aa230933d1
HRW library supports weighted sorting. Weights must be normalized before applying. Since there could be different types of normalization for multiple criteria, there is no point to perform simple normalization in this library. Pass a slice of normalized weights to the `SortByWeight` functions. This commit proposes to: - remove normalization routine from `SortByWeight` function; - add `ValidateWeights` function to check if weights are normalized; - rename `weight` -> `distance` to avoid naming confusion between hash distance and actual weights; - use testify lib in the tests;
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4 KiB
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80 lines
No EOL
4 KiB
Markdown
# Golang HRW implementation
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[](https://travis-ci.org/nspcc-dev/hrw)
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[](https://codecov.io/gh/nspcc-dev/hrw)
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[](https://goreportcard.com/report/github.com/nspcc-dev/hrw)
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[](https://github.com/nspcc-dev/hrw)
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[Rendezvous or highest random weight](https://en.wikipedia.org/wiki/Rendezvous_hashing) (HRW) hashing is an algorithm that allows clients to achieve distributed agreement on a set of k options out of a possible set of n options. A typical application is when clients need to agree on which sites (or proxies) objects are assigned to. When k is 1, it subsumes the goals of consistent hashing, using an entirely different method.
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## Install
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`go get github.com/nspcc-dev/hrw`
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## Benchmark:
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```
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BenchmarkSort_fnv_10-8 5000000 365 ns/op 224 B/op 3 allocs/op
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BenchmarkSort_fnv_100-8 300000 5261 ns/op 1856 B/op 3 allocs/op
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BenchmarkSort_fnv_1000-8 10000 119462 ns/op 16448 B/op 3 allocs/op
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BenchmarkSortByIndex_fnv_10-8 3000000 546 ns/op 384 B/op 7 allocs/op
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BenchmarkSortByIndex_fnv_100-8 200000 5965 ns/op 2928 B/op 7 allocs/op
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BenchmarkSortByIndex_fnv_1000-8 10000 127732 ns/op 25728 B/op 7 allocs/op
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BenchmarkSortByValue_fnv_10-8 2000000 962 ns/op 544 B/op 17 allocs/op
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BenchmarkSortByValue_fnv_100-8 200000 9604 ns/op 4528 B/op 107 allocs/op
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BenchmarkSortByValue_fnv_1000-8 10000 111741 ns/op 41728 B/op 1007 allocs/op
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BenchmarkSortByWeight_fnv_10-8 3000000 501 ns/op 320 B/op 4 allocs/op
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BenchmarkSortByWeight_fnv_100-8 200000 8495 ns/op 2768 B/op 4 allocs/op
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BenchmarkSortByWeight_fnv_1000-8 10000 197880 ns/op 24656 B/op 4 allocs/op
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BenchmarkSortByWeightIndex_fnv_10-8 2000000 702 ns/op 480 B/op 8 allocs/op
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BenchmarkSortByWeightIndex_fnv_100-8 200000 9338 ns/op 3840 B/op 8 allocs/op
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BenchmarkSortByWeightIndex_fnv_1000-8 10000 204669 ns/op 33936 B/op 8 allocs/op
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BenchmarkSortByWeightValue_fnv_10-8 1000000 1083 ns/op 640 B/op 18 allocs/op
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BenchmarkSortByWeightValue_fnv_100-8 200000 11444 ns/op 5440 B/op 108 allocs/op
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BenchmarkSortByWeightValue_fnv_1000-8 10000 148471 ns/op 49936 B/op 1008 allocs/op
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```
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## Example
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```go
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package main
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import (
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"fmt"
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"github.com/nspcc-dev/hrw"
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)
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func main() {
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// given a set of servers
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servers := []string{
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"one.example.com",
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"two.example.com",
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"three.example.com",
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"four.example.com",
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"five.example.com",
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"six.example.com",
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}
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// HRW can consistently select a uniformly-distributed set of servers for
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// any given key
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var (
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key = []byte("/examples/object-key")
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h = hrw.Hash(key)
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)
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hrw.SortSliceByValue(servers, h)
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for id := range servers {
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fmt.Printf("trying GET %s%s\n", servers[id], key)
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}
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// Output:
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// trying GET three.example.com/examples/object-key
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// trying GET two.example.com/examples/object-key
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// trying GET five.example.com/examples/object-key
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// trying GET six.example.com/examples/object-key
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// trying GET one.example.com/examples/object-key
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// trying GET four.example.com/examples/object-key
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}
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``` |