A lock is taken in VectorClock::isEnabled to check if VectorClock is enabled. It appears that VectorClock can only ever be disabled if a node becomes an arbiter and cannot be renabled. Since VectorClock::isEnabled is called several times in a request (gossipIn during request processing, gossipOut during reply processing and potentially over times (like getting legacy runtime constants)). This will help reduce contention on the VectorClock mutex and save time.