分配器上支持QoS的设计与实现

为了让Web集群服务器支持QoS，在分配器上实现了一些QoS的机制，包括区分服务、性能隔离、服务器动态划分、接纳控制和内容自适应。对于高优先级的请求，系统确保其服务质量满足事先商定的服务质量协议；对于低优先级的请求，系统提供尽力而为的服务。尤其，当服务器重载时，分配器不是简单地靠丢弃请求，而是采用内容自适应机制来防止服务器过载。实际测试表明，系统达到了所有的设计要求。

Design and Implementation of Supporting QoS in Dispatcher

To support QoS in Web server cluster, dispatcher is equipped with some QoS mechanisms, including admission control, service differentiation, server repartition, performance isolation, and content adaptation. System satisfies the service level agreement targets for high priority request classes, and supply best-effort service for low priority request classes. The percentage of dropped requests of the system is very low, which mainly benefits from the content adaptation mechanism, Realistic experiments show that the system works as expected.