diff --git a/db.go b/db.go
index d7c5649fb..dfb62ea02 100644
--- a/db.go
+++ b/db.go
@@ -493,6 +493,7 @@ func (db *DB) reload() (err error) {
 		return nil
 	}
 	maxt := blocks[len(db.blocks)-1].Meta().MaxTime
+
 	return errors.Wrap(db.head.Truncate(maxt), "head truncate failed")
 }
 
diff --git a/head.go b/head.go
index 309489119..c1c25bbd4 100644
--- a/head.go
+++ b/head.go
@@ -193,9 +193,9 @@ func NewHead(r prometheus.Registerer, l log.Logger, wal WAL, chunkRange int64) (
 func (h *Head) readWAL() error {
 	r := h.wal.Reader(h.MinTime())
 
-	seriesFunc := func(series []labels.Labels) error {
-		for _, lset := range series {
-			h.create(lset.Hash(), lset)
+	seriesFunc := func(series []RefSeries) error {
+		for _, s := range series {
+			h.create(s.Labels.Hash(), s.Labels)
 		}
 		return nil
 	}
@@ -252,7 +252,12 @@ func (h *Head) Truncate(mint int64) error {
 
 	start = time.Now()
 
-	if err := h.wal.Truncate(mint); err == nil {
+	p, err := h.indexRange(mint, math.MaxInt64).Postings("", "")
+	if err != nil {
+		return err
+	}
+
+	if err := h.wal.Truncate(mint, p); err == nil {
 		h.logger.Log("msg", "WAL truncation completed", "duration", time.Since(start))
 	} else {
 		h.logger.Log("msg", "WAL truncation failed", "err", err, "duration", time.Since(start))
@@ -356,9 +361,9 @@ type headAppender struct {
 	head *Head
 	mint int64
 
-	newSeries []*hashedLabels
-	newLabels []labels.Labels
-	newHashes map[uint64]uint64
+	newSeries     []*hashedLabels
+	createdSeries []RefSeries
+	newHashes     map[uint64]uint64
 
 	samples       []RefSample
 	highTimestamp int64
@@ -461,7 +466,7 @@ func (a *headAppender) createSeries() error {
 	if len(a.newSeries) == 0 {
 		return nil
 	}
-	a.newLabels = make([]labels.Labels, 0, len(a.newSeries))
+	a.createdSeries = make([]RefSeries, 0, len(a.newSeries))
 	base0 := len(a.head.series)
 
 	a.head.mtx.RUnlock()
@@ -481,14 +486,14 @@ func (a *headAppender) createSeries() error {
 			}
 		}
 		// Series is still new.
-		a.newLabels = append(a.newLabels, l.labels)
-
 		s := a.head.create(l.hash, l.labels)
 		l.ref = uint64(s.ref)
+
+		a.createdSeries = append(a.createdSeries, RefSeries{Ref: l.ref, Labels: l.labels})
 	}
 
 	// Write all new series to the WAL.
-	if err := a.head.wal.LogSeries(a.newLabels); err != nil {
+	if err := a.head.wal.LogSeries(a.createdSeries); err != nil {
 		return errors.Wrap(err, "WAL log series")
 	}
 
diff --git a/wal.go b/wal.go
index dcf3fc9e9..3714c8800 100644
--- a/wal.go
+++ b/wal.go
@@ -53,7 +53,7 @@ const (
 type SamplesCB func([]RefSample) error
 
 // SeriesCB is the callback after reading series.
-type SeriesCB func([]labels.Labels) error
+type SeriesCB func([]RefSeries) error
 
 // DeletesCB is the callback after reading deletes.
 type DeletesCB func([]Stone) error
@@ -63,7 +63,7 @@ type SegmentWAL struct {
 	mtx sync.Mutex
 
 	dirFile *os.File
-	files   []*os.File
+	files   []*segmentFile
 
 	logger        log.Logger
 	flushInterval time.Duration
@@ -73,6 +73,10 @@ type SegmentWAL struct {
 	cur   *bufio.Writer
 	curN  int64
 
