This plugin creates the METADATA_LOCK_INFO table in the Information Schema, allowing users to view active metadata locks and their owners.
The METADATA_LOCK_INFO plugin creates the METADATA_LOCK_INFO table in the INFORMATION_SCHEMA database. This table shows active metadata locks. The table is empty if there are no active metadata locks.
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:
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 or the options. This can be specified as a command-line argument to or it can be specified in a relevant server in an :
You can uninstall the plugin dynamically by executing or :
If you installed the plugin by providing the or the options in a relevant server in an , then those options should be removed to prevent the plugin from being loaded the next time the server is restarted.
metadata_lock_infoDescription: 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 table.
This page is licensed: CC BY-SA / Gnu FDL
INSTALL SONAME 'metadata_lock_info';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: --metadata-lock-info=value
Data Type: enumerated
Default Value: ON
Valid Values: OFF, ON, FORCE, FORCE_PLUS_PERMANENT
[mariadb]
...
plugin_load_add = metadata_lock_infoUNINSTALL SONAME 'metadata_lock_info';SELECT * FROM information_schema.metadata_lock_info;
+-----------+--------------------------+---------------+----------------------+-----------------+-------------+
| THREAD_ID | LOCK_MODE | LOCK_DURATION | LOCK_TYPE | TABLE_SCHEMA | TABLE_NAME |
+-----------+--------------------------+---------------+----------------------+-----------------+-------------+
| 31 | MDL_INTENTION_EXCLUSIVE | MDL_EXPLICIT | Global read lock | | |
| 31 | MDL_INTENTION_EXCLUSIVE | MDL_EXPLICIT | Commit lock | | |
| 31 | MDL_INTENTION_EXCLUSIVE | MDL_EXPLICIT | Schema metadata lock | dbname | |
| 31 | MDL_SHARED_NO_READ_WRITE | MDL_EXPLICIT | Table metadata lock | dbname | exotics |
+-----------+--------------------------+---------------+----------------------+-----------------+-------------+
4 rows in set (0.00 sec)SELECT
CONCAT('Thread ',P.ID,' executing "',P.INFO,'" IS LOCKED BY Thread ',
M.THREAD_ID) WhoLocksWho
FROM INFORMATION_SCHEMA.PROCESSLIST P,
INFORMATION_SCHEMA.METADATA_LOCK_INFO M
WHERE LOCATE(lcase(LOCK_TYPE), lcase(STATE))>0;
+-----------------------------------------------------------------------------------+
| WhoLocksWho |
+-----------------------------------------------------------------------------------+
| Thread 3 executing "INSERT INTO foo ( b ) VALUES ( 'FOO' )" IS LOCKED BY Thread 2 |
+-----------------------------------------------------------------------------------+
1 row in set (0.00 sec)
SHOW PROCESSLIST;
+----+------+-----------+------+---------+------+------------------------------+----------------------------------------+----------+
| Id | User | Host | db | Command | Time | State | Info | Progress |
+----+------+-----------+------+---------+------+------------------------------+----------------------------------------+----------+
| 2 | root | localhost | test | Sleep | 123 | | NULL | 0.000 |
| 3 | root | localhost | test | Query | 103 | Waiting for global read lock | INSERT INTO foo ( b ) VALUES ( 'FOO' ) | 0.000 |
| 4 | root | localhost | test | Query | 0 | init | SHOW PROCESSLIST | 0.000 |
+----+------+-----------+------+---------+------+------------------------------+----------------------------------------+----------+
3 rows in set (0.00 sec)