Web proxy cache replacement scheme based on back-propagation neural network

Web proxy caches are used to reduce the strain of contemporary web traffic on web servers and network bandwidth providers. In this research, a novel approach to web proxy cache replacement which utilizes neural networks for replacement decisions is developed and analyzed. Neural networks are trained to classify cacheable objects from real world data sets using information known to be important in web proxy caching, such as frequency and recency. Correct classification ratios between 0.85 and 0.88 are obtained both for data used for training and data not used for training. Our approach is compared with Least Recently Used (LRU), Least Frequently Used (LFU) and the optimal case which always rates an object with the number of future requests. Performance is evaluated in simulation for various neural network structures and cache conditions. The final neural networks achieve hit rates that are 86.60% of the optimal in the worst case and 100% of the optimal in the best case. Byte-hit rates are 93.36% of the optimal in the worst case and 99.92% of the optimal in the best case. We examine the input-to-output mappings of individual neural networks and analyze the resulting caching strategy with respect to specific cache conditions.     

Web cache optimization with nonlinear model using object features

In this paper, Web cache optimization by utilizing syntactic features extracted from cache objects is studied. A nonlinear model is used to predict the value of each cache object by using features from the HTTP responses of the server, the access log of the cache, and from the HTML structure of the object. In a case study, linear and nonlinear models are used to classify about 50,000 HTML documents according to their popularity. The nonlinear model yields classification percentages of 64 and 74 for the documents to be stored or to be removed from the cache, respectively. A synthetic workload is then used to study the performance gain from the classifier in a conventional Least Recently Used cache model. The results suggest that the proposed approach can improve the performance of the cache substantially.     

Latency-sensitive hashing for collaborative Web caching

Many geographically distributed proxies are increasingly used for collaborative Web caching to improve performance. In hashing-based collaborative Web caching, the response times can be negatively impacted for those URL requests hashed into geographically distant or overloaded proxies. In this paper, we present and evaluate a latency-sensitive hashing scheme for collaborative Web caching. It takes into account latency delays due to both geographical distances and dynamic load conditions. Each URL request is first hashed into an anchor hash bucket, with each bucket mapping to one of the proxies. Secondly, a number of nearby hash buckets are examined to select the proxy with the smallest latency delay to the browser. Trace-driven simulations are conducted to evaluate the performance of this new latency-sensitive hashing. The results show that (1) with the presence of load imbalance due to skew in request origination or hot-spot references, latency-sensitive hashing effectively balances the load by hashing into geographically distributed proxies for collaborative Web caching, and (2) when the overall system is lightly loaded, latency-sensitive hashing effectively reduces latency delays by directing requests to geographically closer proxies.     

Web Cache系统的设计与分布技术

1 引言随着因特网技术和应用向广度和深度迅猛发展,人们除了在网上共享信息外,还试图通过无所不在的因特网来大规模地共享计算能力和服务等一切可以共享的资源。但是,由于网络中瓶颈的存在及热点资源的相对集中,这种迅猛发展也带来了一个问题,即人们上网时常常体验到的“World WideWait”问题。要解决这一问题,一种有效的解决办法就是采用Web Caching技术,即将Web上常被人们访问的、热门的信息缓存在Web服务器与最终用户之间的缓存服务器系统中。当前,Web Caching是一个正在迅速发展的领域,无论科研界还是工业界,都在这一方面投入了大量的精力。如果设计和部署得当的话,Web Caching可以带来很多好处,如节约大     

Timing predictability of cache replacement policies

Hard real-time systems must obey strict timing constraints. Therefore, one needs to derive guarantees on the worst-case execution times of a system’s tasks. In this context, predictable behavior of system components is crucial for the derivation of tight and thus useful bounds. This paper presents results about the predictability of common cache replacement policies. To this end, we introduce three metrics, evict, fill, and mls that capture aspects of cache-state predictability. A thorough analysis of the LRU, FIFO, MRU, and PLRU policies yields the respective values under these metrics. To the best of our knowledge, this work presents the first quantitative, analytical results for the predictability of replacement policies. Our results support empirical evidence in static cache analysis.

代理缓存一致性策略和替换策略的研究

针对代理缓存的一致性策略和替换策略还没有很好地结合起来,从而影响了代理缓存系统的整体性能的现状,分别探讨了基于Internet的代理缓存一致性策略和替换策略的处理流程、性能评价指标和研究现状,进而给出将这两种策略结合起来的一致性一替换算法的处理流程,并提出陈旧命中比是其主要性能评价指标,能很好地衡量代理缓存的各种算法的优劣和代理缓存系统的整体性能。     

Frequency-based cache management policies for collaborative and non-collaborative topologies of segment based video caching proxies

This paper examines a novel cache management policy applied to non-collaborative and collaborative environments of more than one proxy server that serve homogeneous or even heterogeneous client requests for video streaming over the Internet. This cache management policy, which we call LRLFU because of a combination between an LRU and an LFU policy, is capable of capturing the changing popularities of the various videos by attaching a caching value to every video according to how recently and how frequently the video was requested, and decides to cache the most ‘valuable’ videos. Our event-driven simulations have shown that LRLFU when applied to a simple non-collaborative topology of proxies and compared with previous work in this area (1) improve the byte-hit ratio (BHR), (2) significantly reduce the fraction of user requests with delayed starts and (3) require less CPU overhead. Furthermore, our simulation results have shown that the collaborative hierarchical tree topology of proxies that we examine achieves a much higher BHR when using the same overall cache capacity with the simple topology and in general provides better performance characteristics.This work was conducted while A. Satsiou was a MSc student in the Department of Electronic and Computer Engineering Technical University of Crete.     

