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What is Lock_wait_timeout?
From the MySQL 5.5 docs for lock_wait_timeout: This variable specifies the timeout in seconds for attempts to acquire metadata locks. The permissible values range from 1 to 31536000 (1 year). The default is 31536000. Translation: by default, MySQL 5.5 will “meta-block” for 1 year!
What is lock wait?
A lock wait occurs when a transaction tries to obtain a lock on a resource that is already held by another transaction. When the duration of the lock wait time is extended, this results in a slow down of SQL query execution.
What is a lock timeout?
A lock timeout occurs when a transaction, waiting for a resource lock, waits long enough to have surpassed the wait time value specified by the locktimeout database configuration parameter. This consumes time which causes a slow down in SQL query performance.
How do I unlock a locked table in mysql?
The correct way to use LOCK TABLES and UNLOCK TABLES with transactional tables, such as InnoDB tables, is to begin a transaction with SET autocommit = 0 (not START TRANSACTION ) followed by LOCK TABLES , and to not call UNLOCK TABLES until you commit the transaction explicitly.
What causes a lock wait timeout exceeded exception?
‘ Lock wait timeout ’ occurs typically when a transaction is waiting on row (s) of data to update which is already been locked by some other transaction. Most of the times, the problem lies on the database side. The possible causes may be a inappropriate table design, large amount of data, constraints etc.
How to check MySQL lock wait timeout exceeded?
The transaction which is timeout, try to lock table which is hold by another process. and your timeout variable set with little number of second. so it shows error. You can see more status by the command.
What causes an InnoDB lock wait timeout exceeded error?
InnoDB lock wait timeout can cause two major implications: 1 The failed statement is not being rolled back by default. 2 Even if innodb_rollback_on_timeout is enabled, when a statement fails in a transaction, ROLLBACK is still a more… More
What happens when row lock is not released?
The offensive transaction is waiting for row lock to be released by another transaction. The failed statement is not being rolled back by default. Even if innodb_rollback_on_timeout is enabled, when a statement fails in a transaction, ROLLBACK is still a more expensive operation than COMMIT.