+	// The max time of samples committed last/being committed. Not global or current
+	// segment values.
+	maxt int64
+
 	stopc chan struct{}
 	donec chan struct{}
 }
@@ -81,10 +85,10 @@ type SegmentWAL struct {
 // It must be completely read before new entries are logged.
 type WAL interface {
 	Reader(mint int64) WALReader
-	LogSeries([]labels.Labels) error
+	LogSeries([]RefSeries) error
 	LogSamples([]RefSample) error
 	LogDeletes([]Stone) error
-	Truncate(maxt int64) error
+	Truncate(int64, Postings) error
 	Close() error
 }
 
@@ -92,10 +96,10 @@ type NopWAL struct{}
 
 func (NopWAL) Read(SeriesCB, SamplesCB, DeletesCB) error { return nil }
 func (w NopWAL) Reader(int64) WALReader                  { return w }
-func (NopWAL) LogSeries([]labels.Labels) error           { return nil }
+func (NopWAL) LogSeries([]RefSeries) error               { return nil }
 func (NopWAL) LogSamples([]RefSample) error              { return nil }
 func (NopWAL) LogDeletes([]Stone) error                  { return nil }
-func (NopWAL) Truncate(int64) error                      { return nil }
+func (NopWAL) Truncate(int64, Postings) error            { return nil }
 func (NopWAL) Close() error                              { return nil }
 
 // WALReader reads entries from a WAL.
@@ -103,6 +107,12 @@ type WALReader interface {
 	Read(SeriesCB, SamplesCB, DeletesCB) error
 }
 
+// RefSeries is the series labels with the series ID.
+type RefSeries struct {
+	Ref    uint64
+	Labels labels.Labels
+}
+
 // RefSample is a timestamp/value pair associated with a reference to a series.
 type RefSample struct {
 	Ref uint64
@@ -110,6 +120,15 @@ type RefSample struct {
 	V   float64
 }
 
+type segmentFile struct {
+	f    *os.File
+	maxt int64
+}
+
+func (f segmentFile) Close() error {
+	return f.f.Close()
+}
+
 const (
 	walSegmentSizeBytes = 256 * 1024 * 1024 // 256 MB
 )
@@ -163,17 +182,102 @@ func OpenSegmentWAL(dir string, logger log.Logger, flushInterval time.Duration)
 
 // Reader returns a new reader over the the write ahead log data.
 // It must be completely consumed before writing to the WAL.
-func (w *SegmentWAL) Reader(int64) WALReader {
-	return newWALReader(w, w.logger)
+func (w *SegmentWAL) Reader(mint int64) WALReader {
+	return newWALReader(w, mint, w.logger)
 }
 
-// Log writes a batch of new series labels and samples to the log.
-//func (w *SegmentWAL) Log(series []labels.Labels, samples []RefSample) error {
-//return nil
-//}
+// Truncate deletes the values prior to mint and the series entries not in p.
+func (w *SegmentWAL) Truncate(mint int64, p Postings) error {
+	// TODO(gouthamve): Handle the deletes too.
+	delFiles := make([]*segmentFile, 0)
+
+	// All files have to be traversed as there could be two segments for a block
+	// with first block having times (10000, 20000) and SECOND one having (0, 10000).
+	for _, f := range w.files {
+		if f.maxt < mint {
+			delFiles = append(delFiles, f)
+		}
+	}
+
+	if len(delFiles) == 0 {
+		return nil
+	}
+
+	tempWAL := &SegmentWAL{
+		logger: w.logger,
+		files:  delFiles,
+	}
+	wr := newWALReader(tempWAL, 0, tempWAL.logger)
+
+	// Create a new tmp file.
+	// TODO: Do it properly.
+	newF, err := os.Create(delFiles[0].f.Name() + ".tmp")
+	if err != nil {
+		return errors.Wrap(err, "create tmp series dump file")
+	}
+	// Write header metadata for new file.
+	metab := make([]byte, 8)
+	binary.BigEndian.PutUint32(metab[:4], WALMagic)
+	metab[4] = WALFormatDefault
+	if _, err := newF.Write(metab); err != nil {
+		return err
+	}
+
+WRLoop:
+	for wr.next() {
+		rt, flag, byt := wr.at()
+
+		if rt != WALEntrySeries {
+			continue
+		}
+
+		series, err := wr.decodeSeries(flag, byt)
+		if err != nil {
+			return errors.Wrap(err, "decode samples while truncating")
+		}
+
+		activeSeries := make([]RefSeries, 0, len(series))
+		for _, s := range series {
+			if !p.Seek(uint32(s.Ref)) {
+				break WRLoop
+			}
+
+			if p.At() == uint32(s.Ref) {
+				activeSeries = append(activeSeries, s)
+			}
+		}
+
+		if len(activeSeries) == 0 {
+			continue
+		}
+		buf := getWALBuffer()
+		buf = encodeSeries(buf, activeSeries)
+		_, err = newF.Write(buf)
+		if err != nil {
+			return errors.Wrap(err, "write series")
+		}
+	}
+
+	if err := newF.Close(); err != nil {
+		return errors.Wrap(err, "close tmp file")
+	}
+
+	if err := renameFile(newF.Name(), w.files[0].f.Name()); err != nil {
+		return err
+	}
+	delFiles = delFiles[1:]
+	for _, f := range delFiles {
+		if err := os.RemoveAll(f.f.Name()); err != nil {
+			return errors.Wrap(err, "delete WAL segment file")
+		}
+	}
+	// TODO: sync parent directory.
+	return nil
+}
 
