Fixup get_room_max_token

synapse/storage/databases/main/stream.py

@@ -356,6 +356,14 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore, metaclass=abc.ABCMeta):
         raise NotImplementedError()
 
     def get_room_max_token(self) -> RoomStreamToken:
+        """Get a `RoomStreamToken` that marks the current maximum persisted
+        position of the events stream. Useful to get a token that represents
+        "now".
+
+        The token returned is a "live" token that may have an instance_map
+        component.
+        """
+
         min_pos = self._stream_id_gen.get_current_token()
 
         positions = {}
@@ -372,9 +380,6 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore, metaclass=abc.ABCMeta):
                 if p > min_pos
             }
 
-            if set(positions.values()) == {min_pos}:
-                positions = {}
-
         return RoomStreamToken(None, min_pos, positions)
 
     async def get_room_events_stream_for_rooms(