diff --git a/index/scorch/segment/zap/dict.go b/index/scorch/segment/zap/dict.go
index 55796ffa..e5d71268 100644
--- a/index/scorch/segment/zap/dict.go
+++ b/index/scorch/segment/zap/dict.go
@@ -38,6 +38,33 @@ func (d *Dictionary) PostingsList(term string, except *roaring.Bitmap) (segment.
 }
 
 func (d *Dictionary) postingsList(term []byte, except *roaring.Bitmap, rv *PostingsList) (*PostingsList, error) {
+	if d.fst == nil {
+		return d.postingsListInit(rv, except), nil
+	}
+
+	postingsOffset, exists, err := d.fst.Get(term)
+	if err != nil {
+		return nil, fmt.Errorf("vellum err: %v", err)
+	}
+	if !exists {
+		return d.postingsListInit(rv, except), nil
+	}
+
+	return d.postingsListFromOffset(postingsOffset, except, rv)
+}
+
+func (d *Dictionary) postingsListFromOffset(postingsOffset uint64, except *roaring.Bitmap, rv *PostingsList) (*PostingsList, error) {
+	rv = d.postingsListInit(rv, except)
+
+	err := rv.read(postingsOffset, d)
+	if err != nil {
+		return nil, err
+	}
+
+	return rv, nil
+}
+
+func (d *Dictionary) postingsListInit(rv *PostingsList, except *roaring.Bitmap) *PostingsList {
 	if rv == nil {
 		rv = &PostingsList{}
 	} else {
@@ -45,21 +72,7 @@ func (d *Dictionary) postingsList(term []byte, except *roaring.Bitmap, rv *Posti
 	}
 	rv.sb = d.sb
 	rv.except = except
-
-	if d.fst != nil {
-		postingsOffset, exists, err := d.fst.Get(term)
-		if err != nil {
-			return nil, fmt.Errorf("vellum err: %v", err)
-		}
-		if exists {
-			err = rv.read(postingsOffset, d)
-			if err != nil {
-				return nil, err
-			}
-		}
-	}
-
-	return rv, nil
+	return rv
 }
 
