6.2 Using myisamchk for Table Maintenance and Crash Recovery.
make_binary_distribution
support.mysql.com for the
convenience of other MySQL users.
mysqlbug
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:
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://www.mysql.com/downloads/mysql-4.0.html.
See section 2.2.1 Installing MySQL on Windows.
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 2.2.2 Installing MySQL on Linux for more
information on the Linux RPM packages.
mysqld but that has the additional features included.
You can find the MySQL-Max binaries on the MySQL AB Web site at http://www.mysql.com/downloads/mysql-4.0.html.
MySQL AB builds the MySQL-Max servers by using the following
configure options:
--with-server-suffix=-max
-max suffix to the mysqld version string.
--with-innodb
InnoDB storage engine. MySQL-Max
servers always include InnoDB support, but this option actually is
used only for MySQL 3.23 because InnoDB is not included by default
until MySQL 4. 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
BDB) storage engine.
CFLAGS=-DUSE_SYMDIR
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:
| System | BDB Support
|
| AIX 4.3 | N |
| HP-UX 11.0 | N |
| Linux-Alpha | N |
| Linux-IA-64 | N |
| Linux-Intel | Y |
| Mac OS X | N |
| NetWare | N |
| SCO OSR5 | Y |
| Solaris-Intel | N |
| Solaris-SPARC | Y |
| UnixWare | Y |
| Windows/NT | Y |
To find out which storage engines your server supports, issue the following statement:
mysql> SHOW ENGINES;
Before MySQL 4.1.2, 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:
| Value | Meaning |
YES | The feature is supported and is active. |
NO | The feature is not supported. |
DISABLED | The feature is supported but has been disabled. |
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
hostname.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 16.3 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 15.4.3 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.
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 run-time
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:
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.
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.
Note that 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 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, though 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
--core-file-size=size
mysqld should be able to create. The option
value is passed to ulimit -c.
--datadir=path
--defaults-extra-file=path
--defaults-file=path
--err-log=path
--log-error option, to be used before MySQL 4.0.
--ledir=path
mysqld program.
Use this option to explicitly indicate the location of the server.
--log-error=path
--mysqld=prog_name
ledir directory) that you
want to start.
--mysqld-version=suffix
--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
nice program to set the server's scheduling priority to the
given value. This option was added in MySQL 4.0.14.
--no-defaults
--open-files-limit=count
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
--port=port_num
--socket=path
--timezone=zone
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}
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 distributoins typically install the server
in slightly different locations.
(See section 2.1.8 Installation Layouts.)
mysqld_safe expects one of the following conditions to be true:
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).
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:
MyISAM and ISAM tables.
mysqld, monitors it, and restarts it if it terminates in error.
mysqld to the `hostname.err' file in the
data directory.
mysqld_safe screen output to the `hostname.safe' file in the
data directory.
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.
Note that 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 2.2.2 Installing MySQL on Linux for more information on the Linux RPM packages.
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 2.4.2.2 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, though you should rename such
sections to [mysql.server] when you begin using MySQL 4.0 or later.)
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 distinquish 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 2.4.2.2 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 5.9 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 start 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
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
--help
--log=name
--mysqladmin=prog_name
mysqladmin binary to be used to stop servers.
--mysqld=prog_name
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 you have the directory where mysqld is
located in your PATH
environment variable setting or fix mysqld_safe.
--no-log
--password=password
mysqladmin.
Note that the password value is not optional for this option, unlike for other MySQL clients.
--tcp-ip
stop and
report operations.
--user=user_name
mysqladmin.
--version
Some notes about mysqld_multi:
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 5.4.2 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.
--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.
mysqld.
--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.
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 5.9 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.
This section discusses MySQL server configuration topics:
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 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:
mysqld Concerning Security.
MyISAM Startup Options,
section 15.4.3 BDB Startup Options,
section 16.5 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, -?
--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
--sql-mode
option instead.
--basedir=path, -b path
--big-tables
--bind-address=IP
--console
--log-error
is specified. On Windows, mysqld will not close the console screen if
this option is used.
--character-sets-dir=path
--chroot=path
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
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.
