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 _cost_gp(self,x):
        """
        Predicts the time cost of evaluating the function at x.
        """
        m, _, _, _ = self.cost_model.predict_withGradients(x)
        return np.exp(m)