 // LogSeries writes a batch of new series labels to the log.
-func (w *SegmentWAL) LogSeries(series []labels.Labels) error {
+// The series have to be ordered.
+func (w *SegmentWAL) LogSeries(series []RefSeries) error {
 	if err := w.encodeSeries(series); err != nil {
 		return err
 	}
@@ -225,13 +329,14 @@ func (w *SegmentWAL) initSegments() error {
 		if err != nil {
 			return err
 		}
-		w.files = append(w.files, f)
+		w.files = append(w.files, &segmentFile{f: f})
 	}
 
 	// Consume and validate meta headers.
-	for _, f := range w.files {
+	for _, sf := range w.files {
 		metab := make([]byte, 8)
 
+		f := sf.f
 		if n, err := f.Read(metab); err != nil {
 			return errors.Wrapf(err, "validate meta %q", f.Name())
 		} else if n != 8 {
@@ -293,7 +398,9 @@ func (w *SegmentWAL) cut() error {
 		return err
 	}
 
-	w.files = append(w.files, f)
+	w.files = append(w.files, &segmentFile{f: f})
+
+	// TODO(gouthamve): make the buffer size a constant.
 	w.cur = bufio.NewWriterSize(f, 4*1024*1024)
 	w.curN = 8
 
@@ -304,7 +411,7 @@ func (w *SegmentWAL) tail() *os.File {
 	if len(w.files) == 0 {
 		return nil
 	}
-	return w.files[len(w.files)-1]
+	return w.files[len(w.files)-1].f
 }
 
 // Sync flushes the changes to disk.
@@ -330,10 +437,6 @@ func (w *SegmentWAL) Sync() error {
 	return fileutil.Fdatasync(tail)
 }
 
-func (w *SegmentWAL) Truncate(maxt int64) error {
-	return nil
-}
-
 func (w *SegmentWAL) sync() error {
 	if err := w.flush(); err != nil {
 		return err
@@ -396,6 +499,7 @@ const (
 	// It should be a multiple of the minimum sector size so that WAL can safely
 	// distinguish between torn writes and ordinary data corruption.
 	walPageBytes = 16 * minSectorSize
+	// TODO(gouthamve): What is this?
 )
 
 func (w *SegmentWAL) entry(et WALEntryType, flag byte, buf []byte) error {
@@ -404,6 +508,7 @@ func (w *SegmentWAL) entry(et WALEntryType, flag byte, buf []byte) error {
 
 	// Cut to the next segment if the entry exceeds the file size unless it would also
 	// exceed the size of a new segment.
+	// TODO(gouthamve): Add a test for this case where the commit is greater than segmentSize.
 	var (
 		// 6-byte header + 4-byte CRC32 + buf.
 		sz    = int64(6 + 4 + len(buf))
@@ -439,6 +544,14 @@ func (w *SegmentWAL) entry(et WALEntryType, flag byte, buf []byte) error {
 	w.curN += sz
 
 	putWALBuffer(buf)
+
+	// set the file's maxt.
+	if len(w.files) > 0 {
+		cf := w.files[len(w.files)-1]
+		if cf.maxt < w.maxt {
+			cf.maxt = w.maxt
+		}
+	}
 	return nil
 }
 
@@ -463,16 +576,31 @@ func putWALBuffer(b []byte) {
 	walBuffers.Put(b)
 }
 
-func (w *SegmentWAL) encodeSeries(series []labels.Labels) error {
+func (w *SegmentWAL) encodeSeries(series []RefSeries) error {
 	if len(series) == 0 {
 		return nil
 	}
 
