Scrape: do not put staleness marker when cache is reused (#7011)

* Scrape: do not put staleness marker when cache is reused

Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>

scrape/scrape.go

@@ -314,6 +314,7 @@ func (sp *scrapePool) reload(cfg *config.ScrapeConfig) error {
 	for fp, oldLoop := range sp.loops {
 		var cache *scrapeCache
 		if oc := oldLoop.getCache(); reuseCache && oc != nil {
+			oldLoop.disableEndOfRunStalenessMarkers()
 			cache = oc
 		} else {
 			cache = newScrapeCache()
@@ -593,6 +594,7 @@ type loop interface {
 	run(interval, timeout time.Duration, errc chan<- error)
 	stop()
 	getCache() *scrapeCache
+	disableEndOfRunStalenessMarkers()
 }
 
 type cacheEntry struct {
@@ -619,6 +621,8 @@ type scrapeLoop struct {
 	ctx       context.Context
 	cancel    func()
 	stopped   chan struct{}
+
+	disabledEndOfRunStalenessMarkers bool
 }
 
 // scrapeCache tracks mappings of exposed metric strings to label sets and
@@ -996,7 +1000,9 @@ mainLoop:
 
 	close(sl.stopped)
 
-	sl.endOfRunStaleness(last, ticker, interval)
+	if !sl.disabledEndOfRunStalenessMarkers {
+		sl.endOfRunStaleness(last, ticker, interval)
+	}
 }
 
 func (sl *scrapeLoop) endOfRunStaleness(last time.Time, ticker *time.Ticker, interval time.Duration) {
@@ -1054,6 +1060,10 @@ func (sl *scrapeLoop) stop() {
 	<-sl.stopped
 }
 
+func (sl *scrapeLoop) disableEndOfRunStalenessMarkers() {
+	sl.disabledEndOfRunStalenessMarkers = true
+}
+
 func (sl *scrapeLoop) getCache() *scrapeCache {
 	return sl.cache
 }

scrape/scrape_test.go

@@ -141,6 +141,9 @@ func (l *testLoop) run(interval, timeout time.Duration, errc chan<- error) {
 	l.startFunc(interval, timeout, errc)
 }
 
+func (l *testLoop) disableEndOfRunStalenessMarkers() {
+}
+
 func (l *testLoop) stop() {
 	l.stopFunc()
 }
@@ -1839,3 +1842,39 @@ func TestScrapeAddFast(t *testing.T) {
 	_, _, _, err = sl.append([]byte("up 1\n"), "", time.Time{}.Add(time.Second))
 	testutil.Ok(t, err)
 }
+
+func TestReuseCacheRace(t *testing.T) {
+	var (
+		app = &nopAppendable{}
+		cfg = &config.ScrapeConfig{
+			JobName:        "Prometheus",
+			ScrapeTimeout:  model.Duration(5 * time.Second),
+			ScrapeInterval: model.Duration(5 * time.Second),
+			MetricsPath:    "/metrics",
+		}
+		sp, _ = newScrapePool(cfg, app, 0, nil)
+		t1    = &Target{
+			discoveredLabels: labels.Labels{
+				labels.Label{
+					Name:  "labelNew",
+					Value: "nameNew",
+				},
+			},
+		}
+	)
+	sp.sync([]*Target{t1})
+
+	start := time.Now()
+	for i := uint(1); i > 0; i++ {
+		if time.Since(start) > 5*time.Second {
+			break
+		}
+		sp.reload(&config.ScrapeConfig{
+			JobName:        "Prometheus",
+			ScrapeTimeout:  model.Duration(1 * time.Millisecond),
+			ScrapeInterval: model.Duration(1 * time.Millisecond),
+			MetricsPath:    "/metrics",
+			SampleLimit:    i,
+		})
+	}
+}