field cardinality temp save

index/scorch/snapshot_index.go

@@ -42,8 +42,9 @@ type asynchSegmentResult struct {
 	dict    segment.TermDictionary
 	dictItr segment.DictionaryIterator
 
-	index int
-	docs  *roaring.Bitmap
+	cardinality int
+	index       int
+	docs        *roaring.Bitmap
 
 	postings segment.PostingsList
 
@@ -146,6 +147,7 @@ func (is *IndexSnapshot) newIndexSnapshotFieldDict(field string,
 
 	results := make(chan *asynchSegmentResult)
 	var totalBytesRead uint64
+	var fieldCardinality int64
 	for _, s := range is.segment {
 		go func(s *SegmentSnapshot) {
 			dict, err := s.segment.Dictionary(field)
@@ -155,6 +157,8 @@ func (is *IndexSnapshot) newIndexSnapshotFieldDict(field string,
 				if dictStats, ok := dict.(segment.DiskStatsReporter); ok {
 					atomic.AddUint64(&totalBytesRead, dictStats.BytesRead())
 				}
+
+				atomic.AddInt64(&fieldCardinality, int64(dict.Cardinality()))
 				if randomLookup {
 					results <- &asynchSegmentResult{dict: dict}
 				} else {
@@ -166,9 +170,11 @@ func (is *IndexSnapshot) newIndexSnapshotFieldDict(field string,
 
 	var err error
 	rv := &IndexSnapshotFieldDict{
-		snapshot: is,
-		cursors:  make([]*segmentDictCursor, 0, len(is.segment)),
+		snapshot:    is,
+		cursors:     make([]*segmentDictCursor, 0, len(is.segment)),
+		cardinality: int(fieldCardinality),
 	}
+
 	for count := 0; count < len(is.segment); count++ {
 		asr := <-results
 		if asr.err != nil && err == nil {

index/scorch/snapshot_index_dict.go

@@ -28,10 +28,12 @@ type segmentDictCursor struct {
 }
 
 type IndexSnapshotFieldDict struct {
-	snapshot  *IndexSnapshot
-	cursors   []*segmentDictCursor
-	entry     index.DictEntry
-	bytesRead uint64
+	cardinality int
+	bytesRead   uint64
+
+	snapshot *IndexSnapshot
+	cursors  []*segmentDictCursor
+	entry    index.DictEntry
 }
 
 func (i *IndexSnapshotFieldDict) BytesRead() uint64 {