Skip calculating unread push actions in /sync when enable_push is false.

changelog.d/14980.misc

@@ -0,0 +1 @@
+Skip calculating unread push actions in /sync when enable_push is false.

synapse/handlers/sync.py

@@ -269,6 +269,8 @@ def __init__(self, hs: "HomeServer"):
         self._state_storage_controller = self._storage_controllers.state
         self._device_handler = hs.get_device_handler()
 
+        self.should_calculate_push_rules = hs.config.push.enable_push
+
         # TODO: flush cache entries on subsequent sync request.
         #    Once we get the next /sync request (ie, one with the same access token
         #    that sets 'since' to 'next_batch'), we know that device won't need a
@@ -1288,6 +1290,12 @@ async def _find_missing_partial_state_memberships(
     async def unread_notifs_for_room_id(
         self, room_id: str, sync_config: SyncConfig
     ) -> RoomNotifCounts:
+        if not self.should_calculate_push_rules:
+            # If push rules have been universally disabled then we know we won't
+            # have any unread counts in the DB, so we may as well skip asking
+            # the DB.
+            return RoomNotifCounts.empty()
+
         with Measure(self.clock, "unread_notifs_for_room_id"):
 
             return await self.store.get_unread_event_push_actions_by_room_for_user(

synapse/storage/databases/main/event_push_actions.py

@@ -203,11 +203,18 @@ class RoomNotifCounts:
     # Map of thread ID to the notification counts.
     threads: Dict[str, NotifCounts]
 
+    @staticmethod
+    def empty() -> "RoomNotifCounts":
+        return _EMPTY_ROOM_NOTIF_COUNTS
+
     def __len__(self) -> int:
         # To properly account for the amount of space in any caches.
         return len(self.threads) + 1
 
 
+_EMPTY_ROOM_NOTIF_COUNTS = RoomNotifCounts(NotifCounts(), {})
+
+
 def _serialize_action(
     actions: Collection[Union[Mapping, str]], is_highlight: bool
 ) -> str: