Databases · Middle · Question 21 of 75

How does optimistic locking work?

1Updates are queued and applied one at a time
✓Correct answer: Rows have a version; an update includes WHERE version = $read_version and fails (0 rows) if someone changed it, so the app retries or reports a conflict
3The database locks rows on read and unlocks them on commit

Explanation

No locks are held while the user thinks, which suits web forms. Under heavy contention many retries happen, and pessimistic locking may be better.

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