Don't keep old stream_ordering_to_exterm around (#15382)

1 files changed, 10 insertions, 0 deletions

diff --git a/synapse/handlers/device.py b/synapse/handlers/device.py
index 9ded6389ac..d2063d4435 100644
--- a/synapse/handlers/device.py
+++ b/synapse/handlers/device.py
@@ -215,6 +215,16 @@ class DeviceWorkerHandler:
         possibly_changed = set(changed)
         possibly_left = set()
         for room_id in rooms_changed:
+            # Check if the forward extremities have changed. If not then we know
+            # the current state won't have changed, and so we can skip this room.
+            try:
+                if not await self.store.have_room_forward_extremities_changed_since(
+                    room_id, stream_ordering
+                ):
+                    continue
+            except errors.StoreError:
+                pass
+
             current_state_ids = await self._state_storage.get_current_state_ids(
                 room_id, await_full_state=False
             )