public function execute(RiakOperation $operation)
    {
        if (empty($this->nodes)) {
            throw new RiakException('There are no nodes in the cluster.');
        }

        $size  = count($this->nodes);
        $index = mt_rand(0, $size - 1);
        $node  = $this->nodes[$index];

        return $node->execute($operation);
    }