diff --git a/db.go b/db.go
index 34f4336a7..823ccf1c0 100644
--- a/db.go
+++ b/db.go
@@ -234,7 +234,7 @@ func (s *Shard) appendBatch(samples []hashedSample) error {
 	}
 
 	// TODO(fabxc): randomize over time
-	if s.head.stats.SampleCount/uint64(s.head.stats.ChunkCount) > 400 {
+	if s.head.stats.SampleCount/(uint64(s.head.stats.ChunkCount)+1) > 400 {
 		select {
 		case s.persistCh <- struct{}{}:
 			go func() {
diff --git a/querier.go b/querier.go
index e1d641b4d..387c26766 100644
--- a/querier.go
+++ b/querier.go
@@ -663,6 +663,11 @@ func (b *BufferedSeriesIterator) PeekBack() (t int64, v float64, ok bool) {
 	return b.buf.last()
 }
 
+// Buffer returns an iterator over the buffered data.
+func (b *BufferedSeriesIterator) Buffer() SeriesIterator {
+	return b.buf.iterator()
+}
+
 // Seek advances the iterator to the element at time t or greater.
 func (b *BufferedSeriesIterator) Seek(t int64) bool {
 	t0 := t - b.buf.delta
@@ -741,6 +746,38 @@ func (r *sampleRing) reset() {
 	r.f = 0
 }
 
+func (r *sampleRing) iterator() SeriesIterator {
+	return &sampleRingIterator{r: r, i: -1}
+}
+
+type sampleRingIterator struct {
+	r *sampleRing
+	i int
+}
+
+func (it *sampleRingIterator) Next() bool {
+	it.i++
+	return it.i < it.r.l
+}
+
+func (it *sampleRingIterator) Seek(int64) bool {
+	return false
+}
+
+func (it *sampleRingIterator) Err() error {
+	return nil
+}
+
+func (it *sampleRingIterator) Values() (int64, float64) {
+	return it.r.at(it.i)
+}
+
+func (r *sampleRing) at(i int) (int64, float64) {
+	j := (r.f + i) % len(r.buf)
+	s := r.buf[j]
+	return s.t, s.v
+}
+
 // add adds a sample to the ring buffer and frees all samples that fall
 // out of the delta range.
 func (r *sampleRing) add(t int64, v float64) {