Query Cache Information Plugin

This plugin exposes the contents of the query cache via the QUERY_CACHE_INFO table in the Information Schema, aiding in performance analysis.

The QUERY_CACHE_INFO plugin creates the QUERY_CACHE_INFO table in the INFORMATION_SCHEMA database. This table shows all queries in the query cache. Querying this table acquires the query cache lock and will result in lock waits for queries that are using or expiring from the query cache. You must have the PROCESS privilege to query this table.

Installing the Plugin

Although the plugin's shared library is distributed with MariaDB by default, the plugin is not actually installed by MariaDB by default. There are two methods that can be used to install the plugin with MariaDB.

The first method can be used to install the plugin without restarting the server. You can install the plugin dynamically by executing INSTALL SONAME or INSTALL PLUGIN:

INSTALL SONAME 'query_cache_info';

The second method can be used to tell the server to load the plugin when it starts up. The plugin can be installed this way by providing the --plugin-load or the --plugin-load-add options. This can be specified as a command-line argument to mysqld or it can be specified in a relevant server option group in an option file:

[mariadb]
...
plugin_load_add = query_cache_info

Uninstalling the Plugin

You can uninstall the plugin dynamically by executing UNINSTALL SONAME or UNINSTALL PLUGIN:

UNINSTALL SONAME 'query_cache_info';

If you installed the plugin by providing the --plugin-load or the --plugin-load-add options in a relevant server option group in an option file, then those options should be removed to prevent the plugin from being loaded the next time the server is restarted.

Example

SELECT statement_schema, statement_text, result_blocks_count, 
  result_blocks_size FROM information_schema.query_cache_info;
+------------------+------------------+---------------------+--------------------+
| statement_schema | statement_text   | result_blocks_count | result_blocks_size |
+------------------+------------------+---------------------+--------------------+
| test             | SELECT * FROM t1 |                   1 |                512 |
+------------------+------------------+---------------------+--------------------+

Options

query_cache_info

• Description: Controls how the server should treat the plugin when the server starts up.

  • Valid values are:

    • OFF - Disables the plugin without removing it from the mysql.plugins table.

    • ON - Enables the plugin. If the plugin cannot be initialized, then the server will still continue starting up, but the plugin will be disabled.

    • FORCE - Enables the plugin. If the plugin cannot be initialized, then the server will fail to start with an error.

    • FORCE_PLUS_PERMANENT - Enables the plugin. If the plugin cannot be initialized, then the server will fail to start with an error. In addition, the plugin cannot be uninstalled with UNINSTALL SONAME or UNINSTALL PLUGIN while the server is running.

  • See Plugin Overview: Configuring Plugin Activation at Server Startup for more information.

• Command line: --query-cache-info=value

• Data Type: enumerated

• Default Value: ON

• Valid Values: OFF, ON, FORCE, FORCE_PLUS_PERMANENT

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