A MySQL deadlock, also known as a "cyclic dependency", occurs when two or more processes are waiting for resources that are held by each other. This can lead to the MySQL server stopping and data loss.
Causes of deadlocks:
Locking: MySQL uses locks to ensure data integrity. When one process locks a resource, other processes that try to access the same resource will be blocked.
Incorrect locking order: If two processes try to access resources in different orders, this can lead to a deadlock.
Lock escalation: MySQL can escalate locks to improve performance. This can lead to a deadlock if two processes try to access the same resource.
Symptoms of deadlocks:
The MySQL server is unresponsive.
MySQL error messages appear indicating a lock.
MySQL queries are not executed.
How to avoid deadlocks:
Use the correct locking order: Always access resources in the same order.
Avoid lock escalation: If possible, do not use lock escalation.
Use timeouts: Set timeouts for MySQL queries so they don't wait forever.
Regularly update MySQL: MySQL updates may contain fixes for bugs that can lead to deadlocks.
