From 20e3c295aea5992a4d8ea8e7e45ed9c9d6639813 Mon Sep 17 00:00:00 2001
From: "Xiaochao Dong (@damnever)" <the.xcdong@gmail.com>
Date: Fri, 24 Mar 2023 17:18:24 +0800
Subject: [PATCH] Optimize constant label pair adding with relabel.Replace

Signed-off-by: Xiaochao Dong (@damnever) <the.xcdong@gmail.com>
---
 model/relabel/relabel.go      | 15 +++++++++
 model/relabel/relabel_test.go | 60 +++++++++++++++++++++++++++++++++++
 2 files changed, 75 insertions(+)

diff --git a/model/relabel/relabel.go b/model/relabel/relabel.go
index d29c3d07a..83b1a9147 100644
--- a/model/relabel/relabel.go
+++ b/model/relabel/relabel.go
@@ -267,6 +267,17 @@ func relabel(cfg *Config, lb *labels.Builder) (keep bool) {
 			return false
 		}
 	case Replace:
+		// Fast path to add or delete label pair.
+		if val == "" && cfg.Regex == DefaultRelabelConfig.Regex &&
+			!varInRegexTemplate(cfg.TargetLabel) && !varInRegexTemplate(cfg.Replacement) {
+			if !model.LabelName(cfg.TargetLabel).IsValid() || cfg.Replacement == "" {
+				lb.Del(cfg.TargetLabel)
+			} else {
+				lb.Set(cfg.TargetLabel, cfg.Replacement)
+			}
+			break
+		}
+
 		indexes := cfg.Regex.FindStringSubmatchIndex(val)
 		// If there is no match no replacement must take place.
 		if indexes == nil {
@@ -316,3 +327,7 @@ func relabel(cfg *Config, lb *labels.Builder) (keep bool) {
 
 	return true
 }
+
+func varInRegexTemplate(template string) bool {
+	return strings.Contains(template, "$")
+}
diff --git a/model/relabel/relabel_test.go b/model/relabel/relabel_test.go
index 517b9b822..d3815afe6 100644
--- a/model/relabel/relabel_test.go
+++ b/model/relabel/relabel_test.go
@@ -15,6 +15,7 @@ package relabel
 
 import (
 	"fmt"
+	"sort"
 	"testing"
 
 	"github.com/prometheus/common/model"
@@ -850,3 +851,62 @@ func BenchmarkRelabel(b *testing.B) {
 		})
 	}
 }
+
+func BenchmarkRelabel_ReplaceAddLabel(b *testing.B) {
+	cfgs := []*Config{}
+	for k, v := range map[string]string{
+		"wwwwww":       "wwwwww",
+		"xxxxxxxxx":    "xxxxxxxxx",
+		"yyyyyyyyyyyy": "yyyyyyyyyyyy",
+		"${0}":         "dropped",
+		"dropped":      "${0}",
+	} {
+		cfgs = append(cfgs, &Config{
+			Action:      DefaultRelabelConfig.Action,
+			Separator:   DefaultRelabelConfig.Separator,
+			Regex:       DefaultRelabelConfig.Regex,
+			TargetLabel: k,
+			Replacement: v,
+		})
+	}
+	expectLset := labels.Labels{
+		labels.Label{Name: "abcdefg01", Value: "hijklmn1"},
+		labels.Label{Name: "abcdefg02", Value: "hijklmn2"},
+		labels.Label{Name: "abcdefg03", Value: "hijklmn3"},
+		labels.Label{Name: "abcdefg04", Value: "hijklmn4"},
+		labels.Label{Name: "abcdefg05", Value: "hijklmn5"},
+		labels.Label{Name: "abcdefg06", Value: "hijklmn6"},
+		labels.Label{Name: "abcdefg07", Value: "hijklmn7"},
+		labels.Label{Name: "abcdefg08", Value: "hijklmn8"},
+		labels.Label{Name: "abcdefg09", Value: "hijklmn9"},
+		labels.Label{Name: "abcdefg10", Value: "hijklmn10"},
+		labels.Label{Name: "abcdefg11", Value: "hijklmn11"},
+		labels.Label{Name: "abcdefg12", Value: "hijklmn12"},
+		labels.Label{Name: "abcdefg13", Value: "hijklmn13"},
+		labels.Label{Name: "wwwwww", Value: "wwwwww"},
+		labels.Label{Name: "xxxxxxxxx", Value: "xxxxxxxxx"},
+		labels.Label{Name: "yyyyyyyyyyyy", Value: "yyyyyyyyyyyy"},
+	}
+	sort.Sort(expectLset)
+
+	for i := 0; i < b.N; i++ {
+		lset := labels.Labels{
+			labels.Label{Name: "abcdefg01", Value: "hijklmn1"},
+			labels.Label{Name: "abcdefg02", Value: "hijklmn2"},
+			labels.Label{Name: "abcdefg03", Value: "hijklmn3"},
+			labels.Label{Name: "abcdefg04", Value: "hijklmn4"},
+			labels.Label{Name: "abcdefg05", Value: "hijklmn5"},
+			labels.Label{Name: "abcdefg06", Value: "hijklmn6"},
+			labels.Label{Name: "abcdefg07", Value: "hijklmn7"},
+			labels.Label{Name: "abcdefg08", Value: "hijklmn8"},
+			labels.Label{Name: "abcdefg09", Value: "hijklmn9"},
+			labels.Label{Name: "abcdefg10", Value: "hijklmn10"},
+			labels.Label{Name: "abcdefg11", Value: "hijklmn11"},
+			labels.Label{Name: "abcdefg12", Value: "hijklmn12"},
+			labels.Label{Name: "abcdefg13", Value: "hijklmn13"},
+		}
+		actual, _ := Process(lset, cfgs...)
+		var _ = actual
+		// require.Equal(b, actual, expectLset)
+	}
+}