24.4. Runtime MySQL Configuration

By default, the server uses built-in values for its configuration variables when it runs. If the default values aren't suitable, you can use runtime options to tell the server to use different values:

• Several options specify the locations of important directories and files. For example, under Windows, the built-in default value for the installation directory (base directory) is C:\mysql. If you install MySQL somewhere else, you must tell the server the correct location by using the --basedir option or the server will not start. Similarly, if you use a data directory other than the directory named data under the installation directory, you must use a --datadir option to tell the server the correct location.

• Options control which log files the server writes.

• Options can be used to override the server's built-in values for performance-related variables, such as those that control the maximum number of simultaneous connections, and the sizes of buffers and caches.

• Some storage engines that are built in can be enabled or disabled at server startup. For example, if the server has been compiled with InnoDB support (which is true by default), the --skip-innodb option can be given to save memory if you are not using InnoDB tables. You can also specify that the default storage engine should be different from the built-in default of MyISAM.

• Several options configure the InnoDB tablespace. If InnoDB is enabled, it creates a default tablespace in the absence of explicit configuration. However, the default tablespace is rather small, so it's better to configure the tablespace yourself.