'Starts a background update running.
Args:
update_name: The update to set running.
progress: The initial state of the progress of the update.
Returns:
A deferred that completes once the task has been added to the
queue.'

def start_background_update(self, update_name, progress):

    self._background_update_queue = []
    progress_json = json.dumps(progress)
    return self._simple_insert('background_updates', {'update_name': update_name, 'progress_json': progress_json})
