Remove sent outbound device list pokes from the database

They just get in the way.

changelog.d/7192.misc

@@ -0,0 +1 @@
+Remove sent outbound device list pokes from the database.

synapse/storage/data_stores/main/devices.py

@@ -228,11 +228,11 @@ def _get_device_updates_by_remote_txn(
         # get the list of device updates that need to be sent
         sql = """
             SELECT user_id, device_id, stream_id, opentracing_context FROM device_lists_outbound_pokes
-            WHERE destination = ? AND ? < stream_id AND stream_id <= ? AND sent = ?
+            WHERE destination = ? AND ? < stream_id AND stream_id <= ?
             ORDER BY stream_id
             LIMIT ?
         """
-        txn.execute(sql, (destination, from_stream_id, now_stream_id, False, limit))
+        txn.execute(sql, (destination, from_stream_id, now_stream_id, limit))
 
         return list(txn)
 

synapse/storage/data_stores/main/schema/delta/57/remove_sent_outbound_pokes.sql

@@ -0,0 +1,21 @@
+/* Copyright 2020 The Matrix.org Foundation C.I.C
+ *
+ * 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.
+ */
+
+-- we no longer keep sent outbound device pokes in the db; clear them out
+-- so that we don't have to worry about them.
+--
+-- This is a sequence scan, but it doesn't take too long.
+
+DELETE FROM device_lists_outbound_pokes WHERE sent;