 // Iterator returns an iterator for this dictionary
diff --git a/index/scorch/segment/zap/enumerator.go b/index/scorch/segment/zap/enumerator.go
new file mode 100644
index 00000000..3c708dd5
--- /dev/null
+++ b/index/scorch/segment/zap/enumerator.go
@@ -0,0 +1,124 @@
+//  Copyright (c) 2018 Couchbase, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 		http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package zap
+
+import (
+	"bytes"
+
+	"github.com/couchbase/vellum"
+)
+
+// enumerator provides an ordered traversal of multiple vellum
+// iterators.  Like JOIN of iterators, the enumerator produces a
+// sequence of (key, iteratorIndex, value) tuples, sorted by key ASC,
+// then iteratorIndex ASC, where the same key might be seen or
+// repeated across multiple child iterators.
+type enumerator struct {
+	itrs   []vellum.Iterator
+	currKs [][]byte
+	currVs []uint64
+
+	lowK    []byte
+	lowIdxs []int
+	lowCurr int
+}
+
+// newEnumerator returns a new enumerator over the vellum Iterators
+func newEnumerator(itrs []vellum.Iterator) (*enumerator, error) {
+	rv := &enumerator{
+		itrs:    itrs,
+		currKs:  make([][]byte, len(itrs)),
+		currVs:  make([]uint64, len(itrs)),
+		lowIdxs: make([]int, 0, len(itrs)),
+	}
+	for i, itr := range rv.itrs {
+		rv.currKs[i], rv.currVs[i] = itr.Current()
+	}
+	rv.updateMatches()
+	if rv.lowK == nil {
+		return rv, vellum.ErrIteratorDone
+	}
+	return rv, nil
+}
+
+// updateMatches maintains the low key matches based on the currKs
+func (m *enumerator) updateMatches() {
+	m.lowK = nil
+	m.lowIdxs = m.lowIdxs[:0]
+	m.lowCurr = 0
+
+	for i, key := range m.currKs {
+		if key == nil {
+			continue
+		}
+
+		cmp := bytes.Compare(key, m.lowK)
+		if cmp < 0 || m.lowK == nil {
+			// reached a new low
+			m.lowK = key
+			m.lowIdxs = m.lowIdxs[:0]
+			m.lowIdxs = append(m.lowIdxs, i)
+		} else if cmp == 0 {
+			m.lowIdxs = append(m.lowIdxs, i)
+		}
+	}
+}
+
+// Current returns the enumerator's current key, iterator-index, and
+// value.  If the enumerator is not pointing at a valid value (because
+// Next returned an error previously), Current will return nil,0,0.
+func (m *enumerator) Current() ([]byte, int, uint64) {
+	var i int
+	var v uint64
+	if m.lowCurr < len(m.lowIdxs) {
+		i = m.lowIdxs[m.lowCurr]
+		v = m.currVs[i]
+	}
+	return m.lowK, i, v
+}
+
+// Next advances the enumerator to the next key/iterator/value result,
+// else vellum.ErrIteratorDone is returned.
+func (m *enumerator) Next() error {
+	m.lowCurr += 1
+	if m.lowCurr >= len(m.lowIdxs) {
+		// move all the current low iterators forwards
+		for _, vi := range m.lowIdxs {
+			err := m.itrs[vi].Next()
+			if err != nil && err != vellum.ErrIteratorDone {
+				return err
+			}
+			m.currKs[vi], m.currVs[vi] = m.itrs[vi].Current()
+		}
+		m.updateMatches()
+	}
+	if m.lowK == nil {
+		return vellum.ErrIteratorDone
+	}
+	return nil
+}
+
+// Close all the underlying Iterators.  The first error, if any, will
+// be returned.
+func (m *enumerator) Close() error {
+	var rv error
+	for _, itr := range m.itrs {
+		err := itr.Close()
+		if rv == nil {
+			rv = err
+		}
+	}
+	return rv
+}
diff --git a/index/scorch/segment/zap/enumerator_test.go b/index/scorch/segment/zap/enumerator_test.go
new file mode 100644
index 00000000..b2778892
--- /dev/null
+++ b/index/scorch/segment/zap/enumerator_test.go
@@ -0,0 +1,233 @@
+//  Copyright (c) 2018 Couchbase, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 		http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+// implied.  See the License for the specific language governing
+// permissions and limitations under the License.
+
+package zap
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/couchbase/vellum"
+)
+
+type enumTestEntry struct {
+	key string
+	val uint64
+}
+
+type enumTestWant struct {
+	key string
+	idx int
+	val uint64
+}
+
+func TestEnumerator(t *testing.T) {
+	tests := []struct {
+		desc string
+		in   [][]enumTestEntry
+		want []enumTestWant
+	}{
+		{
+			desc: "two non-empty enumerators with no duplicate keys",
+			in: [][]enumTestEntry{
+				[]enumTestEntry{
+					{"a", 1},
+					{"c", 3},
+					{"e", 5},
