Analysis and control of correlated web server queues

The research literature is rich with studies that demonstrate various degrees of correlation in the arrival processes found in Web server environments. All of these previous studies either have assumed the arrival process of each Web server to be independent of the corresponding service process or have completely ignored this important issue. Using data from commercial Web servers, we demonstrate the existence of considerable dependencies between arrival times and service times, in addition to a strong dependence structure within the arrival process, and then we explore a likely causal model of this cross correlation. A mathematical approximation of Web server performance is derived, based on heavy-traffic stochastic-process limits, that captures both the correlations within the arrival process and the correlations between the arrival and service processes. We then demonstrate that the results from our approximation, which is asymptotically exact, are in very good agreement with simulation results across all traffic intensities. Our mathematical analysis is further exploited to revisit certain scheduling issues in Web server environments. In particular, we consider a scheduling approach that provides expected response times relatively close to those under the optimal shortest remaining processing time policy while also maintaining better variance properties.     

Evaluation of Strong Consistency Web Caching Techniques

The growth of the World Wide Web (WWW or Web) and its increasing use in all types of business have created bottlenecks that lead to high network and server overload and, eventually, high client latency. Web Caching has become an important topic of research, in the hope that these problems can be addressed by appropriate caching techniques. Conventional wisdom holds that strong cache consistency, with (almost) transactional consistency guarantees, may neither be necessary for Web applications, nor suitable due to its high overhead. However, as business transactions on the Web become more popular, strong consistency will be increasingly necessary. Consequently, it is important to have a comprehensive understanding of the performance behavior of these protocols. The existing studies, unfortunately, are ad hoc and the results cannot be compared across different studies. In this paper we evaluate the performance of different categories of cache consistency algorithms using a standard benchmark: TPC-W, which is the Web commerce benchmark. Our experiments show that we could still enforce strong cache consistency without much overhead, and Invalidation, as an event-driven strong cache consistency algorithm, is most suitable for online e-business. We also evaluate the optimum deployment of caches and find that proxy-side cache has a 30–35% performance advantage over client-side cache with regard to system throughput.     

System support for web hosting services on server clusters

The Web hosting service is becoming increasingly important in which the service providers offer system resources to store and provide Web access to contents from individuals, institutions, and companies who lack resources or expertise to maintain a Web site. Web server cluster is a popular architecture used by the hosting service providers as a way to create scalable and highly available solutions. However, hosting a variety of contents from different customers on such a distributed server system faces new design and management problems and requires new solutions. This paper describes the research work we are pursuing for constructing a system to address the challenges faced by hosting Web content on a server farm environment. We also report performance data measured from a real hosting service.     

Keta中的Socket复用技术

随着信息技术的不断发展,提高Web服务器的性能是个亟待解决的问题。内核级Web Server的实现有效地提高了Web服务器的处理能力。然而,目前的内核级Web服务器通常只处理静态请求,而动态请求需要转发到外部传统Web服务器上进行处理。本文针对一种内核级非对称多线程流水线服务器——Keta,研究并改进了动态请求的转发机制,提出了利用Socket复用技术来实现转发的策略,有效地提高了该服务器的效率。     

一种基于OSI应用层的Web群集负载平衡调序策略研究

本文总结了目前基于L7的Web群集负载平衡调度研究，分析了影响性能的主要因素，在估计Web负载时考虑了请求强度以及Web服务器自身的性能，提出了处理能力异构服务器群集的最小负载调度算法。在算法中还同时考虑了服务器在进入临界状态时性能急剧下降的因素，避免群集进入临界状态．新算法能较为准确地跟踪群集系统的负载，更好地
均衡分配负载。     

具有区分服务等级的可扩展并行服务器集群

采用并行Web服务器集群技术实现高性能的WEB服务器服务已经成为一种趋势,该技术具有性能高,可扩展性好,可靠性高、成本低等特点。文章介绍了目前Web服务器集群的结构和几种关键技术,在此基础上设计一种具有区分服务等级的Web服务器集群,并给出结构描述和资源管理的策略。     

A replication framework for program‐to‐program interaction across unreliable networks and its implementation in a servlet container

We propose a service replication framework for unreliable networks. The service exhibits the same consistency guarantees about the order of execution of operation requests as its non‐replicated implementation. Such guarantees are preserved in spite of server replica failure or network failure (either between server replicas or between a client and a server replica), and irrespective of when the failure occurs. Moreover, the service guarantees that in the case when a client sends an ‘update’ request multiple times, there is no risk that the request be executed multiple times. No hypotheses about the timing retransmission policy of clients are made, e.g. the very same request might even arrive at different server replicas simultaneously. All of these features make the proposed framework particularly suitable for interaction between remote programs, a scenario that is gaining increasing importance. We discuss a prototype implementation of our replication framework based on Tomcat, a very popular Java‐based Web server. The prototype comes into two flavors: replication of HTTP client session data and replication of a counter accessed as a Web service. Copyright © 2005 John Wiley & Sons, Ltd.     

基于Web Service的工作流补偿机制

针对Web Service事务处理机制中的补偿问题,提出一种半自动的事务补偿机制,使用数据库系统中的触发器技术,解决了在Web Service分布、异构平台上对事务活动进行统一的补偿问题,将机制应用在Web Service中,可以规范补偿逻辑,从而保证系统的一致性,Web Service设计者可以确定补偿的规则,并在事务运行时动态生成补偿策略。实验结果表明,该方法有利于集中利用补偿策略,具有良好的可扩展性。     

Proxy-based hybrid cache management in Mobile IP systems

In this paper, we propose and analyze a proxy-based hybrid cache management scheme for client-server applications in Mobile IP (MIP) networks. We leverage a per-user proxy as a gateway between the server and the mobile host (MH) such that any communication between the MH and server must pass through the proxy. The proxy has dual responsibilities in our design. It keeps track of the current location of the MH by acting as a regional Gateway Foreign Agent (GFA) as in the MIP Regional Registration protocol for mobility management. The proxy is also responsible for cache consistency management and query processing on behalf of the MH. To reduce the network traffic, a threshold-based hybrid cache consistency management policy is applied. That is, when a data object is updated at the server, the server sends an invalidation report to the MH through the proxy to invalidate the cached data object, provided that the size of the data object exceeds the given threshold. Otherwise, the server sends a fresh copy of the data object through the proxy to the MH. We identify the best “threshold” value that would minimize the overall network traffic incurred due to mobility management, cache consistency management, and query processing, when given a set of parameter values characterizing the operational and workload conditions of the MIP network.     

网络表格间的快照关系发现

近年来,互联网上涌现出大量结构化的表格数据,网络表格的价值不仅在于数据本身,还在于数据之间的关系。只有探测出表格之间潜在的关系,方能更好地利用这些结构化数据。因此提出发现网络表格间的快照关系,并给出发现快照关系的框架以及检测与给定表之间满足某种匹配关系的快照表的算法,快照表可用于优化查询以及在大数据环境下实时地返回部分查询结果。提出了基于实体和属性重合度的评分方法,并引入实体新鲜度的概念,使得算法在快照关系的发现过程中更多地关注能提供新鲜实体的表;与此同时,基于Bayes模型的表格内容增强算法能更加准确地判断属性列上值的一致性,从而提高快照关系发现的准确率。大量实验表明,该评分模型能发现高质量的快照表,且在快照的查询精度和召回率上表现出色。     

数据库存取图片的优化算法

通过对数据库如何存取图片的研究,提出在.Net平台下基于Web的SQL Server数据库存取图片的优化算法,该算法能有效优化图片大小,节省数据库容量,不占用服务器空间,减少服务器的响应时间,提高网页中的图片加载速度。     

Web 服务器的鲁棒建模和过载控制

给出了一种Web 服务器的建模方法,说明了如何用控制理论管理不可预测的服务器负载。Web 服务器可以被仿真为一个多容器系统。该鲁棒Web 服务器模型适用于未知的负载干扰和不确定的匹配模型。过载控制技术基于自适应允许控制取得时间保证,用一个完整参数变化模型和大的过载来评估模型的性能。     

Modeling and managing the variability of Web service-based systems

Web service-based systems are built orchestrating loosely coupled, standardized, and internetworked programs. If on the one hand, Web services address the interoperability issues of modern information systems, on the other hand, they enable the development of software systems on the basis of reuse, greatly limiting the necessity for reimplementation. Techniques and methodologies to gain the maximum from this emerging computing paradigm are in great need. In particular, a way to explicitly model and manage variability would greatly facilitate the creation and customization of Web service-based systems. By variability we mean the ability of a software system to be extended, changed, customized or configured for use in a specific context.We present a framework and related tool suite for modeling and managing the variability of Web service-based systems for design and run-time, respectively. It is an extension of the COVAMOF framework for the variability management of software product families, which was developed at the University of Groningen. Among the novelties and advantages of the approach are the full modeling of variability via UML diagrams, the run-time support, and the low involvement of the user. All of which leads to a great deal of automation in the management of all kinds of variability.     

