Select total message count from Channel instead of counting posts

store/sqlstore/post_store.go

@@ -2978,7 +2978,7 @@ func (s *SqlPostStore) GetTopDMsForUserSince(userID string, since int64, offset
 		aggregator = "string_agg(distinct cm.UserId, ',') as Participants"
 	}
 
-	topDMsBuilder := s.getQueryBuilder().Select("count(p.id) as MessageCount", aggregator, "vch.Id as ChannelId").FromSelect(channelSelector, "vch").
+	topDMsBuilder := s.getQueryBuilder().Select("vch.TotalMsgCount as MessageCount", aggregator, "vch.Id as ChannelId").FromSelect(channelSelector, "vch").
 		Join("ChannelMembers as cm on cm.ChannelId = vch.Id").
 		Join("Posts as p on p.ChannelId = vch.Id").
 		Where(sq.And{
@@ -3023,9 +3023,6 @@ func postProcessTopDMs(s *SqlPostStore, userID string, topDMs []*model.TopDM) ([
 			// channel with self
 			secondParticipantId = "-1"
 		} else {
-			// divide message count by 2, because it's counted twice due to channel memberships being 2 for dms.
-			topDM.MessageCount = topDM.MessageCount / 2
-
 			if participants[0] == userID {
 				secondParticipantId = participants[1]
 			} else {