Regard in-memory series as new.

This commit ensures that series that exist only in-memory and not
on-disk are not regarded as too old for operation exclusion.

storage/metric/memory.go

@@ -14,11 +14,12 @@
 package metric
 
 import (
-	"github.com/prometheus/prometheus/model"
-	"github.com/prometheus/prometheus/utility"
 	"sort"
 	"sync"
 	"time"
+
+	"github.com/prometheus/prometheus/model"
+	"github.com/prometheus/prometheus/utility"
 )
 
 // Assuming sample rate of 1 / 15Hz, this allows for one hour's worth of
@@ -370,6 +371,15 @@ func (s *memorySeriesStorage) GetMetricForFingerprint(f *model.Fingerprint) (mod
 	return metric, nil
 }
 
+func (s *memorySeriesStorage) HasFingerprint(f *model.Fingerprint) bool {
+	s.RLock()
+	defer s.RUnlock()
+
+	_, has := s.fingerprintToSeries[*f]
+
+	return has
+}
+
 func (s *memorySeriesStorage) CloneSamples(f *model.Fingerprint) model.Values {
 	s.RLock()
 	defer s.RUnlock()

storage/metric/tiered.go

@@ -309,20 +309,35 @@ func (t *TieredStorage) seriesTooOld(f *model.Fingerprint, i time.Time) (bool, e
 	// BUG(julius): Make this configurable by query layer.
 	i = i.Add(-stalenessLimit)
 
-	wm, ok := t.wmCache.Get(f)
-	if !ok {
+	wm, cacheHit := t.wmCache.Get(f)
+	if !cacheHit {
 		value := &dto.MetricHighWatermark{}
-		present, err := t.DiskStorage.MetricHighWatermarks.Get(f.ToDTO(), value)
+		diskHit, err := t.DiskStorage.MetricHighWatermarks.Get(f.ToDTO(), value)
 		if err != nil {
 			return false, err
 		}
-		if present {
+
+		if diskHit {
 			wmTime := time.Unix(*value.Timestamp, 0).UTC()
 			t.wmCache.Set(f, &Watermarks{High: wmTime})
 			return wmTime.Before(i), nil
 		}
-		return true, nil
+
+		if !t.memoryArena.HasFingerprint(f) {
+			return true, nil
+		}
+
+		samples := t.memoryArena.CloneSamples(f)
+		if len(samples) == 0 {
+			return true, nil
+		}
+
+		newest := samples[0].Timestamp
+		t.wmCache.Set(f, &Watermarks{High: newest})
+
+		return false, nil
 	}
+
 	return wm.High.Before(i), nil
 }