Fast path

synapse/handlers/sliding_sync/room_lists.py

@@ -500,11 +500,15 @@ async def _compute_interested_rooms_new_tables(
                 # depending on the `required_state` requested (see below).
                 partial_state_rooms = await self.store.get_partial_rooms()
 
+                # Fetch any rooms that we have not already fetched from the database.
                 subscription_sliding_sync_rooms = (
                     await self.store.get_sliding_sync_room_for_user_batch(
-                        user_id, sync_config.room_subscriptions.keys()
+                        user_id,
+                        sync_config.room_subscriptions.keys()
+                        - room_membership_for_user_map.keys(),
                     )
                 )
+                room_membership_for_user_map.update(subscription_sliding_sync_rooms)
 
                 for (
                     room_id,
@@ -513,13 +517,11 @@ async def _compute_interested_rooms_new_tables(
                     # Check if we have a membership for the room, but didn't pull it out
                     # above. This could be e.g. a leave that we don't pull out by
                     # default.
-                    current_room_entry = subscription_sliding_sync_rooms.get(room_id)
+                    current_room_entry = room_membership_for_user_map.get(room_id)
                     if not current_room_entry:
                         # TODO: Handle rooms the user isn't in.
                         continue
 
-                    room_membership_for_user_map[room_id] = current_room_entry
-
                     all_rooms.add(room_id)
 
                     # Take the superset of the `RoomSyncConfig` for each room.

synapse/storage/databases/main/roommember.py

@@ -1504,6 +1504,9 @@ async def get_sliding_sync_room_for_user_batch(
     ) -> Dict[str, RoomsForUserSlidingSync]:
         """Get the sliding sync room entry for the given user and rooms."""
 
+        if not room_ids:
+            return {}
+
         def get_sliding_sync_room_for_user_batch_txn(
             txn: LoggingTransaction,
         ) -> Dict[str, RoomsForUserSlidingSync]: