package consistenthash import ( "fmt" "math" "testing" "github.com/stretchr/testify/assert" "github.com/stretchr/testify/require" "golang.org/x/exp/maps" ) type node string func (n node) ID() string { return string(n) } func TestHash_SingleNode(t *testing.T) { h := New[node]() n1 := node("1") h.AddNode(&n1) require.Equal(t, &n1, h.GetNode("key0")) } func TestHash_TwoNodes(t *testing.T) { h := New[node]() n1 := node("1") h.AddNode(&n1) n2 := node("2") h.AddNode(&n2) n := h.GetNode("key0") require.True(t, n == &n1 || n == &n2) for i := 0; i < 32; i++ { require.Equal(t, n, h.GetNode("key0")) } differs := false for i := 0; i < 32; i++ { other := h.GetNode(fmt.Sprintf("key%d", i)) if other != n { differs = true } } require.True(t, differs) } func TestHash_EvenDistribution(t *testing.T) { h := New[node]() const K = 32 for i := 0; i < K; i++ { n := node(fmt.Sprint(i)) h.AddNode(&n) } counts := map[*node]int{} const N = 1 << 16 for i := 0; i < N; i++ { counts[h.GetNode(fmt.Sprintf("key%d", i))] += 1 } const P = 1 / float64(K) const variance = N * (P) * (1 - P) stddev := math.Sqrt(variance) t.Logf("P = %v, var = %v, stddev = %v", P, variance, stddev) t.Logf("counts = %v", maps.Values(counts)) for _, count := range counts { require.Greater(t, count, int(N/K-stddev*10)) require.Less(t, count, int(N/K+stddev*10)) } } func TestHash_ConsistentDistribution(t *testing.T) { h := New[node]() const K = 32 for i := 0; i < K; i++ { n := node(fmt.Sprint(i)) h.AddNode(&n) } nodes := map[string]*node{} const N = 1 << 16 for i := 0; i < N; i++ { key := fmt.Sprintf("key%d", i) nodes[key] = h.GetNode(key) } newNode := node("new_node") h.AddNode(&newNode) changed := 0 movedToNewNode := 0 for key, oldNode := range nodes { n := h.GetNode(key) if n != oldNode { changed++ } if n == &newNode { movedToNewNode++ } } t.Logf("changed = %d, movedToNewNode = %d", changed, movedToNewNode) assert.Less(t, changed, N/K*2) assert.Equal(t, movedToNewNode, changed) } func BenchmarkHashSpeed(b *testing.B) { for _, K := range []int{32, 1024, 4096} { h := New[node]() for i := 0; i < K; i++ { n := node(fmt.Sprint(i)) h.AddNode(&n) } b.Run(fmt.Sprintf("K=%d", K), func(b *testing.B) { for i := 0; i < b.N; i++ { _ = h.GetNode(fmt.Sprintf("key%d", i)) } }) } }