Base HRW implementation in golang

.gitignore

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+.idea
+.vscode
+*.out

README.md

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-# hrw
-Golang simple HRW implementation
+# Golang simple HRW implementation

go.mod

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+module github.com/im-kulikov/hrw
+
+require github.com/reusee/mmh3 v0.0.0-20140820141314-64b85163255b

go.sum

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+github.com/reusee/mmh3 v0.0.0-20140820141314-64b85163255b h1:GQkEnyBFqzQXb3RFqGt5z2QcBZJVQxgzXKF/sPCFh7w=
+github.com/reusee/mmh3 v0.0.0-20140820141314-64b85163255b/go.mod h1:ADBBIMrt68BC/v967NyoiPZMwPVq44r8QJ5oRyXJHJs=

hrw.go

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+// Package hrw implements Rendezvous hashing.
+// http://en.wikipedia.org/wiki/Rendezvous_hashing.
+package hrw
+
+import (
+	"errors"
+	"hash/fnv"
+	"reflect"
+	"sort"
+	"strconv"
+)
+
+type (
+	swapper func(i, j int)
+
+	Hasher interface{ Hash() uint64 }
+
+	hashed struct {
+		length int
+		sorted []uint64
+		weight []uint64
+	}
+)
+
+const m64 = 18446744073709551615 // modulus (2**64-1)
+
+func weight(x uint64, y uint64) uint64 {
+	acc := x ^ y
+	acc ^= acc >> 33
+	acc = (acc * 0xff51afd7ed558ccd) % m64
+	acc ^= acc >> 33
+	acc = (acc * 0xc4ceb9fe1a85ec53) % m64
+	acc ^= acc >> 33
+	return acc
+}
+
+func (h hashed) Len() int           { return h.length }
+func (h hashed) Less(i, j int) bool { return h.weight[h.sorted[i]] < h.weight[h.sorted[j]] }
+func (h hashed) Swap(i, j int)      { h.sorted[i], h.sorted[j] = h.sorted[j], h.sorted[i] }
+
+func SortByWeight(nodes []uint64, hash uint64) []uint64 {
+	var (
+		l = len(nodes)
+		h = hashed{
+			length: l,
+			sorted: make([]uint64, 0, l),
+			weight: make([]uint64, 0, l),
+		}
+	)
+
+	for i, node := range nodes {
+		h.sorted = append(h.sorted, uint64(i))
+		h.weight = append(h.weight, weight(node, hash))
+	}
+
+	sort.Sort(h)
+	return h.sorted
+}
+
+func SortSliceByValue(slice interface{}, hash uint64) error {
+	t := reflect.TypeOf(slice)
+	if t.Kind() != reflect.Slice {
+		return errors.New("must be slice")
+	}
+
+	var (
+		val    = reflect.ValueOf(slice)
+		swap   = reflect.Swapper(slice)
+		length = val.Len()
+		rule   = make([]uint64, 0, length)
+	)
+
+	if length == 0 {
+		return nil
+	}
+
+	switch slice := slice.(type) {
+	case []int:
+		hasher := fnv.New64()
+		for i := 0; i < length; i++ {
+			hasher.Reset()
+			// error always nil
+			_, _ = hasher.Write([]byte(strconv.Itoa(slice[i])))
+			rule = append(rule, weight(hash, hasher.Sum64()))
+		}
+	case []string:
+		hasher := fnv.New64()
+		for i := 0; i < length; i++ {
+			hasher.Reset()
+			// error always nil
+			_, _ = hasher.Write([]byte(slice[i]))
+			rule = append(rule, weight(hash, hasher.Sum64()))
+		}
+	default:
+		if _, ok := val.Index(0).Interface().(Hasher); !ok {
+			return errors.New("unknown type")
+		}
+
+		for i := 0; i < length; i++ {
+			h := val.Index(i).Interface().(Hasher)
+			rule = append(rule, weight(hash, h.Hash()))
+		}
+	}
+
+	rule = SortByWeight(rule, hash)
+	sortByRule(swap, uint64(length), rule)
+
+	return nil
+}
+
+func SortSliceByIndex(slice interface{}, hash uint64) {
+	length := uint64(reflect.ValueOf(slice).Len())
+	swap := reflect.Swapper(slice)
+
+	rule := make([]uint64, 0, length)
+	for i := uint64(0); i < length; i++ {
+		rule = append(rule, i)
+	}
+
+	rule = SortByWeight(rule, hash)
+	sortByRule(swap, length, rule)
+}
+
+func sortByRule(swap swapper, length uint64, rule []uint64) {
+	done := make([]bool, length)
+	for i := uint64(0); i < length; i++ {
+		if done[i] {
+			continue
+		}
+
+		done[i] = true
+
+		for j := rule[i]; !done[rule[j]]; j = rule[j] {
+			swap(int(i), int(j))
+			done[j] = true
+		}
+	}
+}

