一个基于集中管理的协作式Web缓存系统

共享不同代理的缓存Web文档是减少通信量和减轻网络瓶颈的重要方法。在分析原有Web缓存通信协议（ICP）的基础上,提出了一种新的协作Web缓存系统（CMCS）并作了分析比较。通过将HTTP请求均匀分散到系统各个代理,消除了代理之间庞大的通信开销以及由此带来的处理负担。在动态变化的网络环境下,有效地将各个代理组织起来,处理来自服务器的文档。另外也克服了以往每个代理里有大量冗余内容,造成各个代理内容趋向的情形。     

集中管理式Web缓存系统及性能分析

共享缓存文件是减少网络通信量和服务器负载的重要方法，本文在介绍Web Caching技术及流行的Web缓存通信协议ICP的基础上，提出了一种集中管理式Web缓存系统，该系统通过将用户的HTTP请求，按照一定的算法分发到系统中某一合适的缓存服务器上，从而消除了缓存系统内部服务器之间庞大的通信开销及缓存处理负担，减少了缓存内容的冗余度．通过分析，证明了集中管理式Web缓存系统比基于ICP的简单缓存系统具有缓存效率高、处理开销低、延迟小等优点，并且该系统具有良好的可扩展性．     

Web缓存流量特征模型研究和应用

根据Web缓存流量访问特征建立数学模型，设计实现了Web缓存流量特征模拟生成器（WebSimGen）。利用两层代理缓存结构、基于ADF（Aggregation、Disaggregation和Filtering）模型对Web缓存流量的访问特征和性能进行测试，实验表明模拟日志具有和真实日志类似的访问特性。Web生成器具有较大的灵活性，能够克服真实日志的一些缺点，为进一步提高Web缓存性能和预取技术提供了重要依据。     

合作式Web缓存系统的性能分析

共享不同代理的缓存文件是减少Web通信量和减轻网络瓶颈的重要方法．在分析现有合作式缓存系统的基础上，提出一种基于混合管理的合作式Web缓存系统(HMCS）．HMCS采用重定向的方法将请求从未命中的代理转发给缓存了请求文件的代理．采用这种方法可以减少缓存文件的冗余度，从而提高了缓存系统的存储利用率，进而提高系统的命中率．性能分析和仿真结果表明HMCS系统性能要优于CRISP和ICPS系统．     

一种新的基于分区的多媒体代理协作管理策略

多媒体代理缓存是提高媒体流化质量和减轻网络负载的重要手段，将基于协作的多媒体代理缓存技术引入无线网络，提出一种新的分区缓存管理模型（Partition-based caching manager,PBCM)，通过对系统中各个代理的部分缓存空间（称为静态分区）采取集中式管理，可以合理配置缓存资源，降低缓存的冗余度，从全局角度优化系统的整体性能，具体地，PBCM中制定了一种全局对象放置策略来管理静态分区缓存的内容，该策略被模型化为一个优化问题，并采用改进遗传算法来求解，仿真实验表明该模型及算法是有效可行的。     

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缓存命中率与字节命中率关系

在研究Web缓存性能时，一般考虑2个评价指标：命中率HR和字节命中率BHR。目前大多侧重于2个指标之一，或仅通过测试2个指标的数值来评价缓存替换算法优劣，没有从2个指标关系的角度来评价缓存替换算法的性能。该文讨论了Web缓存系统中命中率与字节命中率之间的关系，提出了一种Web缓存性能评价指标——命中比（FBR），讨论了该指标在Web缓存替换算法及Web预取性能评价中的应用，为度量缓存系统的性能提供了参考依据。     

流媒体代理缓存技术研究

随着流媒体技术在互联网上的广泛应用，原有用于加速Web内容分发的代理缓存技术也被应用于流媒体内容分发领域。然而，由于流媒体对象的一些独特特点，需要在传统Web缓存技术的基础上提出适用于流媒体对象的缓存技术。本文分析了基于代理缓存的流媒体分发中的关键问题和技术挑战，对现有的各种流媒体缓存方案进行了综述、分类和比较，最后对流媒体代理缓存的未来发展方向进行了展望。     

集群缓存系统中代理缓存技术的研究

针对集群缓存系统的特点,对其内部各代理缓存进行了详细的研究.在缓存副本的存储方面,采用了面向网站的存储方案,更好的实现个性化服务的功能;在缓存副本的管理方面,采用了将替换和一致性结合在一起的RCA算法,使得整个系统有较高的命中陈旧率;在代理协作方面,通过重定向的方法将请求从未命中的代理转发给缓存了请求的代理,避免了代理之间复制对象,有效地减少了缓存对象的冗余度.通过理论分析推导,证明了它能大大减少访问延迟、有效地减轻了Web服务器的负担.实验证明,本协作方案有较高的命中率.     

基于Memcached的缓存资源集中管理方法

Memcached是一个免费开源、高性能的、分布式的内存对象缓存系统,用于在动态Web应用中提升访问速度,在很多高访问量的大型网站中得到广泛应用。然而却一直没有一个对Memcached进行统一集中管理部署的工具,在实际开发中往往会将Memcached模块紧密地和应用程序混在一起,给缓存的独立维护造成困难。文中从Memcached应用特征和Web应用体系结构特征两方面分析了现有Memcached系统的缺点,进而提出了一种缓存资源集中管理和多应用共享方案,并构建了一个Memcached Manager应用系统。相对于传统Web开发方式,文中提出的方案可以很大程度上规范和简化应用程序对Memcached的使用,方便缓存资源的统一分配管理。     

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。     

COPACC: An Architecture of Cooperative Proxy-Client Caching System for On-Demand Media Streaming

