Use buffer pool for head appenders

cmd/tsdb/main.go

@@ -150,7 +150,7 @@ func (b *writeBenchmark) ingestScrapes(metrics []model.Metric, scrapeCount int)
 		lbls = append(lbls, lset)
 	}
 
-	for i := 0; i < scrapeCount; i += 25 {
+	for i := 0; i < scrapeCount; i += 50 {
 		lbls := lbls
 		for len(lbls) > 0 {
 			l := 1000
@@ -162,7 +162,7 @@ func (b *writeBenchmark) ingestScrapes(metrics []model.Metric, scrapeCount int)
 
 			wg.Add(1)
 			go func() {
-				n, err := b.ingestScrapesShard(batch, 25, int64(30000*i))
+				n, err := b.ingestScrapesShard(batch, 50, int64(30000*i))
 				if err != nil {
 					// exitWithError(err)
 					fmt.Println(" err", err)

head.go

@@ -107,7 +107,21 @@ func (h *headBlock) Stats() BlockStats {
 
 func (h *headBlock) Appender() Appender {
 	h.mtx.RLock()
-	return &headAppender{headBlock: h}
+	return &headAppender{headBlock: h, samples: getHeadAppendBuffer()}
+}
+
+var headPool = sync.Pool{}
+
+func getHeadAppendBuffer() []hashedSample {
+	b := headPool.Get()
+	if b == nil {
+		return make([]hashedSample, 0, 512)
+	}
+	return b.([]hashedSample)
+}
+
+func putHeadAppendBuffer(b []hashedSample) {
+	headPool.Put(b[:0])
 }
 
 type headAppender struct {
@@ -213,6 +227,7 @@ func (a *headAppender) createSeries() {
 }
 
 func (a *headAppender) Commit() error {
+	defer putHeadAppendBuffer(a.samples)
 	defer a.mtx.RUnlock()
 
 	// Write all new series and samples to the WAL and add it to the