Track the max_stream_device_id in a separate table, since we delete from the inbox table

synapse/replication/slave/storage/deviceinbox.py

@@ -23,7 +23,7 @@ class SlavedDeviceInboxStore(BaseSlavedStore):
     def __init__(self, db_conn, hs):
         super(SlavedDeviceInboxStore, self).__init__(db_conn, hs)
         self._device_inbox_id_gen = SlavedIdTracker(
-            db_conn, "device_inbox", "stream_id",
+            db_conn, "device_max_stream_id", "stream_id",
         )
         self._device_inbox_stream_cache = StreamChangeCache(
             "DeviceInboxStreamChangeCache",

synapse/storage/__init__.py

@@ -111,7 +111,7 @@ class DataStore(RoomMemberStore, RoomStore,
             db_conn, "presence_stream", "stream_id"
         )
         self._device_inbox_id_gen = StreamIdGenerator(
-            db_conn, "device_inbox", "stream_id"
+            db_conn, "device_max_stream_id", "stream_id"
         )
 
         self._transaction_id_gen = IdGenerator(db_conn, "sent_transactions", "id")

synapse/storage/deviceinbox.py

@@ -130,6 +130,13 @@ class DeviceInboxStore(SQLBaseStore):
 
     def _add_messages_to_local_device_inbox_txn(self, txn, stream_id,
                                                 messages_by_user_then_device):
+        sql = (
+            "UPDATE device_max_stream_id"
+            " SET stream_id = ?"
+            " WHERE stream_id < ?"
+        )
+        txn.execute(sql, (stream_id, stream_id))
+
         local_by_user_then_device = {}
         for user_id, messages_by_device in messages_by_user_then_device.items():
             messages_json_for_user = {}
@@ -148,6 +155,8 @@ class DeviceInboxStore(SQLBaseStore):
                     device = row[0]
                     messages_json_for_user[device] = message_json
             else:
+                if not devices:
+                    continue
                 sql = (
                     "SELECT device_id FROM devices"
                     " WHERE user_id = ? AND device_id IN ("
@@ -164,8 +173,12 @@ class DeviceInboxStore(SQLBaseStore):
                     message_json = ujson.dumps(messages_by_device[device])
                     messages_json_for_user[device] = message_json
 
+            if messages_json_for_user:
                 local_by_user_then_device[user_id] = messages_json_for_user
 
+        if not local_by_user_then_device:
+            return
+
         sql = (
             "INSERT INTO device_inbox"
             " (user_id, device_id, stream_id, message_json)"
@@ -301,7 +314,7 @@ class DeviceInboxStore(SQLBaseStore):
         has_changed = self._device_federation_outbox_stream_cache.has_entity_changed(
             destination, last_stream_id
         )
-        if not has_changed:
+        if not has_changed or last_stream_id == current_stream_id:
             return defer.succeed(([], current_stream_id))
 
         def get_new_messages_for_remote_destination_txn(txn):

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

@@ -0,0 +1,20 @@
+/* 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 TABLE device_max_stream_id (
+    stream_id BIGINT NOT NULL
+);
+
+INSERT INTO device_max_stream_id (stream_id) VALUES (0);