+				},
+				[]enumTestEntry{
+					{"b", 2},
+					{"d", 4},
+					{"f", 6},
+				},
+			},
+			want: []enumTestWant{
+				{"a", 0, 1},
+				{"b", 1, 2},
+				{"c", 0, 3},
+				{"d", 1, 4},
+				{"e", 0, 5},
+				{"f", 1, 6},
+			},
+		},
+		{
+			desc: "two non-empty enumerators with duplicate keys",
+			in: [][]enumTestEntry{
+				[]enumTestEntry{
+					{"a", 1},
+					{"c", 3},
+					{"e", 5},
+				},
+				[]enumTestEntry{
+					{"a", 2},
+					{"c", 4},
+					{"e", 6},
+				},
+			},
+			want: []enumTestWant{
+				{"a", 0, 1},
+				{"a", 1, 2},
+				{"c", 0, 3},
+				{"c", 1, 4},
+				{"e", 0, 5},
+				{"e", 1, 6},
+			},
+		},
+		{
+			desc: "first iterator is empty",
+			in: [][]enumTestEntry{
+				[]enumTestEntry{},
+				[]enumTestEntry{
+					{"a", 2},
+					{"c", 4},
+					{"e", 6},
+				},
+			},
+			want: []enumTestWant{
+				{"a", 1, 2},
+				{"c", 1, 4},
+				{"e", 1, 6},
+			},
+		},
+		{
+			desc: "last iterator is empty",
+			in: [][]enumTestEntry{
+				[]enumTestEntry{
+					{"a", 1},
+					{"c", 3},
+					{"e", 5},
+				},
+				[]enumTestEntry{},
+			},
+			want: []enumTestWant{
+				{"a", 0, 1},
+				{"c", 0, 3},
+				{"e", 0, 5},
+			},
+		},
+		{
+			desc: "two different length enumerators with duplicate keys",
+			in: [][]enumTestEntry{
+				[]enumTestEntry{
+					{"a", 1},
+					{"c", 3},
+					{"e", 5},
+				},
+				[]enumTestEntry{
+					{"a", 2},
+					{"b", 4},
+					{"d", 1000},
+					{"e", 6},
+				},
+			},
+			want: []enumTestWant{
+				{"a", 0, 1},
+				{"a", 1, 2},
+				{"b", 1, 4},
+				{"c", 0, 3},
+				{"d", 1, 1000},
+				{"e", 0, 5},
+				{"e", 1, 6},
+			},
+		},
+	}
+
+	for _, test := range tests {
+		var itrs []vellum.Iterator
+		for _, entries := range test.in {
+			itrs = append(itrs, &testIterator{entries: entries})
+		}
+
+		enumerator, err := newEnumerator(itrs)
+		if err != nil {
+			t.Fatalf("%s - expected no err on newNumerator, got: %v", test.desc, err)
+		}
+
+		wanti := 0
+		for wanti < len(test.want) {
+			if err != nil {
+				t.Fatalf("%s - wanted no err, got: %v", test.desc, err)
+			}
+
+			currK, currIdx, currV := enumerator.Current()
+
+			want := test.want[wanti]
+			if want.key != string(currK) {
+				t.Fatalf("%s - wrong key, wanted: %#v, got: %q, %d, %d", test.desc,
+					want, currK, currIdx, currV)
+			}
+			if want.idx != currIdx {
+				t.Fatalf("%s - wrong idx, wanted: %#v, got: %q, %d, %d", test.desc,
+					want, currK, currIdx, currV)
+			}
+			if want.val != currV {
+				t.Fatalf("%s - wrong val, wanted: %#v, got: %q, %d, %d", test.desc,
+					want, currK, currIdx, currV)
+			}
+
+			wanti += 1
+
+			err = enumerator.Next()
+		}
+
+		if err != vellum.ErrIteratorDone {
+			t.Fatalf("%s - expected ErrIteratorDone, got: %v", test.desc, err)
+		}
+
+		err = enumerator.Close()
+		if err != nil {
+			t.Fatalf("%s - expected nil err on close, got: %v", test.desc, err)
+		}
+
+		for _, itr := range itrs {
+			if itr.(*testIterator).curr != 654321 {
+				t.Fatalf("%s - expected child iter to be closed", test.desc)
+			}
+		}
+	}
+}
+
+type testIterator struct {
+	entries []enumTestEntry
+	curr    int
+}
+
+func (m *testIterator) Current() ([]byte, uint64) {
+	if m.curr >= len(m.entries) {
+		return nil, 0
+	}
+	return []byte(m.entries[m.curr].key), m.entries[m.curr].val
+}
+
+func (m *testIterator) Next() error {
+	m.curr++
+	if m.curr >= len(m.entries) {
+		return vellum.ErrIteratorDone
+	}
+	return nil
+}
+
+func (m *testIterator) Seek(key []byte) error {
+	return fmt.Errorf("not implemented for enumerator unit tests")
+}
+
+func (m *testIterator) Reset(f *vellum.FST,
+	startKeyInclusive, endKeyExclusive []byte, aut vellum.Automaton) error {
+	return fmt.Errorf("not implemented for enumerator unit tests")
+}
+
+func (m *testIterator) Close() error {
+	m.curr = 654321
+	return nil
+}
diff --git a/index/scorch/segment/zap/merge.go b/index/scorch/segment/zap/merge.go
index 751fcb58..525b7f93 100644
--- a/index/scorch/segment/zap/merge.go
+++ b/index/scorch/segment/zap/merge.go
@@ -154,8 +154,8 @@ func computeNewDocCount(segments []*SegmentBase, drops []*roaring.Bitmap) uint64
 	return newDocCount
 }
 
