22.2.2. Plugin API Components

The server plugin implementation comprises several components.

SQL statements:

INSTALL PLUGIN registers a plugin in the mysql.plugin table and loads the plugin code.
UNINSTALL PLUGIN unregisters a plugin from the mysql.plugin table and unloads the plugin code.
The WITH PARSER clause for full-text index creation associates a full-text parser plugin with a given FULLTEXT index.
SHOW PLUGINS displays information about server plugins.

Command-line options and system variables:

The --plugin-load option enables plugins to be loaded at server startup time.
The plugin_dir system variable indicates the location of the directory where all plugins must be installed. The value of this variable can be specified at server startup with a --plugin_dir=path option. mysql_config --plugindir displays the default plugin directory path name.

Plugin-related tables:

The INFORMATION_SCHEMA.PLUGINS table contains plugin information.
The mysql.plugin table lists each plugin that was installed with INSTALL PLUGIN and is required for plugin use. For new MySQL installations, this table is created during the installation process.

The client plugin implementation is simpler:

For the mysql_options() C API function, the MYSQL_DEFAULT_AUTH and MYSQL_PLUGIN_DIR options enable client programs to load authentication plugins.
There are C API functions that enable management of client plugins.

To examine how MySQL implements plugins, consult the following source files in a MySQL source distribution:

In the include/mysql directory, plugin.h exposes the public plugin API. This file should be examined by anyone who wants to write a plugin library. plugin_xxx.h files provide additional information that pertains to specific types of plugins. client_plugin.h contains information specific to client plugins.
In the sql directory, sql_plugin.h and sql_plugin.cc comprise the internal plugin implementation. sql_acl.cc is where the server uses authentication plugins. These files need not be consulted by plugin developers. They may be of interest for those who want to know more about how the server handles plugins.
In the sql-common directory, client_plugin.h implements the C API client plugin functions, and client.c implements client authentication support. These files need not be consulted by plugin developers. They may be of interest for those who want to know more about how the server handles plugins.