OnceAS/Q:一个面向QoS的Web应用服务器

网络分布计算环境下应用系统的需求多样化和复杂性的增长,要求位于中间件层次的Web应用服务器(web application server,简称WAS)从原来的"尽力而为"服务模型转变为服务质量(quality of service,简称QoS)保障模型,为具有不同需求的应用分别提供适宜的服务质量保障.目前的WAS系统在此方面仍然比较薄弱.OnceAS/Q是一个面向QoS的WAS系统,它以QoS规约为基础,为不同应用提供不同的QoS保障能力.OnceAS/Q实现了一个应用QoS保障框架,提供了一组QoS服务组件支持具有QoS需求的应用开发和运行.介绍了OnceAS/Q的体系结构和主要组件,详细阐述了两个关键问题,一是QoS规约的定义及其映射,另一个是面向QoS的服务组件和资源的动态重配.OnceAS/Q原型在Ecperf测试基准下,对其QoS保障能力进行了实验.实验数据表明,在较大规模的应用环境下,OnceAS/Q能够提供更好的服务质量,并且开销是可接受的.

OnceAS/Q: A QoS-Enabled Web Application Server

With the increasing diversity and complexity of distributed systems in network environment, web application server (WAS) is required to transform its service model from Best Effort?to QoS (quality of service) Guarantee". However, most existing WASs are relatively weak in terms of QoS provision. In this paper, OnceAS/Q is presented to show how a QoS-enabled WAS can offer different QoS provisions for applications. OnceAS/Q provides a set of QoS related services and a framework to support QoS guarantee, in order to realize a QoS enabled WAS. This paper first describes the architecture and main components of OnceAS/Q. Then two key issues, related to QoS enabling and the corresponding solutions, are explored in detail: one is the definition and mapping of QoS specifications, and the other is the dynamic reconfiguration of QoS-aware service components and resources. Ecperf benchmark, a well-known performance benchmark for J2EE Application Server, is used to evaluate the effect of QoS enabling of OnceAS/Q. Experimental results show that OnceAS/Q can support better QoS for applications at a reasonable cost.