From d3de110070e0e2635a7e443d3f6e16a17370a681 Mon Sep 17 00:00:00 2001
From: Aliaksandr Valialkin <valyala@victoriametrics.com>
Date: Wed, 21 Dec 2022 20:19:58 -0800
Subject: [PATCH] app/vmselect/promql: make sure that label_replace() doesn't
 create an empty dst_label if the src_label doesn't match regex

---
 app/vmselect/promql/transform.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/app/vmselect/promql/transform.go b/app/vmselect/promql/transform.go
index 80bc96bef..c10e34808 100644
--- a/app/vmselect/promql/transform.go
+++ b/app/vmselect/promql/transform.go
@@ -1873,12 +1873,12 @@ func labelReplace(tss []*timeseries, srcLabel string, r *regexp.Regexp, dstLabel
 	replacementBytes := []byte(replacement)
 	for _, ts := range tss {
 		mn := &ts.MetricName
-		dstValue := getDstValue(mn, dstLabel)
 		srcValue := mn.GetTagValue(srcLabel)
 		if !r.Match(srcValue) {
 			continue
 		}
 		b := r.ReplaceAll(srcValue, replacementBytes)
+		dstValue := getDstValue(mn, dstLabel)
 		*dstValue = append((*dstValue)[:0], b...)
 		if len(b) == 0 {
 			mn.RemoveTag(dstLabel)