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1.
一种域分布式合作Web缓存系统   总被引:7,自引:0,他引:7  
在分析Internet缓存协议(ICP)和基于集中管理的协作式Web缓存系统(CMCS)的基础上,提出了一种域分布合作Web缓存系统模型(DDCCS),该模型克服了ICP的缓存内容冗余问题和CMCS集中管理的不健壮问题,并能充分考虑各代理缓存器的处理能力和缓存能力,采用区间散化方法和加权区间片分配算法,使得各代理的负担更加均匀合理,在性能上较ICP和CMCS有较大的改进。  相似文献   

2.
合作式Web缓存系统的性能分析   总被引:5,自引:1,他引:5  
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.  相似文献   

3.
因特网中日益增长的内容获取需求促使学术界提出了多种以信息为中心的未来网络架构。这类架构将以主机为中心的通信模式转变为以内容为中心。信息中心网络(ICN)最重要的特征之一是利用内置缓存减少用户获取内容的时延、节省网络带宽和缓解网络拥塞。与传统的内容分发网络(CDN)、对等网络(P2P)和Web缓存系统相比,ICN缓存系统呈现出一系列的新特征。分析了缓存新特征对ICN研究带来的挑战;从多方面重点阐述了ICN缓存的优化方法,详细分析对比了不同缓存策略;指出了未来研究方向并总结全文。  相似文献   

4.
一种新的基于分区的多媒体代理协作管理策略   总被引:2,自引:0,他引:2  
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。  相似文献   

5.
为了进一步提升内容分发网络中代理缓存的整体性能,将一致性策略有机的融入到替换策略中,本文提出一种高效的自适应代理缓存一致性替换算法ACRA。本算法中的一致性策略采用了自适应TTL机制,替换策略是在分析了Web轨迹的基础上,找出用户访问Web内容的访问特性:访问再次发生的概率和访问内容大小的分布情况,并以此建立相应代价公式,作为替换标准中计算缓存内容价值的要素。通过Trace-Driven摸拟实验,表明了ACRA在命中陈旧比上优于传统的几个替换算法。  相似文献   

6.
集中管理式Web缓存系统及性能分析   总被引:5,自引:0,他引:5  
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.  相似文献   

7.
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.  相似文献   

8.
流媒体代理缓存技术研究   总被引:1,自引:0,他引:1  
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。  相似文献   

9.
一种新的代理缓存替换策略   总被引:7,自引:0,他引:7  
代理缓存的替换策略事实上可以看做排序问题,排序的标准可能有多种,寻找一个好的代理缓存的替换策略就是寻找一个能够反映真实Web访问特性的标准,基于文档大小的替换策略是一种简单实用的策略,但是并未全部利用WWW访问特性,根据在代理缓存日志中对各种访问特性的分析,使用文档大小,访问频率、文档访问剩余寿命作为计算文档价值的要素,提出了一种新的替换策略,这种策略同时具有较高的文档命中率和文档字节命中率,最后给出了基于日志的模拟。  相似文献   

10.
为了在Web机群代理中有效定位缓存对象在节点机中的位置,必须实现单一缓存映像,以隐藏机群的分布和异构特性,为客户提供一致的缓存资源。为解决该问题,文中首先提出一个缓存摘要管理器体系结构,该结构基于各个缓存节点机的摘要、结合负载平衡信息,可有效定位缓存节点机,然后给出了机群代理中缓存节点机与缓存摘要管理器的实现方法。  相似文献   

11.
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  相似文献   

12.
The sharing of caches among proxies is an important technique to reduce Web traffic, alleviate network bottlenecks, and improve response time of document requests. Most existing work on cooperative caching has been focused on serving misses collaboratively. Very few have studied the effect of cooperation on document placement schemes and its potential enhancements on cache hit ratio and latency reduction. We propose a new document placement scheme which takes into account the contentions at individual caches in order to limit the replication of documents within a cache group and increase document hit ratio. The main idea of this new scheme is to view the aggregate disk space of the cache group as a global resource of the group and uses the concept of cache expiration age to measure the contention of individual caches. The decision of whether to cache a document at a proxy is made collectively among the caches that already have a copy of this document. We refer to this new document placement scheme as the Expiration Age-based scheme (EA scheme). The EA scheme effectively reduces the replication of documents across the cache group, while ensuring that a copy of the document always resides in a cache where it is likely to stay for the longest time. We report our study on the potentials and limits of the EA scheme using both analytic modeling and trace-based simulation. The analytical model compares and contrasts the existing (ad hoc) placement scheme of cooperative proxy caches with our new EA scheme and indicates that the EA scheme improves the effectiveness of aggregate disk usage, thereby increasing the average time duration for which documents stay in the cache. The trace-based simulations show that the EA scheme yields higher hit rates and better response times compared to the existing document placement schemes used in most of the caching proxies.  相似文献   

13.
The Internet now offers more than just simple information to the users. Decision makers can now issue analytical, as opposed to transactional, queries that involve massive data (such as, aggregations of millions of rows in a relational database) in order to identify useful trends and patterns. Such queries are often referred to as On-Line-Analytical Processing (OLAP). Typically, pages carrying query results do not exhibit temporal locality and, therefore, are not considered for caching at Internet proxies. In OLAP processing, this is a major problem as the cost of these queries is significantly larger than that of the transactional queries. This paper proposes a technique to reduce the response time for OLAP queries originating from geographically distributed private LANs and issued through the Web toward a central data warehouse (DW) of an enterprise. An active caching scheme is introduced that enables the LAN proxies to cache some parts of the data, together with the semantics of the DW, in order to process queries and construct the resulting pages. OLAP queries arriving at the proxy are either satisfied locally or from the DW, depending on the relative access costs. We formulate a cost model for characterizing the respective latencies, taking into consideration the combined effects of both common Web access and query processing. We propose a cache admittance and replacement algorithm that operates on a hybrid Web-OLAP input, outperforming both pure-Web and pure-OLAP caching schemes.  相似文献   

14.
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 Hk/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.  相似文献   

15.
研究了代理服务器在流媒体传输和缓存方面对于网络带宽的消耗以及在缓存过程中内存分配和管理等方面存在的问题;在分析了现有的流媒体代理缓存技术的基础上,提出了基于代理服务器的流媒体动态共享缓存(DSB)算法.分析和实验结果表明,与现有的缓存技术相比,DSB算法能够有效地提高缓冲区的利用率,节省代理服务器的内存资源,节省网络带宽,同时能够为更多的客户端请求提供服务,并且可以有效地缩短请求延时.  相似文献   

16.
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.  相似文献   

17.
Building a large and efficient hybrid peer-to-peer Internet caching system   总被引:2,自引:0,他引:2  
Proxy hit ratios tend to decrease as the demand and supply of Web contents are becoming more diverse. By case studies, we quantitatively confirm this trend and observe significant document duplications among a proxy and its client browsers' caches. One reason behind this trend is that the client/server Web caching model does not support direct resource sharing among clients, causing the Web contents and the network bandwidths among clients to be relatively underutilized. To address these limits and improve Web caching performance, we have extensively enhanced and deployed our browsers-aware framework, a peer-to-peer Web caching management scheme. We make the browsers and their proxy share the contents to exploit the neglected but rich data locality in browsers and reduce document duplications among the proxy and browsers' caches to effectively utilize the Web contents and network bandwidth among clients. The objective of our scheme is to improve the scalability of proxy-based caching both in the number of connected clients and in the diversity of Web documents. We show that building such a caching system with considerations of sharing contents among clients, minimizing document duplications, and achieving data integrity and communication anonymity is not only feasible but also highly effective.  相似文献   

18.
符青云  刘心松 《计算机工程》2007,33(11):120-122
提出了一种基于全局内存对象缓冲池的高性能分布式Web Proxy模型,通过在系统范围内构建类似于分布式共享存储器系统的缓冲池,并将分布式Web Proxy系统中访问最频繁的Web对象置于其中,则Web对象的平均服务时间缩短,提高了系统性能。通过实际Proxy服务器的访问日志进行了系统性能仿真,结果表明,该机制可以提高分布式Web Proxy服务器的性能。  相似文献   

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