def get_next_id(self):
        try:
            query = {'_id': 'last_id'}
            update = {'$inc': {'id': 1}}
            fn = self.db.internal.find_and_modify
            row = fn(query, update, upsert=True, new=True)
        except Exception as e:
            raise DatabaseException(e)
        return row['id']
def wait_for_snapshot_status(self, snapshot_id, status):
        """Waits for a Snapshot to reach a given status."""
        start_time = time.time()
        old_value = value = self._get_snapshot_status(snapshot_id)
        while True:
            dtime = time.time() - start_time
            time.sleep(self.build_interval)
            if value != old_value:
                LOG.info('Value transition from "%s" to "%s"'
                         'in %d second(s).', old_value,
                         value, dtime)
            if (value == status):
                return value

            if dtime > self.build_timeout:
                message = ('Time Limit Exceeded! (%ds)'
                           'while waiting for %s, '
                           'but we got %s.' %
                           (self.build_timeout, status, value))
                raise exceptions.TimeoutException(message)
            time.sleep(self.build_interval)
            old_value = value
            value = self._get_snapshot_status(snapshot_id)