diff --git a/posting/list.go b/posting/list.go
index 6b51b18d73e..1fc86cf4754 100644
--- a/posting/list.go
+++ b/posting/list.go
@@ -903,25 +903,7 @@ type rollupOutput struct {
 	newMinTs uint64
 }
 
-// Merge all entries in mutation layer with commitTs <= l.commitTs into
-// immutable layer. Note that readTs can be math.MaxUint64, so do NOT use it
-// directly. It should only serve as the read timestamp for iteration.
-func (l *List) rollup(readTs uint64, split bool) (*rollupOutput, error) {
-	l.AssertRLock()
-
-	// Pick all committed entries
-	if l.minTs > readTs {
-		// If we are already past the readTs, then skip the rollup.
-		return nil, nil
-	}
-
-	out := &rollupOutput{
-		plist: &pb.PostingList{
-			Splits: l.plist.Splits,
-		},
-		parts: make(map[uint64]*pb.PostingList),
-	}
-
+func (l *List) encode(out *rollupOutput, readTs uint64, split bool) error {
 	var plist *pb.PostingList
 	var startUid, endUid uint64
 	var splitIdx int
@@ -968,19 +950,48 @@ func (l *List) rollup(readTs uint64, split bool) (*rollupOutput, error) {
 	})
 	// Finish  writing the last part of the list (or the whole list if not a multi-part list).
 	if err != nil {
-		return nil, errors.Wrapf(err, "cannot iterate through the list")
+		return errors.Wrapf(err, "cannot iterate through the list")
 	}
 	plist.Pack = enc.Done()
 	if plist.Pack != nil {
 		if plist.Pack.BlockSize != uint32(blockSize) {
-			return nil, errors.Errorf("actual block size %d is different from expected value %d",
+			return errors.Errorf("actual block size %d is different from expected value %d",
 				plist.Pack.BlockSize, blockSize)
 		}
 	}
-
-	if len(l.plist.Splits) > 0 {
+	if split && len(l.plist.Splits) > 0 {
 		out.parts[startUid] = plist
 	}
+	return nil
+}
+
+// Merge all entries in mutation layer with commitTs <= l.commitTs into
+// immutable layer. Note that readTs can be math.MaxUint64, so do NOT use it
+// directly. It should only serve as the read timestamp for iteration.
+func (l *List) rollup(readTs uint64, split bool) (*rollupOutput, error) {
+	l.AssertRLock()
+
+	// Pick all committed entries
+	if l.minTs > readTs {
+		// If we are already past the readTs, then skip the rollup.
+		return nil, nil
+	}
+
+	out := &rollupOutput{
+		plist: &pb.PostingList{
+			Splits: l.plist.Splits,
+		},
+		parts: make(map[uint64]*pb.PostingList),
+	}
+
+	if len(out.plist.Splits) > 0 || len(l.mutationMap) > 0 {
+		if err := l.encode(out, readTs, split); err != nil {
+			return nil, errors.Wrapf(err, "while encoding")
+		}
+	} else {
+		// We already have a nicely packed posting list. Just use it.
+		out.plist = l.plist
+	}
 
 	maxCommitTs := l.minTs
 	{
@@ -1354,7 +1365,7 @@ func shouldSplit(plist *pb.PostingList) bool {
 }
 
 func (out *rollupOutput) updateSplits() {
-	if out.plist == nil {
+	if out.plist == nil || len(out.parts) > 0 {
 		out.plist = &pb.PostingList{}
 	}
 	out.plist.Splits = out.splits()
@@ -1438,13 +1449,11 @@ func binSplit(lowUid uint64, plist *pb.PostingList) ([]uint64, []*pb.PostingList
 	}
 
 	// Add elements in plist.Postings to the corresponding list.
-	for _, posting := range plist.Postings {
-		if posting.Uid < midUid {
-			lowPl.Postings = append(lowPl.Postings, posting)
-		} else {
-			highPl.Postings = append(highPl.Postings, posting)
-		}
-	}
+	pidx := sort.Search(len(plist.Postings), func(idx int) bool {
+		return plist.Postings[idx].Uid >= midUid
+	})
+	lowPl.Postings = plist.Postings[:pidx]
+	highPl.Postings = plist.Postings[pidx:]
 
 	return []uint64{lowUid, midUid}, []*pb.PostingList{lowPl, highPl}
 }
diff --git a/posting/list_test.go b/posting/list_test.go
index a970bc6bd74..1e29d9f23f8 100644
--- a/posting/list_test.go
+++ b/posting/list_test.go
@@ -945,6 +945,8 @@ func createMultiPartList(t *testing.T, size int, addLabel bool) (*List, int) {
 	require.NoError(t, writePostingListToDisk(kvs))
 	ol, err = getNew(key, ps, math.MaxUint64)
 	require.NoError(t, err)
+	require.Nil(t, ol.plist.Pack)
+	require.Equal(t, 0, len(ol.plist.Postings))
 	require.True(t, len(ol.plist.Splits) > 0)
 	verifySplits(t, ol.plist.Splits)