-func persistMergedRest(segments []*SegmentBase, drops []*roaring.Bitmap,
-	fieldsInv []string, fieldsMap map[string]uint16, newDocNums [][]uint64,
+func persistMergedRest(segments []*SegmentBase, dropsIn []*roaring.Bitmap,
+	fieldsInv []string, fieldsMap map[string]uint16, newDocNumsIn [][]uint64,
 	newSegDocCount uint64, chunkFactor uint32,
 	w *CountHashWriter) ([]uint64, uint64, error) {
 
@@ -168,7 +168,6 @@ func persistMergedRest(segments []*SegmentBase, drops []*roaring.Bitmap,
 
 	rv := make([]uint64, len(fieldsInv))
 	fieldDvLocs := make([]uint64, len(fieldsInv))
-	fieldDvLocsOffset := uint64(fieldNotUninverted)
 
 	// docTermMap is keyed by docNum, where the array impl provides
 	// better memory usage behavior than a sparse-friendlier hashmap
@@ -188,36 +187,31 @@ func persistMergedRest(segments []*SegmentBase, drops []*roaring.Bitmap,
 			return nil, 0, err
 		}
 
-		// collect FST iterators from all segments for this field
+		// collect FST iterators from all active segments for this field
+		var newDocNums [][]uint64
+		var drops []*roaring.Bitmap
 		var dicts []*Dictionary
 		var itrs []vellum.Iterator
-		for _, segment := range segments {
+
+		for segmentI, segment := range segments {
 			dict, err2 := segment.dictionary(fieldName)
 			if err2 != nil {
 				return nil, 0, err2
 			}
-			dicts = append(dicts, dict)
-
 			if dict != nil && dict.fst != nil {
 				itr, err2 := dict.fst.Iterator(nil, nil)
 				if err2 != nil && err2 != vellum.ErrIteratorDone {
 					return nil, 0, err2
 				}
 				if itr != nil {
+					newDocNums = append(newDocNums, newDocNumsIn[segmentI])
+					drops = append(drops, dropsIn[segmentI])
+					dicts = append(dicts, dict)
 					itrs = append(itrs, itr)
 				}
 			}
 		}
 
-		// create merging iterator
-		mergeItr, err := vellum.NewMergeIterator(itrs, func(postingOffsets []uint64) uint64 {
-			// we don't actually use the merged value
-			return 0
-		})
-
-		tfEncoder := newChunkedIntCoder(uint64(chunkFactor), newSegDocCount-1)
-		locEncoder := newChunkedIntCoder(uint64(chunkFactor), newSegDocCount-1)
-
 		if uint64(cap(docTermMap)) < newSegDocCount {
 			docTermMap = make([][]byte, newSegDocCount)
 		} else {
@@ -227,71 +221,17 @@ func persistMergedRest(segments []*SegmentBase, drops []*roaring.Bitmap,
 			}
 		}
 
-		for err == nil {
-			term, _ := mergeItr.Current()
+		var prevTerm []byte
 
-			newRoaring := roaring.NewBitmap()
-			newRoaringLocs := roaring.NewBitmap()
+		newRoaring := roaring.NewBitmap()
+		newRoaringLocs := roaring.NewBitmap()
 
-			tfEncoder.Reset()
-			locEncoder.Reset()
+		tfEncoder := newChunkedIntCoder(uint64(chunkFactor), newSegDocCount-1)
+		locEncoder := newChunkedIntCoder(uint64(chunkFactor), newSegDocCount-1)
 
