Use stream_change cache to make get_forward_extremeties_for_room cache more effective

1 files changed, 5 insertions, 0 deletions

diff --git a/synapse/util/caches/stream_change_cache.py b/synapse/util/caches/stream_change_cache.py

index 3c051dabc4..5c2a433e41 100644
--- a/synapse/util/caches/stream_change_cache.py
+++ b/synapse/util/caches/stream_change_cache.py
@@ -121,3 +121,8 @@ class StreamChangeCache(object):
                 k, r = self._cache.popitem()
                 self._earliest_known_stream_pos = max(k, self._earliest_known_stream_pos)
                 self._entity_to_key.pop(r, None)
+
+    def get_pos_of_last_change(self, entity):
+        """Returns the stream pos of the last change for an entitiy, if known.
+        """
+        return self._entity_to_key.get(entity, None)