Wrap entry optimization

[druminski]

Alternative implementation of wrap entry optimization proposed by @wendigo in #5

Instead of using global sync.Pool with locks, entry byte buffer is allocated per shard.

Bench test results before and after optimization:

go test -bench=WriteToCacheWith -benchtime=5s

BenchmarkWriteToCacheWith1Shard-4                       5000000      1520 ns/op
BenchmarkWriteToCacheWith500Shards-4                        10000000          647 ns/op
BenchmarkWriteToCacheWith1kShards-4                     10000000          627 ns/op
BenchmarkWriteToCacheWith10kShards-4                        10000000          646 ns/op
BenchmarkWriteToCacheWith1kShardsAndSmallShardInitSize-4    10000000          789 ns/op

BenchmarkWriteToCacheWith1Shard-4                       5000000      1320 ns/op
BenchmarkWriteToCacheWith500Shards-4                        20000000          594 ns/op
BenchmarkWriteToCacheWith1kShards-4                     20000000          616 ns/op
BenchmarkWriteToCacheWith10kShards-4                        10000000          629 ns/op
BenchmarkWriteToCacheWith1kShardsAndSmallShardInitSize-4    10000000          717 ns/op

Total time spent on entries wrapping during bench tests:

//before opt
1.13s     15.34s    104:    w := wrapEntry(currentTimestamp, hashedKey, key, entry)

//after opt
2.50s      3.84s    106:    w := wrapEntry(currentTimestamp, hashedKey, key, entry, &shard.entryBuffer)

[wendigo]

Wow, nice one :) It seems that using sync.Pool has no sense here and this kind of buffer is fine in wrapEntry

[druminski]

I am glad you like it, although credits goes to you with this pr as you discovered the optimization possibility and proposed a solution with comparable results, thanks :)

[wendigo]

👍

[janisz]

5 arguments is quite much. How about introducing

type Entry struct {
    timestamp uint64
    hash uint64
    key uint64
    entry []byte
}

[druminski]

I think it's a little bit to soon for this structure, I will happily use it if it will be use more than in one place (only to pass its values to func)

[janisz]

I left one comment but it looks good. 👍