hrw_test.go

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+package hrw
+
+import (
+	"encoding/binary"
+	"fmt"
+	"hash/fnv"
+	"reflect"
+	"strconv"
+	"testing"
+
+	"github.com/reusee/mmh3"
+)
+
+type hashString string
+
+var testKey = []byte("Golang simple HRW implementation")
+
+func Example() {
+	// given a set of servers
+	servers := []string{
+		"one.example.com",
+		"two.example.com",
+		"three.example.com",
+		"four.example.com",
+		"five.example.com",
+		"six.example.com",
+	}
+
+	// HRW can consistently select a uniformly-distributed set of servers for
+	// any given key
+	var (
+		key = []byte("/examples/object-key")
+		h   = hash(key)
+		err = SortSliceByValue(servers, h)
+	)
+
+	if err != nil {
+		panic(err)
+	}
+
+	for id := range servers {
+		fmt.Printf("trying GET %s%s\n", servers[id], key)
+	}
+
+	// Output:
+	// trying GET six.example.com/examples/object-key
+	// trying GET one.example.com/examples/object-key
+	// trying GET three.example.com/examples/object-key
+	// trying GET four.example.com/examples/object-key
+	// trying GET five.example.com/examples/object-key
+	// trying GET two.example.com/examples/object-key
+}
+func (h hashString) Hash() uint64 {
+	hs := fnv.New64()
+	// error always nil
+	_, _ = hs.Write([]byte(h))
+	return (hs.Sum64() >> 1) % m64
+}
+
+func hash(key []byte) uint64 {
+	h := fnv.New64()
+	// error always nil
+	_, _ = h.Write(key)
+	return (h.Sum64() >> 1) ^ m64
+}
+
+func mur3hash(key []byte) uint64 {
+	h := mmh3.New128()
+	// error always nil
+	_, _ = h.Write(key)
+
+	var (
+		data   = h.Sum(nil)
+		length = len(data)
+		result uint64
+	)
+
+	for i := 0; i < length; i++ {
+		result += uint64(data[i]) << uint64(length-i)
+	}
+
+	return result
+}
+
+func TestSortSliceByIndex(t *testing.T) {
+	actual := []string{"a", "b", "c", "d", "e", "f"}
+	expect := []string{"e", "a", "c", "d", "b", "f"}
+
+	hash := hash(testKey)
+
+	SortSliceByIndex(actual, hash)
+	if !reflect.DeepEqual(actual, expect) {
+		t.Errorf("Was %#v, but expected %#v", actual, expect)
+	}
+}
+
+func TestSortSliceByValue(t *testing.T) {
+	actual := []string{"a", "b", "c", "d", "e", "f"}
+	expect := []string{"e", "b", "c", "d", "f", "a"}
+
+	hash := hash(testKey)
+
+	if err := SortSliceByValue(actual, hash); err != nil {
+		t.Fatal(err)
+	}
+
+	if !reflect.DeepEqual(actual, expect) {
+		t.Errorf("Was %#v, but expected %#v", actual, expect)
+	}
+}
+
+func TestSortSliceByValueFail(t *testing.T) {
+	t.Run("empty slice", func(t *testing.T) {
+		actual := make([]int, 0)
+		hash := hash(testKey)
+
+		if err := SortSliceByValue(actual, hash); err != nil {
+			t.Fatal(err)
+		}
+
+	})
+
+	t.Run("must be slice", func(t *testing.T) {
+		actual := 10
+		hash := hash(testKey)
+
+		if err := SortSliceByValue(actual, hash); err == nil {
+			t.Fatal("must fail for bad type")
+		}
+
+	})
+
+	t.Run("must fail for unknown type", func(t *testing.T) {
+		actual := []byte{1, 2, 3, 4, 5}
+		hash := hash(testKey)
+
+		if err := SortSliceByValue(actual, hash); err == nil {
+			t.Fatal("must fail for bad type")
+		}
+	})
+}
+
+func TestSortSliceByValueHasher(t *testing.T) {
+	actual := []hashString{"a", "b", "c", "d", "e", "f"}
+	expect := []hashString{"e", "d", "c", "a", "b", "f"}
+
+	hash := hash(testKey)
+
+	if err := SortSliceByValue(actual, hash); err != nil {
+		t.Fatal(err)
+	}
+
+	if !reflect.DeepEqual(actual, expect) {
+		t.Errorf("Was %#v, but expected %#v", actual, expect)