Proxy caching is a key technique to reduce transmission cost for on-demand multimedia streaming. The effectiveness of current caching schemes, however, is limited by the insufficient storage space and weak cooperation among proxies and their clients, particularly considering the high bandwidth demands from media objects. In this paper, we propose COPACC, a cooperative proxy-and-client caching system that addresses the above deficiencies. This innovative approach combines the advantages of both proxy caching and peer-to-peer client communications. It leverages the client-side caching to amplify the aggregated cache space and rely on dedicated proxies to effectively coordinate the communications. We propose a comprehensive suite of distributed protocols to facilitate the interactions among different network entities in COPACC. It also realizes a smart and cost-effective cache indexing, searching, and verifying scheme. Furthermore, we develop an efficient cache allocation algorithm for distributing video segments among the proxies and clients. The algorithm not only minimizes the aggregated transmission cost of the whole system, but also accommodates heterogeneous computation and storage constraints of proxies and clients. We have extensively evaluated the performance of COPACC under various network and end-system configurations. The results demonstrate that it achieves remarkably lower transmission cost as compared to pure proxy-based caching with limited storage space. On the other hand, it is much more robust than a pure peer-to-peer communication system in the presence of node failures. Meanwhile, its computation and control overheads are both kept in low levels     

Exploiting Regularities in Web Traffic Patterns for Cache Replacement

Abstract. Caching web pages at proxies and in web servers' memories can greatly enhance performance. Proxy caching is known to reduce network load and both proxy and server caching can significantly decrease latency. Web caching problems have different properties than traditional operating systems caching, and cache replacement can benefit by recognizing and exploiting these differences. We address two aspects of the predictability of traffic patterns: the overall load experienced by large proxy and web servers, and the distinct access patterns of individual pages. We formalize the notion of ``cache load' under various replacement policies, including LRU and LFU, and demonstrate that the trace of a large proxy server exhibits regular load. Predictable load allows for improved design, analysis, and experimental evaluation of replacement policies. We provide a simple and (near) optimal replacement policy when each page request has an associated distribution function on the next request time of the page. Without the predictable load assumption, no such online policy is possible and it is known that even obtaining an offline optimum is hard. For experiments, predictable load enables comparing and evaluating cache replacement policies using partial traces , containing requests made to only a subset of the pages. Our results are based on considering a simpler caching model which we call the interval caching model . We relate traditional and interval caching policies under predictable load, and derive (near)-optimal replacement policies from their optimal interval caching counterparts.     

一种基于分散协作的Web缓存集群体系结构

Web对象缓存技术是一种减少Web访问通信量和访问延迟的重要手段，该文通过分析现有的各种Web缓存系统，提出了一种基于分散协作的Web缓存集群体系结构。该体系结构克服了集中式系统需要额外配备一台管理服务器的缺陷，消除了管理服务器瓶颈失效造成系统瘫痪的危险，减少由于管理服务器带来的延迟；同时消除了分散系统的缓存不命中情况下的多级转发的延迟和缓存内容重叠，提高了资源利用率和系统效率，具有良好的可扩展性和健壮性。     

一种新的基于连续哈希函数的合作式Web缓存系统

提出了一种新的基于连续哈希函数的合作式缓存系统。针对传统合作式缓存系统中多级转发造成的高时延和多重哈希计算问题，设计了一种高效的Web对象定位和路由模式，保证任意Web请求只需计算一次哈希且至多经过一次转发就可到达目标节点。采用失效-触发的策略来解决路由表一致性维护的问题，减少了网络开销，提高了系统的可扩展性和可靠性。仿真实验表明，该系统性能优于基于互联网缓存协议和缓存阵列路由协议的系统。     

Lease-based consistency schemes in the web environment

There are many methods to maintain consistency in the distributed computing environment. Ideally, efficient schemes for maintaining consistency should take into account the following factors: lease duration of replicated data, data access pattern and system parameters. One method used to supply strong consistency in the web environment is the lease method. During the proxy’s lease time from a web server, the web server can notify the modification to the proxy by invalidation or update. In this paper, we analyze lease protocol performance by the varying update/invalidation scheme, lease duration and read rates. By using these analyses, we can choose the adaptive lease time and proper protocol (invalidation or update scheme of the modification for each proxy in the web environment). As the number of proxies for web caching increases exponentially, a more efficient method for maintaining consistency needs to be designed. We also present three-tier hierarchies on which each group and node independently and adaptively choose the proper lease time and protocol for each proxy cache. These classifications of the scheme make proxy caching adaptive to client access pattern and system parameters.     

分布式视频服务器系统中的协同缓存策略

在分布式视频服务器系统中,利用协同缓存(CooperativeCaching)技术,可以达到充分利用系统中各服务器上的空闲内存,以形成一个更大的、逻辑上完整的协同缓存,提升总体的缓存命中率,进而提升整个系统性能的目的。文章就来对这一背景下的协同缓存技术进行研究,分析采用协同缓存的动因,比较几种传统的协同缓存机制,并提出了一种适合于分布式视频服务器系统的协同缓存策略。     

Coordinated multimedia object replacement in transcoding proxies

Finding replacement candidates for accommodating a new object is an important research issue in web caching. Due to the new emerging factors in the transcoding proxy and the aggregate effect of caching multiple versions of the same multimedia object, this problem becomes more important and complex as audio and video applications have proliferated over the Internet, especially in the environment of mobile computing systems. This paper addresses coordinated cache replacement in transcoding proxies. First, we propose an original model which determines cache replacement candidates on all candidate nodes in a coordinated fashion with the objective of minimizing the total cost loss for linear topology. We formulate this problem as an optimization problem and present a low-cost optimal solution for deciding cache replacement candidates. Second, we extend this problem to solve the same problem for tree networks. Finally, we conduct extensive simulations to evaluate the performance of our solutions by comparing with existing models.