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 __init__(self, test, rx_index, tx_index, nh_addr):
        self._test = test
        self._rx_index = rx_index
        self._tx_index = tx_index
        self._nh_addr = ip_address(nh_addr)