--datadir=path, -h path
--debug[=debug_options], -# [debug_options]
--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,filename'.
See section D.1.2 Creating Trace Files.
--default-character-set=charset
charset as the default character set. See section 5.7.1 The Character Set Used for Data and Sorting.
--default-collation=collation
collation as the default collation.
This option is available as of MySQL 4.1.1.
See section 5.7.1 The Character Set Used for Data and Sorting.
--default-storage-engine=type
--default-table-type.
It is available as of MySQL 4.1.2.
--default-table-type=type
--delay-key-write[= OFF | ON | ALL]
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 15.1.1 MyISAM Startup Options.
NOTE: If you set this variable to ALL, you should not use
MyISAM tables from another program (like 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
--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
DES_ENCRYPT() and DES_DECRYPT()
from this file.
--enable-external-locking
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:
--delay-key-write=ALL or DELAY_KEY_WRITE=1
on any shared tables.
--enable-locking
together with --delay-key-write=OFF --query-cache-size=0.
(This is not done by default as in many setups it's useful to have a mixture
of the above options).
--enable-named-pipe
mysqld-nt and mysqld-max-nt servers that support
named pipe connections.
--exit-info, -T
mysqld server. Do not use this option unless you know
exactly what it does!
--flush
--init-file=file
--language=lang_name, -L lang_name
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 5.7.2 Setting the Error Message Language.
--log[=file], -l [file]
hostname.log as filename.
--log-bin=[file]
hostname-bin as filename.
--log-bin-index[=file]
hostname-bin.index as
filename.
--log-error[=file]
hostname.err as filename.
--log-isam[=file]
ISAM/MyISAM changes to this file (used only when
debugging ISAM/MyISAM).
--log-long-format
--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
queries log.
--log-queries-not-using-indexes
--log-slow-queries, then also
queries that are not using indexes are logged to the slow query log. This
option is available as of MySQL 4.1. See section 5.8.5 The Slow Query Log.
--log-short-format
--log-slow-queries[=file]
long_query_time seconds
to execute to file. Note that the default for the amount of information
logged has changed in MySQL 4.1. See the --log-long-format and
--log-long-format options for details. See section 5.8.5 The Slow Query Log.
--log-update[=file]
file.# where # is a unique number if not
given. See section 5.8.3 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 5.8.4 The Binary Log. Starting from version 5.0.0,
using --log-update will just turn on the binary log instead
(see section C.1.2 Changes in release 5.0.0 (22 Dec 2003: Alpha)).
--log-warnings, -W
Aborted connection... to the
`.err' file. 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). See section A.2.11 Communication Errors / Aborted Connection.
This option was named --warnings before MySQL 4.0.
--low-priority-updates
INSERT/DELETE/UPDATE)
will have lower priority than selects. It can also be done via
{INSERT | REPLACE | UPDATE | DELETE} 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
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...]]]
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, seprate them by commas.
You can also use a value of "" to disable this
option. If this option is used, mysqld will on open check if the
table is marked as crashed or if the table 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
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 table was changed during recover, save a backup of the `tbl_name.MYD' datafile 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. |
BACKUP,FORCE. This will force a repair of a table even if some rows
would be deleted, but it will keep the old datafile as a backup so that
you can later examine what happened.
--new
--new option can be used to make the server
behave as 4.1 in certain respects, easing a 4.0 to 4.1 upgrade:
TIMESTAMP is returned as a string with the format
'YYYY-MM-DD HH:MM:SS'.
See section 12 Column Types.
--pid-file=path
mysqld_safe.
--port=num, -P num
--old-protocol, -o
--one-thread
--open-files-limit=
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
--safe-show-database
SHOW DATABASES statement returns only those
databases for which the user has some kind of privilege.
From version 4.0.2 this option is deprecated and doesn't do anything
(the option is enabled by default) as we now have the
SHOW DATABASES privilege. See section 14.5.1.2 GRANT and REVOKE Syntax.
--safe-user-create
GRANT
statement, if the user doesn't have INSERT privilege to the
mysql.user table or any column in this table.
