MVCC is optimistic concurrency control – you may end up having to retry your write transaction multiple times, which might suck if the transaction is expensive.

MVCC is optimistic concurrency control – you may end up having to retry your write transaction multiple times, which might suck if the transaction is expensive. Pessimistic concurrency control like locking may be cheaper in those cases, since the cost of locking may be drastically lower. Having one doesn't preclude the other!