Fix race condition between gc and committing (#378)

Signed-off-by: Chris Marchbanks <csmarchbanks@gmail.com>

head.go

@@ -620,21 +620,22 @@ func (a *headAppender) Add(lset labels.Labels, t int64, v float64) (uint64, erro
 }
 
 func (a *headAppender) AddFast(ref uint64, t int64, v float64) error {
-	s := a.head.series.getByID(ref)
+	if t < a.minValidTime {
+		return ErrOutOfBounds
+	}
 
+	s := a.head.series.getByID(ref)
 	if s == nil {
 		return errors.Wrap(ErrNotFound, "unknown series")
 	}
 	s.Lock()
-	err := s.appendable(t, v)
+	if err := s.appendable(t, v); err != nil {
 		s.Unlock()
-
-	if err != nil {
 		return err
 	}
-	if t < a.minValidTime {
-		return ErrOutOfBounds
-	}
+	s.pendingCommit = true
+	s.Unlock()
+
 	if t < a.mint {
 		a.mint = t
 	}
@@ -694,6 +695,7 @@ func (a *headAppender) Commit() error {
 	for _, s := range a.samples {
 		s.series.Lock()
 		ok, chunkCreated := s.series.append(s.T, s.V)
+		s.series.pendingCommit = false
 		s.series.Unlock()
 
 		if !ok {
@@ -713,6 +715,11 @@ func (a *headAppender) Commit() error {
 
 func (a *headAppender) Rollback() error {
 	a.head.metrics.activeAppenders.Dec()
+	for _, s := range a.samples {
+		s.series.Lock()
+		s.series.pendingCommit = false
+		s.series.Unlock()
+	}
 	a.head.putAppendBuffer(a.samples)
 
 	// Series are created in the head memory regardless of rollback. Thus we have
@@ -1165,7 +1172,7 @@ func (s *stripeSeries) gc(mint int64) (map[uint64]struct{}, int) {
 				series.Lock()
 				rmChunks += series.truncateChunksBefore(mint)
 
-				if len(series.chunks) > 0 {
+				if len(series.chunks) > 0 || series.pendingCommit {
 					series.Unlock()
 					continue
 				}
@@ -1256,9 +1263,10 @@ type memSeries struct {
 	chunkRange   int64
 	firstChunkID int
 
-	nextAt    int64 // timestamp at which to cut the next chunk.
+	nextAt        int64 // Timestamp at which to cut the next chunk.
 	lastValue     float64
 	sampleBuf     [4]sample
+	pendingCommit bool // Whether there are samples waiting to be committed to this series.
 
 	app chunkenc.Appender // Current appender for the chunk.
 }

head_test.go

@@ -781,6 +781,64 @@ func TestGCSeriesAccess(t *testing.T) {
 	testutil.Equals(t, ErrNotFound, err)
 }
 
+func TestUncommittedSamplesNotLostOnTruncate(t *testing.T) {
+	h, err := NewHead(nil, nil, nil, 1000)
+	testutil.Ok(t, err)
+	defer h.Close()
+
+	h.initTime(0)
+
+	app := h.appender()
+	lset := labels.FromStrings("a", "1")
+	_, err = app.Add(lset, 2100, 1)
+	testutil.Ok(t, err)
+
+	testutil.Ok(t, h.Truncate(2000))
+	testutil.Assert(t, nil != h.series.getByHash(lset.Hash(), lset), "series should not have been garbage collected")
+
+	testutil.Ok(t, app.Commit())
+
+	q, err := NewBlockQuerier(h, 1500, 2500)
+	testutil.Ok(t, err)
+	defer q.Close()
+
+	ss, err := q.Select(labels.NewEqualMatcher("a", "1"))
+	testutil.Ok(t, err)
+
+	testutil.Equals(t, true, ss.Next())
+}
+
+func TestRemoveSeriesAfterRollbackAndTruncate(t *testing.T) {
+	h, err := NewHead(nil, nil, nil, 1000)
+	testutil.Ok(t, err)
+	defer h.Close()
+
+	h.initTime(0)
+
+	app := h.appender()
+	lset := labels.FromStrings("a", "1")
+	_, err = app.Add(lset, 2100, 1)
+	testutil.Ok(t, err)
+
+	testutil.Ok(t, h.Truncate(2000))
+	testutil.Assert(t, nil != h.series.getByHash(lset.Hash(), lset), "series should not have been garbage collected")
+
+	testutil.Ok(t, app.Rollback())
+
+	q, err := NewBlockQuerier(h, 1500, 2500)
+	testutil.Ok(t, err)
+	defer q.Close()
+
+	ss, err := q.Select(labels.NewEqualMatcher("a", "1"))
+	testutil.Ok(t, err)
+
+	testutil.Equals(t, false, ss.Next())
+
+	// Truncate again, this time the series should be deleted
+	testutil.Ok(t, h.Truncate(2050))
+	testutil.Equals(t, (*memSeries)(nil), h.series.getByHash(lset.Hash(), lset))
+}
+
 func TestHead_LogRollback(t *testing.T) {
 	dir, err := ioutil.TempDir("", "wal_rollback")
 	testutil.Ok(t, err)