diff --git a/tsdb/index/index.go b/tsdb/index/index.go
index 1470c7776..06c7e2563 100644
--- a/tsdb/index/index.go
+++ b/tsdb/index/index.go
@@ -110,6 +110,8 @@ type Writer struct {
 	// For the main index file.
 	f *fileWriter
 
+	// Temporary file for postings.
+	fP *fileWriter
 	// Temporary file for posting offsets table.
 	fPO   *fileWriter
 	cntPO uint64
@@ -196,6 +198,11 @@ func NewWriter(ctx context.Context, fn string) (*Writer, error) {
 	if err != nil {
 		return nil, err
 	}
+	// Temporary file for postings.
+	fP, err := newFileWriter(fn + "_tmp_p")
+	if err != nil {
+		return nil, err
+	}
 	// Temporary file for posting offset table.
 	fPO, err := newFileWriter(fn + "_tmp_po")
 	if err != nil {
@@ -208,6 +215,7 @@ func NewWriter(ctx context.Context, fn string) (*Writer, error) {
 	iw := &Writer{
 		ctx:   ctx,
 		f:     f,
+		fP:    fP,
 		fPO:   fPO,
 		stage: idxStageNone,
 
@@ -323,6 +331,10 @@ func (w *Writer) ensureStage(s indexWriterStage) error {
 	if w.stage == s {
 		return nil
 	}
+	if w.stage+1 < s {
+		// A stage has been skipped.
+		w.ensureStage(s - 1)
+	}
 	if w.stage > s {
 		return errors.Errorf("invalid stage %q, currently at %q", s, w.stage)
 	}
@@ -342,6 +354,11 @@ func (w *Writer) ensureStage(s indexWriterStage) error {
 
 	case idxStageDone:
 		w.toc.LabelIndices = w.f.pos
+		// LabelIndices generation depends on the posting offset
+		// table produced at this stage.
+		if err := w.writePostingsToTmpFiles(); err != nil {
+			return err
+		}
 		if err := w.writeLabelIndices(); err != nil {
 			return err
 		}
@@ -355,6 +372,7 @@ func (w *Writer) ensureStage(s indexWriterStage) error {
 		if err := w.writeLabelIndexesOffsetTable(); err != nil {
 			return err
 		}
+
 		w.toc.PostingsTable = w.f.pos
 		if err := w.writePostingsOffsetTable(); err != nil {
 			return err
@@ -631,12 +649,16 @@ func (w *Writer) writePostingsOffsetTable() error {
 		return err
 	}
 
-	w.buf1.Reset()
-	w.buf1.PutBE32int(int(w.fPO.pos) + 4) // Length, including the count.
-	if err := w.write(w.buf1.Get()); err != nil {
+	startPos := w.f.pos
+	// Leave 4 bytes of space for the length, which will be calculated later.
+	if err := w.write([]byte("alen")); err != nil {
 		return err
 	}
 
+	// Copy over the tmp posting offset table, however we need to
+	// adjust the offsets.
+	adjustment := w.toc.Postings
+
 	w.buf1.Reset()
 	w.crc32.Reset()
 	w.buf1.PutBE32int(int(w.cntPO)) // Count.
@@ -644,29 +666,28 @@ func (w *Writer) writePostingsOffsetTable() error {
 	if err := w.write(w.buf1.Get()); err != nil {
 		return err
 	}
-	// Copy temporary file into main index.
-	if _, err := w.fPO.f.Seek(0, 0); err != nil {
+
+	f, err := fileutil.OpenMmapFile(w.fPO.name)
+	if err != nil {
 		return err
 	}
-
-	buf := make([]byte, 1<<20)
-	l := 0
-	for {
-		n, err := w.fPO.f.Read(buf)
-		if err != nil && err != io.EOF {
-			return err
-		}
-		if n == 0 {
-			break
-		}
-		l += n
-		w.crc32.Write(buf[:n])
-		if err := w.write(buf[:n]); err != nil {
+	defer f.Close()
+	d := encoding.NewDecbufRaw(realByteSlice(f.Bytes()), int(w.fPO.pos))
+	cnt := w.cntPO
+	for d.Err() == nil && cnt > 0 {
+		w.buf1.Reset()
+		w.buf1.PutUvarint(d.Uvarint())                     // Keycount.
+		w.buf1.PutUvarintStr(yoloString(d.UvarintBytes())) // Label name.
+		w.buf1.PutUvarintStr(yoloString(d.UvarintBytes())) // Label value.
+		w.buf1.PutUvarint64(d.Uvarint64() + adjustment)    // Offset.
+		w.buf1.WriteToHash(w.crc32)
+		if err := w.write(w.buf1.Get()); err != nil {
 			return err
 		}
+		cnt--
 	}
-	if w.fPO.pos != uint64(l) {
-		return errors.Errorf("wrote %d bytes to posting offset temporary file, but only read back %d", w.fPO.pos, l)
+	if d.Err() != nil {
+		return d.Err()
 	}
 
