面向Web服务器集群系统的Web QoS机制研究

Web QoS是当前Web计算中的重要研完内容，用于解决Web计算环境中端到端QoS保证问题。本文提出一种支持QoS的Web服务器集群系统方案以及实现技术，整个系统由支持QoS的集群交换机和Web服务器集群两级结构组成，通过集群交换机和Web服务器的协同工作，实现优先转发与优先服务相结合的分布式QoS保证体系，充分满足Web用户的服务质量需求。通过系统测试，原型系统的性能指标达到了设计要求。     

一种支持WebQoS的前置服务器解决方案

服务质量(Qos)描述了-个产品或服务满足消费者需求的能力.如何为不同类型的用户提供区分服务正在引起研究领域的关注.通过改进Web服务器应用软件来提供WebQoS支持是一种非常直观的Web QoS控制思路,但在实际应用中却存在着通用性和可扩展性等方面的局限.以此思路为出发点,将QoS控制部分功能提取出来,在一个前置服务器中去实现,该服务器置于客户端与Web服务器中间,主要负责完成Web请求的截取、QoS控制及请求转发.实验证明以引入前置服务器的方式实现Web请求的QoS控制,能够保证高级别用户请求的较高完成率以及较低响应延时,以低优先级请求的尽早拒绝防止了服务器过载,有效地实现web服务区分.     

Web QoS控制研究综述

Internet的服务模式正由传统的数据通信与信息浏览向电子交易与服务转变 ,Web服务器系统作为支持电子商务的核心设施 ,需要对不同的用户或HTTP请求提供区分服务和性能保证 ,因此必须具备建立和支持服务质量 (QualityofService ,QoS)控制的机制与策略 .该文综述了WebQoS控制的研究现状 ,包括Web请求的分类机制、Web服务器应用软件的QoS控制机制、操作系统的WebQoS控制机制、中间件的WebQoS控制机制以及Web服务器集群系统的QoS控制机制与策略 ,并分析了进一步的研究方向 .     

Web QoS的测控技术

随着基于Web的Internet应用越来越广泛,提高Web服务器的性能(QoS),已成为当前研究的热点课题.为了提高Web服务器的性能,必须研究Web QoS的测控技术.系统地阐述了Web QoS的测控技术中的几个主要问题,包括:测量技术中的负载发生器、网络流量的自相似模型和测试软件等问题,控制技术中的Web QoS反馈控制、控制目标、建模和控制算法等问题.     

基于灰色关联分析的Web服务选择

为方便用户选择最优Web服务,利用灰色系统理论对Web服务质量QoS属性因子进行分析,提出了一种基于用户QoS偏好的Web服务灰色关联分析方法。考虑到Web服务QoS的不确定性,该方法使用区间对Web服务QoS值进行建模。为了确定候选服务的QoS与用户QoS需求的符合程度,先针对服务的每个QoS属性,计算其与用户QoS需求的灰色区间关联系数;然后结合各个QoS属性的关联系数计算候选服务的QoS与用户QoS需求的综合灰色区间关联度,关联度越大的服务越符合用户的要求;最后从满足用户功能需求的Web服务中选择灰色关联度最大的Web服务推荐给用户。与其它Web服务评价模型相比较,该模型更加符合Web服务QoS的实际情况,能够在服务QoS信息不充分、不确定的环境下,对QoS属性进行合乎实际的分析处理,从而得到更加合理有效的QoS评价。     

服务质量(QoS)走入Web

QoS控制技术的基本目标是为Internet应用提供性能保证和服务区分。如何在Web服务器及其系统中引入和实现QoS控制的机制与策略,从而满足不断增长的Web性能需求,为不同类型的用户或请求提供服务区分和性能保证,这是目前Web发展迫切需要解决的问题,也是实现下一代网络QoS控制技术不可或缺的关键环节。     

Web QoS及其保证方法

Internet的服务模式正由传统的数据通信与信息浏览向电子交易与服务转变,仅靠网络QoS机制并不能完全解决端到端的QoS控制问题。Web服务器系统作为核心设施,必须同样具备建立和支持QoS的机制与策略,对不同的用户或HTTP请求提供区分服务和性能保证。文中综述了Web QoS的发展情况、研究现状以及保证方法(包括请求分类机制的划分方法、Web服务供应商的Web系统解决方案以及无线网络的保证方法),并分析了进一步的研究方向。     

