Improve Performance of MakeLabelPairs

prometheus/desc.go

@@ -22,8 +22,6 @@ import (
 	dto "github.com/prometheus/client_model/go"
 	"github.com/prometheus/common/model"
 	"google.golang.org/protobuf/proto"
-
-	"github.com/prometheus/client_golang/prometheus/internal"
 )
 
 // Desc is the descriptor used by every Prometheus Metric. It is essentially
@@ -47,12 +45,15 @@ type Desc struct {
 	fqName string
 	// help provides some helpful information about this metric.
 	help string
-	// constLabelPairs contains precalculated DTO label pairs based on
-	// the constant labels.
-	constLabelPairs []*dto.LabelPair
 	// variableLabels contains names of labels and normalization function for
 	// which the metric maintains variable values.
 	variableLabels *compiledLabels
+	// constLabelPairs contains the sorted DTO label pairs based on the constant labels
+	// and variable labels
+	constLabelPairs []*dto.LabelPair
+	// orderedLabels contains the sorted labels with necessary fields to construct the
+	// final label pairs when needed.
+	orderedLabels []labelMapping
 	// id is a hash of the values of the ConstLabels and fqName. This
 	// must be unique among all registered descriptors and can therefore be
 	// used as an identifier of the descriptor.
@@ -66,6 +67,21 @@ type Desc struct {
 	err error
 }
 
+type labelMapping struct {
+	constLabelIndex int
+
+	variableLabelIndex int
+	variableLabelName  *string
+}
+
+func newLabelMapping() labelMapping {
+	return labelMapping{
+		constLabelIndex:    -1,
+		variableLabelIndex: -1,
+		variableLabelName:  nil,
+	}
+}
+
 // NewDesc allocates and initializes a new Desc. Errors are recorded in the Desc
 // and will be reported on registration time. variableLabels and constLabels can
 // be nil if no such labels should be set. fqName must not be empty.
@@ -133,7 +149,7 @@ func (v2) NewDesc(fqName, help string, variableLabels ConstrainableLabels, const
 			d.err = fmt.Errorf("%q is not a valid label name for metric %q", label, fqName)
 			return d
 		}
-		labelNames = append(labelNames, "$"+label)
+		labelNames = append(labelNames, label)
 		labelNameSet[label] = struct{}{}
 	}
 	if len(labelNames) != len(labelNameSet) {
@@ -161,13 +177,26 @@ func (v2) NewDesc(fqName, help string, variableLabels ConstrainableLabels, const
 	d.dimHash = xxh.Sum64()
 
 	d.constLabelPairs = make([]*dto.LabelPair, 0, len(constLabels))
-	for n, v := range constLabels {
-		d.constLabelPairs = append(d.constLabelPairs, &dto.LabelPair{
-			Name:  proto.String(n),
-			Value: proto.String(v),
-		})
+	d.orderedLabels = make([]labelMapping, len(labelNames))
+	for i, n := range labelNames {
+		lm := newLabelMapping()
+		if l, ok := constLabels[n]; ok {
+			d.constLabelPairs = append(d.constLabelPairs, &dto.LabelPair{
+				Name:  proto.String(n),
+				Value: proto.String(l),
+			})
+			lm.constLabelIndex = len(d.constLabelPairs) - 1
+		} else {
+			for variableLabelIndex, variableLabel := range variableLabels.labelNames() {
+				if variableLabel == n {
+					lm.variableLabelIndex = variableLabelIndex
+					lm.variableLabelName = proto.String(variableLabel)
+				}
+			}
+		}
+		d.orderedLabels[i] = lm
 	}
-	sort.Sort(internal.LabelPairSorter(d.constLabelPairs))
+
 	return d
 }
 

prometheus/desc_test.go

@@ -14,6 +14,7 @@
 package prometheus
 
 import (
+	"fmt"
 	"testing"
 )
 
@@ -61,3 +62,31 @@ func TestNewInvalidDesc_String(t *testing.T) {
 		t.Errorf("String: unexpected output: %s", desc.String())
 	}
 }
+
+func BenchmarkNewDesc(b *testing.B) {
+	for _, bm := range []struct {
+		labelCount int
+		descFunc   func() *Desc
+	}{
+		{
+			labelCount: 1,
+			descFunc:   new1LabelDescFunc,
+		},
+		{
+			labelCount: 3,
+			descFunc:   new3LabelsDescFunc,
+		},
+		{
+			labelCount: 10,
+			descFunc:   new10LabelsDescFunc,
+		},
+	} {
+		b.Run(fmt.Sprintf("labels=%v", bm.labelCount), func(b *testing.B) {
+			b.ReportAllocs()
+			b.ResetTimer()
+			for i := 0; i < b.N; i++ {
+				bm.descFunc()
+			}
+		})
+	}
+}

