scorch zap Dict.postingsList() takes []byte for more mem control

This allows callers that already have a []byte term to avoid
string'ification garbage.

index/scorch/segment/zap/dict.go

@@ -35,10 +35,10 @@ 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 d.postingsList(term, except)
+	return d.postingsList([]byte(term), except)
 }
 
-func (d *Dictionary) postingsList(term string, except *roaring.Bitmap) (*PostingsList, error) {
+func (d *Dictionary) postingsList(term []byte, except *roaring.Bitmap) (*PostingsList, error) {
 	rv := &PostingsList{
 		sb:     d.sb,
 		term:   term,
@@ -46,7 +46,7 @@ func (d *Dictionary) postingsList(term string, except *roaring.Bitmap) (*Posting
 	}
 
 	if d.fst != nil {
-		postingsOffset, exists, err := d.fst.Get([]byte(term))
+		postingsOffset, exists, err := d.fst.Get(term)
 		if err != nil {
 			return nil, fmt.Errorf("vellum err: %v", err)
 		}
@@ -96,7 +96,6 @@ func (d *Dictionary) postingsList(term string, except *roaring.Bitmap) (*Posting
 
 // Iterator returns an iterator for this dictionary
 func (d *Dictionary) Iterator() segment.DictionaryIterator {
-
 	rv := &DictionaryIterator{
 		d: d,
 	}

index/scorch/segment/zap/merge.go

@@ -206,7 +206,7 @@ func persistMergedRest(segments []*Segment, drops []*roaring.Bitmap,
 				if dict == nil {
 					continue
 				}
-				postings, err2 := dict.postingsList(string(term), drops[dictI])
+				postings, err2 := dict.postingsList(term, drops[dictI])
 				if err2 != nil {
 					return nil, 0, err2
 				}

index/scorch/segment/zap/posting.go

@@ -28,7 +28,7 @@ import (
 // PostingsList is an in-memory represenation of a postings list
 type PostingsList struct {
 	sb             *SegmentBase
-	term           string
+	term           []byte
 	postingsOffset uint64
 	freqOffset     uint64
 	locOffset      uint64

index/scorch/segment/zap/segment.go

@@ -344,7 +344,7 @@ func (s *SegmentBase) DocNumbers(ids []string) (*roaring.Bitmap, error) {
 		}
 
 		for _, id := range ids {
-			postings, err := idDict.postingsList(id, nil)
+			postings, err := idDict.postingsList([]byte(id), nil)
 			if err != nil {
 				return nil, err
 			}