Change get_pos_of_last_change to return upper bound

1 files changed, 4 insertions, 3 deletions

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

index 5c2a433e41..b72bb0ff02 100644
--- a/synapse/util/caches/stream_change_cache.py
+++ b/synapse/util/caches/stream_change_cache.py
@@ -122,7 +122,8 @@ class StreamChangeCache(object):
                 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.
+    def get_max_pos_of_last_change(self, entity):
+        """Returns an upper bound of the stream id of the last change to an
+        entity.
         """
-        return self._entity_to_key.get(entity, None)
+        return self._entity_to_key.get(entity, self._earliest_known_stream_pos)