Add cache for get_current_hosts_in_room

synapse/storage/roommember.py

@@ -482,6 +482,44 @@ class RoomMemberStore(SQLBaseStore):
 
         defer.returnValue(False)
 
+    def get_joined_hosts(self, room_id, state_group, state_ids):
+        if not state_group:
+            # If state_group is None it means it has yet to be assigned a
+            # state group, i.e. we need to make sure that calls with a state_group
+            # of None don't hit previous cached calls with a None state_group.
+            # To do this we set the state_group to a new object as object() != object()
+            state_group = object()
+
+        return self._get_joined_hosts(
+            room_id, state_group, state_ids
+        )
+
+    @cachedInlineCallbacks(num_args=3)
+    def _get_joined_hosts(self, room_id, state_group, current_state_ids):
+        # We don't use `state_group`, its there so that we can cache based
+        # on it. However, its important that its never None, since two current_state's
+        # with a state_group of None are likely to be different.
+        # See bulk_get_push_rules_for_room for how we work around this.
+        assert state_group is not None
+
+        joined_hosts = set()
+        for (etype, state_key), event_id in current_state_ids.items():
+            if etype == EventTypes.Member:
+                try:
+                    host = get_domain_from_id(state_key)
+                except:
+                    logger.warn("state_key not user_id: %s", state_key)
+                    continue
+
+                if host in joined_hosts:
+                    continue
+
+                event = yield self.get_event(event_id, allow_none=True)
+                if event and event.content["membership"] == Membership.JOIN:
+                    joined_hosts.add(host)
+
+        defer.returnValue(joined_hosts)
+
     @defer.inlineCallbacks
     def _background_add_membership_profile(self, progress, batch_size):
         target_min_stream_id = progress.get(