What's the practical difference between pessimistic and optimistic concurrency control?
Pessimistic control locks a row before touching it, so conflicting transactions wait — safe by construction, but you pay for locks even when conflicts are rare. Optimistic control lets everyone proceed unlocked and checks for conflicts at commit time, retrying the loser — fast under low contention, but wasteful and retry-heavy under high contention. The right choice depends on how often two transactions actually collide.
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Database Transactions Explained: ACID, Isolation Levels, and Concurrency ControlWhat ACID actually guarantees, and how pessimistic vs optimistic concurrency control decide whether your app locks or retries under load.
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