Pre-General Availability Draft: 2018-02-23
This section describes locking information as exposed by the
data_lock_waits tables, which
INNODB_LOCK_WAITS tables in MySQL
8.0. For similar discussion written in terms of the
INFORMATION_SCHEMA tables, see
InnoDB INFORMATION_SCHEMA Transaction and Locking Information
in MySQL 5.7 Reference Manual.
INFORMATION_SCHEMA table and two
Performance Schema tables enable you to monitor
InnoDB transactions and diagnose potential
INFORMATION_SCHEMAtable contains information about every transaction currently executing inside
InnoDB, including the transaction state (for example, whether it is running or waiting for a lock), when the transaction started, and the particular SQL statement the transaction is executing.
data_locks: This Performance Schema table contains a row for each hold lock and each lock request that is blocked waiting for a held lock to be released:
There is one row for each held lock, whatever the state of the transaction that holds the lock (
Each transaction in InnoDB that is waiting for another transaction to release a lock (
LOCK WAIT) is blocked by exactly one blocking lock request. That blocking lock request is for a row or table lock held by another transaction in an incompatible mode. A lock request always has a mode that is incompatible with the mode of the held lock that blocks the request (read vs. write, shared vs. exclusive).
The blocked transaction cannot proceed until the other transaction commits or rolls back, thereby releasing the requested lock. For every blocked transaction,
data_lockscontains one row that describes each lock the transaction has requested, and for which it is waiting.
data_lock_waits: This Performance Schema table indicates which transactions are waiting for a given lock, or for which lock a given transaction is waiting. This table contains one or more rows for each blocked transaction, indicating the lock it has requested and any locks that are blocking that request. The
REQUESTING_ENGINE_LOCK_IDvalue refers to the lock requested by a transaction, and the
BLOCKING_ENGINE_LOCK_IDvalue refers to the lock (held by another transaction) that prevents the first transaction from proceeding. For any given blocked transaction, all rows in
data_lock_waitshave the same value for
REQUESTING_ENGINE_LOCK_IDand different values for
For more information about the preceding tables, see Section 25.32.29, “The INFORMATION_SCHEMA INNODB_TRX Table”, Section 220.127.116.11, “The data_locks Table”, and Section 18.104.22.168, “The data_lock_waits Table”.