From 8c0881eab2caef301835eb9b0660e0b727d06687 Mon Sep 17 00:00:00 2001
From: Steve Yen <steve.yen@gmail.com>
Date: Sun, 4 Mar 2018 12:03:02 -0800
Subject: [PATCH] scorch zap build reuses mem postingsList/Iterator structs

---
 index/scorch/segment/mem/dict.go    | 20 ++++++++++++++------
 index/scorch/segment/mem/posting.go | 11 +++++++++--
 index/scorch/segment/zap/build.go   |  8 ++++++--
 3 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/index/scorch/segment/mem/dict.go b/index/scorch/segment/mem/dict.go
index cf92ef71..b564ed1f 100644
--- a/index/scorch/segment/mem/dict.go
+++ b/index/scorch/segment/mem/dict.go
@@ -33,12 +33,20 @@ type Dictionary struct {
 // PostingsList returns the postings list for the specified term
 func (d *Dictionary) PostingsList(term string,
 	except *roaring.Bitmap) (segment.PostingsList, error) {
-	return &PostingsList{
-		dictionary: d,
-		term:       term,
-		postingsID: d.segment.Dicts[d.fieldID][term],
-		except:     except,
-	}, nil
+	return d.InitPostingsList(term, except, nil)
+}
+
+func (d *Dictionary) InitPostingsList(term string, except *roaring.Bitmap,
+	prealloc *PostingsList) (*PostingsList, error) {
+	rv := prealloc
+	if rv == nil {
+		rv = &PostingsList{}
+	}
+	rv.dictionary = d
+	rv.term = term
+	rv.postingsID = d.segment.Dicts[d.fieldID][term]
+	rv.except = except
+	return rv, nil
 }
 
 // Iterator returns an iterator for this dictionary
diff --git a/index/scorch/segment/mem/posting.go b/index/scorch/segment/mem/posting.go
index 25cbeb45..2554333a 100644
--- a/index/scorch/segment/mem/posting.go
+++ b/index/scorch/segment/mem/posting.go
@@ -46,9 +46,16 @@ func (p *PostingsList) Count() uint64 {
 
 // Iterator returns an iterator for this postings list
 func (p *PostingsList) Iterator() segment.PostingsIterator {
-	rv := &PostingsIterator{
-		postings: p,
+	return p.InitIterator(nil)
+}
+func (p *PostingsList) InitIterator(prealloc *PostingsIterator) *PostingsIterator {
+	rv := prealloc
+	if rv == nil {
+		rv = &PostingsIterator{postings: p}
+	} else {
+		*rv = PostingsIterator{postings: p}
 	}
+
 	if p.postingsID > 0 {
 		allbits := p.dictionary.segment.Postings[p.postingsID-1]
 		rv.locations = p.dictionary.segment.PostingsLocs[p.postingsID-1]
diff --git a/index/scorch/segment/zap/build.go b/index/scorch/segment/zap/build.go
index b075496c..7fbc995f 100644
--- a/index/scorch/segment/zap/build.go
+++ b/index/scorch/segment/zap/build.go
@@ -532,6 +532,9 @@ func persistDocValues(memSegment *mem.Segment, w *CountHashWriter,
 	fieldChunkOffsets := make(map[uint16]uint64, len(memSegment.FieldsInv))
 	fdvEncoder := newChunkedContentCoder(uint64(chunkFactor), uint64(len(memSegment.Stored)-1))
 
+	var postings *mem.PostingsList
+	var postingsItr *mem.PostingsIterator
+
 	for fieldID := range memSegment.DocValueFields {
 		field := memSegment.FieldsInv[fieldID]
 		docTermMap := make(map[uint64][]byte, 0)
@@ -543,12 +546,13 @@ func persistDocValues(memSegment *mem.Segment, w *CountHashWriter,
 		dictItr := dict.Iterator()
 		next, err := dictItr.Next()
 		for err == nil && next != nil {
-			postings, err1 := dict.PostingsList(next.Term, nil)
+			var err1 error
+			postings, err1 = dict.(*mem.Dictionary).InitPostingsList(next.Term, nil, postings)
 			if err1 != nil {
 				return nil, err
 			}
 
-			postingsItr := postings.Iterator()
+			postingsItr = postings.InitIterator(postingsItr)
 			nextPosting, err2 := postingsItr.Next()
 			for err2 == nil && nextPosting != nil {
 				docNum := nextPosting.Number()