package hrw import ( "encoding/binary" "fmt" "math" "reflect" "strconv" "testing" ) type ( hashString string unknown byte slices struct { actual interface{} expect interface{} } Uint32Slice []uint32 ) var testKey = []byte("0xff51afd7ed558ccd") func (p Uint32Slice) Len() int { return len(p) } func (p Uint32Slice) Less(i, j int) bool { return p[i] < p[j] } func (p Uint32Slice) Swap(i, j int) { p[i], p[j] = p[j], p[i] } 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) ) SortSliceByValue(servers, h) for id := range servers { fmt.Printf("trying GET %s%s\n", servers[id], key) } // Output: // trying GET four.example.com/examples/object-key // trying GET three.example.com/examples/object-key // trying GET one.example.com/examples/object-key // trying GET two.example.com/examples/object-key // trying GET six.example.com/examples/object-key // trying GET five.example.com/examples/object-key } func (h hashString) Hash() uint64 { return Hash([]byte(h)) } func TestSortSliceByIndex(t *testing.T) { actual := []string{"a", "b", "c", "d", "e", "f"} expect := []string{"e", "a", "c", "f", "d", "b"} 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{"d", "b", "a", "f", "c", "e"} hash := Hash(testKey) SortSliceByValue(actual, hash) if !reflect.DeepEqual(actual, expect) { t.Errorf("Was %#v, but expected %#v", actual, expect) } } func TestSortByRule(t *testing.T) { t.Run("direct", func(t *testing.T) { // 0 1 2 3 4 5 actual := []string{"a", "b", "c", "d", "e", "f"} // 4 2 0 5 3 1 expect := []string{"c", "f", "b", "e", "a", "d"} rule := []uint64{4, 2, 0, 5, 3, 1} sortByRuleDirect( func(i, j int) { actual[i], actual[j] = actual[j], actual[i] }, 6, rule) if !reflect.DeepEqual(actual, expect) { t.Errorf("Was %#v, but expected %#v", actual, expect) } }) t.Run("inverse", func(t *testing.T) { // 0 1 2 3 4 5 actual := []string{"a", "b", "c", "d", "e", "f"} // 4 2 0 5 3 1 expect := []string{"e", "c", "a", "f", "d", "b"} rule := []uint64{4, 2, 0, 5, 3, 1} sortByRuleInverse( func(i, j int) { actual[i], actual[j] = actual[j], actual[i] }, 6, rule) 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) { var ( actual []int hash = Hash(testKey) ) SortSliceByValue(actual, hash) }) t.Run("must be slice", func(t *testing.T) { actual := 10 hash := Hash(testKey) SortSliceByValue(actual, hash) }) t.Run("must 'fail' for unknown type", func(t *testing.T) { actual := []unknown{1, 2, 3, 4, 5} expect := []unknown{1, 2, 3, 4, 5} hash := Hash(testKey) SortSliceByValue(actual, hash) if !reflect.DeepEqual(actual, expect) { t.Errorf("Was %#v, but expected %#v", actual, expect) } }) } func TestSortSliceByValueHasher(t *testing.T) { actual := []hashString{"a", "b", "c", "d", "e", "f"} expect := []hashString{"d", "b", "a", "f", "c", "e"} hash := Hash(testKey) SortSliceByValue(actual, hash) if !reflect.DeepEqual(actual, expect) { t.Errorf("Was %#v, but expected %#v", actual, expect) } } func TestSortSliceByValueIntSlice(t *testing.T) { cases := []slices{ { actual: []int{0, 1, 2, 3, 4, 5}, expect: []int{2, 3, 1, 4, 0, 5}, }, { actual: []uint{0, 1, 2, 3, 4, 5}, expect: []uint{2, 3, 1, 4, 0, 5}, }, { actual: []int8{0, 1, 2, 3, 4, 5}, expect: []int8{2, 0, 5, 1, 4, 3}, }, { actual: []uint8{0, 1, 2, 3, 4, 5}, expect: []uint8{2, 0, 5, 1, 4, 3}, }, { actual: []int16{0, 1, 2, 3, 4, 5}, expect: []int16{5, 4, 0, 3, 2, 1}, }, { actual: []uint16{0, 1, 2, 3, 4, 5}, expect: []uint16{5, 4, 0, 3, 2, 1}, }, { actual: []int32{0, 1, 2, 3, 4, 5}, expect: []int32{1, 3, 5, 4, 2, 0}, }, { actual: []uint32{0, 1, 2, 3, 4, 5}, expect: []uint32{1, 3, 5, 4, 2, 0}, }, { actual: Uint32Slice{0, 1, 2, 3, 4, 5}, expect: Uint32Slice{0, 1, 2, 3, 4, 5}, }, { actual: []int64{0, 1, 2, 3, 4, 5}, expect: []int64{1, 5, 3, 4, 2, 0}, }, { actual: []uint64{0, 1, 2, 3, 4, 5}, expect: []uint64{1, 5, 3, 4, 2, 0}, }, } hash := Hash(testKey) for _, tc := range cases { SortSliceByValue(tc.actual, hash) if !reflect.DeepEqual(tc.actual, tc.expect) { t.Errorf("Was %#v, but expected %#v", tc.actual, tc.expect) } } } func TestSortByWeight(t *testing.T) { nodes := []uint64{1, 2, 3, 4, 5} hash := Hash(testKey) actual := SortByWeight(nodes, hash) expected := []uint64{3, 1, 4, 2, 0} if !reflect.DeepEqual(actual, expected) { t.Errorf("Was %#v, but expected %#v", actual, expected) } } func TestUniformDistribution(t *testing.T) { const ( size = 10 keys = 100000 percent = 0.03 ) // We use χ2 method to determine similarity of distribution