Magento的负载多少数据显示订单？

$orders = Mage::getResourceModel('sales/order_collection')
            ->addAttributeToSelect('*')
            //->joinAttribute('shipping_firstname', 'order_address/firstname', 'shipping_address_id', null, 'left')
            //->joinAttribute('shipping_lastname', 'order_address/lastname', 'shipping_address_id', null, 'left')
            ->addAttributeToFilter('customer_id', Mage::getSingleton('customer/session')->getCustomer()->getId())
            //->addAttributeToFilter('state', array('in' => Mage::getSingleton('sales/order_config')->getVisibleOnFrontStates()))
            //->addAttributeToSort('created_at', 'desc')
        ;

        $this->setOrders($orders);
        print_r($this->getOrders());