do not send "select" in cluster mode

internal/reader/scan_reader.go

@@ -68,8 +68,7 @@ func (r *scanReader) scan() {
 		scanDbIdUpper = 0
 	}
 	for dbId := 0; dbId <= scanDbIdUpper; dbId++ {
-		var cursor uint64 = 0
-
+		if !r.isCluster {
 			reply := r.clientScan.DoWithStringReply("SELECT", strconv.Itoa(dbId))
 			if reply != "OK" {
 				log.Panicf("scanReader select db failed. db=[%d]", dbId)
@@ -77,7 +76,9 @@ func (r *scanReader) scan() {
 
 			r.clientDump.Send("SELECT", strconv.Itoa(dbId))
 			r.innerChannel <- &dbKey{dbId, "", true}
+		}
 
+		var cursor uint64 = 0
 		for {
 			var keys []string
 			cursor, keys = r.clientScan.Scan(cursor)