scrape: Allow disabling end-of-run staleness markers for targets

Signed-off-by: Piotr <17101802+thampiotr@users.noreply.github.com>

scrape/manager.go

@@ -409,3 +409,22 @@ func (m *Manager) ScrapePoolConfig(scrapePool string) (*config.ScrapeConfig, err
 
 	return sp.config, nil
 }
+
+// DisableEndOfRunStalenessMarkers disables the end-of-run staleness markers for the provided targets in the given
+// targetSet. When the end-of-run staleness is disabled for a target, when it goes away, there will be no staleness
+// markers written for its series.
+func (m *Manager) DisableEndOfRunStalenessMarkers(targetSet string, targets []*Target) {
+	// This avoids mutex lock contention.
+	if len(targets) == 0 {
+		return
+	}
+
+	// Only hold the lock to find the scrape pool
+	m.mtxScrape.Lock()
+	sp, ok := m.scrapePools[targetSet]
+	m.mtxScrape.Unlock()
+
+	if ok {
+		sp.disableEndOfRunStalenessMarkers(targets)
+	}
+}

scrape/manager_test.go

@@ -1588,3 +1588,50 @@ scrape_configs:
 		[]string{fmt.Sprintf("http://%s/metrics", otherJobTargetURL)},
 	)
 }
+
+func TestManagerDisableEndOfRunStalenessMarkers(t *testing.T) {
+	cfgText := `
+scrape_configs:
+ - job_name: one
+   scrape_interval: 1m
+   scrape_timeout: 1m
+ - job_name: two
+   scrape_interval: 1m
+   scrape_timeout: 1m
+`
+
+	cfg := loadConfiguration(t, cfgText)
+
+	m, err := NewManager(&Options{}, nil, nil, &nopAppendable{}, prometheus.NewRegistry())
+	require.NoError(t, err)
+	defer m.Stop()
+	require.NoError(t, m.ApplyConfig(cfg))
+
+	// Pass targets to the manager.
+	tgs := map[string][]*targetgroup.Group{
+		"one": {{Targets: []model.LabelSet{{"__address__": "h1"}, {"__address__": "h2"}, {"__address__": "h3"}}}},
+		"two": {{Targets: []model.LabelSet{{"__address__": "h4"}}}},
+	}
+	m.updateTsets(tgs)
+	m.reload()
+
+	activeTargets := m.TargetsActive()
+	targetsToDisable := []*Target{
+		activeTargets["one"][0],
+		activeTargets["one"][2],
+	}
+
+	// Disable end of run staleness markers for some targets.
+	m.DisableEndOfRunStalenessMarkers("one", targetsToDisable)
+	// This should be a no-op
+	m.DisableEndOfRunStalenessMarkers("non-existent-job", targetsToDisable)
+
+	// Check that the end of run staleness markers are disabled for the correct targets.
+	for _, group := range []string{"one", "two"} {
+		for _, tg := range activeTargets[group] {
+			loop := m.scrapePools[group].loops[tg.hash()].(*scrapeLoop)
+			expectedDisabled := slices.Contains(targetsToDisable, tg)
+			require.Equal(t, expectedDisabled, loop.disabledEndOfRunStalenessMarkers.Load())
+		}
+	}
+}

scrape/scrape.go

@@ -41,6 +41,7 @@ import (
 	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
 	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/trace"
+	"go.uber.org/atomic"
 
 	"github.com/prometheus/prometheus/config"
 	"github.com/prometheus/prometheus/discovery/targetgroup"
@@ -641,6 +642,16 @@ func (sp *scrapePool) refreshTargetLimitErr() error {
 	return nil
 }
 
+func (sp *scrapePool) disableEndOfRunStalenessMarkers(targets []*Target) {
+	sp.mtx.Lock()
+	defer sp.mtx.Unlock()
+	for i := range targets {
+		if l, ok := sp.loops[targets[i].hash()]; ok {
+			l.disableEndOfRunStalenessMarkers()
+		}
+	}
+}
+
 func verifyLabelLimits(lset labels.Labels, limits *labelLimits) error {
 	if limits == nil {
 		return nil
@@ -957,7 +968,7 @@ type scrapeLoop struct {
 	cancel      func()
 	stopped     chan struct{}
 
