From 8b9ebf625a64a2f94d61f66fe95efaedee985e54 Mon Sep 17 00:00:00 2001
From: Aliaksandr Valialkin <valyala@victoriametrics.com>
Date: Wed, 1 Feb 2023 12:00:50 -0800
Subject: [PATCH] lib/promscrape: add a comment explaining the logic behind
 adding `exported_` perfix to metric names

This is a follow-up for 7b87fac8e7eaae9deef68a9812de5bd4aee292e7

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3557
Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3406
---
 lib/promscrape/scrapework.go | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/lib/promscrape/scrapework.go b/lib/promscrape/scrapework.go
index 95f068b80..98e564d8d 100644
--- a/lib/promscrape/scrapework.go
+++ b/lib/promscrape/scrapework.go
@@ -904,14 +904,24 @@ func (sw *scrapeWork) addAutoTimeseries(wc *writeRequestCtx, name string, value
 
 func (sw *scrapeWork) addRowToTimeseries(wc *writeRequestCtx, r *parser.Row, timestamp int64, needRelabel bool) {
 	metric := r.Metric
-	if needRelabel && isAutoMetric(metric) {
-		if !sw.Config.HonorLabels && len(r.Tags) == 0 {
-			bb := bbPool.Get()
-			bb.B = append(bb.B, "exported_"...)
-			bb.B = append(bb.B, metric...)
-			metric = bytesutil.InternBytes(bb.B)
-			bbPool.Put(bb)
-		}
+
+	// Add `exported_` prefix to metrics, which clash with the automatically generated
+	// metric names only if the following conditions are met:
+	//
+	// - The `honor_labels` option isn't set to true in the scrape_config.
+	//   If `honor_labels: true`, then the scraped metric name must remain unchanged
+	//   because the user explicitly asked about it in the config.
+	// - The metric has no labels (tags). If it has labels, then the metric value
+	//   will be written into a separate time series comparing to automatically generated time series.
+	//
+	// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3557
+	// and https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3406
+	if needRelabel && !sw.Config.HonorLabels && len(r.Tags) == 0 && isAutoMetric(metric) {
+		bb := bbPool.Get()
+		bb.B = append(bb.B, "exported_"...)
+		bb.B = append(bb.B, metric...)
+		metric = bytesutil.InternBytes(bb.B)
+		bbPool.Put(bb)
 	}
 	labelsLen := len(wc.labels)
 	targetLabels := sw.Config.Labels.GetLabels()