Add index to event_push_actions

and remove room_id caluse so it uses it

Mostly from @negativemjark

synapse/storage/event_push_actions.py

@@ -353,12 +353,14 @@ class EventPushActionsStore(SQLBaseStore):
                     before_clause += " "
                 before_clause += "AND epa.highlight = 1"
 
+            # NB. This assumes event_ids are globally unique since
+            # it makes the query easier to index
             sql = (
                 "SELECT epa.event_id, epa.room_id,"
                 " epa.stream_ordering, epa.topological_ordering,"
                 " epa.actions, epa.profile_tag, e.received_ts"
                 " FROM event_push_actions epa, events e"
-                " WHERE epa.room_id = e.room_id AND epa.event_id = e.event_id"
+                " WHERE epa.event_id = e.event_id"
                 " AND epa.user_id = ? %s"
                 " ORDER BY epa.stream_ordering DESC"
                 " LIMIT ?"

synapse/storage/schema/delta/35/event_push_actions_index.sql

@@ -0,0 +1,18 @@
+/* Copyright 2016 OpenMarket Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+ CREATE INDEX event_push_actions_user_id_highlight_stream_ordering on event_push_actions(
+     user_id, highlight, stream_ordering
+ );