【作者】 张超群；

【导师】 张增芳； 李淘深；

【作者基本信息】 广西大学 ， 控制理论与控制工程， 2003， 硕士

【摘要】 随着Internet技术和Web服务的发展，Web流量继续以指数增长，造成网络带宽严重不足，用户面临的两大问题是网络阻塞和服务器过载，严重影响了Internet的持续发展。基于Internet的代理缓存技术是解决这些问题的一个主要和有效的技术，在国际上已经形成一个独立的主流研究领域。其中，一致性策略和替换策略的研究一直是提高代理缓存系统性能的两个研究方向，而如何将一致性策略和替换策略有机地结合起来，以便有效地提高代理缓存系统的性能是代理缓存技术的研究前沿。本文对基于Internet的代理缓存技术进行了比较深入地研究，主要完成了以下几方面的工作： 1、通过对代理缓存的一致性策略的研究，论述了自适应TTL机制是较好的弱一致性维护技术，它容易实现并能降低将灰本响应给用户的概率。 2、通过对代理缓存的替换策略的研究，论述了基于成本／价值模型的替换算法是较优的，但必须修正和简化其模型，使计算相对简单，又能体现Web的访问特性，减少延迟。 3、提出了一个新的性能评价指标——陈旧命中比。它体现了陈旧率和命中率的对比程度，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。 广西大学硕士论文 基于Internet的代理缓存技术研究 摘要 4、提出、设计和实现了自适应一致性一替换算法（即ACR算法人该算法包括一致性策略和替换策略两部分，一致性策略采用自适应TTL机制，替换策略是基于成本／价值模型的算法。ACR算法的独到之处在于将代理缓存的一致性策略和替换策略较好地结合起来，并体现Web的访问特性，保证以较小的代价从代理缓存中提供更新鲜的资源给用户，体现了将代理缓存的一致性策略和替换策略结合起来的优越性，同时提高了代理缓存系统的整体性能。通过 Trace－D＊ yen 4g拟实验，结果表明ACR算法在陈旧命中比上均忧于传统的几个替换算法，从而证明了新提出的ACR算法是合理、有效和实用的。更多还原

【Abstract】 With the development of Internet technologies and Web services, Web traffic still increases exponentially. It results in severe network bandwidth scarcity, network congestion and server overloading, which are the key issues affecting the continuous growing of the Internet. Proxy cache is the main and effective technique to solve these issues. Now it has become an international main research area in which the studies on consistency policies and replacement policies always are the two directions of research, while the front of research on proxy caching techniques is how to better incorporate these two policies which results in a desirable performance of a proxy caching system. In this paper, the research is made more thoroughly on the proxy caching techniques for the Internet. The main results are as follows.1.According to the research on proxy cache consistency policies, it is discussed that Adaptive TTL is more attractive in weak consistency policies, which can be easily implemented and reduce the probability of returning stale data to users.2.According to the research on proxy cache replacement policies, it is discussed that replacement algorithms based on cost/value model arepreferable. However, the model requires to be modified and simplified to easily calculate, to reflect Web access characteristics and to reduce access latency.3. A new performance metric called staleness-hit rate is proposed. It balances these two performance metrics. Therefore, it can better estimate all the algorithms of proxy cache and the overall performance of a proxy caching system.4. A new algorithm called ACR (Adaptive Consistency and Replacement algorithm) is proposed, designed and implemented. It incorporates cache consistency policy with cache replacement policy in which the cache consistency policy is Adaptive TTL mechanism, while the cache replacement policy is based on a cost/value model. It can better incorporate these two policies and reflect Web access characteristics. It also can guarantee returning the fresher data to users with the lower cost, which reflects the superiority of a combination of these two policies and improves the overall performance of a proxy caching system. Using Trace-Driven simulation, the results show that ACR algorithm is better than several traditional algorithms in staleness-hit rate, hence ACR algorithm proves to be rational, effective and practical.更多还原