From f09db5c9918b6aaeb1f53ab4fac3a7f05f512c5f Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Tue, 14 Feb 2023 12:10:29 +0100
Subject: [PATCH] Skip calculating unread push actions in `/sync` when
 `enable_push` is false. (#14980)

---
 changelog.d/14980.misc                               | 1 +
 synapse/handlers/sync.py                             | 8 ++++++++
 synapse/storage/databases/main/event_push_actions.py | 7 +++++++
 3 files changed, 16 insertions(+)
 create mode 100644 changelog.d/14980.misc

diff --git a/changelog.d/14980.misc b/changelog.d/14980.misc
new file mode 100644
index 0000000000..145f4a788b
--- /dev/null
+++ b/changelog.d/14980.misc
@@ -0,0 +1 @@
+Skip calculating unread push actions in /sync when enable_push is false.
diff --git a/synapse/handlers/sync.py b/synapse/handlers/sync.py
index 4bae46158a..3a9cddf15a 100644
--- a/synapse/handlers/sync.py
+++ b/synapse/handlers/sync.py
@@ -269,6 +269,8 @@ class SyncHandler:
         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 @@ class SyncHandler:
     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(
diff --git a/synapse/storage/databases/main/event_push_actions.py b/synapse/storage/databases/main/event_push_actions.py
index 3a0c370fde..eeccf5db24 100644
--- a/synapse/storage/databases/main/event_push_actions.py
+++ b/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: