diff --git a/tsdb/index/index.go b/tsdb/index/index.go
index 06c7e2563..700c5da7e 100644
--- a/tsdb/index/index.go
+++ b/tsdb/index/index.go
@@ -15,6 +15,7 @@ package index
 
 import (
 	"bufio"
+	"bytes"
 	"context"
 	"encoding/binary"
 	"hash"
@@ -116,8 +117,9 @@ type Writer struct {
 	fPO   *fileWriter
 	cntPO uint64
 
-	toc   TOC
-	stage indexWriterStage
+	toc           TOC
+	stage         indexWriterStage
+	postingsStart uint64 // Due to padding, can differ from TOC entry.
 
 	// Reusable memory.
 	buf1 encoding.Encbuf
@@ -128,9 +130,8 @@ type Writer struct {
 	symbolFile *fileutil.MmapFile
 	lastSymbol string
 
-	labelIndexes []labelIndexHashEntry          // Label index offsets.
-	labelValues  map[string]map[uint32]struct{} // Label names, and their values's symbol indexes.
-	labelNames   map[string]uint64              // Label names, and their usage.
+	labelIndexes []labelIndexHashEntry // Label index offsets.
+	labelNames   map[string]uint64     // Label names, and their usage.
 
 	// Hold last series to validate that clients insert new series in order.
 	lastSeries labels.Labels
@@ -223,9 +224,8 @@ func NewWriter(ctx context.Context, fn string) (*Writer, error) {
 		buf1: encoding.Encbuf{B: make([]byte, 0, 1<<22)},
 		buf2: encoding.Encbuf{B: make([]byte, 0, 1<<22)},
 
-		labelNames:  make(map[string]uint64, 1<<8),
-		labelValues: make(map[string]map[uint32]struct{}, 1<<8),
-		crc32:       newCRC32(),
+		labelNames: make(map[string]uint64, 1<<8),
+		crc32:      newCRC32(),
 	}
 	if err := iw.writeMeta(); err != nil {
 		return nil, err
@@ -277,7 +277,7 @@ func (fw *fileWriter) write(bufs ...[]byte) error {
 		// Once we move to compressed/varint representations in those areas, this limitation
 		// can be lifted.
 		if fw.pos > 16*math.MaxUint32 {
-			return errors.Errorf("exceeding max size of 64GiB")
+			return errors.Errorf("%q exceeding max size of 64GiB", fw.name)
 		}
 	}
 	return nil
@@ -331,9 +331,11 @@ func (w *Writer) ensureStage(s indexWriterStage) error {
 	if w.stage == s {
 		return nil
 	}
-	if w.stage+1 < s {
+	if w.stage < s-1 {
 		// A stage has been skipped.
-		w.ensureStage(s - 1)
+		if err := w.ensureStage(s - 1); err != nil {
+			return err
+		}
 	}
 	if w.stage > s {
 		return errors.Errorf("invalid stage %q, currently at %q", s, w.stage)
@@ -420,7 +422,6 @@ func (w *Writer) AddSeries(ref uint64, lset labels.Labels, chunks ...chunks.Meta
 	w.buf2.PutUvarint(len(lset))
 
 	for _, l := range lset {
-		// here we have an index for the symbol file if v2, otherwise it's an offset
 		index, err := w.symbols.ReverseLookup(l.Name)
 		if err != nil {
 			return errors.Errorf("symbol entry for %q does not exist, %v", l.Name, err)
@@ -433,11 +434,6 @@ func (w *Writer) AddSeries(ref uint64, lset labels.Labels, chunks ...chunks.Meta
 			return errors.Errorf("symbol entry for %q does not exist, %v", l.Value, err)
 		}
 		w.buf2.PutUvarint32(index)
-
-		if _, ok := w.labelValues[l.Name]; !ok {
-			w.labelValues[l.Name] = map[uint32]struct{}{}
-		}
-		w.labelValues[l.Name][index] = struct{}{}
 	}
 
 	w.buf2.PutUvarint(len(chunks))
@@ -536,19 +532,52 @@ func (w *Writer) finishSymbols() error {
 }
 
 func (w *Writer) writeLabelIndices() error {
-	names := make([]string, 0, len(w.labelValues))
-	for n := range w.labelValues {
-		names = append(names, n)
+	if err := w.fPO.flush(); err != nil {
+		return err
 	}
-	sort.Strings(names)
 
-	for _, n := range names {
-		values := make([]uint32, 0, len(w.labelValues[n]))
-		for v := range w.labelValues[n] {
-			values = append(values, v)
+	// Find all the label values in the tmp posting offset table.
+	f, err := fileutil.OpenMmapFile(w.fPO.name)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	d := encoding.NewDecbufRaw(realByteSlice(f.Bytes()), int(w.fPO.pos))
+	cnt := w.cntPO
+	current := []byte{}
+	values := []uint32{}
+	for d.Err() == nil && cnt > 0 {
+		cnt--
+		d.Uvarint()                           // Keycount.
+		name := d.UvarintBytes()              // Label name.
+		value := yoloString(d.UvarintBytes()) // Label value.
+		d.Uvarint64()                         // Offset.
+		if len(name) == 0 {
+			continue // All index is ignored.
 		}
-		sort.Sort(uint32slice(values))
-		if err := w.writeLabelIndex(n, values); err != nil {
+
+		if !bytes.Equal(name, current) && len(values) > 0 {
+			// We've reached a new label name.
+			if err := w.writeLabelIndex(string(current), values); err != nil {
+				return err
+			}
+			values = values[:0]
+		}
+		current = name
+		sid, err := w.symbols.ReverseLookup(value)
+		if err != nil {
+			return err
+		}
+		values = append(values, sid)
+	}
+	if d.Err() != nil {
+		return d.Err()
+	}
+
+	// Handle the last label.
+	if len(values) > 0 {
+		if err := w.writeLabelIndex(string(current), values); err != nil {
 			return err
 		}
 	}
@@ -657,7 +686,7 @@ func (w *Writer) writePostingsOffsetTable() error {
 
 	// Copy over the tmp posting offset table, however we need to
 	// adjust the offsets.
-	adjustment := w.toc.Postings
+	adjustment := w.postingsStart
 
 	w.buf1.Reset()
 	w.crc32.Reset()
@@ -888,10 +917,11 @@ func (w *Writer) writePosting(name, value string, offs []uint32) error {
 }
 
 func (w *Writer) writePostings() error {
-	// There's padding in the tmp filem make sure it actually works.
+	// There's padding in the tmp file, make sure it actually works.
 	if err := w.f.addPadding(4); err != nil {
 		return err
 	}
+	w.postingsStart = w.f.pos
 
 	// Copy temporary file into main index.
 	if err := w.fP.flush(); err != nil {
@@ -910,6 +940,9 @@ func (w *Writer) writePostings() error {
 	}
 	w.f.pos += uint64(n)
 
+	if err := w.fP.close(); err != nil {
+		return err
+	}
 	if err := w.fP.remove(); err != nil {
 		return err
 	}
@@ -928,11 +961,6 @@ type labelIndexHashEntry struct {
 	offset uint64
 }
 
-type postingsHashEntry struct {
-	name, value string
-	offset      uint64
-}
-
 func (w *Writer) Close() error {
 	if err := w.ensureStage(idxStageDone); err != nil {
 		return err