Add NonConsistentHashPoolProvider

[bisho]

A NonConsistent hash is more heavy in CPU than a simple crc32 and it can also be less balanced. Since we have plenty of options to manage out pools, we usually grow a pool by migrating into a new one, not expanding a present one, having a simple non-consistent is a good option.

INITIAL.multithreaded: Overall: 110779.55 RPS / 9.03 us/req
INITIAL.singlethreaded:Overall: 111545.63 RPS / 8.96 us/req
NON_CONSISTENT_SHARDING.multithreaded:Overall: 124463.31 RPS / 8.03 us/req
NON_CONSISTENT_SHARDING.singlethreaded:Overall: 126979.22 RPS / 7.88 us/req

Before:

After:

[thecadams]

Nice! Any other hashing algorithms considered, or ok with crc32 for now? Lots of others on https://github.com/rurban/smhasher including issues with each

[bisho]

Nice! Any other hashing algorithms considered, or ok with crc32 for now? Lots of others on https://github.com/rurban/smhasher including issues with each

I tried a few (like meow hash, liked the name punch) but most are rust and the bridging kills the performance wins. But we can definitely try and add others.

Note collisions are not significant as we are using this for sharding, we will "collision" all keys over a few servers anyway, so the characteristics of the hash are not as important as the evenness of the output :)

Also note we are not (yet) changing to use a different sharding, this just offers the choice and makes an example on how to add other sharding algs.