*: use fxhash

[BusyJay]

FlatMap sorts keys, which is unnecessary for small groups. A Raft group usually has 3 ~ 5 nodes.

[siddontang]

can you give a benchmark with them?

[BusyJay]

Simple benchmark for querying on 6 nodes.

test bench_default_hashmap ... bench:          55 ns/iter (+/- 33)
test bench_flatmap_hashmap ... bench:          11 ns/iter (+/- 0)
test bench_fnv_hashmap     ... bench:           3 ns/iter (+/- 0)
test bench_fxhash_hashmap  ... bench:           4 ns/iter (+/- 5)
test bench_number_hashmap  ... bench:           4 ns/iter (+/- 3)
test bench_vecmap_hashmap  ... bench:           3 ns/iter (+/- 3)

Another benchmark by the crate author.

[siddontang]

how about 3 nodes?

[BusyJay]

I don't think there will be much difference as it only cost 4ns already. We don't just use it for progresses but also for read index.

[Hoverbear]

Hm, this library has has an open PR since December that hasn't been addressed: cbreeden/fxhash#3. It does appear to be used in Firefox though. The code seems good overall. I am kind of sad to move away from servo maintained libraries like fnv though.

[siddontang]

LGTM

PTAL @Hoverbear

[BusyJay]

PTAL

[Hoverbear]

My primary concern in this case is just that fxhash doesn't seem to be seriously maintained, while fnv does.

[siddontang]

I find that servo also uses it, so I think it is fine.

[Hoverbear]

Then let's do it. :)