From d11ee103acd9eb46a28b621828604b2446a0887a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Gy=C3=B6rgy=20Krajcsovits?= <gyorgy.krajcsovits@grafana.com>
Date: Mon, 6 Oct 2025 21:44:34 +0200
Subject: [PATCH] perf(tsdb): reuse map of sample types to speed up head
 appender
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While investigating +10% CPU in v3.7 release, found that ~5% is from
expanding the types map. Try reuse.

Also fix a linter error.

Signed-off-by: György Krajcsovits <gyorgy.krajcsovits@grafana.com>
---
 tsdb/head.go                       |  1 +
 tsdb/head_append.go                | 21 ++++++++++++++++++++-
 util/testutil/synctest/disabled.go |  2 +-
 3 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/tsdb/head.go b/tsdb/head.go
index 45f425cea9..f3242b8ba7 100644
--- a/tsdb/head.go
+++ b/tsdb/head.go
@@ -93,6 +93,7 @@ type Head struct {
 	floatHistogramsPool zeropool.Pool[[]record.RefFloatHistogramSample]
 	metadataPool        zeropool.Pool[[]record.RefMetadata]
 	seriesPool          zeropool.Pool[[]*memSeries]
+	typeMapPool         zeropool.Pool[map[chunks.HeadSeriesRef]sampleType]
 	bytesPool           zeropool.Pool[[]byte]
 	memChunkPool        sync.Pool
 
diff --git a/tsdb/head_append.go b/tsdb/head_append.go
index 659c09f7e7..9f930a763f 100644
--- a/tsdb/head_append.go
+++ b/tsdb/head_append.go
@@ -173,7 +173,7 @@ func (h *Head) appender() *headAppender {
 		oooTimeWindow:         h.opts.OutOfOrderTimeWindow.Load(),
 		seriesRefs:            h.getRefSeriesBuffer(),
 		series:                h.getSeriesBuffer(),
-		typesInBatch:          map[chunks.HeadSeriesRef]sampleType{},
+		typesInBatch:          h.getTypeMap(),
 		appendID:              appendID,
 		cleanupAppendIDsBelow: cleanupAppendIDsBelow,
 	}
@@ -297,6 +297,19 @@ func (h *Head) putSeriesBuffer(b []*memSeries) {
 	h.seriesPool.Put(b[:0])
 }
 
+func (h *Head) getTypeMap() map[chunks.HeadSeriesRef]sampleType {
+	b := h.typeMapPool.Get()
+	if b == nil {
+		return make(map[chunks.HeadSeriesRef]sampleType)
+	}
+	return b
+}
+
+func (h *Head) putTypeMap(b map[chunks.HeadSeriesRef]sampleType) {
+	clear(b)
+	h.typeMapPool.Put(b)
+}
+
 func (h *Head) getBytesBuffer() []byte {
 	b := h.bytesPool.Get()
 	if b == nil {
@@ -1687,8 +1700,13 @@ func (a *headAppender) Commit() (err error) {
 	h := a.head
 
 	defer func() {
+		if a.closed {
+			// Don't double-close in case Rollback() was called.
+			return
+		}
 		h.putRefSeriesBuffer(a.seriesRefs)
 		h.putSeriesBuffer(a.series)
+		h.putTypeMap(a.typesInBatch)
 		a.closed = true
 	}()
 
@@ -2216,6 +2234,7 @@ func (a *headAppender) Rollback() (err error) {
 		a.closed = true
 		h.putRefSeriesBuffer(a.seriesRefs)
 		h.putSeriesBuffer(a.series)
+		h.putTypeMap(a.typesInBatch)
 	}()
 
 	var series *memSeries
diff --git a/util/testutil/synctest/disabled.go b/util/testutil/synctest/disabled.go
index 2cdcc72e07..e87454afcf 100644
--- a/util/testutil/synctest/disabled.go
+++ b/util/testutil/synctest/disabled.go
@@ -19,7 +19,7 @@ import (
 	"testing"
 )
 
-func Test(t *testing.T, f func(t *testing.T)) {
+func Test(t *testing.T, _ func(t *testing.T)) {
 	t.Skip("goexperiment.synctest is not enabled")
 }