Web对象流行度的数学建模方法

Web对象的流行度满足Zipf分布。利用Zipf第一定律和Zipf第二定律建立Web对象访问流行度模型。对于访问频率较高的Web对象，利用Zipf第一定律建模；而对于访问频率较低的Web对象，则使用Zipf第二定律进行描述。该模型为分析和模拟Web用户访问行为提供了依据。     

基于协同过滤的Web缓存替换算法研究

针对GDSF替换算法中对访问频率缺少预测的不足,提出了一种基于协同过滤的GDSF缓存替换算法(GDSF-CF)。该算法考虑了Web对象之间相似性与用户访问时间间隔,运用协同过滤算法生成Web对象的预测访问频率,并采用齐普夫定律参数对GDSF算法的目标函数进行了改进。当需要进行缓存替换时,利用目标函数价值计算缓存空间中的每个Web对象缓存价值,将最小缓存价值的Web对象进行替换。仿真实验结果表明,该算法的命中率HR和字节命中率BHR都有较大提升。     

基于Web流行度的选择Markov预取模型

Web预取技术是目前WWW中减少用户的访问延迟、提高服务质量的主要解决方案之一。该文利用Zipf第1定律和第2定律对Web对象访问流行度建模,并在此基础上,提出了基于Web流行度的选择Markov预取模型。实验表明,该预取模型不仅具有较高的命中率,而且在一定程度上还减少了对带宽的需求。     

基于比例命中率的Web缓存区分服务

基于反馈控制理论,通过系统辨识设计了缓存控制器。动态调整不同类别缓存对象的缓存空间,可保证高优先级Web对象的高命中率,而不同类别的Web对象命中率之比保持不变。在服务器端实现了基于比例命中率的缓存区分服务。经实验验证,在GDSF,LRU,LFU缓存替换算法下,无论是请求命中率还是字节命中率,均有良好的区分效果。     

一种新的基于预测的网页预取模型和缓存算法

为了提高Web缓存算法的命中率,在传统的GDSF算法基础上,提出一种新的使用预测机制的缓存替换算法。该算法使用改进后的WAP算法对Web日志挖掘生成频繁访问序列,建立预测模型,产生预测队列,当需要替换缓存中的对象时使用预测队列提供替换依据。仿真实验表明,新的算法可以在一定程度上提高缓存的文档命中率和字节命中率,尤其在缓存空间相对较小时,效果更为明显。     

Web页面流行度模拟器的设计与实现

研究Web访问特征是有效进行Web缓存管理的基础。该文使用Zipf第一法则和第二法则建立数学模型,分别模拟Web页面高频区及低频区流行度特征,设计并实现了一个Web日志模拟生成器POPSIM。这种模拟器不仅可以模拟生成Web页面访问日志,而且具有很大的灵活性,为进一步研究Web缓存技术和预取技术提供依据。     

一种有效的Web代理缓存替换算法

设计良好的Web缓存替换策略能使网络上的资源得到最有效的利用。文章设计了一个较有效率的Web缓存替换策略LFRU,期望以较佳的方式获得网络资源及改善Web缓存的性能和服务质量。实验结果表明该策略有较高的文档命中率和字节命中率。     

基于最小延迟代价的Web缓存替换算法研究

命中率、字节命中率和延迟时间是Web缓存系统中最重要的性能指标,但是却难以准确、合理地度量不同大小的Web对象的访问延迟.引入字节延迟的概念,为不同的对象延迟建立了一个比较合理的评价标准.提出最小延迟代价的Web缓存替换算法LLC,使用户访问的延迟时间尽可能缩短.实验结果表明,与常用的缓存替换算法相比,LLC算法在有效减少用户感知的访问延迟方面具有较好的性能表现.     

基于机器学习的Web代理缓存替换策略性能改进

在Web代理缓存中,传统的缓存替换策略往往不够有效,会缓存一些不会再次被访问的Web对象。基于此,笔者使用机器学习技术对这部分Web对象进行过滤,使用Web代理日志文件进行训练,以预测Web对象的类别。实验结果表明,与最近最少使用（Least Recently Used,LRU）替换策略相比,使用机器学习技术的命中率最大提高了18.92%,字节命中率最大提高了45.61%。     

基于谱聚类的Web多级缓存替换策略

服务器缓存性能的核心是缓存替换策略,缓存替换策略直接影响缓存的命中率, Web缓存可以解决网络拥塞和用户访问延迟问题,提高服务器的性能.传统缓存替换算法的命中率往往不高,为此文中提出了一种基于谱聚类的多级缓存替换策略.该策略利用循环滑动窗口机制提取日志文件的多项时序特征和访问属性,通过谱聚类对过滤后的数据集进行聚类分析从而得到访问预测结果.多级缓存替换策略综合考虑了缓存对象的局部频率、全局频率以及资源大小能更好地对低价值资源进行剔除,同时对高价值资源进行保留.通过与传统替换算法LRU、LFU、RC、FIFO进行实验对比,实验结果表明本文将谱聚类和多级缓存替换策略进行结合有效地提高了缓存请求命中率和字节命中率.     

Evolutionary Techniques for Web Caching

Web caching has been proposed as an effective solution to the problems of network traffic and congestion, Web objects access and Web load balancing. This paper presents a model for optimizing Web cache content by applying either a genetic algorithm or an evolutionary programming scheme for Web cache content replacement. Three policies are proposed for each of the genetic algorithm and the evolutionary programming techniques, in relation to objects staleness factors and retrieval rates. A simulation model is developed and long term trace-driven simulation is used to experiment on the proposed techniques. The results indicate that all evolutionary techniques are beneficial to the cache replacement, compared to the conventional replacement applied in most Web cache server. Under an appropriate objective function the genetic algorithm has been proven to be the best of all approaches with respect to cache hit and byte hit ratios.     

