We record a lot of metrics in serverStatus that are of type CounterMetric. The increment() function of CounterMetric uses atomic fetch_add() which by default uses memory order std::memory_order_seq_cst that is expensive since it needs to synchronize cpu cores with memory fences. Since they are for metrics, it seems we can use fetchAndAddRelaxed instead which uses a relaxed memory ordering, to reduce the synchronization overheads.