-	b := make([]byte, binary.MaxVarintLen32)
 	buf := getWALBuffer()
+	buf = encodeSeries(buf, series)
+
+	return w.entry(WALEntrySeries, walSeriesSimple, buf)
+}
+
+func encodeSeries(buf []byte, series []RefSeries) []byte {
+	b := make([]byte, binary.MaxVarintLen64)
+	// Store the base reference number of the first series.
+	// All series encode their ref as a delta to the first.
+	first := series[0]
+	binary.BigEndian.PutUint64(b, first.Ref)
+	buf = append(buf, b[:8]...)
 
-	for _, lset := range series {
-		n := binary.PutUvarint(b, uint64(len(lset)))
+	for _, s := range series {
+		n := binary.PutVarint(b, int64(s.Ref)-int64(first.Ref))
+		buf = append(buf, b[:n]...)
+
+		lset := s.Labels
+		n = binary.PutUvarint(b, uint64(len(lset)))
 		buf = append(buf, b[:n]...)
 
 		for _, l := range lset {
@@ -486,7 +614,7 @@ func (w *SegmentWAL) encodeSeries(series []labels.Labels) error {
 		}
 	}
 
-	return w.entry(WALEntrySeries, walSeriesSimple, buf)
+	return buf
 }
 
 func (w *SegmentWAL) encodeSamples(samples []RefSample) error {
@@ -508,7 +636,12 @@ func (w *SegmentWAL) encodeSamples(samples []RefSample) error {
 	binary.BigEndian.PutUint64(b, uint64(first.T))
 	buf = append(buf, b[:8]...)
 
+	w.maxt = 0
 	for _, s := range samples {
+		if w.maxt < s.T {
+			w.maxt = s.T
+		}
+
 		n := binary.PutVarint(b, int64(s.Ref)-int64(first.Ref))
 		buf = append(buf, b[:n]...)
 
@@ -543,6 +676,7 @@ func (w *SegmentWAL) encodeDeletes(stones []Stone) error {
 type walReader struct {
 	logger log.Logger
 
+	mint  int64
 	wal   *SegmentWAL
 	cur   int
 	buf   []byte
@@ -555,12 +689,13 @@ type walReader struct {
 	err error
 }
 
-func newWALReader(w *SegmentWAL, l log.Logger) *walReader {
+func newWALReader(w *SegmentWAL, mint int64, l log.Logger) *walReader {
 	if l == nil {
 		l = log.NewNopLogger()
 	}
 	return &walReader{
 		logger: l,
+		mint:   mint,
 		wal:    w,
 		buf:    make([]byte, 0, 128*4096),
 		crc32:  newCRC32(),
@@ -589,7 +724,24 @@ func (r *walReader) Read(seriesf SeriesCB, samplesf SamplesCB, deletesf DeletesC
 			if err != nil {
 				return err
 			}
-			samplesf(s)
+
+			// Update the times for the wal segment file and select only valid samples.
+			cf := r.wal.files[r.cur]
+			validSamples := make([]RefSample, 0, len(s))
+
+			for _, smpl := range s {
+				if smpl.T < r.mint {
+					continue
+				}
+
+				if cf.maxt < smpl.T {
+					cf.maxt = smpl.T
+				}
+
+				validSamples = append(validSamples, smpl)
+			}
+
+			samplesf(validSamples)
 		case WALEntryDeletes:
 			s, err := r.decodeDeletes(flag, b)
 			if err != nil {
@@ -607,7 +759,7 @@ func (r *walReader) nextEntry() (WALEntryType, byte, []byte, error) {
 	if r.cur >= len(r.wal.files) {
 		return 0, 0, nil, io.EOF
 	}
-	cf := r.wal.files[r.cur]
+	cf := r.wal.files[r.cur].f
 
 	et, flag, b, err := r.entry(cf)
 	// If we reached the end of the reader, advance to the next one
@@ -634,7 +786,7 @@ func (r *walReader) next() bool {
 	if r.cur >= len(r.wal.files) {
 		return false
 	}
-	cf := r.wal.files[r.cur]
+	cf := r.wal.files[r.cur].f
 
