Limit retrievable samples to retention window.

The storage does not delete data immediately after the retention period.
We don't want to retrieve this data as it causes artifacts.

storage/local/interface.go

@@ -44,6 +44,8 @@ type Storage interface {
 	// Get the metric associated with the provided fingerprint.
 	MetricForFingerprint(clientmodel.Fingerprint) clientmodel.COWMetric
 	// Construct an iterator for a given fingerprint.
+	// The iterator will never return samples older than retention time,
+	// relative to the time NewIterator was called.
 	NewIterator(clientmodel.Fingerprint) SeriesIterator
 	// Run the various maintenance loops in goroutines. Returns when the
 	// storage is ready to use. Keeps everything running in the background

storage/local/storage.go

@@ -286,7 +286,47 @@ func (s *memorySeriesStorage) NewIterator(fp clientmodel.Fingerprint) SeriesIter
 		// return any values.
 		return nopSeriesIterator{}
 	}
-	return series.newIterator()
+	return &boundedIterator{
+		it:    series.newIterator(),
+		start: clientmodel.Now().Add(-s.dropAfter),
+	}
+}
+
+// boundedIterator wraps a SeriesIterator and does not allow fetching
+// data from earlier than the configured start time.
+type boundedIterator struct {
+	it    SeriesIterator
+	start clientmodel.Timestamp
+}
+
+// ValueAtTime implements the SeriesIterator interface.
+func (bit *boundedIterator) ValueAtTime(ts clientmodel.Timestamp) metric.Values {
+	if ts < bit.start {
+		return metric.Values{}
+	}
+	return bit.it.ValueAtTime(ts)
+}
+
+// BoundaryValues implements the SeriesIterator interface.
+func (bit *boundedIterator) BoundaryValues(interval metric.Interval) metric.Values {
+	if interval.NewestInclusive < bit.start {
+		return metric.Values{}
+	}
+	if interval.OldestInclusive < bit.start {
+		interval.OldestInclusive = bit.start
+	}
+	return bit.it.BoundaryValues(interval)
+}
+
+// RangeValues implements the SeriesIterator interface.
+func (bit *boundedIterator) RangeValues(interval metric.Interval) metric.Values {
+	if interval.NewestInclusive < bit.start {
+		return metric.Values{}
+	}
+	if interval.OldestInclusive < bit.start {
+		interval.OldestInclusive = bit.start
+	}
+	return bit.it.RangeValues(interval)
 }
 
 // NewPreloader implements Storage.

storage/local/storage_test.go

@@ -140,6 +140,70 @@ func TestFingerprintsForLabelMatchers(t *testing.T) {
 	}
 }
 
+func TestRetentionCutoff(t *testing.T) {
+	now := clientmodel.Now()
+	insertStart := now.Add(-2 * time.Hour)
+
+	s, closer := NewTestStorage(t, 1)
+	defer closer.Close()
+
+	// Stop maintenance loop to prevent actual purging.
+	s.loopStopping <- struct{}{}
+
+	s.dropAfter = 1 * time.Hour
+
+	samples := make(clientmodel.Samples, 120)
+	for i := range samples {
+		smpl := &clientmodel.Sample{
+			Metric:    clientmodel.Metric{"job": "test"},
+			Timestamp: insertStart.Add(time.Duration(i) * time.Minute), // 1 minute intervals.
+			Value:     1,
+		}
+		s.Append(smpl)
+	}
+	s.WaitForIndexing()
+
+	lm, err := metric.NewLabelMatcher(metric.Equal, "job", "test")
+	if err != nil {
+		t.Fatalf("error creating label matcher: %s", err)
+	}
+	fp := s.FingerprintsForLabelMatchers(metric.LabelMatchers{lm})[0]
+
+	pl := s.NewPreloader()
+	defer pl.Close()
+
+	// Preload everything.
+	err = pl.PreloadRange(fp, insertStart, now, 5*time.Minute)
+	if err != nil {
+		t.Fatalf("Error preloading outdated chunks: %s", err)
+	}
+
+	it := s.NewIterator(fp)
+
+	vals := it.ValueAtTime(now.Add(-61 * time.Minute))
+	if len(vals) != 0 {
+		t.Errorf("unexpected result for timestamp before retention period")
+	}
+
+	vals = it.RangeValues(metric.Interval{insertStart, now})
+	// We get 59 values here because the clientmodel.Now() is slightly later
+	// than our now.
+	if len(vals) != 59 {
+		t.Errorf("expected 59 values but got %d", len(vals))
+	}
+	if expt := now.Add(-1 * time.Hour).Add(time.Minute); vals[0].Timestamp != expt {
+		t.Errorf("unexpected timestamp for first sample: %v, expected %v", vals[0].Timestamp.Time(), expt.Time())
+	}
+
+	vals = it.BoundaryValues(metric.Interval{insertStart, now})
+	if len(vals) != 2 {
+		t.Errorf("expected 2 values but got %d", len(vals))
+	}
+	if expt := now.Add(-1 * time.Hour).Add(time.Minute); vals[0].Timestamp != expt {
+		t.Errorf("unexpected timestamp for first sample: %v, expected %v", vals[0].Timestamp.Time(), expt.Time())
+	}
+}
+
 // TestLoop is just a smoke test for the loop method, if we can switch it on and
 // off without disaster.
 func TestLoop(t *testing.T) {