--skip-bdb
BDB storage engine. This saves memory and might speed
up some operations.
Do not use this operation if you require BDB tables.
--skip-concurrent-insert
MyISAM
tables. (This is only to be used if you think you have found a bug in this
feature.)
--skip-delay-key-write
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
isamchk or myisamchk you must
shut down the server. See section 1.2.3 MySQL Stability. Note that in MySQL Version
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
mysqladmin
flush-privileges or mysqladmin reload command, or by issuing a
FLUSH PRIVILEGES statement.)
--skip-host-cache
--skip-innodb
InnoDB storage engine. This saves memory and disk
space and might speed up some operations.
Do not use this operation if you require InnoDB tables.
--skip-isam
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
Host column values in the
grant tables must be IP numbers or localhost. See section 7.5.5 How MySQL uses DNS.
--skip-networking
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 7.5.5 How MySQL uses DNS.
--skip-new
--skip-symlink
--skip-symbolic-links, for use before MySQL
4.0.13.
--symbolic-links, --skip-symbolic-links
directory.sym file that contains the path to the real directory.
See section 7.6.1.3 Using Symbolic Links for Databases on Windows.
MyISAM index file or datafile 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 14.2.5 CREATE TABLE Syntax.
--skip-safemalloc
--with-debug=full, all MySQL programs
checks 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
SHOW DATABASES statement, unless the user has the
SHOW DATABASES privilege.
--skip-stack-trace
mysqld under a debugger. On some systems, you also must use
this option to get a core file. See section D.1 Debugging a MySQL server.
--skip-thread-priority
--socket=path
MySQL.
--sql-mode=value[,value[,value...]]
--temp-pool
--transaction-isolation=level
READ-UNCOMMITTED,
READ-COMMITTED,
REPEATABLE-READ, or
SERIALIZABLE.
See section 14.4.6 SET TRANSACTION Syntax.
--tmpdir=path, -t path
/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}
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 5.3.1 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
You can assign a value to a server system variables 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 14.5.3.1 SET Syntax.
If you want to restrict the maximum value a startup option can be set to
with SET, you can define this by using the
--maximum-var_name command-line option.
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 applications to tailor server operation to their 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. Beginning with MySQL 4.1, you can also
change the mode after startup time by setting the sql_mode variable
with a SET [SESSION|GLOBAL] sql_mode='modes' statement.
Setting the GLOBAL variable affects the operation of all clients that
connect from that time on. Setting the SESSION variable affects only
the current client.
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 value also can be empty
(--sql-mode="") if you want to reset it.
The following list describes the supported modes:
ANSI_QUOTES
ANSI_QUOTES
enabled, you cannot use double quotes to quote a literal string, because it
will be intepreted as an identifier.
(New in MySQL 4.0.0.)
IGNORE_SPACE
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
INDEX DIRECTORY and DATA
DIRECTORY directives. This option is useful on slave replication servers.
(New in MySQL 4.0.15.)
NO_FIELD_OPTIONS
SHOW CREATE
TABLE. This mode is used by mysqldump in portability mode.
(New in MySQL 4.1.1.)
NO_KEY_OPTIONS
SHOW CREATE
TABLE. This mode is used by mysqldump in portability mode.
(New in MySQL 4.1.1.)
NO_TABLE_OPTIONS
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
UNSIGNED if one
of the operands is unsigned. Note that this makes UNSIGNED BIGINT not
100% usable in all contexts. See section 13.7 Cast Functions.
(New in MySQL 4.0.2.)
ONLY_FULL_GROUP_BY
GROUP BY part refers to a not
selected column.
(New in MySQL 4.0.0.)
PIPES_AS_CONCAT
|| as a string concatenation operator (same as CONCAT())
rather than as a synonym for OR.
(New in MySQL 4.0.0.)
REAL_AS_FLOAT
REAL as a synonym for FLOAT rather than as a synonym for
DOUBLE.
(New in MySQL 4.0.0.)
The following special modes are provided as shorthand for combinations of mode values from the preceding list. They are available as of MySQL 4.1.1.
ANSI
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
PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS.
MAXDB
PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS.
MSSQL
PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS.
