How to avoid and recover from deadlocks in MySQL?
For more information about avoiding and recovering from deadlock conditions, see Section 14.7.5.3, “How to Minimize and Handle Deadlocks” . When deadlock detection is enabled (the default) and a deadlock does occur, InnoDB detects the condition and rolls back one of the transactions (the victim).
How are table level locks used in MySQL?
Table-level locks prevent concurrent updates to the table, avoiding deadlocks at the expense of less responsiveness for a busy system. Another way to serialize transactions is to create an auxiliary “semaphore” table that contains just a single row. Have each transaction update that row before accessing other tables.
Why do you get deadlocks in InnoDB transactions?
InnoDB uses automatic row-level locking. You can get deadlocks even in the case of transactions that just insert or delete a single row. That is because these operations are not really “atomic”; they automatically set locks on the (possibly several) index records of the row inserted or deleted.
When do transactions lock rows in multiple tables?
A deadlock can occur when transactions lock rows in multiple tables (through statements such as UPDATE or SELECT FOR UPDATE ), but in the opposite order. A deadlock can also occur when such statements lock ranges of index records and gaps, with each transaction acquiring some locks but not others due to a timing issue.
How to see the last deadlock in InnoDB?
To see the last deadlock in an InnoDB user transaction, use the SHOW ENGINE INNODB STATUS command. If frequent deadlocks highlight a problem with transaction structure or application error handling, run with the innodb_print_all_deadlocks setting enabled to print information about all deadlocks to the mysqld error log.
Why are transactions unable to proceed in a deadlock?
A deadlock is a situation where different transactions are unable to proceed because each holds a lock that the other needs. Because both transactions are waiting for a resource to become available, neither ever release the locks it holds.