Memcached: preallocate slice used for grouping cache keys by server

cache/memcached_client.go

@@ -488,7 +488,7 @@ func (c *memcachedClient) sortKeysByServer(keys []string) []string {
 		bucketed[addrString] = append(bucketed[addrString], key)
 	}
 
-	var out []string
+	out := make([]string, 0, len(keys))
 	for srv := range bucketed {
 		out = append(out, bucketed[srv]...)
 	}

cache/memcached_client_test.go

@@ -2,7 +2,8 @@ package cache
 
 import (
 	"context"
-	"errors"
+	"fmt"
+	"hash/crc32"
 	"net"
 	"testing"
 	"time"
@@ -56,6 +57,50 @@ func TestMemcachedClient_GetMulti(t *testing.T) {
 	})
 }
 
+func BenchmarkMemcachedClient_sortKeysByServer(b *testing.B) {
+	mockSelector := &mockServerSelector{
+		servers: []mockServer{
+			{addr: "127.0.0.1"},
+			{addr: "127.0.0.2"},
+			{addr: "127.0.0.3"},
+			{addr: "127.0.0.4"},
+			{addr: "127.0.0.5"},
+			{addr: "127.0.0.6"},
+			{addr: "127.0.0.7"},
+			{addr: "127.0.0.8"},
+		},
+	}
+
+	client, err := newMemcachedClient(
+		log.NewNopLogger(),
+		newMockMemcachedClientBackend(),
+		mockSelector,
+		MemcachedClientConfig{
+			Addresses:           []string{"localhost"},
+			MaxAsyncConcurrency: 1,
+			MaxAsyncBufferSize:  10,
+		},
+		prometheus.NewPedanticRegistry(),
+		"test",
+	)
+
+	if err != nil {
+		b.Fatal("unexpected error creating memcachedClient", err)
+	}
+
+	const numKeys = 10_000
+
+	keys := make([]string, numKeys)
+	for i := 0; i < numKeys; i++ {
+		keys[i] = fmt.Sprintf("some-key:%d", i)
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		client.sortKeysByServer(keys)
+	}
+}
+
 type mockMemcachedClientBackend struct {
 	allocations int
 	values      map[string]*memcache.Item
@@ -99,17 +144,36 @@ func (m *mockMemcachedClientBackend) Delete(key string) error {
 
 func (m *mockMemcachedClientBackend) Close() {}
 
-type mockServerSelector struct{}
+type mockServer struct {
+	addr string
+}
 
-func (m mockServerSelector) SetServers(_ ...string) error {
-	return nil
+func (m mockServer) Network() string {
+	return "tcp"
+}
+
+func (m mockServer) String() string {
+	return m.addr
+}
+
+type mockServerSelector struct {
+	servers []mockServer
 }
 
-func (m mockServerSelector) PickServer(key string) (net.Addr, error) {
-	return nil, errors.New("mock server selector")
+func (s *mockServerSelector) PickServer(key string) (net.Addr, error) {
+	cs := crc32.ChecksumIEEE([]byte(key))
+	return s.servers[cs%uint32(len(s.servers))], nil
 }
+func (s *mockServerSelector) Each(f func(net.Addr) error) error {
+	for _, srv := range s.servers {
+		if err := f(srv); err != nil {
+			return err
+		}
+	}
 
-func (m mockServerSelector) Each(f func(net.Addr) error) error {
+	return nil
+}
+func (s *mockServerSelector) SetServers(_ ...string) error {
 	return nil
 }