Reduce allocations

Store temporary buffers in a sync.Pool.

Create one httpGetter per peer when Set() is called so we don't
allocate a new one on each call PickPeer().

http.go

@@ -17,8 +17,9 @@ limitations under the License.
 package groupcache
 
 import (
+ "bytes"
  "fmt"
- "io/ioutil"
+ "io"
  "net/http"
  "net/url"
  "strings"
@@ -51,8 +52,9 @@ type HTTPPool struct {
  // this peer's base URL, e.g. "https://example.net:8000"
  self string
 
- mu sync.Mutex
- peers *consistenthash.Map
+ mu sync.Mutex // guards peers and httpGetters
+ peers *consistenthash.Map
+ httpGetters map[string]*httpGetter // keyed by e.g. "http:https://10.0.0.2:8008"
 }
 
 // HTTPPoolOptions are the configurations of a HTTPPool.
@@ -103,9 +105,10 @@ func NewHTTPPoolOpts(self string, o *HTTPPoolOptions) *HTTPPool {
  }
 
  p := &HTTPPool{
- basePath: opts.BasePath,
- self: self,
- peers: consistenthash.New(opts.Replicas, opts.HashFn),
+ basePath: opts.BasePath,
+ self: self,
+ peers: consistenthash.New(opts.Replicas, opts.HashFn),
+ httpGetters: make(map[string]*httpGetter),
  }
  RegisterPeerPicker(func() PeerPicker { return p })
  return p
@@ -119,6 +122,10 @@ func (p *HTTPPool) Set(peers ...string) {
  defer p.mu.Unlock()
  p.peers = consistenthash.New(defaultReplicas, nil)
  p.peers.Add(peers...)
+ p.httpGetters = make(map[string]*httpGetter, len(peers))
+ for _, peer := range peers {
+ p.httpGetters[peer] = &httpGetter{transport: p.Transport, baseURL: peer + p.basePath}
+ }
 }
 
 func (p *HTTPPool) PickPeer(key string) (ProtoGetter, bool) {
@@ -128,9 +135,7 @@ func (p *HTTPPool) PickPeer(key string) (ProtoGetter, bool) {
  return nil, false
  }
  if peer := p.peers.Get(key); peer != p.self {
- // TODO: pre-build a slice of *httpGetter when Set()
- // is called to avoid these two allocations.
- return &httpGetter{p.Transport, peer + p.basePath}, true
+ return p.httpGetters[peer], true
  }
  return nil, false
 }
@@ -182,6 +187,10 @@ type httpGetter struct {
  baseURL string
 }
 
+var bufferPool = sync.Pool{
+ New: func() interface{} { return new(bytes.Buffer) },
+}
+
 func (h *httpGetter) Get(context Context, in *pb.GetRequest, out *pb.GetResponse) error {
  u := fmt.Sprintf(
  "%v%v/%v",
@@ -205,12 +214,14 @@ func (h *httpGetter) Get(context Context, in *pb.GetRequest, out *pb.GetResponse
  if res.StatusCode != http.StatusOK {
  return fmt.Errorf("server returned: %v", res.Status)
  }
- // TODO: avoid this garbage.
- b, err := ioutil.ReadAll(res.Body)
+ b := bufferPool.Get().(*bytes.Buffer)
+ b.Reset()
+ defer bufferPool.Put(b)
+ _, err = io.Copy(b, res.Body)
  if err != nil {
  return fmt.Errorf("reading response body: %v", err)
  }
- err = proto.Unmarshal(b, out)
+ err = proto.Unmarshal(b.Bytes(), out)
  if err != nil {
  return fmt.Errorf("decoding response body: %v", err)
  }