Github user ben-manes commented on the issue:
https://github.com/apache/metron/pull/940
Guava defaults to a `concurrencyLevel` of 4, given its age and a desire to
not abuse memory in low concurrent situations. You probably want to increase it
to 64 in a heavy workload, which has a ~4x throughput gain on reads. It won't
scale much higher, since it has internal bottlenecks and I could never get
patches reviewed to fix those.
I've only noticed overall throughput be based on threads, and never
realized there was a capacity constraint to its performance. One should expect
some due to the older hash table design resulting in more collisions, whereas
CHMv8 does much better there. Still, I would have expected it to even out
enough unless have a bad hash code?
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