Performance Schema metadata_locks Table

The metadata_locks table lists currently held and requested metadata locks, which protect database object definitions from concurrent modification.

The metadata_locks table is available from 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 variable.

The table is read-only, and TRUNCATE TABLE cannot be used to empty the table.

The table contains the following columns:

• OBJECT_TYPE

  • VARCHAR(64)

  • Null: No

  • Default: NULL

  • Description: 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)

  • Null: Yes

  • Default: NULL

  • Description: Object schema.

• OBJECT_NAME

  • VARCHAR(64)

  • Null: Yes

  • Default: NULL

  • Description: Object name.

• OBJECT_INSTANCE_BEGIN

  • BIGINT(20) UNSIGNED

  • Null: No

  • Default: NULL

  • Description: Address in memory of the instrumented object.

• LOCK_TYPE

  • VARCHAR(32)

  • Null: No

  • Default: NULL

  • Description: 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)

  • Null: No

  • Default: NULL

  • Description: 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)

  • Null: No

  • Default: NULL

  • Description: Lock status. One of GRANTED, KILLED, PENDING, POST_RELEASE_NOTIFY, PRE_ACQUIRE_NOTIFY, TIMEOUT, or VICTIM.

• SOURCE

  • VARCHAR(64)

  • Null: Yes

  • Default: NULL

  • Description: 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

  • Null: Yes

  • Default: NULL

  • Description: Thread that requested the lock.

• OWNER_EVENT_ID

  • BIGINT(20) UNSIGNED

  • Null: Yes

  • Default: NULL

  • Description: Event that requested the lock.

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