perf issue was due to duplicate fieldIDs getting

inserted to the list of dv enabled fields list -
DocValueFields in mem segment.
Moved back to the original type `DocValueFields map[uint16]bool`
for easy look up to check whether the fieldID is
configured for dv storage.

index/scorch/segment/mem/build.go

@@ -121,7 +121,7 @@ func (s *Segment) processDocument(result *index.AnalysisResult) {
 		}
 		// TODO with mapping changes for dv
 		//if field.Options().IncludeDocValues() {
-		s.DocValueFields = append(s.DocValueFields, fieldID)
+		s.DocValueFields[fieldID] = true
 		//}
 	}
 

index/scorch/segment/mem/segment.go

@@ -89,9 +89,8 @@ type Segment struct {
 	StoredPos []map[uint16][][]uint64
 
 	// for storing the docValue persisted fields
-	// field id
-	DocValueFields []uint16
-	
+	DocValueFields map[uint16]bool
+
 	// footprint of the segment, updated when analyzed document mutations
 	// are added into the segment
 	sizeInBytes uint64
@@ -100,7 +99,8 @@ type Segment struct {
 // New builds a new empty Segment
 func New() *Segment {
 	return &Segment{
-		FieldsMap: map[string]uint16{},
+		FieldsMap:      map[string]uint16{},
+		DocValueFields: map[uint16]bool{},
 	}
 }
 

index/scorch/segment/zap/build.go

@@ -440,7 +440,7 @@ func persistDocValues(memSegment *mem.Segment, w *CountHashWriter,
 	fieldChunkOffsets := make(map[uint16]uint64, len(memSegment.FieldsInv))
 	fdvEncoder := newChunkedContentCoder(uint64(chunkFactor), uint64(len(memSegment.Stored)-1))
 
-	for _, fieldID := range memSegment.DocValueFields {
+	for fieldID := range memSegment.DocValueFields {
 		field := memSegment.FieldsInv[fieldID]
 		docTermMap := make(map[uint64][]byte, 0)
 		dict, err := memSegment.Dictionary(field)