Rechercher dans le manuel MySQL

26.12.12.2 The data_lock_waits Table

Contents

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:

  1. mysql> SELECT * FROM performance_schema.data_lock_waits\G
  2. *************************** 1. row ***************************
  3.                           ENGINE: INNODB
  4.        REQUESTING_ENGINE_LOCK_ID: 140211201964816:2:4:2:140211086465800
  5. REQUESTING_ENGINE_TRANSACTION_ID: 1555
  6.             REQUESTING_THREAD_ID: 47
  7.              REQUESTING_EVENT_ID: 5
  8. REQUESTING_OBJECT_INSTANCE_BEGIN: 140211086465800
  9.          BLOCKING_ENGINE_LOCK_ID: 140211201963888:2:4:2:140211086459880
  10.   BLOCKING_ENGINE_TRANSACTION_ID: 1554
  11.               BLOCKING_THREAD_ID: 46
  12.                BLOCKING_EVENT_ID: 12
  13.   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:

  • ENGINE

    The storage engine that requested the lock.

  • REQUESTING_ENGINE_LOCK_ID

    The ID of the lock requested by the storage engine. To obtain details about the lock, join this column with the ENGINE_LOCK_ID column of the data_locks table.

  • REQUESTING_ENGINE_TRANSACTION_ID

    The storage engine internal ID of the transaction that requested the lock.

  • REQUESTING_THREAD_ID

    The thread ID of the session that requested the lock.

  • REQUESTING_EVENT_ID

    The Performance Schema event that caused the lock request in the session that requested the lock.

  • REQUESTING_OBJECT_INSTANCE_BEGIN

    The address in memory of the requested lock.

  • BLOCKING_ENGINE_LOCK_ID

    The ID of the blocking lock. To obtain details about the lock, join this column with the ENGINE_LOCK_ID column of the data_locks table.

  • BLOCKING_ENGINE_TRANSACTION_ID

    The storage engine internal ID of the transaction that holds the blocking lock.

  • BLOCKING_THREAD_ID

    The thread ID of the session that holds the blocking lock.

  • BLOCKING_EVENT_ID

    The Performance Schema event that caused the blocking lock in the session that holds it.

  • BLOCKING_OBJECT_INSTANCE_BEGIN

    The address in memory of the blocking lock.

The data_lock_waits table has these indexes:

  • Index on (REQUESTING_ENGINE_LOCK_ID, ENGINE)

  • Index on (BLOCKING_ENGINE_LOCK_ID, ENGINE)

  • Index on (REQUESTING_ENGINE_TRANSACTION_ID, ENGINE)

  • Index on (BLOCKING_ENGINE_TRANSACTION_ID, ENGINE)

  • Index on (REQUESTING_THREAD_ID, REQUESTING_EVENT_ID)

  • Index on (BLOCKING_THREAD_ID, BLOCKING_EVENT_ID)

TRUNCATE TABLE is not permitted for the data_lock_waits table.


Find a PHP function

Document created the 26/06/2006, last modified the 26/10/2018
Source of the printed document:https://www.gaudry.be/en/mysql-rf-data-lock-waits-table.html

The infobrol is a personal site whose content is my sole responsibility. The text is available under CreativeCommons license (BY-NC-SA). More info on the terms of use and the author.

References

  1. View the html document Language of the document:en Manuel MySQL : https://dev.mysql.com/

These references and links indicate documents consulted during the writing of this page, or which may provide additional information, but the authors of these sources can not be held responsible for the content of this page.
The author This site is solely responsible for the way in which the various concepts, and the freedoms that are taken with the reference works, are presented here. Remember that you must cross multiple source information to reduce the risk of errors.

Contents Haut