Yesterday I met a performance issue: the consumer threads’ CPU utilisation are nearly 100%. From the perf report, these consumer threads spent remarkable time in searching from the hash tables. Since every consumer thread has its own hash table, we don’t need to worry about lock-contention issue, but the buckets number of the hash table is not large enough, so every bucket holds too many elements, and searching from these elements costs a lot of time. The fix is straightforward: increase the number of buckets.