Add stream change cache

synapse/util/caches/stream_change_cache.py

@@ -89,6 +89,21 @@ class StreamChangeCache(object):
 
         return result
 
+    def has_any_entity_changed(self, stream_pos):
+        """Returns if any entity has changed
+        """
+        assert type(stream_pos) is int
+
+        if stream_pos >= self._earliest_known_stream_pos:
+            self.metrics.inc_hits()
+            if stream_pos >= max(self._cache):
+                return False
+            else:
+                return True
+        else:
+            self.metrics.inc_misses()
+            return True
+
     def get_all_entities_changed(self, stream_pos):
         """Returns all entites that have had new things since the given
         position. If the position is too old it will return None.