public function alter_column_family($keyspace, $column_family, $attrs) {
        $cfdef = $this->get_cfdef($keyspace, $column_family);
        $cfdef = $this->make_cfdef($keyspace, $column_family, $attrs, $cfdef);
        $this->client->set_keyspace($cfdef->keyspace);
        $this->client->system_update_column_family($cfdef);
        $this->wait_for_agreement();
    }