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What causes a MySQL deadlock?
A deadlock in MySQL happens when two or more transactions mutually hold and request for locks, creating a cycle of dependencies. InnoDB automatically detects transaction deadlocks, rollbacks a transaction immediately and returns an error. It uses a metric to pick the easiest transaction to rollback.
How do I stop deadlocks in MySQL?
To avoid deadlock, you must then make sure that concurrent transactions don’t update row in an order that could result in a deadlock. Generally speaking, to avoid deadlock you must acquire lock always in the same order even in different transaction (e.g. always table A first, then table B).
What is a MySQL 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.
What is the default isolation level in MySQL?
REPEATABLE READ
The default isolation level is REPEATABLE READ . Other permitted values are READ COMMITTED , READ UNCOMMITTED , and SERIALIZABLE .
How can deadlock be reduced?
Tips on avoiding deadlocks
- Ensure the database design is properly normalized.
- Develop applications to access server objects in the same order each time.
- Do not allow any user input during transactions.
- Avoid cursors.
- Keep transactions as short as possible.
What is DB deadlock?
In a database, a deadlock is a situation in which two or more transactions are waiting for one another to give up locks. All activity comes to a halt and remains at a standstill forever unless the DBMS detects the deadlock and aborts one of the transactions.
What does deadlock mean in MySQL error 1213?
ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction At that point, the lock request for the other client can be granted and it deletes the row from the table. PREV HOME UP NEXT
What happens when you try to get a deadlock in InnoDB?
As a result, InnoDB generates an error for one of the clients and releases its locks. The client returns this error: ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction. At that point, the lock request for the other client can be granted and it deletes the row from the table.
Why is the lock not granted in MySQL?
The lock cannot be granted because it is incompatible with the S lock that client A holds, so the request goes on the queue of lock requests for the row and client B blocks. Finally, client A also attempts to delete the row from the table: