17.15.2 InnoDB INFORMATION_SCHEMA Transaction and Locking Information

17.15.2.1 Using InnoDB Transaction and Locking Information

17.15.2.2 InnoDB Lock and Lock-Wait Information

17.15.2.3 Persistence and Consistency of InnoDB Transaction and Locking Information

One INFORMATION_SCHEMA table and two Performance Schema tables enable you to monitor InnoDB transactions and diagnose potential locking problems:

• INNODB_TRX: This INFORMATION_SCHEMA table provides 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 (INNODB_TRX.TRX_STATE is RUNNING, LOCK WAIT, ROLLING BACK or COMMITTING).

  • Each transaction in InnoDB that is waiting for another transaction to release a lock (INNODB_TRX.TRX_STATE is 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_locks contains 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_ID value refers to the lock requested by a transaction, and the BLOCKING_ENGINE_LOCK_ID value 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_waits have the same value for REQUESTING_ENGINE_LOCK_ID and different values for BLOCKING_ENGINE_LOCK_ID.

For more information about the preceding tables, see Section 28.4.28, “The INFORMATION_SCHEMA INNODB_TRX Table”, Section 29.12.13.1, “The data_locks Table”, and Section 29.12.13.2, “The data_lock_waits Table”.