MQM:一种用于Web服务查找的多维QoS模型

随着Web的发展,可供选择的功能相同或相似的Web服务越来越多,因此有必要为用户提供一种高效的基于服务质量(QoS)的Web服务查询机制.然而现有的Web服务QoS管理模型并不能很好的支持如动态查询等查询需求,其查询性能也有待提高.鉴于此,本文提出一种新的Web服务管理模型——多维QoS模型(MQM:Multi-dimensional QoS Model),并介绍了该模型的创建方法和相关算法.MQM通过多维模型来管理QoS数据,提供查询和OLAP操作.实验证明MQM能够使用户能更准确和快速的按QoS查询现有服务,很好地解决了传统查询方法无法确定查询条件、无法动态改变查询区间、查询性能不高等问题,进而改善了用户体验.     

基于用户反馈QoS的动态Web服务发现方法

由于传统的基于关键字和简单分类的Web服务发现机制缺少服务质量(QoS)考虑,因此不能很好满足用户的需求。针对该问题,提出一种基于QoS的Web服务发现模型,通过引入QoS代理机制,对终端用户使用Web服务后反馈的QoS信息进行量化和度量处理,以支持基于QoS的Web服务发现;在此基础上,根据Web服务的动态性特点和不同用户的QoS需求,给出了基于用户反馈的QoS数据度量方法,并提出一种基于QoS的Web服务发现算法。实验结果表明,提出的Web服务发现方法能够较好地满足用户的需求。     

支持QoS和用户需求的Web服务选择模糊算法*

基于QoS的Web服务选择能为用户提供更好的服务质量,而基于用户对QoS的需求和偏好的模糊性来进行Web服务选择是其中的一种方法。如何通过这种方法合理地获得最优候选服务集,是Web服务架构亟待解决的一个问题。本文提出了一种支持QoS和用户需求的Web服务选择模糊算法,该算法将用户对QoS的需求及偏好的语言描述进行去模糊化,然后选择出最符合用户需求的服务集。通过对模拟的服务质量数据进行实验,验证了该算法的优越性和有效性。     

QCWS: an implementation of QoS-capable multimedia web services

QoS (Quality of Service), which defines service quality such as latency, availability, timeliness and reliability, is important for web applications that provide real-time information, multimedia content, or time-critical services. Many web applications are best implemented by servers with a guaranteed server processing capacity. In this research, we study the QoS control issues using the current Web services standards. We propose a QoS-capable Web service architecture, QCWS, by deploying a QoS broker between Web service clients and providers. The functions of the QoS broker module include tracking QoS information about servers, making selection decisions for clients, and negotiating with servers to get QoS agreements. We have implemented a QCWS prototype using IBM WSDK, enhanced with simple QoS capabilities. We have measured the performance running under different service priorities.     

QoS获益驱动的中间件调度框架研究

Web应用服务器目前普遍采用的先到先得式(FCFS)的调度框架在过载时难以保障应用的服务质量(QoS)需求.QoS获益驱动(QBD)的调度框架是一种针对这些不足而提出的请求调度解决方案.QoS获益根据应用的QoS需求得到,用于评价QoS保障对应用需求的满足情况.QBD调度框架包含了多个用于保障应用QoS需求的组件,实现了基于QoS获益的资源规划算法,能够提高服务器对应用QoS需求的保障能力.在OnceAS平台上的实验结果验证了QBD调度框架的有效性.     

Web服务器群的QoS确保及其接纳控制研究

WWW访问的爆炸性发展正是Internet成功的重要原因，然而目前的Web服务器却缺乏相应的QoS机制，导致在过载时造成巨大的经济损失。一个提供多类服务的多服务器Web平台的服务质量确保体系被提出来，它以服务响应延迟为核心度量标准，将同一类服务抽象为一台虚拟服务器，并以该度量黏合起系统的各个组件．同时据此提出了一个动态自适应的服务接纳算法(DASAC)．测试表明，即使经历严重的过载与业务突发，也能保证用户感知的服务质量．     

