create users index on creation_ts

synapse/storage/schema/delta/50/add_creation_ts_users_index.sql

@@ -0,0 +1,20 @@
+/* Copyright 2018 New Vector 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 users_creation_ts ON users(creation_ts);
+INSERT into background_updates (update_name, progress_json)
+    VALUES ('users_creation_ts', '{}');