Added additional check for lazy Postings.

Debugging #335.

Potentially broken preloadPosting is missing some postings, because
of bad partitioning. Unit tests are there, but we might not get all edge cases?

If with this check we will have still panic - it can only mean races.
However, -race is not showing anything interesting on, even extended tests.

Signed-off-by: Bartek Plotka <bwplotka@gmail.com>

pkg/store/bucket.go

@@ -482,10 +482,13 @@ func (s *BucketStore) blockSeries(
 	if lazyPostings == index.EmptyPostings() {
 		return storepb.EmptySeriesSet(), stats, nil
 	}
+
 	if err := indexr.preloadPostings(); err != nil {
 		return nil, stats, errors.Wrap(err, "preload postings")
 	}
+
 	// Get result postings list by resolving the postings tree.
+	// TODO(bwplotka): Users are seeing panics here, because of lazyPosting being not loaded by preloadPostings.
 	ps, err := index.ExpandPostings(lazyPostings)
 	if err != nil {
 		return nil, stats, errors.Wrap(err, "expand postings")
@@ -673,6 +676,9 @@ func debugFoundBlockSetOverview(logger log.Logger, mint, maxt int64, lset labels
 }
 
 // Series implements the storepb.StoreServer interface.
+// TODO(bwplotka): It buffers all chunks in memory and only then streams to client.
+// 1. Either count chunk sizes and error out too big query.
+// 2. Stream posting -> series -> chunk all together.
 func (s *BucketStore) Series(req *storepb.SeriesRequest, srv storepb.Store_SeriesServer) error {
 	matchers, err := translateMatchers(req.Matchers)
 	if err != nil {
@@ -1207,14 +1213,35 @@ func (r *bucketIndexReader) preloadPostings() error {
 			}
 		})
 	}
-	return g.Run()
+
+	if err := g.Run(); err != nil {
+		return err
+	}
+
+	// TODO(bwplotka): Users are seeing lazyPostings not fully loaded. Double checking it here and printing more info
+	// on failure case.
+	for _, postings := range ps {
+		if postings.Postings != nil {
+			continue
+		}
+
+		msg := fmt.Sprintf("found parts: %v bases on:", parts)
+		for _, p := range ps {
+			msg += fmt.Sprintf(" [start: %v; end: %v]", p.ptr.Start, p.ptr.End)
+		}
+
+		return errors.Errorf("expected all postings to be loaded but spotted malformed one with key: %v; start: %v; end: %v. Additional info: %s",
+			postings.key, postings.ptr.Start, postings.ptr.End, msg)
+	}
+
+	return nil
 }
 
 // loadPostings loads given postings using given start + length. It is expected to have given postings data within given range.
 func (r *bucketIndexReader) loadPostings(ctx context.Context, postings []*lazyPostings, start, end int64) error {
 	begin := time.Now()
 
-	b, err := r.block.readIndexRange(r.ctx, int64(start), int64(end-start))
+	b, err := r.block.readIndexRange(ctx, int64(start), int64(end-start))
 	if err != nil {
 		return errors.Wrap(err, "read postings range")
 	}