#### 15.15.2.2 InnoDB Lock and Lock-Wait Information

Note

 This section describes locking information as exposed by the Performance Schema [`data_locks`](performance-schema-data-locks-table.html) and [`data_lock_waits`](performance-schema-data-lock-waits-table.html) tables, which supersede the `INFORMATION_SCHEMA` `INNODB_LOCKS` and `INNODB_LOCK_WAITS` tables in MySQL 8.0. For similar discussion written in terms of the older `INFORMATION_SCHEMA` tables, see [InnoDB Lock and Lock-Wait Information](https://dev.mysql.com/doc/refman/5.7/en/innodb-information-schema-understanding-innodb-locking.html), in [MySQL 5.7 Reference Manual](https://dev.mysql.com/doc/refman/5.7/en/).

 When a transaction updates a row in a table, or locks it with `SELECT FOR UPDATE`, `InnoDB` establishes a list or queue of locks on that row. Similarly, `InnoDB` maintains a list of locks on a table for table-level locks. If a second transaction wants to update a row or lock a table already locked by a prior transaction in an incompatible mode, `InnoDB` adds a lock request for the row to the corresponding queue. For a lock to be acquired by a transaction, all incompatible lock requests previously entered into the lock queue for that row or table must be removed (which occurs when the transactions holding or requesting those locks either commit or roll back).

 A transaction may have any number of lock requests for different rows or tables. At any given time, a transaction may request a lock that is held by another transaction, in which case it is blocked by that other transaction. The requesting transaction must wait for the transaction that holds the blocking lock to commit or roll back. If a transaction is not waiting for a lock, it is in a `RUNNING` state. If a transaction is waiting for a lock, it is in a `LOCK WAIT` state. (The `INFORMATION_SCHEMA` [`INNODB_TRX`](information-schema-innodb-trx-table.html) table indicates transaction state values.)

 The Performance Schema [`data_locks`](performance-schema-data-locks-table.html) table holds one or more rows for each `LOCK WAIT` transaction, indicating any lock requests that prevent its progress. This table also contains one row describing each lock in a queue of locks pending for a given row or table. The Performance Schema [`data_lock_waits`](performance-schema-data-lock-waits-table.html) table shows which locks already held by a transaction are blocking locks requested by other transactions.

