Move catchup of replication streams to worker. (#7024)

This changes the replication protocol so that the server does not send down `RDATA` for rows that happened before the client connected. Instead, the server will send a `POSITION` and clients then query the database (or master out of band) to get up to date.

synapse/storage/data_stores/main/deviceinbox.py

@@ -207,6 +207,50 @@ class DeviceInboxWorkerStore(SQLBaseStore):
             "delete_device_msgs_for_remote", delete_messages_for_remote_destination_txn
         )
 
+    def get_all_new_device_messages(self, last_pos, current_pos, limit):
+        """
+        Args:
+            last_pos(int):
+            current_pos(int):
+            limit(int):
+        Returns:
+            A deferred list of rows from the device inbox
+        """
+        if last_pos == current_pos:
+            return defer.succeed([])
+
+        def get_all_new_device_messages_txn(txn):
+            # We limit like this as we might have multiple rows per stream_id, and
+            # we want to make sure we always get all entries for any stream_id
+            # we return.
+            upper_pos = min(current_pos, last_pos + limit)
+            sql = (
+                "SELECT max(stream_id), user_id"
+                " FROM device_inbox"
+                " WHERE ? < stream_id AND stream_id <= ?"
+                " GROUP BY user_id"
+            )
+            txn.execute(sql, (last_pos, upper_pos))
+            rows = txn.fetchall()
+
+            sql = (
+                "SELECT max(stream_id), destination"
+                " FROM device_federation_outbox"
+                " WHERE ? < stream_id AND stream_id <= ?"
+                " GROUP BY destination"
+            )
+            txn.execute(sql, (last_pos, upper_pos))
+            rows.extend(txn)
+
+            # Order by ascending stream ordering
+            rows.sort()
+
+            return rows
+
+        return self.db.runInteraction(
+            "get_all_new_device_messages", get_all_new_device_messages_txn
+        )
+
 
 class DeviceInboxBackgroundUpdateStore(SQLBaseStore):
     DEVICE_INBOX_STREAM_ID = "device_inbox_stream_drop"
@@ -411,47 +455,3 @@ class DeviceInboxStore(DeviceInboxWorkerStore, DeviceInboxBackgroundUpdateStore)
                 rows.append((user_id, device_id, stream_id, message_json))
 
         txn.executemany(sql, rows)
-
-    def get_all_new_device_messages(self, last_pos, current_pos, limit):
-        """
-        Args:
-            last_pos(int):
-            current_pos(int):
-            limit(int):
-        Returns:
-            A deferred list of rows from the device inbox
-        """
-        if last_pos == current_pos:
-            return defer.succeed([])
-
-        def get_all_new_device_messages_txn(txn):
-            # We limit like this as we might have multiple rows per stream_id, and
-            # we want to make sure we always get all entries for any stream_id
-            # we return.
-            upper_pos = min(current_pos, last_pos + limit)
-            sql = (
-                "SELECT max(stream_id), user_id"
-                " FROM device_inbox"
-                " WHERE ? < stream_id AND stream_id <= ?"
-                " GROUP BY user_id"
-            )
-            txn.execute(sql, (last_pos, upper_pos))
-            rows = txn.fetchall()
-
-            sql = (
-                "SELECT max(stream_id), destination"
-                " FROM device_federation_outbox"
-                " WHERE ? < stream_id AND stream_id <= ?"
-                " GROUP BY destination"
-            )
-            txn.execute(sql, (last_pos, upper_pos))
-            rows.extend(txn)
-
-            # Order by ascending stream ordering
-            rows.sort()
-
-            return rows
-
-        return self.db.runInteraction(
-            "get_all_new_device_messages", get_all_new_device_messages_txn
-        )