Lock Now or Check Later: Optimistic vs. Pessimistic Concurrency

Pessimistic concurrency control locks data first, assuming conflict is likely ('ask permission'). It's for high-contention systems like booking an airline seat. Optimistic control assumes conflict is rare, proceeding without locks and checking for changes before committing ('ask forgiveness'). It suits low-contention tasks like editing a wiki page. The footgun is misjudging contention: pessimistic locking kills performance in low-conflict scenarios, while optimistic locking causes constant, wasteful rollbacks in high-conflict ones.