hrw/hrw_test.go

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package hrw
import (
"encoding/binary"
"fmt"
"math"
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"reflect"
"strconv"
"testing"
)
type hashString string
var testKey = []byte("0xff51afd7ed558ccd")
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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)
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)
SortSliceByValue(servers, h)
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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
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// trying GET two.example.com/examples/object-key
// trying GET six.example.com/examples/object-key
// trying GET five.example.com/examples/object-key
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}
func (h hashString) Hash() uint64 {
return Hash([]byte(h))
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}
func TestSortSliceByIndex(t *testing.T) {
actual := []string{"a", "b", "c", "d", "e", "f"}
expect := []string{"e", "a", "c", "f", "d", "b"}
hash := Hash(testKey)
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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)
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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}
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sortByRuleDirect(
func(i, j int) { actual[i], actual[j] = actual[j], actual[i] },
6, rule)
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if !reflect.DeepEqual(actual, expect) {
t.Errorf("Was %#v, but expected %#v", actual, expect)
}
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})
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)
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if !reflect.DeepEqual(actual, expect) {
t.Errorf("Was %#v, but expected %#v", actual, expect)
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}
})
}
func TestSortSliceByValueFail(t *testing.T) {
t.Run("empty slice", func(t *testing.T) {
var (
actual []int
hash = Hash(testKey)
)
SortSliceByValue(actual, hash)
})
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t.Run("must be slice", func(t *testing.T) {
actual := 10
hash := Hash(testKey)
SortSliceByValue(actual, hash)
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})
t.Run("must 'fail' for unknown type", func(t *testing.T) {
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actual := []byte{1, 2, 3, 4, 5}
expect := []byte{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)
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}
})
}
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)
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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, 3, 1, 4, 0, 5}
hash := Hash(testKey)
SortSliceByValue(actual, hash)
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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 := Hash(testKey)
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actual := SortByWeight(nodes, hash)
expected := []uint64{3, 1, 4, 2, 0}
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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
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)
// 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
}
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for i = 0; i < keys; i++ {
binary.BigEndian.PutUint64(key, i)
hash := Hash(key)
counts[SortByWeight(nodes[:], hash)[0]]++
}
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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])
}
})
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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] {
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t.Errorf(
"Chi2 condition for .9 is not met (expected %.2f <= %.2f)",
chi2, chiTable[size-1])
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}
})
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("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)
}
}
})
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}
func BenchmarkSortByWeight_fnv_10(b *testing.B) {
hash := Hash(testKey)
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_ = benchmarkSortByWeight(b, 10, hash)
}
func BenchmarkSortByWeight_fnv_100(b *testing.B) {
hash := Hash(testKey)
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_ = benchmarkSortByWeight(b, 100, hash)
}
func BenchmarkSortByWeight_fnv_1000(b *testing.B) {
hash := Hash(testKey)
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_ = benchmarkSortByWeight(b, 1000, hash)
}
func BenchmarkSortByIndex_fnv_10(b *testing.B) {
hash := Hash(testKey)
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benchmarkSortByIndex(b, 10, hash)
}
func BenchmarkSortByIndex_fnv_100(b *testing.B) {
hash := Hash(testKey)
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benchmarkSortByIndex(b, 100, hash)
}
func BenchmarkSortByIndex_fnv_1000(b *testing.B) {
hash := Hash(testKey)
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benchmarkSortByIndex(b, 1000, hash)
}
func BenchmarkSortByValue_fnv_10(b *testing.B) {
hash := Hash(testKey)
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benchmarkSortByValue(b, 10, hash)
}
func BenchmarkSortByValue_fnv_100(b *testing.B) {
hash := Hash(testKey)
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benchmarkSortByValue(b, 100, hash)
}
func BenchmarkSortByValue_fnv_1000(b *testing.B) {
hash := Hash(testKey)
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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)
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}
}