Performance Schema metadata_locks Table
MariaDB starting with 10.5.2
The metadata_locks table was introduced in MariaDB 10.5.2.
The metadata_locks table contains metadata lock information.
To enable metadata lock instrumention, at runtime:
UPDATE performance_schema.setup_instruments SET enabled='YES', timed='YES' WHERE name LIKE 'wait/lock/metadata%';
or in the configuration file:
performance-schema-instrument='wait/lock/metadata/sql/mdl=ON'
The table is by default autosized, but the size can be configured with the performance_schema_max_metadata_locks system variabe.
The table is read-only, and TRUNCATE TABLE cannot be used to empty the table.
The table contains the following columns:
| Field | Type | Null | Default | Description |
|---|---|---|---|---|
| OBJECT_TYPE | varchar(64) | NO | NULL | Object type. One of BACKUP, COMMIT, EVENT, FUNCTION, GLOBAL, LOCKING SERVICE, PROCEDURE, SCHEMA, TABLE, TABLESPACE, TRIGGER (unused) or USER LEVEL LOCK. |
| OBJECT_SCHEMA | varchar(64) | YES | NULL | Object schema. |
| OBJECT_NAME | varchar(64) | YES | NULL | Object name. |
| OBJECT_INSTANCE_BEGIN | bigint(20) unsigned | NO | NULL | Address in memory of the instrumented object. |
| LOCK_TYPE | varchar(32) | NO | NULL | Lock type. One of BACKUP_FTWRL1, BACKUP_START, BACKUP_TRANS_DML, EXCLUSIVE, INTENTION_EXCLUSIVE, SHARED, SHARED_HIGH_PRIO, SHARED_NO_READ_WRITE, SHARED_NO_WRITE, SHARED_READ, SHARED_UPGRADABLE or SHARED_WRITE. |
| LOCK_DURATION | varchar(32) | NO | NULL | Lock duration. One of EXPLICIT (locks released by explicit action, for example a global lock acquired with FLUSH TABLES WITH READ LOCK) , STATEMENT (locks implicitly released at statement end) or TRANSACTION (locks implicitly released at transaction end). |
| LOCK_STATUS | varchar(32) | NO | NULL | Lock status. One of GRANTED, KILLED, PENDING, POST_RELEASE_NOTIFY, PRE_ACQUIRE_NOTIFY, TIMEOUT or VICTIM. |
| SOURCE | varchar(64) | YES | NULL | Source file containing the instrumented code that produced the event, as well as the line number where the instrumentation occurred. This allows one to examine the source code involved. |
| OWNER_THREAD_ID | bigint(20) unsigned | YES | NULL | Thread that requested the lock. |
| OWNER_EVENT_ID | bigint(20) unsigned | YES | NULL | Event that requested the lock. |
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https://mariadb.com/kb/en/performance-schema-metadata_locks-table/