MYSQL323
NO_FIELD_OPTIONS.
MYSQL40
NO_FIELD_OPTIONS.
ORACLE
PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS.
POSTGRESQL
PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS.
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 intialized 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. 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 at
startup 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. Many variables have both global and
session values. See section 10.4 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 | OFF | | 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. InnoDB system variables
are listed at
section 16.5 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.
The system variables have the following meanings. Variables with no version indicated have been present since at least MySQL 3.22.
ansi_mode
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.
back_log
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(2) 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
--basedir option.
bdb_cache_size
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
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
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
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
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
ON if you are using --bdb-shared-data.
This variable was added in MySQL 3.23.29.
bdb_tmpdir
--bdb-tmpdir option.
This variable was added in MySQL 3.23.14.
bdb_version
binlog_cache_size
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 5.8.4 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
character_set_xxx variables.
character_set_client
character_set_connection
character_set_database
character_set_server.
This variable was added in MySQL 4.1.1.
character_set_results
character_set_server
character_set_system
utf8.
This variable was added in MySQL 4.1.1.
character_sets
collation_connection
collation_database
collation_server.
This variable was added in MySQL 4.1.1.
collation_server
concurrent_inserts
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
mysqld server waits for a connect
packet before responding with Bad handshake.
datadir
--datadir option.
default_week_format
WEEK() function.
This variable is available as of MySQL 4.0.14.
delay_key_write
MyISAM tables. It can have one of the
following values to affect handling of the DELAY_KEY_WRITE table
option that can be given 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.
|
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. See section 15.1.1 MyISAM Startup Options.
Note that --external-lock doesn't offer any protection against
index corruption for tables that uses delayed key writes.
This variable was added in MySQL 3.23.8.
delayed_insert_limit
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
INSERT DELAYED handler thread should wait for
INSERT statements before terminating.
delayed_queue_size
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
ON if you have started mysqld with the --flush
option.
This variable was added in MySQL 3.22.9.
flush_time
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
IN BOOLEAN MODE.
This variable was added in MySQL 4.0.1.
See section 13.6.1 Boolean Full-text Searches.
The default variable value is '+ -><()~*:""&|'. The rules for
changing the value are as follows:
ft_max_word_len
FULLTEXT index.
This variable was added in MySQL 4.0.0.
Note: FULLTEXT indexes must be rebuilt after changing
this variable.
ft_min_word_len
FULLTEXT index.
This variable was added in MySQL 4.0.0.
Note: FULLTEXT indexes must be rebuilt after changing
this variable.
ft_query_expansion_limit
WITH QUERY EXPANSION.
This variable was added in MySQL 4.1.1.
ft_stopword_file
'') disables stopword filtering. This variable was added in
MySQL 4.0.10.
Note: FULLTEXT indexes must be rebuilt after changing
this variable.
group_concat_max_len
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_innodb
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
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'
init_file
--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
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
InnoDB system variables are listed at
section 16.5 InnoDB Startup Options.
interactive_timeout
CLIENT_INTERACTIVE option to
mysql_real_connect(). See also wait_timeout.
join_buffer_size
key_buffer_size
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. Remember that
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. See section 14.4.5 LOCK TABLES and UNLOCK TABLES Syntax.
You can check the performance of the key buffer by issuing a SHOW
STATUS statement and examining the Key_read_requests,
Key_reads, Key_write_requests, and Key_writes status
variables.
See section 14.5.3 SET and SHOW Syntax.
The Key_reads/Key_read_requests ratio should normally be
less than 0.01. The Key_writes/Key_write_requests ratio is usually
near 1 if you are using mostly updates and deletes, but might be much
smaller if you tend to do updates that affect many rows at the same time or
if you are using the DELAY_KEY_WRITE table option.
The fraction of the key buffer in use can be determined using
key_buffer_size in conjunction with the Key_blocks_used status
variable and the buffer blocksize. 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_sizeBefore 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_sizeSee section 7.4.6 The
MyISAM Key Cache.
key_cache_age_threshold
MyISAM Key Cache.
key_cache_block_size
MyISAM Key Cache.
key_cache_division_limit
MyISAM Key Cache.
language
large_file_support
mysqld was compiled with options for big file support.