A Tiered System for Serving Differentiated Content

Contemporary Web sites typically consist of front–end Web servers, application servers, and back-end information systems such as database servers. There has been limited research on how to provide overload control and service differentiation for the back-end systems. In this paper we propose an architecture called tiered service (TS) for these purposes. In TS, there are several heterogeneous back-end systems to serve the Web applications. The Web applications communicate with a routing intermediary to intelligently route the queries to the appropriate back-end servers based on various policies such as client profiles and server load. In our system the back ends may store different qualities of data; lower quality data typically requires less overhead to serve. The main contributions of this paper include (i) a tiered content replication scheme that replicates tiered qualities of data on heterogeneous back ends with different capacity to satisfy clients with diverse requirements for latency and quality of data, and (ii) an application-transparent query routing architecture that automatically routes the queries to the appropriate back ends. The architecture was implemented in our test bed, and its performance was benchmarked. The experimental results demonstrate that TS offers significant performance improvement.     

A Scalable Web Server Architecture

This paper describes a scalable architecture for Web servers designed to cope with the ongoing increase of the Internet requirements. In the paper, first the drawbacks of the traditional Web server architecture are discussed, and the need for an innovative solution is described. The proposed design addresses two of the parameters that can dramatically impact the performance of Web servers: (1) the need for a powerful data management system to cope with the increase in the complexity of users' requests; and (2) an efficient caching mechanism to reduce the amount of redundant traffic. In this direction, a scalable solution based on distributed database technology to replace the file system is described, and performance test results of the system are provided. This architecture is further extended by a collaborative caching system that builds up an adaptive hierarchy of caches for Web servers, which allows them to keep up with the changes in the traffic generated by the applications they are running. Finally, some improvements to the proposed architecture are addressed.     

An analytical approach to providing controllable differentiated quality of service in Web servers

Provisioning quality of service (QoS) in Web servers has gained immense importance because Web servers are a major part of the Internet. To deliver the pledged QoS, Web service providers need control over the allocation of the resources in their Web servers. Control is also necessary for reaching the optimal resource allocation through proper service differentiation. In this paper, we propose and investigate an analytic approach that enables the service providers to deploy a differentiated service policy that offers this control. The proposed service policy is configurable by tunable control parameters. We devise the relationships between the performance measures and these parameters by adopting a unique queuing theoretic approach. Once these relationships are established, we describe how these parameters can be set to their most appropriate values depending on the objectives of the service providers. We illustrate the usefulness of our approach by conducting the analysis on a real Web trace.     

SLA-Driven Clustering of QoS-Aware Application Servers

In this paper, we discuss the design, implementation, and experimental evaluation of a middleware architecture for enabling service level agreement (SLA)-driven clustering of QoS-aware application servers. Our middleware architecture supports application server technologies with dynamic resource management: application servers can dynamically change the amount of clustered resources assigned to hosted applications on-demand so as to meet application-level quality of service (QoS) requirements. These requirements can include timeliness, availability, and high throughput and are specified in SLAs. A prototype of our architecture has been implemented using the open-source J2EE application server JBoss. The evaluation of this prototype shows that our approach makes possible JBoss' resource usage optimization and allows JBoss to effectively meet the QoS requirements of the applications it hosts, i.e., to honor the SLAs of those applications     

QoS-Broker for transactional workloads

Typical request processing systems, such as web servers and database servers, try to accommodate all requests as fast as possible, which can be described as a Best-Effort approach. However, different application items may have different quality-of-service (QoS) requirements, and this can be viewed as an orthogonal concern to the basic system functionality. In this paper we propose the QoS-Broker, a middleware for delivering QoS over servers and applications. We show its architecture to support contracts over varied targets including queries, transactions, services or sessions, also allowing expressions on variables to be specified in those targets. We also discuss how the QoS-Broker implements basic strategies for QoS over workloads. Our experimental results illustrate the middleware by applying priority and weighted- fair-queuing based differentiation over clients and over transactions, and also admission control, using a benchmark as a case-study.     

Connection management for QoS service on the Web

The current Web service model treats all requests equivalently, both while being processed by servers and while being transmitted over the network. For some uses, such as multiple priority schemes, different levels of service are desirable. We propose application-level TCP connection management mechanisms for Web servers to provide two different levels of Web service, high and low service, by setting different time-outs for inactive TCP connections. We evaluated the performance of the mechanism under heavy and light loading conditions on the Web server. Our experiments show that, though heavy traffic saturates the network, high level class performance is improved by as much as 25–28%. Therefore, this mechanism can effectively provide QoS guaranteed services even in the absence of operating system and network support.