optimize map allocation

.chloggen/prometheusremotewritereceiver-optimize-map-allocation.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. receiver/filelog)
+component: receiver/prometheusremotewrite
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Map.PutStr causes excessive memory allocations due to repeated slice expansions
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [44612]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]

receiver/prometheusremotewritereceiver/receiver.go

@@ -737,7 +737,10 @@ func convertAbsoluteBuckets(spans []writev2.BucketSpan, counts []float64, bucket
 // extractAttributes return all attributes different from job, instance, metric name and scope name/version
 func extractAttributes(ls labels.Labels) pcommon.Map {
 	attrs := pcommon.NewMap()
-	for labelName, labelValue := range ls.Map() {
+	labelMap := ls.Map()
+	// job, instance and metric name will always become labels
+	attrs.EnsureCapacity(len(labelMap) - 3)
+	for labelName, labelValue := range labelMap {
 		if labelName == "instance" || labelName == "job" || // Become resource attributes
 			labelName == labels.MetricName || // Becomes metric name
 			labelName == "otel_scope_name" || labelName == "otel_scope_version" { // Becomes scope name and version

receiver/prometheusremotewritereceiver/receiver_bench_test.go

@@ -0,0 +1,42 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package prometheusremotewritereceiver
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/prometheus/prometheus/model/labels"
+)
+
+// makeLabels builds a labels.Labels with the given total number of labels.
+// It always includes "job", "instance", and the metric name label, plus (total-3) extra labels.
+func makeLabels(total int) labels.Labels {
+	if total < 3 {
+		total = 3
+	}
+	m := make(map[string]string, total)
+	m["job"] = "job"
+	m["instance"] = "instance"
+	m["__name__"] = "metric"
+	for i := 0; i < total-3; i++ {
+		m[fmt.Sprintf("k%d", i)] = fmt.Sprintf("v%d", i)
+	}
+	return labels.FromMap(m)
+}
+
+func BenchmarkExtractAttributes(b *testing.B) {
+	sizes := []int{5, 20, 100, 500, 1000, 2000}
+	for _, sz := range sizes {
+		ls := makeLabels(sz)
+		b.Run(fmt.Sprintf("%d", sz), func(b *testing.B) {
+			b.ReportAllocs()
+			b.ResetTimer()
+			for i := 0; i < b.N; i++ {
+				m := extractAttributes(ls)
+				_ = m.Len()
+			}
+		})
+	}
+}