We are still discussing if we want to continue to use the current sliding window rate limiter or reconfigure to use sharding's queryAnalysis token bucket rate limiter. If we indeed continue to use the former, we should investigate which type of lock gives the best performance. We should use the google micro benchmark (rate_limiting_bm.cpp) and also flamegraphs to determine the performance of stdx::unique_lock, stdx::lock_guard or something lock free (William's idea).