Put WAL lock down into encoder

wal.go

@@ -111,9 +111,6 @@ func (w *WAL) ReadAll(h *walHandler) error {
 
 // Log writes a batch of new series labels and samples to the log.
 func (w *WAL) Log(series []labels.Labels, samples []hashedSample) error {
-	w.mtx.Lock()
-	defer w.mtx.Unlock()
-
 	if err := w.enc.encodeSeries(series); err != nil {
 		return err
 	}
@@ -148,12 +145,9 @@ func (w *WAL) run(interval time.Duration) {
 		case <-w.stopc:
 			return
 		case <-tick:
-			w.mtx.Lock()
-
 			if err := w.sync(); err != nil {
 				w.logger.Log("msg", "sync failed", "err", err)
 			}
-			w.mtx.Unlock()
 		}
 	}
 }
@@ -170,9 +164,8 @@ func (w *WAL) Close() error {
 }
 
 type walEncoder struct {
+	mtx sync.Mutex
 	w   *ioutil.PageWriter
-
-	buf []byte
 }
 
 const (
@@ -191,16 +184,21 @@ func newWALEncoder(f *os.File) (*walEncoder, error) {
 	}
 	enc := &walEncoder{
 		w: ioutil.NewPageWriter(f, walPageBytes, int(offset)),
-		buf: make([]byte, 0, 1024*1024),
 	}
 	return enc, nil
 }
 
 func (e *walEncoder) flush() error {
+	e.mtx.Lock()
+	defer e.mtx.Unlock()
+
 	return e.w.Flush()
 }
 
-func (e *walEncoder) entry(et WALEntryType, flag byte, n int) error {
+func (e *walEncoder) entry(et WALEntryType, flag byte, buf []byte) error {
+	e.mtx.Lock()
+	defer e.mtx.Unlock()
+
 	h := crc32.NewIEEE()
 	w := io.MultiWriter(h, e.w)
 
@@ -208,20 +206,19 @@ func (e *walEncoder) entry(et WALEntryType, flag byte, n int) error {
 	b[0] = byte(et)
 	b[1] = flag
 
-	binary.BigEndian.PutUint32(b[2:], uint32(len(e.buf)))
+	binary.BigEndian.PutUint32(b[2:], uint32(len(buf)))
 
 	if _, err := w.Write(b); err != nil {
 		return err
 	}
-	if _, err := w.Write(e.buf[:n]); err != nil {
+	if _, err := w.Write(buf); err != nil {
 		return err
 	}
 	if _, err := e.w.Write(h.Sum(nil)); err != nil {
 		return err
 	}
 
-	e.buf = e.buf[:0]
-
+	putWALBuffer(buf)
 	return nil
 }
 
@@ -230,29 +227,45 @@ const (
 	walSamplesSimple = 1
 )
 
+var walBuffers = sync.Pool{}
+
+func getWALBuffer() []byte {
+	b := walBuffers.Get()
+	if b == nil {
+		return make([]byte, 0, 64*1024)
+	}
+	return b.([]byte)
+}
+
+func putWALBuffer(b []byte) {
+	b = b[:0]
+	walBuffers.Put(b)
+}
+
 func (e *walEncoder) encodeSeries(series []labels.Labels) error {
 	if len(series) == 0 {
 		return nil
 	}
 
 	b := make([]byte, binary.MaxVarintLen32)
+	buf := getWALBuffer()
 
 	for _, lset := range series {
 		n := binary.PutUvarint(b, uint64(len(lset)))
-		e.buf = append(e.buf, b[:n]...)
+		buf = append(buf, b[:n]...)
 
 		for _, l := range lset {
 			n = binary.PutUvarint(b, uint64(len(l.Name)))
-			e.buf = append(e.buf, b[:n]...)
-			e.buf = append(e.buf, l.Name...)
+			buf = append(buf, b[:n]...)
+			buf = append(buf, l.Name...)
 
 			n = binary.PutUvarint(b, uint64(len(l.Value)))
-			e.buf = append(e.buf, b[:n]...)
-			e.buf = append(e.buf, l.Value...)
+			buf = append(buf, b[:n]...)
+			buf = append(buf, l.Value...)
 		}
 	}
 
-	return e.entry(WALEntrySeries, walSeriesSimple, len(e.buf))
+	return e.entry(WALEntrySeries, walSeriesSimple, buf)
 }
 
 func (e *walEncoder) encodeSamples(samples []hashedSample) error {
@@ -261,6 +274,7 @@ func (e *walEncoder) encodeSamples(samples []hashedSample) error {
 	}
 
 	b := make([]byte, binary.MaxVarintLen64)
+	buf := getWALBuffer()
 
 	// Store base timestamp and base reference number of first sample.
 	// All samples encode their timestamp and ref as delta to those.
@@ -269,22 +283,22 @@ func (e *walEncoder) encodeSamples(samples []hashedSample) error {
 	first := samples[0]
 
 	binary.BigEndian.PutUint32(b, first.ref)
-	e.buf = append(e.buf, b[:4]...)
+	buf = append(buf, b[:4]...)
 	binary.BigEndian.PutUint64(b, uint64(first.t))
-	e.buf = append(e.buf, b[:8]...)
+	buf = append(buf, b[:8]...)
 
 	for _, s := range samples {
 		n := binary.PutVarint(b, int64(s.ref)-int64(first.ref))
-		e.buf = append(e.buf, b[:n]...)
+		buf = append(buf, b[:n]...)
 
 		n = binary.PutVarint(b, s.t-first.t)
-		e.buf = append(e.buf, b[:n]...)
+		buf = append(buf, b[:n]...)
 
 		binary.BigEndian.PutUint64(b, math.Float64bits(s.v))
-		e.buf = append(e.buf, b[:8]...)
+		buf = append(buf, b[:8]...)
 	}
 
-	return e.entry(WALEntrySamples, walSamplesSimple, len(e.buf))
+	return e.entry(WALEntrySamples, walSamplesSimple, buf)
 }
 
 type walDecoder struct {