perf: Reduce allocations for JSON and logfmt parser (#18637)

pkg/logql/log/fmt.go

@@ -414,7 +414,7 @@ func (lf *LabelsFormatter) Process(ts int64, l []byte, lbs *LabelsBuilder) ([]by
 		if f.Rename {
 			v, _, ok := lbs.GetWithCategory(f.Value)
 			if ok {
-				lbs.Set(ParsedLabel, f.Name, v)
+				lbs.Set(ParsedLabel, unsafeGetBytes(f.Name), v)
 				lbs.Del(f.Value)
 			}
 			continue
@@ -428,7 +428,7 @@ func (lf *LabelsFormatter) Process(ts int64, l []byte, lbs *LabelsBuilder) ([]by
 			lbs.SetErrorDetails(err.Error())
 			continue
 		}
-		lbs.Set(ParsedLabel, f.Name, lf.buf.String())
+		lbs.Set(ParsedLabel, unsafeGetBytes(f.Name), lf.buf.Bytes())
 	}
 	return l, true
 }

pkg/logql/log/keep_labels.go

@@ -17,28 +17,31 @@ func (kl *KeepLabels) Process(_ int64, line []byte, lbls *LabelsBuilder) ([]byte
 		return line, true
 	}
 
-	// TODO: Reuse buf?
-	for _, lb := range lbls.UnsortedLabels(nil) {
-		if isSpecialLabel(lb.Name) {
-			continue
+	del := make([]string, 0, 10)
+	lbls.Range(func(name, value []byte) {
+		if isSpecialLabel(unsafeGetString(name)) {
+			return
 		}
 
 		var keep bool
 		for _, keepLabel := range kl.labels {
-			if keepLabel.Matcher != nil && keepLabel.Matcher.Name == lb.Name && keepLabel.Matcher.Matches(lb.Value) {
+			if keepLabel.Matcher != nil && keepLabel.Matcher.Name == unsafeGetString(name) && keepLabel.Matcher.Matches(unsafeGetString(value)) {
 				keep = true
 				break
 			}
 
-			if keepLabel.Name == lb.Name {
+			if keepLabel.Name == unsafeGetString(name) {
 				keep = true
 				break
 			}
 		}
 
 		if !keep {
-			lbls.Del(lb.Name)
+			del = append(del, unsafeGetString(name))
 		}
+	})
+	for _, name := range del {
+		lbls.Del(name)
 	}
 
 	return line, true

pkg/logql/log/label_filter_test.go

@@ -4,6 +4,7 @@ import (
 	"reflect"
 	"strings"
 	"testing"
+
 	"time"
 
 	"github.com/prometheus/prometheus/model/labels"