Cache empty responses from `/user/devices` (#11587)

If we've never made a request to a remote homeserver, we should cache the response---even if the response is "this user has no devices".

1 files changed, 6 insertions, 2 deletions

diff --git a/synapse/storage/databases/main/devices.py b/synapse/storage/databases/main/devices.py
index 273adb61fd..52fbf50db6 100644
--- a/synapse/storage/databases/main/devices.py
+++ b/synapse/storage/databases/main/devices.py
@@ -713,7 +713,7 @@ class DeviceWorkerStore(SQLBaseStore):
     @cached(max_entries=10000)
     async def get_device_list_last_stream_id_for_remote(
         self, user_id: str
-    ) -> Optional[Any]:
+    ) -> Optional[str]:
         """Get the last stream_id we got for a user. May be None if we haven't
         got any information for them.
         """
@@ -729,7 +729,9 @@ class DeviceWorkerStore(SQLBaseStore):
         cached_method_name="get_device_list_last_stream_id_for_remote",
         list_name="user_ids",
     )
-    async def get_device_list_last_stream_id_for_remotes(self, user_ids: Iterable[str]):
+    async def get_device_list_last_stream_id_for_remotes(
+        self, user_ids: Iterable[str]
+    ) -> Dict[str, Optional[str]]:
         rows = await self.db_pool.simple_select_many_batch(
             table="device_lists_remote_extremeties",
             column="user_id",
@@ -1316,6 +1318,7 @@ class DeviceStore(DeviceWorkerStore, DeviceBackgroundUpdateStore):
         content: JsonDict,
         stream_id: str,
     ) -> None:
+        """Delete, update or insert a cache entry for this (user, device) pair."""
         if content.get("deleted"):
             self.db_pool.simple_delete_txn(
                 txn,
@@ -1375,6 +1378,7 @@ class DeviceStore(DeviceWorkerStore, DeviceBackgroundUpdateStore):
     def _update_remote_device_list_cache_txn(
         self, txn: LoggingTransaction, user_id: str, devices: List[dict], stream_id: int
     ) -> None:
+        """Replace the list of cached devices for this user with the given list."""
         self.db_pool.simple_delete_txn(
             txn, table="device_lists_remote_cache", keyvalues={"user_id": user_id}
         )