Merge pull request #12084 from bboreham/target-labels

scraping: reduce memory allocations on Target labels

scrape/scrape.go

@@ -500,9 +500,12 @@ func (sp *scrapePool) Sync(tgs []*targetgroup.Group) {
 		}
 		targetSyncFailed.WithLabelValues(sp.config.JobName).Add(float64(len(failures)))
 		for _, t := range targets {
-			if !t.Labels().IsEmpty() {
+			// Replicate .Labels().IsEmpty() with a loop here to avoid generating garbage.
+			nonEmpty := false
+			t.LabelsRange(func(l labels.Label) { nonEmpty = true })
+			if nonEmpty {
 				all = append(all, t)
-			} else if !t.DiscoveredLabels().IsEmpty() {
+			} else if !t.discoveredLabels.IsEmpty() {
 				sp.droppedTargets = append(sp.droppedTargets, t)
 			}
 		}
@@ -666,17 +669,16 @@ func verifyLabelLimits(lset labels.Labels, limits *labelLimits) error {
 
 func mutateSampleLabels(lset labels.Labels, target *Target, honor bool, rc []*relabel.Config) labels.Labels {
 	lb := labels.NewBuilder(lset)
-	targetLabels := target.Labels()
 
 	if honor {
-		targetLabels.Range(func(l labels.Label) {
+		target.LabelsRange(func(l labels.Label) {
 			if !lset.Has(l.Name) {
 				lb.Set(l.Name, l.Value)
 			}
 		})
 	} else {
 		var conflictingExposedLabels []labels.Label
-		targetLabels.Range(func(l labels.Label) {
+		target.LabelsRange(func(l labels.Label) {
 			existingValue := lset.Get(l.Name)
 			if existingValue != "" {
 				conflictingExposedLabels = append(conflictingExposedLabels, labels.Label{Name: l.Name, Value: existingValue})
@@ -686,7 +688,7 @@ func mutateSampleLabels(lset labels.Labels, target *Target, honor bool, rc []*re
 		})
 
 		if len(conflictingExposedLabels) > 0 {
-			resolveConflictingExposedLabels(lb, lset, targetLabels, conflictingExposedLabels)
+			resolveConflictingExposedLabels(lb, conflictingExposedLabels)
 		}
 	}
 
@@ -699,42 +701,27 @@ func mutateSampleLabels(lset labels.Labels, target *Target, honor bool, rc []*re
 	return res
 }
 
-func resolveConflictingExposedLabels(lb *labels.Builder, exposedLabels, targetLabels labels.Labels, conflictingExposedLabels []labels.Label) {
+func resolveConflictingExposedLabels(lb *labels.Builder, conflictingExposedLabels []labels.Label) {
 	sort.SliceStable(conflictingExposedLabels, func(i, j int) bool {
 		return len(conflictingExposedLabels[i].Name) < len(conflictingExposedLabels[j].Name)
 	})
 
-	for i, l := range conflictingExposedLabels {
+	for _, l := range conflictingExposedLabels {
 		newName := l.Name
 		for {
 			newName = model.ExportedLabelPrefix + newName
-			if !exposedLabels.Has(newName) &&
-				!targetLabels.Has(newName) &&
-				!labelSliceHas(conflictingExposedLabels[:i], newName) {
-				conflictingExposedLabels[i].Name = newName
+			if lb.Get(newName) == "" {
+				lb.Set(newName, l.Value)
 				break
 			}
 		}
 	}
-
-	for _, l := range conflictingExposedLabels {
-		lb.Set(l.Name, l.Value)
-	}
-}
-
-func labelSliceHas(lbls []labels.Label, name string) bool {
-	for _, l := range lbls {
-		if l.Name == name {
-			return true
-		}
-	}
-	return false
 }
 
 func mutateReportSampleLabels(lset labels.Labels, target *Target) labels.Labels {
 	lb := labels.NewBuilder(lset)
 
-	target.Labels().Range(func(l labels.Label) {
+	target.LabelsRange(func(l labels.Label) {
 		lb.Set(model.ExportedLabelPrefix+l.Name, lset.Get(l.Name))
 		lb.Set(l.Name, l.Value)
 	})

scrape/target.go

@@ -181,6 +181,15 @@ func (t *Target) Labels() labels.Labels {
 	return b.Labels()
 }
 
+// LabelsRange calls f on each public label of the target.
+func (t *Target) LabelsRange(f func(l labels.Label)) {
+	t.labels.Range(func(l labels.Label) {
+		if !strings.HasPrefix(l.Name, model.ReservedLabelPrefix) {
+			f(l)
+		}
+	})
+}
+
 // DiscoveredLabels returns a copy of the target's labels before any processing.
 func (t *Target) DiscoveredLabels() labels.Labels {
 	t.mtx.Lock()

scrape/target_test.go

@@ -43,6 +43,17 @@ func TestTargetLabels(t *testing.T) {
 	want := labels.FromStrings(model.JobLabel, "some_job", "foo", "bar")
 	got := target.Labels()
 	require.Equal(t, want, got)
+	i := 0
+	target.LabelsRange(func(l labels.Label) {
+		switch i {
+		case 0:
+			require.Equal(t, labels.Label{Name: "foo", Value: "bar"}, l)
+		case 1:
+			require.Equal(t, labels.Label{Name: model.JobLabel, Value: "some_job"}, l)
+		}
+		i++
+	})
+	require.Equal(t, 2, i)
 }
 
 func TestTargetOffset(t *testing.T) {