Fix queries after a failed snapshot replay (#9980) (#9987)

Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>

tsdb/head.go

@@ -466,7 +466,9 @@ const cardinalityCacheExpirationTime = time.Duration(30) * time.Second
 // limits the ingested samples to the head min valid time.
 func (h *Head) Init(minValidTime int64) error {
 	h.minValidTime.Store(minValidTime)
-	defer h.postings.EnsureOrder()
+	defer func() {
+		h.postings.EnsureOrder()
+	}()
 	defer h.gc() // After loading the wal remove the obsolete data from the head.
 	defer func() {
 		// Loading of m-mapped chunks and snapshot can make the mint of the Head

tsdb/head_test.go

@@ -2827,3 +2827,107 @@ func TestSnapshotError(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, 0, len(tm))
 }
+
+// Tests https://github.com/prometheus/prometheus/issues/9725.
+func TestChunkSnapshotReplayBug(t *testing.T) {
+	dir := t.TempDir()
+	wlog, err := wal.NewSize(nil, nil, filepath.Join(dir, "wal"), 32768, true)
+	require.NoError(t, err)
+
+	// Write few series records and samples such that the series references are not in order in the WAL
+	// for status_code="200".
+	var buf []byte
+	for i := 1; i <= 1000; i++ {
+		var ref uint64
+		if i <= 500 {
+			ref = uint64(i * 100)
+		} else {
+			ref = uint64((i - 500) * 50)
+		}
+		seriesRec := record.RefSeries{
+			Ref: ref,
+			Labels: labels.Labels{
+				{Name: "__name__", Value: "request_duration"},
+				{Name: "status_code", Value: "200"},
+				{Name: "foo", Value: fmt.Sprintf("baz%d", rand.Int())},
+			},
+		}
+		// Add a sample so that the series is not garbage collected.
+		samplesRec := record.RefSample{Ref: ref, T: 1000, V: 1000}
+		var enc record.Encoder
+
+		rec := enc.Series([]record.RefSeries{seriesRec}, buf)
+		buf = rec[:0]
+		require.NoError(t, wlog.Log(rec))
+		rec = enc.Samples([]record.RefSample{samplesRec}, buf)
+		buf = rec[:0]
+		require.NoError(t, wlog.Log(rec))
+	}
+
+	// Write a corrupt snapshot to fail the replay on startup.
+	snapshotName := chunkSnapshotDir(0, 100)
+	cpdir := filepath.Join(dir, snapshotName)
+	require.NoError(t, os.MkdirAll(cpdir, 0o777))
+
+	err = ioutil.WriteFile(filepath.Join(cpdir, "00000000"), []byte{1, 5, 3, 5, 6, 7, 4, 2, 2}, 0o777)
+	require.NoError(t, err)
+
+	opts := DefaultHeadOptions()
+	opts.ChunkDirRoot = dir
+	opts.EnableMemorySnapshotOnShutdown = true
+	head, err := NewHead(nil, nil, wlog, opts, nil)
+	require.NoError(t, err)
+	require.NoError(t, head.Init(math.MinInt64))
+	defer func() {
+		require.NoError(t, head.Close())
+	}()
+
+	// Snapshot replay should error out.
+	require.Equal(t, 1.0, prom_testutil.ToFloat64(head.metrics.snapshotReplayErrorTotal))
+
+	// Querying `request_duration{status_code!="200"}` should return no series since all of
+	// them have status_code="200".
+	q, err := NewBlockQuerier(head, math.MinInt64, math.MaxInt64)
+	require.NoError(t, err)
+	series := query(t, q,
+		labels.MustNewMatcher(labels.MatchEqual, "__name__", "request_duration"),
+		labels.MustNewMatcher(labels.MatchNotEqual, "status_code", "200"),
+	)
+	require.Len(t, series, 0, "there should be no series found")
+}
+
+func TestChunkSnapshotTakenAfterIncompleteSnapshot(t *testing.T) {
+	dir := t.TempDir()
+	wlog, err := wal.NewSize(nil, nil, filepath.Join(dir, "wal"), 32768, true)
+	require.NoError(t, err)
+
+	// Write a snapshot with .tmp suffix. This used to fail taking any further snapshots or replay of snapshots.
+	snapshotName := chunkSnapshotDir(0, 100) + ".tmp"
+	cpdir := filepath.Join(dir, snapshotName)
+	require.NoError(t, os.MkdirAll(cpdir, 0o777))
+
+	opts := DefaultHeadOptions()
+	opts.ChunkDirRoot = dir
+	opts.EnableMemorySnapshotOnShutdown = true
+	head, err := NewHead(nil, nil, wlog, opts, nil)
+	require.NoError(t, err)
+	require.NoError(t, head.Init(math.MinInt64))
+
+	require.Equal(t, 0.0, prom_testutil.ToFloat64(head.metrics.snapshotReplayErrorTotal))
+
+	// Add some samples for the snapshot.
+	app := head.Appender(context.Background())
+	_, err = app.Append(0, labels.Labels{{Name: "foo", Value: "bar"}}, 10, 10)
+	require.NoError(t, err)
+	require.NoError(t, app.Commit())
+
+	// Should not return any error for a successful snapshot.
+	require.NoError(t, head.Close())
+
+	// Verify the snapshot.
+	name, idx, offset, err := LastChunkSnapshot(dir)
+	require.NoError(t, err)
+	require.True(t, name != "")
+	require.Equal(t, 0, idx)
+	require.Greater(t, offset, 0)
+}

tsdb/head_wal.go

@@ -752,7 +752,8 @@ func LastChunkSnapshot(dir string) (string, int, int, error) {
 
 		splits := strings.Split(fi.Name()[len(chunkSnapshotPrefix):], ".")
 		if len(splits) != 2 {
-			return "", 0, 0, errors.Errorf("chunk snapshot %s is not in the right format", fi.Name())
+			// Chunk snapshots is not in the right format, we do not care about it.
+			continue
 		}
 
 		idx, err := strconv.Atoi(splits[0])