MySQL 8.0 Reference Manual Including MySQL NDB Cluster 8.0

26.12.12.2 The data_lock_waits Table

The data_lock_waits table implements a many-to-many relationship showing which data lock requests in the data_locks table are blocked by which held data locks in the data_locks table. Held locks in data_locks appear in data_lock_waits only if they block some lock request.

This information enables you to understand data lock dependencies between sessions. The table exposes not only which lock a session or transaction is waiting for, but which session or transaction currently holds that lock.

Example data lock wait information:

mysql> SELECT * FROM performance_schema.data_lock_waits\G
*************************** 1. row ***************************
                          ENGINE: INNODB
       REQUESTING_ENGINE_LOCK_ID: 140211201964816:2:4:2:140211086465800
REQUESTING_ENGINE_TRANSACTION_ID: 1555
            REQUESTING_THREAD_ID: 47
             REQUESTING_EVENT_ID: 5
REQUESTING_OBJECT_INSTANCE_BEGIN: 140211086465800
         BLOCKING_ENGINE_LOCK_ID: 140211201963888:2:4:2:140211086459880
  BLOCKING_ENGINE_TRANSACTION_ID: 1554
              BLOCKING_THREAD_ID: 46
               BLOCKING_EVENT_ID: 12
  BLOCKING_OBJECT_INSTANCE_BEGIN: 140211086459880

Unlike most Performance Schema data collection, there are no instruments for controlling whether data lock information is collected or system variables for controlling data lock table sizes. The Performance Schema collects information that is already available in the server, so there is no memory or CPU overhead to generate this information or need for parameters that control its collection.

Use the data_lock_waits table to help diagnose performance problems that occur during times of heavy concurrent load. For InnoDB, see the discussion of this topic at Section 15.14.2, “InnoDB INFORMATION_SCHEMA Transaction and Locking Information”.

Because the columns in the data_lock_waits table are similar to those in the data_locks table, the column descriptions here are abbreviated. For more detailed column descriptions, see Section 26.12.12.1, “The data_locks Table”.

The data_lock_waits table has these columns:

The data_lock_waits table has these indexes:

TRUNCATE TABLE is not permitted for the data_lock_waits table.