Faster room joins: Avoid blocking `/keys/changes` (#13888)

Part of the work for #12993.

Once #12993 is fully resolved, we expect `/keys/changes` to behave
sensibly when joined to a room with partial state.

Signed-off-by: Sean Quah <seanq@matrix.org>

3 files changed, 12 insertions, 3 deletions

diff --git a/changelog.d/13888.misc b/changelog.d/13888.misc
new file mode 100644

index 0000000000..4ffd9bcede
--- /dev/null
+++ b/changelog.d/13888.misc
@@ -0,0 +1 @@
+Faster room joins: Avoid waiting for full state when processing `/keys/changes` requests.
diff --git a/synapse/handlers/device.py b/synapse/handlers/device.py

index 6566b3bf3d..bad262731c 100644
--- a/synapse/handlers/device.py
+++ b/synapse/handlers/device.py
@@ -195,7 +195,9 @@ class DeviceWorkerHandler:
         possibly_changed = set(changed)
         possibly_left = set()
         for room_id in rooms_changed:
-            current_state_ids = await self._state_storage.get_current_state_ids(room_id)
+            current_state_ids = await self._state_storage.get_current_state_ids(
+                room_id, await_full_state=False
+            )
 
             # The user may have left the room
             # TODO: Check if they actually did or if we were just invited.
@@ -234,7 +236,8 @@ class DeviceWorkerHandler:
 
             # mapping from event_id -> state_dict
             prev_state_ids = await self._state_storage.get_state_ids_for_events(
-                event_ids
+                event_ids,
+                await_full_state=False,
             )
 
             # Check if we've joined the room? If so we just blindly add all the users to
diff --git a/synapse/storage/controllers/state.py b/synapse/storage/controllers/state.py

index b1aa17047c..bb60130afe 100644
--- a/synapse/storage/controllers/state.py
+++ b/synapse/storage/controllers/state.py
@@ -407,6 +407,7 @@ class StateStorageController:
         self,
         room_id: str,
         state_filter: Optional[StateFilter] = None,
+        await_full_state: bool = True,
         on_invalidate: Optional[Callable[[], None]] = None,
     ) -> StateMap[str]:
         """Get the current state event ids for a room based on the
@@ -419,13 +420,17 @@ class StateStorageController:
             room_id: The room to get the state IDs of. state_filter: The state
             filter used to fetch state from the
                 database.
+            await_full_state: if true, will block if we do not yet have complete
+               state for the room.
             on_invalidate: Callback for when the `get_current_state_ids` cache
                 for the room gets invalidated.
 
         Returns:
             The current state of the room.
         """
-        if not state_filter or state_filter.must_await_full_state(self._is_mine_id):
+        if await_full_state and (
+            not state_filter or state_filter.must_await_full_state(self._is_mine_id)
+        ):
             await self._partial_state_room_tracker.await_full_state(room_id)
 
         if state_filter and not state_filter.is_full():