Don't pull out full state when sending dummy events

changelog.d/13310.misc

@@ -0,0 +1 @@
+Reduce memory usage of sending dummy events.

synapse/handlers/message.py

@@ -1849,13 +1849,8 @@ async def _send_dummy_event_for_room(self, room_id: str) -> bool:
 
         # For each room we need to find a joined member we can use to send
         # the dummy event with.
-        latest_event_ids = await self.store.get_prev_events_for_room(room_id)
-        members = await self.state.get_current_users_in_room(
-            room_id, latest_event_ids=latest_event_ids
-        )
+        members = await self.store.get_local_users_in_room(room_id)
         for user_id in members:
-            if not self.hs.is_mine_id(user_id):
-                continue
             requester = create_requester(user_id, authenticated_entity=self.server_name)
             try:
                 event, context = await self.create_event(
@@ -1866,7 +1861,6 @@ async def _send_dummy_event_for_room(self, room_id: str) -> bool:
                         "room_id": room_id,
                         "sender": user_id,
                     },
-                    prev_event_ids=latest_event_ids,
                 )
 
                 event.internal_metadata.proactively_send = False