Use servers list approx to send read receipts when in partial state

changelog.d/14549.misc

@@ -0,0 +1 @@
+Faster joins: use servers list approximation to send read receipts when in partial state instead of waiting for the full state of the room.

synapse/federation/sender/__init__.py

@@ -647,7 +647,7 @@ async def send_read_receipt(self, receipt: ReadReceipt) -> None:
         room_id = receipt.room_id
 
         # Work out which remote servers should be poked and poke them.
-        domains_set = await self._storage_controllers.state.get_current_hosts_in_room(
+        domains_set = await self._storage_controllers.state.get_current_hosts_in_room_or_partial_state_approximation(
             room_id
         )
         domains = [

tests/federation/test_federation_sender.py

@@ -38,6 +38,10 @@ def make_homeserver(self, reactor, clock):
             return_value=make_awaitable({"test", "host2"})
         )
 
+        hs.get_storage_controllers().state.get_current_hosts_in_room_or_partial_state_approximation = (
+            hs.get_storage_controllers().state.get_current_hosts_in_room
+        )
+
         return hs
 
     @override_config({"send_federation": True})