This variable was added in MySQL 3.23.28.
local_infile
LOCAL is supported for LOAD DATA INFILE statements.
This variable was added in MySQL 4.0.3.
locked_in_memory
mysqld was locked in memory with --memlock.
This variable was added in MySQL 3.23.25.
log
log_bin
log_slave_updates
log_slow_queries
long_query_time variable.
This variable was added in MySQL 4.0.2.
See section 5.8.5 The Slow Query Log.
log_update
long_query_time
Slow_queries counter
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 5.8.5 The Slow Query Log.
low_priority_updates
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
lower_case_table_names to 2.
max_allowed_packet
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 or
long strings. 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
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
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
FLUSH HOSTS statement.
max_connections
mysqld requires. See
section 7.4.8 How MySQL Opens and Closes Tables for comments on file descriptor limits.
See section A.2.7 Too many connections.
max_delayed_threads
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
SHOW ERRORS or SHOW WARNINGS.
This variable was added in MySQL 4.1.0.
max_heap_table_size
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
max_delayed_threads.
It was added in MySQL 4.0.19.
max_join_size
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 will
not burden the server to send it to the client.
This variable previously was named sql_max_join_size.
max_relay_log_size
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 6.3 Replication Implementation Details.
max_seeks_for_key
max_sort_length
BLOB or TEXT
values. Only the first max_sort_length bytes of each value
are used; the rest are ignored.
max_tmp_tables
max_user_connections
max_write_lock_count
myisam_max_extra_sort_file_size
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
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
--myisam-recover option.
This variable was added in MySQL 3.23.36.
myisam_repair_threads
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
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
net_buffer_length
max_allowed_packet bytes.
net_read_timeout
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
net_write_timeout
net_read_timeout.
This variable was added in MySQL 3.23.20.
open_files_limit
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
--pid-file option.
This variable was added in MySQL 3.23.23.
port
--port option.
protocol_version
query_alloc_block_size
query_cache_limit
query_cache_min_res_unit
query_cache_size
query_cache_type is set to 0.
This variable was added in MySQL 4.0.1.
query_cache_type
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.
| Option | Description |
0 or OFF | Don't cache or retrieve results.
Note that this will not deallocate the query cache buffer. To
do that, you should set query_cache_size to 0.
|
1 or ON | Cache all query results except for those that
begin with SELECT SQL_NO_CACHE.
|
2 or DEMAND | Cache results only for queries that
begin with SELECT SQL_CACHE.
|
query_cache_wlock_invalidate
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
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
read_buffer_size
record_buffer.
read_only
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
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
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
--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.
Note that 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
--server-id option. It is used for master and slave
replication servers.
This variable was added in MySQL 3.23.26.
skip_external_locking
OFF if mysqld uses external locking.
This variable was added in MySQL 4.0.3.
Previously, it was named skip_locking.
skip_networking
ON if we allow 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
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.
slave_net_timeout
slow_launch_time
Slow_launch_threads status variable.
This variable was added in MySQL 3.23.15.
socket
sort_buffer_size
ORDER BY or GROUP BY
operations.
See section A.4.4 Where MySQL Stores Temporary Files.
sql_mode
storage_engine
table_type.
It was added in MySQL 4.1.2.
table_cache
mysqld requires.
You can check whether you need to increase the table cache by checking the
Opened_tables status variable.
See section 5.2.4 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 reopenend),
then you should increase the value of the table_cache variable.
For more information about the table cache, see section 7.4.8 How MySQL Opens and Closes Tables.
table_type
--default-table-type
option.
This variable was added in MySQL 3.23.0.
See section 5.2.1 mysqld Command-line Options.
thread_cache_size
thread_cache_size threads there. Requests for threads are
satsified 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 examing the difference between the Connections
and Threads_created status variables (see section 5.2.4 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
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
crash-me test are dependent on this value. The default is
large enough for normal operation. See section 7.1.4 The MySQL Benchmark Suite.
timezone
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
MyISAM table.
Increase the value o