Merge erikj/faster_device_lists_fetch into matrix-org-hotfixes

1 files changed, 8 insertions, 4 deletions

diff --git a/synapse/handlers/sync.py b/synapse/handlers/sync.py

index d15efd474e..6c49e821d9 100644
--- a/synapse/handlers/sync.py
+++ b/synapse/handlers/sync.py
@@ -1146,10 +1146,14 @@ class SyncHandler(object):
                 user_id
             )
 
-            tracked_users = set(users_who_share_room)
-
-            # Always tell the user about their own devices
-            tracked_users.add(user_id)
+            # Always tell the user about their own devices. We check as the user
+            # ID is almost certainly already included (unless they're not in any
+            # rooms) and taking a copy of the set is relatively expensive.
+            if user_id not in users_who_share_room:
+                users_who_share_room = set(users_who_share_room)
+                users_who_share_room.add(user_id)
+
+            tracked_users = users_who_share_room
 
             # Step 1a, check for changes in devices of users we share a room with
             users_that_have_changed = await self.store.get_users_whose_devices_changed(