 	// Save position after last valid entry if we have to truncate the WAL.
 	lastOffset, err := cf.Seek(0, os.SEEK_CUR)
@@ -675,7 +827,7 @@ func (r *walReader) next() bool {
 }
 
 func (r *walReader) current() *os.File {
-	return r.wal.files[r.cur]
+	return r.wal.files[r.cur].f
 }
 
 // truncate the WAL after the last valid entry.
@@ -684,7 +836,8 @@ func (r *walReader) truncate(lastOffset int64) error {
 		"err", r.err, "file", r.current().Name(), "pos", lastOffset)
 
 	// Close and delete all files after the current one.
-	for _, f := range r.wal.files[r.cur+1:] {
+	for _, sf := range r.wal.files[r.cur+1:] {
+		f := sf.f
 		if err := f.Close(); err != nil {
 			return err
 		}
@@ -754,9 +907,25 @@ func (r *walReader) entry(cr io.Reader) (WALEntryType, byte, []byte, error) {
 	return etype, flag, buf, nil
 }
 
-func (r *walReader) decodeSeries(flag byte, b []byte) ([]labels.Labels, error) {
-	series := []labels.Labels{}
+func (r *walReader) decodeSeries(flag byte, b []byte) ([]RefSeries, error) {
+	series := []RefSeries{}
+	if len(b) < 8 {
+		return nil, errors.Wrap(errInvalidSize, "header length")
+	}
+
+	baseRef := binary.BigEndian.Uint64(b)
+	b = b[8:]
+
 	for len(b) > 0 {
+		var ser RefSeries
+		// TODO: Check again.
+		dref, n := binary.Varint(b)
+		if n < 1 {
+			return nil, errors.Wrap(errInvalidSize, "series ref delta")
+		}
+		b = b[n:]
+		ser.Ref = uint64(int64(baseRef) + dref)
+
 		l, n := binary.Uvarint(b)
 		if n < 1 {
 			return nil, errors.Wrap(errInvalidSize, "number of labels")
@@ -779,8 +948,9 @@ func (r *walReader) decodeSeries(flag byte, b []byte) ([]labels.Labels, error) {
 			lset[i].Value = string(b[n : n+int(vl)])
 			b = b[n+int(vl):]
 		}
+		ser.Labels = lset
 
-		series = append(series, lset)
+		series = append(series, ser)
 	}
 	return series, nil
 }
diff --git a/wal_test.go b/wal_test.go
index 4f1d3f046..dd2f4cf55 100644
--- a/wal_test.go
+++ b/wal_test.go
@@ -23,7 +23,6 @@ import (
 
 	"github.com/coreos/etcd/pkg/fileutil"
 	"github.com/go-kit/kit/log"
-	"github.com/prometheus/tsdb/labels"
 	"github.com/stretchr/testify/require"
 )
 
@@ -57,7 +56,7 @@ func TestSegmentWAL_initSegments(t *testing.T) {
 
 	// Validate that files are locked properly.
 	for _, of := range w.files {
-		f, err := os.Open(of.Name())
+		f, err := os.Open(of.f.Name())
 		require.NoError(t, err, "open locked segment %s", f.Name())
 
 		_, err = f.Read([]byte{0})
@@ -74,7 +73,7 @@ func TestSegmentWAL_initSegments(t *testing.T) {
 	}
 
 	// Make initialization fail by corrupting the header of one file.
-	f, err := os.OpenFile(w.files[3].Name(), os.O_WRONLY, 0666)
+	f, err := os.OpenFile(w.files[3].f.Name(), os.O_WRONLY, 0666)
 	require.NoError(t, err)
 
 	_, err = f.WriteAt([]byte{0}, 4)
@@ -110,7 +109,7 @@ func TestSegmentWAL_cut(t *testing.T) {
 	require.NoError(t, w.Close())
 
 	for _, of := range w.files {
-		f, err := os.Open(of.Name())
+		f, err := os.Open(of.f.Name())
 		require.NoError(t, err)
 
 		// Verify header data.
@@ -122,7 +121,7 @@ func TestSegmentWAL_cut(t *testing.T) {
 
