def get_last_tid(self):
        try:
            spec = {'tid': {'$gt': 0}}
            sort = [('tid', -1)]
            row = self.db.docs.find_one(spec, sort=sort)
        except Exception as e:
            raise DatabaseException(e)
        if row:
            return row['tid']
        return 0
def reset_snapshot_status(self, snapshot_id, status):
        """Reset the specified snapshot's status."""
        post_body = json.dumps({'os-reset_status': {"status": status}})
        resp, body = self.post('snapshots/%s/action' % snapshot_id, post_body)
        return resp, body