app/victoria-metrics: properly send staleness markers on victoriametrics shutdown if -selfScrapeInterval > 0

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/943
Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1526

app/victoria-metrics/self_scraper.go

@@ -8,6 +8,7 @@ import (
 	"github.com/VictoriaMetrics/VictoriaMetrics/app/vmstorage"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/appmetrics"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/bytesutil"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/decimal"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/prompb"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/protoparser/prometheus"
@@ -49,16 +50,8 @@ func selfScraper(scrapeInterval time.Duration) {
 	var mrs []storage.MetricRow
 	var labels []prompb.Label
 	t := time.NewTicker(scrapeInterval)
-	var currentTimestamp int64
+	f := func(currentTime time.Time, sendStaleMarkers bool) {
-	for {
+		currentTimestamp := currentTime.UnixNano() / 1e6
-		select {
-		case <-selfScraperStopCh:
-			t.Stop()
-			logger.Infof("stopped self-scraping `/metrics` page")
-			return
-		case currentTime := <-t.C:
-			currentTimestamp = currentTime.UnixNano() / 1e6
-		}
 		bb.Reset()
 		appmetrics.WritePrometheusMetrics(&bb)
 		s := bytesutil.ToUnsafeString(bb.B)
@@ -83,12 +76,27 @@ func selfScraper(scrapeInterval time.Duration) {
 			mr := &mrs[len(mrs)-1]
 			mr.MetricNameRaw = storage.MarshalMetricNameRaw(mr.MetricNameRaw[:0], labels)
 			mr.Timestamp = currentTimestamp
-			mr.Value = r.Value
+			if sendStaleMarkers {
+				mr.Value = decimal.StaleNaN
+			} else {
+				mr.Value = r.Value
+			}
 		}
 		if err := vmstorage.AddRows(mrs); err != nil {
 			logger.Errorf("cannot store self-scraped metrics: %s", err)
 		}
 	}
+	for {
+		select {
+		case <-selfScraperStopCh:
+			f(time.Now(), true)
+			t.Stop()
+			logger.Infof("stopped self-scraping `/metrics` page")
+			return
+		case currentTime := <-t.C:
+			f(currentTime, false)
+		}
+	}
 }
 
 func addLabel(dst []prompb.Label, key, value string) []prompb.Label {

docs/CHANGELOG.md

@@ -15,6 +15,7 @@ The following `tip` changes can be tested by building VictoriaMetrics components
 
 * BUGFIX: [MetricsQL](https://docs.victoriametrics.com/MetricsQL.html): properly propagate [label filters](https://docs.victoriametrics.com/keyconcepts/#filtering) from multiple arguments passed to [aggregate functions](https://docs.victoriametrics.com/metricsql/#aggregate-functions). For example, `sum({job="foo"}, {job="bar"}) by (job) + a` was improperly optimized to `sum({job="foo"}, {job="bar"}) by (job) + a{job="foo"}` before being executed. This could lead to unexpected results. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5604).
 * BUGFIX: [MetricsQL](https://docs.victoriametrics.com/MetricsQL.html): properly handle precision errors when calculating [changes](https://docs.victoriametrics.com/metricsql/#changes), [changes_prometheus](https://docs.victoriametrics.com/metricsql/#changes_prometheus), [increases_over_time](https://docs.victoriametrics.com/metricsql/#increases_over_time) and [resets](https://docs.victoriametrics.com/metricsql/#resets) functions. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/767).
+* BUGFIX: properly store [staleness markers](https://docs.victoriametrics.com/vmagent/#prometheus-staleness-markers) for [self-scraped metrics](https://docs.victoriametrics.com/#monitoring) on single-node VictoriaMetrics shutdown. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/943).
 * BUGFIX: prevent from possible `too big indexBlockSize` panic when samples with too long label values (~64Kb) are ingested into VictoriaMetrics.
 
 ## [v1.93.11](https://github.com/VictoriaMetrics/VictoriaMetrics/releases/tag/v1.93.11)