arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2009.08142cs.IRcs.LGcs.SImath.PRstat.ML
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网页变化率的在线估计算法

Online Algorithms for Estimating Change Rates of Web Pages

INRIA Sophia Antipolis(法国国家信息与自动化研究所索菲亚-安提波利斯研究中心);Indian Institute of Science(印度科学研究所)

Konstantin Avrachenkov, Kishor Patil, Gugan Thoppe

摘要:

搜索引擎维护不同网页的本地副本以提供快速搜索结果。这个本地缓存由网络爬虫保持最新,网络爬虫经常访问这些不同的页面以跟踪它们的变化。理想情况下,本地副本应在网页更改后立即更新。然而,有限的带宽可用性和服务器限制限制了抓取不同页面的频率。这带来了以下优化问题:最大化的新鲜度的本地缓存的爬行频率是在规定的范围内。虽然存在易于处理的算法来解决这个问题,但这些算法要么假设确切的页面更改率的知识,要么使用诸如MLE之类的低效方法来估计页面更改率。我们在这里讨论这个问题。我们提供了三个新的计划,在线估计的页面更改率,所有这些都有非常低的每次迭代的运行时间。第一个是基于大数定律,第二个是基于随机近似。第三个是第二个的延伸,包括一个重球动量项。所有这些方案仅需要关于页面改变过程的部分信息,即,他们只需要知道自从上次抓取的实例以来页面是否已经改变。我们的主要理论结果涉及这三个格式的渐近收敛性和收敛速度。事实上,我们的工作是第一次显示收敛的原始随机重球方法的梯度和噪声方差都是一致有界的。我们还提供了一些数值实验(基于真实和合成数据),以证明我们提出的估计优于现有的,如MLE。我们强调,我们的算法也很容易适用于数据库和网络库存管理的同步。

英文摘要:

A search engine maintains local copies of different web pages to provide quick search results. This local cache is kept up-to-date by a web crawler that frequently visits these different pages to track changes in them. Ideally, the local copy should be updated as soon as a page changes on the web. However, finite bandwidth availability and server restrictions limit how frequently different pages can be crawled. This brings forth the following optimization problem: maximize the freshness of the local cache subject to the crawling frequencies being within prescribed bounds. While tractable algorithms do exist to solve this problem, these either assume the knowledge of exact page change rates or use inefficient methods such as MLE for estimating the same. We address this issue here. We provide three novel schemes for online estimation of page change rates, all of which have extremely low running times per iteration. The first is based on the law of large numbers and the second on stochastic approximation. The third is an extension of the second and includes a heavy-ball momentum term. All these schemes only need partial information about the page change process, i.e., they only need to know if the page has changed or not since the last crawled instance. Our main theoretical results concern asymptotic convergence and convergence rates of these three schemes. In fact, our work is the first to show convergence of the original stochastic heavy-ball method when neither the gradient nor the noise variance is uniformly bounded. We also provide some numerical experiments (based on real and synthetic data) to demonstrate the superiority of our proposed estimators over existing ones such as MLE. We emphasize that our algorithms are also readily applicable to the synchronization of databases and network inventory management.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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