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5.2. mysqld — The MySQL Server

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

  • Startup options that the server supports

  • Server system variables

  • Server status variables

  • How to set the server SQL mode

  • The server shutdown process

MySQL servers include the BerkeleyDB (BDB) storage engine whenever possible, but not all platforms support BDB.

Currently, MySQL Cluster is supported on Linux (on most platforms), Solaris, Mac OS X, and HP-UX only. Some users have reported success in using MySQL Cluster built from source on BSD operating systems, but these are not officially supported at this time. Note that, even for servers compiled with Cluster support, the NDB Cluster storage engine is not enabled by default. You must start the server with the --ndbcluster option to use it as part of a MySQL Cluster. (For details, see Section 16.4, “MySQL Cluster Configuration”.)

The following table shows the platforms for which MySQL server binaries include support for BDB and NDB Cluster.

System BDB Support NDB Support
AIX 5.2 N N
Linux-IA-64 N Y
Linux-Intel Y Y
Mac OS X N Y
NetWare N N
Solaris-SPARC Y Y
Solaris-Intel N Y
Solaris-AMD 64 Y Y
Windows NT/2000/XP Y N

To find out which storage engines your server supports, use the SHOW ENGINES statement. (See Section, “SHOW ENGINES Syntax”.) For example:

*************************** 1. row ***************************
      Engine: MEMORY
     Support: YES
     Comment: Hash based, stored in memory, useful for temporary tables
Transactions: NO
          XA: NO
  Savepoints: NO
*************************** 2. row ***************************
      Engine: CSV
     Support: YES
     Comment: CSV storage engine
Transactions: NO
          XA: NO
  Savepoints: NO
*************************** 3. row ***************************
      Engine: MRG_MYISAM
     Support: YES
     Comment: Collection of identical MyISAM tables
Transactions: NO
          XA: NO
  Savepoints: NO
*************************** 4. row ***************************
      Engine: MyISAM
     Support: DEFAULT
     Comment: Default engine as of MySQL 3.23 with great performance
Transactions: NO
          XA: NO
  Savepoints: NO

The precise output from SHOW ENGINES may vary according to the MySQL version used (and the features that are enabled). The Support values in the output indicate the server's level of support for each feature, as shown here:

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 error log file should contain a reason indicating why the option is disabled. See Section 5.11.2, “The Error Log”.

You might also see DISABLED for a storage engine if the server was compiled to support it, but was started with a --skip-engine option. For example, --skip-innodb disables the InnoDB engine. For the NDB Cluster storage engine, DISABLED means the server was compiled with support for MySQL Cluster, but was not started with the --ndb-cluster option.

All MySQL servers support MyISAM tables, because MyISAM is the default storage engine.

  Published under the terms of the GNU General Public License Design by Interspire