5.1.8.1 Installing and Uninstalling Plugins

Server plugins must be loaded in to the server before they can be used. MySQL enables you to load a plugin at server startup or at runtime. It is also possible to control the activation of loaded plugins at startup, and to unload them at runtime.

Installing Plugins

Server plugins must be known to the server before they can be used. A plugin can be made known several ways, as described here. In the following descriptions, plugin_name stands for a plugin name such as innodb or csv.

Built-in plugins:

A plugin that is built in to the server is known by the server automatically. Normally, the server enables the plugin at startup, although this can be changed with the --plugin_name option.

Plugins registered in the mysql.plugin table:

The mysql.plugin table serves as a registry of plugins. The server normally enables each plugin listed in the table at startup, although whether a given plugin is enabled can be changed with the --plugin_name option. If the server is started with the --skip-grant-tables option, it does not consult this table and does not load the plugins listed there.

Plugins named with the --plugin-load option:

A plugin that is located in a plugin library file can be loaded at server startup with the --plugin-load option. Normally, the server enables the plugin at startup, although this can be changed with the --plugin_name option.

The option value is a semicolon-separated list of name=plugin_library pairs. Each name is the name of the plugin, and plugin_library is the name of the shared library that contains the plugin code. If a plugin library is named without any preceding plugin name, the server loads all plugins in the library. Each library file must be located in the directory named by the plugin_dir system variable.

This option does not register any plugin in the mysql.plugin table. For subsequent restarts, the server loads the plugin again only if --plugin-load is given again. That is, this option effects a one-time installation that persists only for one server invocation.

--plugin-load enables plugins to be loaded even when --skip-grant-tables is given (which causes the server to ignore the mysql.plugin table). --plugin-load also enables plugins to be loaded at startup under configurations when plugins cannot be loaded at runtime.

Plugins installed with the INSTALL PLUGIN statement:

A plugin that is located in a plugin library file can be loaded at runtime with the INSTALL PLUGIN statement. The statement also registers the plugin in the mysql.plugin table to cause the server to load it on subsequent restarts. For this reason, INSTALL PLUGIN requires the INSERT privilege for the mysql.plugin table.

If a plugin is named both using a --plugin-load option and in the mysql.plugin table, the server starts but writes these messages to the error log:

100310 19:15:44 [ERROR] Function 'plugin_name' already exists
100310 19:15:44 [Warning] Couldn't load plugin named 'plugin_name'
with soname 'plugin_object_file'.

Example: The --plugin-load option installs a plugin at server startup. To install a plugin named myplugin in a plugin library file named somepluglib.so, use these lines in a my.cnf file:

[mysqld]
plugin-load=myplugin=somepluglib.so

In this case, the plugin is not registered in mysql.plugin. Restarting the server without the --plugin-load option causes the plugin not to be loaded at startup.

Alternatively, the INSTALL PLUGIN statement causes the server to load the plugin code from the library file at runtime:

mysql> INSTALL PLUGIN myplugin SONAME 'somepluglib.so';

INSTALL PLUGIN also causes permanent plugin registration: The server lists the plugin in the mysql.plugin table to ensure that it is loaded on subsequent server restarts.

Many plugins can be loaded either at server startup or at runtime. However, if a plugin is designed such that it must be loaded and initialized during server startup, use --plugin-load rather than INSTALL PLUGIN.

While a plugin is loaded, information about it is available at runtime from several sources, such as the INFORMATION_SCHEMA.PLUGINS table and the SHOW PLUGINS statement. For more information, see Section 5.1.8.2, “Obtaining Server Plugin Information”.

Controlling Plugin Activation

If the server knows about a plugin when it starts (for example, because the plugin is named using a --plugin-load option or registered in the mysql.plugin table), the server loads and enables the plugin by default. It is possible to control activation for such a plugin using a --plugin_name[=value] startup option named after the plugin. In the following descriptions, plugin_name stands for a plugin name such as innodb or csv. As with other options, dashes and underscores are interchangeable in option names. For example, --my_plugin=ON and --my-plugin=ON are equivalent.

As of MySQL 5.1.36, these options control plugin loading:

The values OFF, ON, and FORCE are not case sensitive.

Suppose that CSV, BLACKHOLE, and ARCHIVE are built-in pluggable storage engines and that you want the server to load them at startup, subject to these conditions: The server is permitted to run if CSV initialization fails, but must require that BLACKHOLE initialization succeeds, and ARCHIVE should be disabled. To accomplish that, use these lines in an option file:

[mysqld]
csv=ON
blackhole=FORCE
archive=OFF

The --enable-plugin_name option format is supported as a synonym for --plugin_name=ON. The --disable-plugin_name and --skip-plugin_name option formats are supported as synonyms for --plugin_name=OFF.

Before MySQL 5.1.36, plugin options are boolean options (see Section 4.2.5, “Program Option Modifiers”). That is, any of these options enable the plugin:

--plugin_name
--plugin_name=1
--enable-plugin_name

And these options disable the plugin:

--plugin_name=0
--disable-plugin_name
--skip-plugin_name

If you upgrade to MySQL 5.1.36 or later from an older version and previously used options of the form --plugin_name=0 or --plugin_name=1, the equivalent options are now --plugin_name=OFF and --plugin_name=ON, respectively. You also have the choice of requiring plugins to start successfully by using --plugin_name=FORCE.

If a plugin is disabled, either explicitly with OFF or implicitly because it was enabled with ON but failed to initialize, aspects of server operation that require the plugin will change. For example, if the plugin implements a storage engine, existing tables for the storage engine become inaccessible, and attempts to create new tables for the storage engine result in tables that use the default storage engine unless the NO_ENGINE_SUBSTITUTION SQL mode has been enabled to cause an error to occur instead.

Disabling a plugin may require adjustment to other options. For example, if you start the server using --skip-innodb to disable InnoDB, other innodb_xxx options likely will need to be omitted from the startup command. In addition, if the server is configured to use InnoDB as the default storage engine, it will not start unless you specify another available storage engine with --default-storage-engine.

Uninstalling Plugins

A plugin known to the server can be uninstalled to disable it at runtime with the UNINSTALL PLUGIN statement. The statement unloads the plugin and removes it from the mysql.plugin table if it is registered there. For this reason, UNINSTALL PLUGIN statement requires the DELETE privilege for the mysql.plugin table. With the plugin no longer registered in the table, the server will not load the plugin automatically for subsequent restarts.

UNINSTALL PLUGIN can unload plugins regardless of whether they were loaded with INSTALL PLUGIN or --plugin-load.

UNINSTALL PLUGIN cannot unload plugins that are built in to the server. These can be identified as those that have a library name of NULL in the output from INFORMATION_SCHEMA.PLUGINS or SHOW PLUGINS.