-			// now go back and get posting list for this term
-			// but pass in the deleted docs for that segment
-			for dictI, dict := range dicts {
-				if dict == nil {
-					continue
-				}
-				var err2 error
-				postings, err2 = dict.postingsList(term, drops[dictI], postings)
-				if err2 != nil {
-					return nil, 0, err2
-				}
-
-				postItr = postings.iterator(postItr)
-				next, err2 := postItr.Next()
-				for next != nil && err2 == nil {
-					hitNewDocNum := newDocNums[dictI][next.Number()]
-					if hitNewDocNum == docDropped {
-						return nil, 0, fmt.Errorf("see hit with dropped doc num")
-					}
-					newRoaring.Add(uint32(hitNewDocNum))
-					// encode norm bits
-					norm := next.Norm()
-					normBits := math.Float32bits(float32(norm))
-					err = tfEncoder.Add(hitNewDocNum, next.Frequency(), uint64(normBits))
-					if err != nil {
-						return nil, 0, err
-					}
-					locs := next.Locations()
-					if len(locs) > 0 {
-						newRoaringLocs.Add(uint32(hitNewDocNum))
-						for _, loc := range locs {
-							if cap(bufLoc) < 5+len(loc.ArrayPositions()) {
-								bufLoc = make([]uint64, 0, 5+len(loc.ArrayPositions()))
-							}
-							args := bufLoc[0:5]
-							args[0] = uint64(fieldsMap[loc.Field()])
-							args[1] = loc.Pos()
-							args[2] = loc.Start()
-							args[3] = loc.End()
-							args[4] = uint64(len(loc.ArrayPositions()))
-							args = append(args, loc.ArrayPositions()...)
-							err = locEncoder.Add(hitNewDocNum, args...)
-							if err != nil {
-								return nil, 0, err
-							}
-						}
-					}
-
-					docTermMap[hitNewDocNum] =
-						append(append(docTermMap[hitNewDocNum], term...), termSeparator)
-
-					next, err2 = postItr.Next()
-				}
-				if err2 != nil {
-					return nil, 0, err2
-				}
+		finishTerm := func(term []byte) error {
+			if term == nil {
+				return nil
 			}
 
 			tfEncoder.Close()
@@ -300,59 +240,140 @@ func persistMergedRest(segments []*SegmentBase, drops []*roaring.Bitmap,
 			if newRoaring.GetCardinality() > 0 {
 				// this field/term actually has hits in the new segment, lets write it down
 				freqOffset := uint64(w.Count())
-				_, err = tfEncoder.Write(w)
+				_, err := tfEncoder.Write(w)
 				if err != nil {
-					return nil, 0, err
+					return err
 				}
 				locOffset := uint64(w.Count())
 				_, err = locEncoder.Write(w)
 				if err != nil {
-					return nil, 0, err
+					return err
 				}
 				postingLocOffset := uint64(w.Count())
 				_, err = writeRoaringWithLen(newRoaringLocs, w, &bufReuse, bufMaxVarintLen64)
 				if err != nil {
-					return nil, 0, err
+					return err
 				}
 				postingOffset := uint64(w.Count())
+
 				// write out the start of the term info
-				buf := bufMaxVarintLen64
-				n := binary.PutUvarint(buf, freqOffset)
-				_, err = w.Write(buf[:n])
+				n := binary.PutUvarint(bufMaxVarintLen64, freqOffset)
+				_, err = w.Write(bufMaxVarintLen64[:n])
 				if err != nil {
-					return nil, 0, err
+					return err
 				}
-
 				// write out the start of the loc info
-				n = binary.PutUvarint(buf, locOffset)
-				_, err = w.Write(buf[:n])
+				n = binary.PutUvarint(bufMaxVarintLen64, locOffset)
+				_, err = w.Write(bufMaxVarintLen64[:n])
 				if err != nil {
-					return nil, 0, err
+					return err
 				}
-
-				// write out the start of the loc posting list
-				n = binary.PutUvarint(buf, postingLocOffset)
-				_, err = w.Write(buf[:n])
+				// write out the start of the posting locs
+				n = binary.PutUvarint(bufMaxVarintLen64, postingLocOffset)
+				_, err = w.Write(bufMaxVarintLen64[:n])
 				if err != nil {
-					return nil, 0, err
+					return err
 				}
 				_, err = writeRoaringWithLen(newRoaring, w, &bufReuse, bufMaxVarintLen64)
 				if err != nil {
-					return nil, 0, err
+					return err
 				}
 
 				err = newVellum.Insert(term, postingOffset)
 				if err != nil {
-					return nil, 0, err
+					return err
 				}
 			}
 