基于内容的Web Caching

提出一个新的 Web Caching结构模型—基于内容的 Web Caching.模型综合考虑了 Proxy的操作信息和 Web文档的内容特性 ,界定了虚拟用户团体和 Proxy个性 ,并利用 Ontology技术来刻画 Proxy的个性 ,模拟实验表明 ,结合内容属性可以使得 Web Caching性能得到进一步提高     

基于高斯混合模型的Web代理服务器缓存替换策略

Web代理服务器缓存能够在一定程度上解决用户访问延迟和网络拥塞问题,Web代理缓存的缓存替换策略直接影响缓存的命中率,从而影响网络请求响应的效果;为此,使用一种通过固定大小的循环滑动窗口提取Web日志数据的多项特征,并使用高斯混合模型对Web日志数据进行聚类分析,预测在窗口时间内可能再次访问到Web对象,结合最近最少使用(LRU)算法,提出一种新的基于高斯混合模型的Web代理服务器缓存替换策略;实验结果表明,与传统的缓存替换策略LRU、LFU、FIFO、GDSF相比,该策略有效提高了Web代理缓存的请求命中率和字节命中率。     

Web合作缓存置换算法的改进与实现

在LRU算法的基础上,提出一种改进的Web合作缓存置换算法。该算法针对不同大小的文档采取不同的存储策略,如增加小文档在缓存组中的存储数量,以提高其本地缓存的命中率,减少大文档在缓存组中存储的数量,以节约整个缓存组的空间。仿真实验结果表明该算法能够获得较好的性能。     

Web object-based storage management in proxy caches

Proxy caches are essential to improve the performance of the World Wide Web and to enhance user perceived latency. Appropriate cache management strategies are crucial to achieve these goals. In our previous work, we have introduced Web object-based caching policies. A Web object consists of the main HTML page and all of its constituent embedded files. Our studies have shown that these policies improve proxy cache performance substantially.In this paper, we propose a new Web object-based policy to manage the storage system of a proxy cache. We propose two techniques to improve the storage system performance. The first technique is concerned with prefetching the related files belonging to a Web object, from the disk to main memory. This prefetching improves performance as most of the files can be provided from the main memory rather than from the proxy disk. The second technique stores the Web object members in contiguous disk blocks in order to reduce the disk access time. We used trace-driven simulations to study the performance improvements one can obtain with these two techniques. Our results show that the first technique by itself provides up to 50% reduction in hit latency, which is the delay involved in providing a hit document by the proxy. An additional 5% improvement can be obtained by incorporating the second technique.     

Performance evaluation of Web proxy cache replacement policies

The continued growth of the World-Wide Web and the emergence of new end-user technologies such as cable modems necessitate the use of proxy caches to reduce latency, network traffic and Web server loads. In this paper we analyze the importance of different Web proxy workload characteristics in making good cache replacement decisions. We evaluate workload characteristics such as object size, recency of reference, frequency of reference, and turnover in the active set of objects. Trace-driven simulation is used to evaluate the effectiveness of various replacement policies for Web proxy caches. The extended duration of the trace (117 million requests collected over 5 months) allows long term side effects of replacement policies to be identified and quantified.

Our results indicate that higher cache hit rates are achieved using size-based replacement policies. These policies store a large number of small objects in the cache, thus increasing the probability of an object being in the cache when requested. To achieve higher byte hit rates a few larger files must be retained in the cache. We found frequency-based policies to work best for this metric, as they keep the most popular files, regardless of size, in the cache. With either approach it is important that inactive objects be removed from the cache to prevent performance degradation due to pollution.     

Proxy Cache Replacement Algorithms: A History-Based Approach

Accesing and circulation of Web objects has been facilitated by the design and implementation of effective caching schemes. Web caching has been integrated in prototype and commercial Web-based information systems in order to reduce the overall bandwidth and increase system's fault tolerance. This paper presents an overview of a series of Web cache replacement algorithms based on the idea of preserving a history record for cached Web objects. The number of references to Web objects over a certain time period is a critical parameter for the cache content replacement. The proposed algorithms are simulated and experimented under a real workload of Web cache traces provided by a major (Squid) proxy cache server installation. Cache and bytes hit rates are given with respect to different cache sizes and a varying number of request workload sets and it is shown that the proposed cache replacement algorithms improve both cache and byte hit rates.     

A novel server-side proxy caching strategy for large-scale multimedia applications

Nowadays, server-side Web caching becomes an important technique used to reduce the User Perceived Latency (UPL). In large-scale multimedia systems, there are many Web proxies, connected with a multimedia server, that can cache some most popular multimedia objects and respond to the requests for them. Multimedia objects have some particular characteristic, e.g., strict QoS requirements. Hence, even some efficient conventional caching strategies based on cache hit ratio, meant for non-multimedia objects, will confront some problems in dealing with the multimedia objects. If we consider additional resources of proxy besides cache space, say bandwidth, we can readily observe that high hit ratios may deteriorate the entire system performance. In this paper, we propose a novel placement model for networked multimedia systems, referred to as the H^k/T model, which considers the combined influence of arrival rate, size, and playback time to select the objects to be cached. Based on this model, we propose an innovative Web caching algorithm, named as the ART-Greedy algorithm, which can balance the load among the proxies and achieve a minimum Average Response Time (ART) of the requests. Our experimental results conclusively demonstrate that the ART-Greedy algorithm outperforms the most popular and commonly used LFU (Least Frequently Used) algorithm significantly, and can achieve a better performance than the byte-hit algorithm when the system utilization is medium and high.