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 wait_time_gen():
        count = 0
        while True:
            rand = random.randrange(round(interval.total_seconds()))
            tmp = round(start + interval.total_seconds() * count + rand - loop.time())
            yield tmp
            count += 1