-			err = mergeItr.Next()
+			newRoaring = roaring.NewBitmap()
+			newRoaringLocs = roaring.NewBitmap()
+
+			tfEncoder.Reset()
+			locEncoder.Reset()
+
+			return nil
+		}
+
+		enumerator, err := newEnumerator(itrs)
+
+		for err == nil {
+			term, itrI, postingsOffset := enumerator.Current()
+
+			if !bytes.Equal(prevTerm, term) {
+				// if the term changed, write out the info collected
+				// for the previous term
+				err2 := finishTerm(prevTerm)
+				if err2 != nil {
+					return nil, 0, err2
+				}
+			}
+
+			var err2 error
+			postings, err2 = dicts[itrI].postingsListFromOffset(
+				postingsOffset, drops[itrI], postings)
+			if err2 != nil {
+				return nil, 0, err2
+			}
+
+			postItr = postings.iterator(postItr)
+			next, err2 := postItr.Next()
+			for next != nil && err2 == nil {
+				hitNewDocNum := newDocNums[itrI][next.Number()]
+				if hitNewDocNum == docDropped {
+					return nil, 0, fmt.Errorf("see hit with dropped doc num")
+				}
+				newRoaring.Add(uint32(hitNewDocNum))
+				// encode norm bits
+				norm := next.Norm()
+				normBits := math.Float32bits(float32(norm))
+				err = tfEncoder.Add(hitNewDocNum, next.Frequency(), uint64(normBits))
+				if err != nil {
+					return nil, 0, err
+				}
+				locs := next.Locations()
+				if len(locs) > 0 {
+					newRoaringLocs.Add(uint32(hitNewDocNum))
+					for _, loc := range locs {
+						if cap(bufLoc) < 5+len(loc.ArrayPositions()) {
+							bufLoc = make([]uint64, 0, 5+len(loc.ArrayPositions()))
+						}
+						args := bufLoc[0:5]
+						args[0] = uint64(fieldsMap[loc.Field()])
+						args[1] = loc.Pos()
+						args[2] = loc.Start()
+						args[3] = loc.End()
+						args[4] = uint64(len(loc.ArrayPositions()))
+						args = append(args, loc.ArrayPositions()...)
+						err = locEncoder.Add(hitNewDocNum, args...)
+						if err != nil {
+							return nil, 0, err
+						}
+					}
+				}
+
+				docTermMap[hitNewDocNum] =
+					append(append(docTermMap[hitNewDocNum], term...), termSeparator)
+
+				next, err2 = postItr.Next()
+			}
+			if err2 != nil {
+				return nil, 0, err2
+			}
+
+			prevTerm = prevTerm[:0] // copy to prevTerm in case Next() reuses term mem
+			prevTerm = append(prevTerm, term...)
+
+			err = enumerator.Next()
 		}
 		if err != nil && err != vellum.ErrIteratorDone {
 			return nil, 0, err
 		}
 
+		err = finishTerm(prevTerm)
+		if err != nil {
+			return nil, 0, err
+		}
+
 		dictOffset := uint64(w.Count())
 
 		err = newVellum.Close()
@@ -401,7 +422,7 @@ func persistMergedRest(segments []*SegmentBase, drops []*roaring.Bitmap,
 		}
 	}
 
-	fieldDvLocsOffset = uint64(w.Count())
+	fieldDvLocsOffset := uint64(w.Count())
 
 	buf := bufMaxVarintLen64
 	for _, offset := range fieldDvLocs {