 	// Cleanup temporary file.
@@ -678,6 +699,13 @@ func (w *Writer) writePostingsOffsetTable() error {
 	}
 	w.fPO = nil
 
+	// Write out the length.
+	w.buf1.Reset()
+	w.buf1.PutBE32int(int(w.f.pos - startPos - 4))
+	if err := w.writeAt(w.buf1.Get(), startPos); err != nil {
+		return err
+	}
+
 	// Finally write the hash.
 	w.buf1.Reset()
 	w.buf1.PutHashSum(w.crc32)
@@ -701,7 +729,7 @@ func (w *Writer) writeTOC() error {
 	return w.write(w.buf1.Get())
 }
 
-func (w *Writer) writePostings() error {
+func (w *Writer) writePostingsToTmpFiles() error {
 	names := make([]string, 0, len(w.labelNames))
 	for n := range w.labelNames {
 		names = append(names, n)
@@ -729,9 +757,10 @@ func (w *Writer) writePostings() error {
 		}
 		offsets = append(offsets, uint32(startPos/16))
 		// Skip to next series.
-		d.Skip(d.Uvarint() + crc32.Size)
+		x := d.Uvarint()
+		d.Skip(x + crc32.Size)
 		if err := d.Err(); err != nil {
-			return nil
+			return err
 		}
 	}
 	if err := w.writePosting("", "", offsets); err != nil {
@@ -827,7 +856,7 @@ func (w *Writer) writePostings() error {
 
 func (w *Writer) writePosting(name, value string, offs []uint32) error {
 	// Align beginning to 4 bytes for more efficient postings list scans.
-	if err := w.addPadding(4); err != nil {
+	if err := w.fP.addPadding(4); err != nil {
 		return err
 	}
 
@@ -836,7 +865,7 @@ func (w *Writer) writePosting(name, value string, offs []uint32) error {
 	w.buf1.PutUvarint(2)
 	w.buf1.PutUvarintStr(name)
 	w.buf1.PutUvarintStr(value)
-	w.buf1.PutUvarint64(w.f.pos)
+	w.buf1.PutUvarint64(w.fP.pos) // This is relative to the postings tmp file, not the final index file.
 	if err := w.fPO.write(w.buf1.Get()); err != nil {
 		return err
 	}
@@ -855,7 +884,37 @@ func (w *Writer) writePosting(name, value string, offs []uint32) error {
 	w.buf2.Reset()
 	w.buf2.PutBE32int(w.buf1.Len())
 	w.buf1.PutHash(w.crc32)
-	return w.write(w.buf2.Get(), w.buf1.Get())
+	return w.fP.write(w.buf2.Get(), w.buf1.Get())
+}
+
+func (w *Writer) writePostings() error {
+	// There's padding in the tmp filem make sure it actually works.
+	if err := w.f.addPadding(4); err != nil {
+		return err
+	}
+
+	// Copy temporary file into main index.
+	if err := w.fP.flush(); err != nil {
+		return err
+	}
+	if _, err := w.fP.f.Seek(0, 0); err != nil {
+		return err
+	}
+	// Don't need to calculate a checksum, so can copy directly.
+	n, err := io.CopyBuffer(w.f.fbuf, w.fP.f, make([]byte, 1<<20))
+	if err != nil {
+		return err
+	}
+	if uint64(n) != w.fP.pos {
+		return errors.Errorf("wrote %d bytes to posting temporary file, but only read back %d", w.fP.pos, n)
+	}
+	w.f.pos += uint64(n)
+
+	if err := w.fP.remove(); err != nil {
+		return err
+	}
+	w.fP = nil
+	return nil
 }
 
 type uint32slice []uint32
@@ -883,6 +942,11 @@ func (w *Writer) Close() error {
 			return err
 		}
 	}
+	if w.fP != nil {
+		if err := w.fP.close(); err != nil {
+			return err
+		}
+	}
 	if w.fPO != nil {
 		if err := w.fPO.close(); err != nil {
 			return err