+	}
+}
+
+func TestSortSliceByValueIntSlice(t *testing.T) {
+	actual := []int{0, 1, 2, 3, 4, 5}
+	expect := []int{2, 0, 5, 3, 4, 1}
+
+	hash := hash(testKey)
+
+	if err := SortSliceByValue(actual, hash); err != nil {
+		t.Fatal(err)
+	}
+
+	if !reflect.DeepEqual(actual, expect) {
+		t.Errorf("Was %#v, but expected %#v", actual, expect)
+	}
+}
+
+func TestSortByWeight(t *testing.T) {
+	nodes := []uint64{1, 2, 3, 4, 5}
+	hash := mur3hash(testKey)
+
+	actual := SortByWeight(nodes, hash)
+	expected := []uint64{0, 1, 4, 2, 3}
+	if !reflect.DeepEqual(actual, expected) {
+		t.Errorf("Was %#v, but expected %#v", actual, expected)
+	}
+}
+
+func TestUniformDistribution(t *testing.T) {
+	var (
+		i      uint64
+		size   = uint64(4)
+		nodes  = make([]uint64, 0, size)
+		counts = make(map[uint64]uint64)
+		key    = make([]byte, 16)
+		keys   = uint64(10000000)
+	)
+
+	for i = 0; i < size; i++ {
+		nodes = append(nodes, i)
+	}
+
+	for i = 0; i < keys; i++ {
+		binary.BigEndian.PutUint64(key, i)
+		hash := hash(key)
+		counts[SortByWeight(nodes, hash)[0]]++
+	}
+
+	mean := float64(keys) / float64(len(nodes))
+	delta := mean * 0.002 // 0.2%
+	for node, count := range counts {
+		d := mean - float64(count)
+		if d > delta || (0-d) > delta {
+			t.Errorf(
+				"Node %d received %d keys, expected %v (+/- %v)",
+				node, count, mean, delta,
+			)
+		}
+	}
+}
+
+func BenchmarkSortByWeight_fnv_10(b *testing.B) {
+	hash := hash(testKey)
+	_ = benchmarkSortByWeight(b, 10, hash)
+}
+
+func BenchmarkSortByWeight_fnv_100(b *testing.B) {
+	hash := hash(testKey)
+	_ = benchmarkSortByWeight(b, 100, hash)
+}
+
+func BenchmarkSortByWeight_fnv_1000(b *testing.B) {
+	hash := hash(testKey)
+	_ = benchmarkSortByWeight(b, 1000, hash)
+}
+
+func BenchmarkSortByIndex_fnv_10(b *testing.B) {
+	hash := hash(testKey)
+	benchmarkSortByIndex(b, 10, hash)
+}
+
+func BenchmarkSortByIndex_fnv_100(b *testing.B) {
+	hash := hash(testKey)
+	benchmarkSortByIndex(b, 100, hash)
+}
+
+func BenchmarkSortByIndex_fnv_1000(b *testing.B) {
+	hash := hash(testKey)
+	benchmarkSortByIndex(b, 1000, hash)
+}
+
+func BenchmarkSortByValue_fnv_10(b *testing.B) {
+	hash := hash(testKey)
+	benchmarkSortByValue(b, 10, hash)
+}
+
+func BenchmarkSortByValue_fnv_100(b *testing.B) {
+	hash := hash(testKey)
+	benchmarkSortByValue(b, 100, hash)
+}
+
+func BenchmarkSortByValue_fnv_1000(b *testing.B) {
+	hash := hash(testKey)
+	benchmarkSortByValue(b, 1000, hash)
+}
+
+func benchmarkSortByWeight(b *testing.B, n int, hash uint64) uint64 {
+	servers := make([]uint64, n)
+	for i := uint64(0); i < uint64(len(servers)); i++ {
+		servers[i] = i
+	}
+
+	b.ResetTimer()
+	b.ReportAllocs()
+
+	var x uint64
+	for i := 0; i < b.N; i++ {
+		x += SortByWeight(servers, hash)[0]
+	}
+	return x
+}
+
+func benchmarkSortByIndex(b *testing.B, n int, hash uint64) {
+	servers := make([]uint64, n)
+	for i := uint64(0); i < uint64(len(servers)); i++ {
+		servers[i] = i
+	}
+
+	b.ResetTimer()
+	b.ReportAllocs()
+
+	for i := 0; i < b.N; i++ {
+		SortSliceByIndex(servers, hash)
+	}
+}
+
+func benchmarkSortByValue(b *testing.B, n int, hash uint64) {
+	servers := make([]string, n)
+	for i := uint64(0); i < uint64(len(servers)); i++ {
+		servers[i] = "localhost:" + strconv.FormatUint(60000-i, 10)
+	}
+
+	b.ResetTimer()
+	b.ReportAllocs()
+
+	for i := 0; i < b.N; i++ {
+		if err := SortSliceByValue(servers, hash); err != nil {
+			b.Fatal(err)
+		}
+	}
+}