If reading the WAL fails, try again. Also, read from the segment containing the index for the last checkpoint, not the first segment.

Signed-off-by: Tom Wilkie <tom.wilkie@gmail.com>

storage/remote/storage.go

@@ -60,7 +60,7 @@ func NewStorage(l log.Logger, reg prometheus.Registerer, stCallback startTimeCal
 	}
 	shardUpdateDuration := 10 * time.Second
 	s := &Storage{
-		logger:                 logging.RateLimit(logging.Dedupe(l, 1*time.Minute), 1),
+		logger:                 logging.Dedupe(l, 1*time.Minute),
 		localStartTimeCallback: stCallback,
 		flushDeadline:          flushDeadline,
 		walDir:                 walDir,

storage/remote/wal_watcher.go

@@ -19,6 +19,7 @@ import (
 	"math"
 	"os"
 	"path"
+	"sort"
 	"strconv"
 	"strings"
 	"time"
@@ -182,7 +183,7 @@ func NewWALWatcher(logger log.Logger, name string, writer writeTo, walDir string
 
 func (w *WALWatcher) Start() {
 	level.Info(w.logger).Log("msg", "starting WAL watcher", "queue", w.name)
-	go w.runWatcher()
+	go w.loop()
 }
 
 func (w *WALWatcher) Stop() {
@@ -190,71 +191,95 @@ func (w *WALWatcher) Stop() {
 	close(w.quit)
 }
 
-func (w *WALWatcher) runWatcher() {
+func (w *WALWatcher) loop() {
-	// The WAL dir may not exist when Prometheus first starts up.
+	// We may encourter failures processing the WAL; we should wait and retry.
+
 	for {
-		if _, err := os.Stat(w.walDir); os.IsNotExist(err) {
+		if err := w.run(); err != nil {
-			time.Sleep(time.Second)
+			level.Error(w.logger).Log("msg", "error tailing WAL", "err", err)
-		} else {
+		}
-			break
+
+		select {
+		case <-w.quit:
+			return
+		case <-time.After(5 * time.Second):
 		}
 	}
+}
 
+func (w *WALWatcher) run() error {
 	nw, err := wal.New(nil, nil, w.walDir)
 	if err != nil {
-		level.Error(w.logger).Log("err", err)
+		return errors.Wrap(err, "wal.New")
-		return
-	}
-
-	first, last, err := nw.Segments()
-	if err != nil {
-		level.Error(w.logger).Log("err", err)
-		return
-	}
-
-	if last == -1 {
-		level.Error(w.logger).Log("err", err)
-		return
 	}
 
 	// Backfill from the checkpoint first if it exists.
-	dir, _, err := tsdb.LastCheckpoint(w.walDir)
+	var nextIndex int
+	w.lastCheckpoint, nextIndex, err = tsdb.LastCheckpoint(w.walDir)
 	if err != nil && err != tsdb.ErrNotFound {
-		level.Error(w.logger).Log("msg", "error looking for existing checkpoint, some samples may be dropped", "err", errors.Wrap(err, "find last checkpoint"))
+		return err
 	}
 
-	level.Debug(w.logger).Log("msg", "reading checkpoint", "dir", dir)
+	level.Debug(w.logger).Log("msg", "reading checkpoint", "dir", w.lastCheckpoint, "startFrom", nextIndex)
 	if err == nil {
-		w.lastCheckpoint = dir
+		if err = w.readCheckpoint(w.lastCheckpoint); err != nil {
-		err = w.readCheckpoint(dir)
+			return err
-		if err != nil {
-			level.Error(w.logger).Log("msg", "error reading existing checkpoint, some samples may be dropped", "err", err)
 		}
 	}
 
-	w.currentSegment = first
+	w.currentSegment, err = w.findSegmentForIndex(nextIndex)
-	tail := false
+	if err != nil {
+		return err
+	}
+
+	level.Debug(w.logger).Log("msg", "starting from", "currentSegment", w.currentSegment)
 
 	for {
-		if w.currentSegment == last {
-			tail = true
-		}
-
 		w.currentSegmentMetric.Set(float64(w.currentSegment))
-		level.Info(w.logger).Log("msg", "process segment", "segment", w.currentSegment, "tail", tail)
+		level.Info(w.logger).Log("msg", "process segment", "segment", w.currentSegment)
 
 		// On start, after reading the existing WAL for series records, we have a pointer to what is the latest segment.
 		// On subsequent calls to this function, currentSegment will have been incremented and we should open that segment.
-		if err := w.watch(nw, w.currentSegment, tail); err != nil {
+		if err := w.watch(nw, w.currentSegment, true); err != nil {
 			level.Error(w.logger).Log("msg", "runWatcher is ending", "err", err)
-			return
+			return err
 		}
 
 		w.currentSegment++
 	}
 }
 
-// Use tail true to indicate that the reader is currently on a segment that is
+func (w *WALWatcher) findSegmentForIndex(index int) (int, error) {
+	files, err := fileutil.ReadDir(w.walDir)
+	if err != nil {
+		return -1, err
+	}
+
+	var refs []int
+	var last int
+	for _, fn := range files {
+		k, err := strconv.Atoi(fn)
+		if err != nil {
+			continue
+		}
+		if len(refs) > 0 && k > last+1 {
+			return -1, errors.New("segments are not sequential")
+		}
+		refs = append(refs, k)
+		last = k
+	}
+	sort.Sort(sort.IntSlice(refs))
+
+	for _, r := range refs {
+		if r >= index {
+			return r, nil
+		}
+	}
+
+	return -1, errors.New("failed to find segment for index")
+}
+
+// Use tail true to indicate thatreader is currently on a segment that is
 // actively being written to. If false, assume it's a full segment and we're
 // replaying it on start to cache the series records.
 func (w *WALWatcher) watch(wl *wal.WAL, segmentNum int, tail bool) error {
@@ -444,11 +469,15 @@ func (w *WALWatcher) readCheckpoint(checkpointDir string) error {
 
 	// w.readSeriesRecords(wal.NewLiveReader(sr), i, size)
 	r := wal.NewLiveReader(sr)
-	w.readSegment(r)
+	if err := w.readSegment(r); err != nil {
+		return errors.Wrap(err, "readSegment")
+	}
+
 	if r.TotalRead() != size {
 		level.Warn(w.logger).Log("msg", "may not have read all data from checkpoint")
 	}
 	level.Debug(w.logger).Log("msg", "read series references from checkpoint", "checkpoint", checkpointDir)
+
 	return nil
 }