Add a small cache get_all_new_events

synapse/storage/events.py

@@ -28,6 +28,7 @@
 from synapse.api.constants import EventTypes
 from synapse.api.errors import SynapseError
 from synapse.state import resolve_events
+from synapse.util.caches.descriptors import cached
 
 from canonicaljson import encode_canonical_json
 from collections import deque, namedtuple, OrderedDict
@@ -1579,6 +1580,7 @@ def get_current_backfill_token(self):
         """The current minimum token that backfilled events have reached"""
         return -self._backfill_id_gen.get_current_token()
 
+    @cached(num_args=5, max_entries=10)
     def get_all_new_events(self, last_backfill_id, last_forward_id,
                            current_backfill_id, current_forward_id, limit):
         """Get all the new events that have arrived at the server either as