prometheus/registry.go

@@ -962,28 +962,31 @@ func checkDescConsistency(
 	}
 
 	// Is the desc consistent with the content of the metric?
-	lpsFromDesc := make([]*dto.LabelPair, len(desc.constLabelPairs), len(dtoMetric.Label))
-	copy(lpsFromDesc, desc.constLabelPairs)
-	for _, l := range desc.variableLabels.names {
-		lpsFromDesc = append(lpsFromDesc, &dto.LabelPair{
-			Name: proto.String(l),
-		})
-	}
-	if len(lpsFromDesc) != len(dtoMetric.Label) {
+	if len(desc.orderedLabels) != len(dtoMetric.Label) {
 		return fmt.Errorf(
 			"labels in collected metric %s %s are inconsistent with descriptor %s",
 			metricFamily.GetName(), dtoMetric, desc,
 		)
 	}
-	sort.Sort(internal.LabelPairSorter(lpsFromDesc))
-	for i, lpFromDesc := range lpsFromDesc {
+	for i, lm := range desc.orderedLabels {
 		lpFromMetric := dtoMetric.Label[i]
-		if lpFromDesc.GetName() != lpFromMetric.GetName() ||
-			lpFromDesc.Value != nil && lpFromDesc.GetValue() != lpFromMetric.GetValue() {
-			return fmt.Errorf(
-				"labels in collected metric %s %s are inconsistent with descriptor %s",
-				metricFamily.GetName(), dtoMetric, desc,
-			)
+		if lm.constLabelIndex > -1 {
+			lpFromDesc := desc.constLabelPairs[lm.constLabelIndex]
+			if lpFromDesc.GetName() != lpFromMetric.GetName() ||
+				lpFromDesc.Value != nil && lpFromDesc.GetValue() != lpFromMetric.GetValue() {
+				return fmt.Errorf(
+					"labels in collected metric %s %s are inconsistent with descriptor %s",
+					metricFamily.GetName(), dtoMetric, desc,
+				)
+			}
+		} else {
+			variableLabelName := *lm.variableLabelName
+			if variableLabelName != lpFromMetric.GetName() {
+				return fmt.Errorf(
+					"labels in collected metric %s %s are inconsistent with descriptor %s",
+					metricFamily.GetName(), dtoMetric, desc,
+				)
+			}
 		}
 	}
 	return nil

prometheus/value.go

@@ -16,12 +16,9 @@ package prometheus
 import (
 	"errors"
 	"fmt"
-	"sort"
 	"time"
 	"unicode/utf8"
 
-	"github.com/prometheus/client_golang/prometheus/internal"
-
 	dto "github.com/prometheus/client_model/go"
 	"google.golang.org/protobuf/proto"
 	"google.golang.org/protobuf/types/known/timestamppb"
@@ -215,24 +212,25 @@ func populateMetric(
 // This function is only needed for custom Metric implementations. See MetricVec
 // example.
 func MakeLabelPairs(desc *Desc, labelValues []string) []*dto.LabelPair {
-	totalLen := len(desc.variableLabels.names) + len(desc.constLabelPairs)
-	if totalLen == 0 {
+	if len(desc.orderedLabels) == 0 {
 		// Super fast path.
 		return nil
 	}
 	if len(desc.variableLabels.names) == 0 {
 		// Moderately fast path.
 		return desc.constLabelPairs
 	}
-	labelPairs := make([]*dto.LabelPair, 0, totalLen)
-	for i, l := range desc.variableLabels.names {
-		labelPairs = append(labelPairs, &dto.LabelPair{
-			Name:  proto.String(l),
-			Value: proto.String(labelValues[i]),
-		})
+	labelPairs := make([]*dto.LabelPair, len(desc.orderedLabels))
+	for i, lm := range desc.orderedLabels {
+		if lm.constLabelIndex != -1 {
+			labelPairs[i] = desc.constLabelPairs[lm.constLabelIndex]
+		} else {
+			labelPairs[i] = &dto.LabelPair{
+				Name:  lm.variableLabelName,
+				Value: proto.String(labelValues[lm.variableLabelIndex]),
+			}
+		}
 	}
-	labelPairs = append(labelPairs, desc.constLabelPairs...)
-	sort.Sort(internal.LabelPairSorter(labelPairs))
 	return labelPairs
 }