Deadlock vs Lockwait Timeout on MySQL -


can explain me on details difference of deadlock , lockwait errors found on mysql 5.1. same? when deadlock error occur , when lockwait timeout occur?

a deadlock occurs circular dependency exists amongst locks transactions must acquire in order proceed: example, imagine transaction 1 holds lock needs acquire lock b proceed; , transaction 2 holds lock b needs acquire lock proceed—the transactions immediately deadlocked (no timeout required) , neither can proceed until 1 releases locks. solution 1 transaction rolled (one's application code should detect eventuality , handle accordingly, attempting transaction again).

a wait timeout occurs when configured timeout period (e.g. innodb_lock_wait_timeout in case of innodb locks) elapses whilst transaction awaits lock, perhaps because slow query holding lock , has not finished executing. it's possible (even, likely) lock have become available , been acquired if transaction had waited longer, timeout exists avoid applications waiting on database indefinitely.


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