-	disabledEndOfRunStalenessMarkers bool
+	disabledEndOfRunStalenessMarkers atomic.Bool
 
 	reportExtraMetrics  bool
 	appendMetadataToWAL bool
@@ -1397,7 +1408,7 @@ mainLoop:
 
 	close(sl.stopped)
 
-	if !sl.disabledEndOfRunStalenessMarkers {
+	if !sl.disabledEndOfRunStalenessMarkers.Load() {
 		sl.endOfRunStaleness(last, ticker, sl.interval)
 	}
 }
@@ -1563,6 +1574,11 @@ func (sl *scrapeLoop) endOfRunStaleness(last time.Time, ticker *time.Ticker, int
 	case <-time.After(interval / 10):
 	}
 
+	// Check if end-of-run staleness markers have been disabled while we were waiting.
+	if sl.disabledEndOfRunStalenessMarkers.Load() {
+		return
+	}
+
 	// Call sl.append again with an empty scrape to trigger stale markers.
 	// If the target has since been recreated and scraped, the
 	// stale markers will be out of order and ignored.
@@ -1597,7 +1613,7 @@ func (sl *scrapeLoop) stop() {
 }
 
 func (sl *scrapeLoop) disableEndOfRunStalenessMarkers() {
-	sl.disabledEndOfRunStalenessMarkers = true
+	sl.disabledEndOfRunStalenessMarkers.Store(true)
 }
 
 func (sl *scrapeLoop) getCache() *scrapeCache {

scrape/scrape_test.go

@@ -50,6 +50,7 @@ import (
 	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/propagation"
 	sdktrace "go.opentelemetry.io/otel/sdk/trace"
+	"go.uber.org/atomic"
 
 	"github.com/prometheus/prometheus/config"
 	"github.com/prometheus/prometheus/discovery"
@@ -5897,3 +5898,47 @@ func TestScrapeLoopAppendSampleLimitReplaceAllSamples(t *testing.T) {
 	}...)
 	requireEqual(t, want, resApp.resultFloats, "Appended samples not as expected:\n%s", slApp)
 }
+
+func TestScrapeLoopDisableStalenessMarkerInjection(t *testing.T) {
+	var (
+		loopDone = atomic.NewBool(false)
+		appender = &collectResultAppender{}
+		scraper  = &testScraper{}
+		app      = func(_ context.Context) storage.Appender { return appender }
+	)
+
+	sl := newBasicScrapeLoop(t, context.Background(), scraper, app, 10*time.Millisecond)
+	scraper.scrapeFunc = func(ctx context.Context, w io.Writer) error {
+		if _, err := w.Write([]byte("metric_a 42\n")); err != nil {
+			return err
+		}
+		return ctx.Err()
+	}
+
+	// Start the scrape loop.
+	go func() {
+		sl.run(nil)
+		loopDone.Store(true)
+	}()
+
+	// Wait for some samples to be appended.
+	require.Eventually(t, func() bool {
+		appender.mtx.Lock()
+		defer appender.mtx.Unlock()
+		return len(appender.resultFloats) > 2
+	}, 5*time.Second, 100*time.Millisecond, "Scrape loop didn't append any samples.")
+
+	// Disable end of run staleness markers and stop the loop.
+	sl.disableEndOfRunStalenessMarkers()
+	sl.stop()
+	require.Eventually(t, func() bool {
+		return loopDone.Load()
+	}, 5*time.Second, 100*time.Millisecond, "Scrape loop didn't stop.")
+
+	// No stale markers should be appended, since they were disabled.
+	for _, s := range appender.resultFloats {
+		if value.IsStaleNaN(s.f) {
+			t.Fatalf("Got stale NaN samples while end of run staleness is disabled: %x", math.Float64bits(s.f))
+		}
+	}
+}