 		// We cannot actually check for correct pre-allocation as it is
 		// optional per filesystem and handled transparently.
-		et, flag, b, err := newWALReader(nil, nil).entry(f)
+		et, flag, b, err := newWALReader(nil, 0, nil).entry(f)
 		require.NoError(t, err)
 		require.Equal(t, WALEntrySeries, et)
 		require.Equal(t, flag, byte(walSeriesSimple))
@@ -147,7 +146,7 @@ func TestSegmentWAL_Log_Restore(t *testing.T) {
 	defer os.RemoveAll(dir)
 
 	var (
-		recordedSeries  [][]labels.Labels
+		recordedSeries  [][]RefSeries
 		recordedSamples [][]RefSample
 		recordedDeletes [][]Stone
 	)
@@ -165,16 +164,16 @@ func TestSegmentWAL_Log_Restore(t *testing.T) {
 		r := w.Reader(0)
 
 		var (
-			resultSeries  [][]labels.Labels
+			resultSeries  [][]RefSeries
 			resultSamples [][]RefSample
 			resultDeletes [][]Stone
 		)
 
-		serf := func(lsets []labels.Labels) error {
-			if len(lsets) > 0 {
-				clsets := make([]labels.Labels, len(lsets))
-				copy(clsets, lsets)
-				resultSeries = append(resultSeries, clsets)
+		serf := func(series []RefSeries) error {
+			if len(series) > 0 {
+				clsets := make([]RefSeries, len(series))
+				copy(clsets, series)
+				resultSeries = append(resultSeries, series)
 			}
 
 			return nil
@@ -224,13 +223,20 @@ func TestSegmentWAL_Log_Restore(t *testing.T) {
 			}
 
 			lbls := series[i : i+stepSize]
+			series := make([]RefSeries, 0, len(series))
+			for j, l := range lbls {
+				series = append(series, RefSeries{
+					Ref:    uint64(i + j),
+					Labels: l,
+				})
+			}
 
-			require.NoError(t, w.LogSeries(lbls))
+			require.NoError(t, w.LogSeries(series))
 			require.NoError(t, w.LogSamples(samples))
 			require.NoError(t, w.LogDeletes(stones))
 
 			if len(lbls) > 0 {
-				recordedSeries = append(recordedSeries, lbls)
+				recordedSeries = append(recordedSeries, series)
 			}
 			if len(samples) > 0 {
 				recordedSamples = append(recordedSamples, samples)
@@ -254,7 +260,7 @@ func TestWALRestoreCorrupted(t *testing.T) {
 		{
 			name: "truncate_checksum",
 			f: func(t *testing.T, w *SegmentWAL) {
-				f, err := os.OpenFile(w.files[0].Name(), os.O_WRONLY, 0666)
+				f, err := os.OpenFile(w.files[0].f.Name(), os.O_WRONLY, 0666)
 				require.NoError(t, err)
 				defer f.Close()
 
@@ -267,7 +273,7 @@ func TestWALRestoreCorrupted(t *testing.T) {
 		{
 			name: "truncate_body",
 			f: func(t *testing.T, w *SegmentWAL) {
-				f, err := os.OpenFile(w.files[0].Name(), os.O_WRONLY, 0666)
+				f, err := os.OpenFile(w.files[0].f.Name(), os.O_WRONLY, 0666)
 				require.NoError(t, err)
 				defer f.Close()
 
@@ -280,7 +286,7 @@ func TestWALRestoreCorrupted(t *testing.T) {
 		{
 			name: "body_content",
 			f: func(t *testing.T, w *SegmentWAL) {
-				f, err := os.OpenFile(w.files[0].Name(), os.O_WRONLY, 0666)
+				f, err := os.OpenFile(w.files[0].f.Name(), os.O_WRONLY, 0666)
 				require.NoError(t, err)
 				defer f.Close()
 
@@ -295,7 +301,7 @@ func TestWALRestoreCorrupted(t *testing.T) {
 		{
 			name: "checksum",
 			f: func(t *testing.T, w *SegmentWAL) {
-				f, err := os.OpenFile(w.files[0].Name(), os.O_WRONLY, 0666)
+				f, err := os.OpenFile(w.files[0].f.Name(), os.O_WRONLY, 0666)
 				require.NoError(t, err)
 				defer f.Close()
 
@@ -341,7 +347,8 @@ func TestWALRestoreCorrupted(t *testing.T) {
 			require.NoError(t, err)
 
 			r := w2.Reader(0)
-			serf := func(l []labels.Labels) error {
+
+			serf := func(l []RefSeries) error {
 				require.Equal(t, 0, len(l))
 				return nil
 			}