Speed up the get_pagination_rows as well

synapse/handlers/presence.py

@@ -1154,14 +1154,28 @@ class PresenceEventSource(object):
         presence = self.hs.get_handlers().presence_handler
         cachemap = presence._user_cachemap
 
+        user_ids_to_check = {user}
+        presence_list = yield presence.store.get_presence_list(
+            user.localpart, accepted=True
+        )
+        if presence_list is None:
+            presence_list = ()
+        user_ids_to_check |= set(
+            UserID.from_string(p["observed_user_id"]) for p in presence_list
+        )
+        room_ids = yield presence.get_joined_rooms_for_user(user)
+        for room_id in set(room_ids) & set(presence._room_serials):
+            if presence._room_serials[room_id] >= from_key:
+                joined = yield presence.get_joined_users_for_room_id(room_id)
+                user_ids_to_check |= set(joined)
+
         updates = []
         # TODO(paul): use a DeferredList ? How to limit concurrency.
-        for observed_user in cachemap.keys():
+        for observed_user in user_ids_to_check & set(cachemap):
             if not (to_key < cachemap[observed_user].serial <= from_key):
                 continue
 
-            if (yield self.is_visible(observer_user, observed_user)):
+            updates.append((observed_user, cachemap[observed_user]))
-                updates.append((observed_user, cachemap[observed_user]))
 
         # TODO(paul): limit