Merge pull request #12680 from bboreham/faster-has

labels: improve Has() method for stringlabels build

model/labels/labels_stringlabels.go

@@ -300,13 +300,26 @@ func (ls Labels) Get(name string) string {
 
 // Has returns true if the label with the given name is present.
 func (ls Labels) Has(name string) bool {
+	if name == "" { // Avoid crash in loop if someone asks for "".
+		return false // Prometheus does not store blank label names.
+	}
 	for i := 0; i < len(ls.data); {
-		var lName string
-		lName, i = decodeString(ls.data, i)
-		_, i = decodeString(ls.data, i)
-		if lName == name {
-			return true
+		var size int
+		size, i = decodeSize(ls.data, i)
+		if ls.data[i] == name[0] {
+			lName := ls.data[i : i+size]
+			i += size
+			if lName == name {
+				return true
+			}
+		} else {
+			if ls.data[i] > name[0] { // Stop looking if we've gone past.
+				break
+			}
+			i += size
 		}
+		size, i = decodeSize(ls.data, i)
+		i += size
 	}
 	return false
 }

model/labels/labels_test.go

@@ -472,16 +472,22 @@ func BenchmarkLabels_Get(b *testing.B) {
 			for _, scenario := range []struct {
 				desc, label string
 			}{
-				{"get first label", allLabels[0].Name},
-				{"get middle label", allLabels[size/2].Name},
-				{"get last label", allLabels[size-1].Name},
-				{"get not-found label", "benchmark"},
+				{"first label", allLabels[0].Name},
+				{"middle label", allLabels[size/2].Name},
+				{"last label", allLabels[size-1].Name},
+				{"not-found label", "benchmark"},
 			} {
 				b.Run(scenario.desc, func(b *testing.B) {
-					b.ResetTimer()
-					for i := 0; i < b.N; i++ {
-						_ = labels.Get(scenario.label)
-					}
+					b.Run("get", func(b *testing.B) {
+						for i := 0; i < b.N; i++ {
+							_ = labels.Get(scenario.label)
+						}
+					})
+					b.Run("has", func(b *testing.B) {
+						for i := 0; i < b.N; i++ {
+							_ = labels.Has(scenario.label)
+						}
+					})
 				})
 			}
 		})