Reduce device lists replication traffic. (#17333)

Reduce the replication traffic of device lists, by not sending every
destination that needs to be sent the device list update over
replication. Instead a "hosts to send to have been calculated"
notification over replication, and then federation senders read the
destinations from the DB.

For non federation senders this should heavily reduce the impact of a
user in many large rooms changing a device.

1 files changed, 8 insertions, 0 deletions

diff --git a/tests/storage/test_devices.py b/tests/storage/test_devices.py
index 7f975d04ff..ba01b038ab 100644
--- a/tests/storage/test_devices.py
+++ b/tests/storage/test_devices.py
@@ -36,6 +36,14 @@ class DeviceStoreTestCase(HomeserverTestCase):
     def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.store = hs.get_datastores().main
 
+    def default_config(self) -> JsonDict:
+        config = super().default_config()
+
+        # We 'enable' federation otherwise `get_device_updates_by_remote` will
+        # throw an exception.
+        config["federation_sender_instances"] = ["master"]
+        return config
+
     def add_device_change(self, user_id: str, device_ids: List[str], host: str) -> None:
         """Add a device list change for the given device to
         `device_lists_outbound_pokes` table.