A scalable Web cache sharing scheme

A new Web cache sharing scheme is presented. Our scheme reduces the duplicated copies of the same objects in global shared Web caches. It also reduces the message overhead of existing schemes significantly. Trace-driven simulations with actual Web cache logs show that the proposed scheme performs better than the two well-known Web cache sharing schemes, the Internet Cache Protocol and the Cache Array Routing Protocol.     

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.     

Scalable Federation of Web Cache Servers

Web caches are traditionally organised in a simple tree like hierarchy. In this paper, a new architecture is proposed, where federations of caches are distributed globally, caching data partially. The advantages of the proposed system are that contention on global caches is reduced, while at the same time improving the scalability of the system since extra cache resources can be added on the fly. Among other topics discussed in this papers, is the scalability of the proposed system, the algorithms used to control the federation of Web caches and the approach used to identify the potential Web cache partners. In order to obtain a successful collaborative Web caching system, the formation of federations must be controlled by an algorithm that takes the dynamics of the Internet traffic into consideration. We use the history of Web cache access in order to determine how federations should be formed. Initial performance results of a simulation of a number of nodes are promising.     

Web代理缓存算法的性能比较

Web代理是现代Internet的一个重要中间网络器件．代理缓存算法的优劣不但影响到客户端的浏览速度,还关系到目标服务器的性能以及中间通信网络的整体表现。对目前几种流行的Web代理缓存算法进行比较与研究。     

Performance improvement of web caching in Web 2.0 via knowledge discovery

Web 2.0 systems are more unpredictable and customizable than traditional web applications. This causes that performance techniques, such as web caching, limit their improvements. Our study was based on the hypotheses that the use of web caching in Web 2.0 applications, particularly in content aggregation systems, can be improved by adapting the content fragment designs. We proposed to base this adaptation on the analysis of the characterization parameters of the content elements and on the creation of a classification algorithm. This algorithm was deployed with decision trees, created in an off-line knowledge discovery process. We also defined a framework to create and adapt fragments of the web documents to reduce the user-perceived latency in web caches. The experiment results showed that our solution had a remarkable reduction in the user-perceived latency even losses in the cache hit ratios and in the overhead generated on the system, in comparison with other web cache schemes.     

本地缓存和代理服务器环境下的网络日志挖掘

介绍了网络日志挖掘的基本概念，提出了一个网络日志挖掘通用系统的结构，分析了本地缓存和代理服务器对日志挖掘的影响，并给出了一种近似解决方案。这种方案通过网络拓扑结构和日志文件记录的结合，将杂乱无章的日志记录组合成具有语义信息的事务记录，从而使挖掘结果更有意义。     

代理Web Cache性能分析

采用WebCache技术提高当前Internet性能已成为一个主流的研究领域,其功能原理就象处理器和文件系统中的多级高速缓存一样。大规模Web高速缓存系统已成为许多国家Internet基础设施的重要组成部分。该文从三个不同访问规模的代理WebCache的跟踪日志出发,分析了WebCache的用户访问模式、Cache命中率、Cache服务器处理延迟等统计特征,提出基于分布式共享RAM和外存储结合的两级协同WebCache集群技术,可以提供可扩展的高性能并行Web高速缓存服务。     

基于缓存技术的Web应用性能优化研究

在Internet快速发展的今天,用户通过网络获取大量的信息,各种各样的Web应用系统也随之产生,用户对Web应用系统的响应速度上升到最高需求。为提高用户的感受并降低企业和服务提供者的成本,经过研究和分析,发现缓存技术是在不增加成本的前提下提高Web应用系统性能的最有效的解决方案之一。     

Enhanced Proxy Caching with Content Management

In this paper, we propose a novel approach to enhancing web proxy caching, an approach that integrates content management with performance tuning techniques. We first develop a hierarchical model for management of web data, which consists of physical pages, logical pages and topics corresponding to different abstraction levels. Content management based on this model enables active utilization of the cached web contents. By defining priority on each abstraction level, the cache manager can make replacement decisions on topics, logical pages, and physical pages hierarchically. As a result, a cache can always keep the most relevant, popular, and high-quality content. To verify the proposed approach, we have designed a content-aware replacement algorithm, LRU-SP+. We evaluate the algorithm through preliminary experiments. The results show that content management can achieve 30% improvement of caching performance in terms of hit ratios and profit ratios (considering significance of topics) compared to content-blind schemes. Received 19 March 2001 / Revised 17 April 2001 / Accepted in revised form 25 May 2001     

组合Web服务访问控制策略合成研究

针对Web服务多域环境下组合服务的访问控制策略合成问题,首先提出基于属性的Web服务访问控制策略描述框架,并结合原子属性值限制的属性描述方法,对服务访问控制策略进行了形式化表达。然后,通过分析服务组合描述文档中的控制结构,并研究访问控制策略合成算子和访问控制策略规则的合成运算,提出组合Web服务访问控制策略合成方法,实现了组合服务访问控制策略的合成。最后,结合实例给出组合Web服务的访问控制策略合成流程,验证了合成方法的实用性。     

Web Services解决方案性能分析及其优化策略

Web Services提供了更好的互操作性和可扩展性,当然也需要更多的计算资源开销。本文在对产生Web Services额外性能开销的主要因素分析的基础上,讨论了缓存技术在Web Services解决方案性能优化中的应用。     

Web应用性能测试进展

Web性能测试是Web应用开发过程中的一个关键环节，然而Web站点的复杂性及其用户行为的不可预见性使得对其性能测试极其困难，大多数Web站点性能测试不精确并且不现实，不能够反映真实情况的性能测试用处不大或者是容易引起误导。本文主要介绍了Web站点性能测试的重要性、概念及其流程，国内外研究的现状，介绍了性能测试时用到的几个重要的指标，最后总结全文并进行了展望。