Intern sender, event_id and room_id in events

synapse/events/__init__.py

@@ -146,6 +146,11 @@ class FrozenEvent(EventBase):
         event_dict["type"] = intern_string(event_dict["type"])
         if "state_key" in event_dict:
             event_dict["state_key"] = intern_string(event_dict["state_key"])
+        if "sender" in event_dict:
+            event_dict["sender"] = intern_string(event_dict["sender"])
+
+        event_dict["event_id"] = intern(event_dict["event_id"].encode('ascii'))
+        event_dict["room_id"] = intern(event_dict["room_id"].encode('ascii'))
 
         if USE_FROZEN_DICTS:
             frozen_dict = freeze(event_dict)