Use the room type from stats in hierarchy response. (#14263)

This avoids pulling additional state information (and events) from
the database for each item returned in the hierarchy response.

The room type might be out of date until a background update finishes
running, the worst impact of this would be spaces being treated as rooms
in the hierarchy response. This should self-heal once the background
update finishes.

changelog.d/14263.misc

@@ -0,0 +1 @@
+Improve performance of the `/hierarchy` endpoint.

synapse/handlers/room_summary.py

@@ -20,7 +20,6 @@ from typing import TYPE_CHECKING, Dict, Iterable, List, Optional, Sequence, Set,
 import attr
 
 from synapse.api.constants import (
-    EventContentFields,
     EventTypes,
     HistoryVisibility,
     JoinRules,
@@ -701,13 +700,6 @@ class RoomSummaryHandler:
         # there should always be an entry
         assert stats is not None, "unable to retrieve stats for %s" % (room_id,)
 
-        current_state_ids = await self._storage_controllers.state.get_current_state_ids(
-            room_id
-        )
-        create_event = await self._store.get_event(
-            current_state_ids[(EventTypes.Create, "")]
-        )
-
         entry = {
             "room_id": stats["room_id"],
             "name": stats["name"],
@@ -720,7 +712,7 @@ class RoomSummaryHandler:
                 stats["history_visibility"] == HistoryVisibility.WORLD_READABLE
             ),
             "guest_can_join": stats["guest_access"] == "can_join",
-            "room_type": create_event.content.get(EventContentFields.ROOM_TYPE),
+            "room_type": stats["room_type"],
         }
 
         if self._msc3266_enabled:
@@ -730,7 +722,11 @@ class RoomSummaryHandler:
         # Federation requests need to provide additional information so the
         # requested server is able to filter the response appropriately.
         if for_federation:
+            current_state_ids = (
+                await self._storage_controllers.state.get_current_state_ids(room_id)
+            )
             room_version = await self._store.get_room_version(room_id)
+
             if await self._event_auth_handler.has_restricted_join_rules(
                 current_state_ids, room_version
             ):