Keta的Web QoS机制与实现

随着Web应用的急剧增长,为了提高Web服务器的处理能力,人们提出和实现了多种Web Server结构。在此基础上,对Web应用提供性能保证和区分服务,实现QoS的控制成为目前Web发展所迫切需要解决的问题。本文针对一种非对称多线程流水线服务器结构--Keta,研究并实现了请求的分级调度控制、高负载的内容自适应降级服务等内容。实验结果表 表明,这些策略机制是有效的。     

A clustering-based prefetching scheme on a Web cache environment

Web prefetching is an attractive solution to reduce the network resources consumed by Web services as well as the access latencies perceived by Web users. Unlike Web caching, which exploits the temporal locality, Web prefetching utilizes the spatial locality of Web objects. Specifically, Web prefetching fetches objects that are likely to be accessed in the near future and stores them in advance. In this context, a sophisticated combination of these two techniques may cause significant improvements on the performance of the Web infrastructure. Considering that there have been several caching policies proposed in the past, the challenge is to extend them by using data mining techniques. In this paper, we present a clustering-based prefetching scheme where a graph-based clustering algorithm identifies clusters of “correlated” Web pages based on the users’ access patterns. This scheme can be integrated easily into a Web proxy server, improving its performance. Through a simulation environment, using a real data set, we show that the proposed integrated framework is robust and effective in improving the performance of the Web caching environment.     

网络控制系统Web服务器服务质量管理方案的研究

提出一种基于Web的自适应内容传输管理方案,为不同网络客户提供不同优先级的性能服务,并且各种服务相互独立,同时能基于请求率和传输带宽共享系统资源。这种方案在传统的允入控制基础上改善了服务性能,根据网络负载情况和服务质量需求自适应选择传输内容,满足了客户对网络传输服务质量需求。该管理方案可以在三层模型的中间层实施,便于修改和维护,给出的实验结果显示了该方案的有效性。     

Web服务器安全防护技术研究

Web是目前在Internet上使用最广泛的信息服务类型.探讨Web服务器的安全现状以及常见的安全防护技术,对于Web服务器的安全管理能起到一定的借鉴作用.     

Web应用服务器研究综述

Web应用服务器是Web计算环境下产生的新型中间件,为创建、部署、运行、集成和管理事务性Web应用提供一个跨平台的运行环境,被认为是自关系型数据库以来最令人激动的企业应用技术.诸多IT企业纷纷推出其各自的Web应用服务器产品和系统,学术界也对这种热门领域产生了浓厚的兴趣.在分析Web计算环境下传统中间件发展所遇到的问题的基础上,介绍Web应用服务器的起源和发展、运行模式以及评测基准,然后对Web应用服务器研究现状进行综述,主要包括Web应用服务器的定义、体系结构、组件容器、分布事务处理、负载平衡、高速缓存、Web Service等研究热点和关键技术.根据评测基准,对若干主流Web应用服务器从功能和性能两个方面进行分析和比较.此外,还指出了Web应用服务器目前存在的不足以及未来的发展趋势.     

基于Web的全国计算机等级考试报名系统设计

本文论述基于Web的计算机等级考试报名系统开发的目的和意义、设计思想、系统设计、功能设计和安全性设计等。给出了几个重要模块:考生报名注册模块,班级管理模块,公告管理模块,考生管理模块,数据导出模块和管理员信息修改模块。本系统在Web服务器上实现。     

Web访问挖掘的预处理技术的研究

Web日志挖掘就是运用数据挖掘技术从Web日志中发现和抽取信息的过程。数据预处理是Web日志挖掘的一个关键环节。对数据预处理的各个环节进行研究,并介绍各个环节中的一些特殊处理方法,根据对Web服务期日志数据格式的分析,对会话概念进行了形式化描述,然后在分析目前会话构造算法的基础上,提出了基于时间和引用的启发式方法来构造会话。