with uniform distribution. // χ2 = Σ((n-N)**2/N) // https://www.medcalc.org/manual/chi-square-table.php p=0.1 var chiTable = map[int]float64{9: 14.68, 99: 117.407} t.Run("sortByWeight", func(t *testing.T) { var ( i uint64 nodes [size]uint64 counts = make(map[uint64]uint64, size) key = make([]byte, 16) ) for i = 0; i < size; i++ { nodes[i] = i } for i = 0; i < keys; i++ { binary.BigEndian.PutUint64(key, i) hash := Hash(key) counts[SortByWeight(nodes[:], hash)[0]]++ } var chi2 float64 mean := float64(keys) / float64(size) delta := mean * percent for node, count := range counts { d := mean - float64(count) chi2 += math.Pow(float64(count)-mean, 2) / mean if d > delta || (0-d) > delta { t.Errorf( "Node %d received %d keys, expected %.0f (+/- %.2f)", node, count, mean, delta, ) } } if chi2 > chiTable[size-1] { t.Errorf( "Chi2 condition for .9 is not met (expected %.2f <= %.2f)", chi2, chiTable[size-1]) } }) t.Run("sortByIndex", func(t *testing.T) { var ( i uint64 a, b [size]uint64 counts = make(map[uint64]int, size) key = make([]byte, 16) ) for i = 0; i < size; i++ { a[i] = i } for i = 0; i < keys; i++ { copy(b[:], a[:]) binary.BigEndian.PutUint64(key, i) hash := Hash(key) SortSliceByIndex(b[:], hash) counts[b[0]]++ } var chi2 float64 mean := float64(keys) / float64(size) delta := mean * percent for node, count := range counts { d := mean - float64(count) chi2 += math.Pow(float64(count)-mean, 2) / mean if d > delta || (0-d) > delta { t.Errorf( "Node %d received %d keys, expected %.0f (+/- %.2f)", node, count, mean, delta, ) } } if chi2 > chiTable[size-1] { t.Errorf( "Chi2 condition for .9 is not met (expected %.2f <= %.2f)", chi2, chiTable[size-1]) } }) t.Run("sortByValue", func(t *testing.T) { var ( i uint64 a, b [size]int counts = make(map[int]int, size) key = make([]byte, 16) ) for i = 0; i < size; i++ { a[i] = int(i) } for i = 0; i < keys; i++ { copy(b[:], a[:]) binary.BigEndian.PutUint64(key, i) hash := Hash(key) SortSliceByValue(b[:], hash) counts[b[0]]++ } var chi2 float64 mean := float64(keys) / float64(size) delta := mean * percent for node, count := range counts { d := mean - float64(count) chi2 += math.Pow(float64(count)-mean, 2) / mean if d > delta || (0-d) > delta { t.Errorf( "Node %d received %d keys, expected %.0f (+/- %.2f)", node, count, mean, delta, ) } } if chi2 > chiTable[size-1] { t.Errorf( "Chi2 condition for .9 is not met (expected %.2f <= %.2f)", chi2, chiTable[size-1]) } }) t.Run("sortByStringValue", func(t *testing.T) { var ( i uint64 a, b [size]string counts = make(map[string]int, size) key = make([]byte, 16) ) for i = 0; i < size; i++ { a[i] = strconv.FormatUint(i, 10) } for i = 0; i < keys; i++ { copy(b[:], a[:]) binary.BigEndian.PutUint64(key, i) hash := Hash(key) SortSliceByValue(b[:], hash) counts[b[0]]++ } var chi2 float64 mean := float64(keys) / float64(size) delta := mean * percent for node, count := range counts { d := mean - float64(count) chi2 += math.Pow(float64(count)-mean, 2) / mean if d > delta || (0-d) > delta { t.Errorf( "Node %s received %d keys, expected %.0f (+/- %.2f)", node, count, mean, delta, ) } } if chi2 > chiTable[size-1] { t.Errorf( "Chi2 condition for .9 is not met (expected %.2f <= %.2f)", chi2, chiTable[size-1]) } }) t.Run("sortByInt32Value", func(t *testing.T) { var ( i uint64 a, b [size]int32 counts = make(map[int32]int, size) key = make([]byte, 16) ) for i = 0; i < size; i++ { a[i] = int32(i) } for i = 0; i < keys; i++ { copy(b[:], a[:]) binary.BigEndian.PutUint64(key, i) hash := Hash(key) SortSliceByValue(b[:], hash) counts[b[0]]++ } var chi2 float64 mean := float64(keys) / float64(size) delta := mean * percent for node, count := range counts { d := mean - float64(count) chi2 += math.Pow(float64(count)-mean, 2) / mean if d > delta || (0-d) > delta { t.Errorf( "Node %d received %d keys, expected %.0f (+/- %.2f)", node, count, mean, delta, ) } } if chi2 > chiTable[size-1] { t.Errorf( "Chi2 condition for .9 is not met (expected %.2f <= %.2f)", chi2, chiTable[size-1]) } }) t.Run("hash collision", func(t *testing.T) { var ( i uint64 counts = make(map[uint64]uint64) key = make([]byte, 16) ) for i = 0; i < keys; i++ { binary.BigEndian.PutUint64(key, i) hash := Hash(key) counts[hash]++ } for node, count := range counts { if count > 1 { t.Errorf("Node %d received %d keys", node, count) } } }) } 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++ { SortSliceByValue(servers, hash) } }