public function create_column_family($keyspace, $column_family, $attrs=null) {
        if ($attrs === null)
            $attrs = array();

        $this->client->set_keyspace($keyspace);
        $cfdef = $this->make_cfdef($keyspace, $column_family, $attrs);
        $this->client->system_add_column_family($cfdef);
        $this->wait_for_agreement();
    }