面向大规模机群的可扩展OLAP查询技术

大数据时代,由中低端硬件组成的大规模机群逐渐成为海量数据处理的主流平台之一.然而传统基于高端硬件平台设计的并行OLAP查询算法并不适应这种由不可靠计算单元组成的大规模并行计算的环境.为改善其在新计算环境下的的扩展性和容错性,该文对传统数据仓库的数据组织模式及处理模式进行改造,提出了全新的无连接雪花模型和TRM执行模型.无连接雪花模型基于层次编码技术,将维表层次等关键信息压缩进事实表,使得事实表可以独立处理数据,从数据模型层保证了数据计算的独立性;TRM执行模型将OLAP查询的处理抽象为Transform、Reduce、Merge3个操作,使得OLAP查询可被划分为众多可并行执行的独立子任务,从执行层保证了系统的高度可扩展特性.在性能优化方面,该文提出了Scan-index扫描和跳跃式扫描算法,以尽可能地减少I/O访问操作;设计了并行谓词判断、批量谓词判断等优化算法,以加速本地计算速度.实验表明:LaScOLAP原型可以获得较好的扩展性和容错性,其性能比HadoopDB高出一个数量级.     

OLAP查询多维数据的新模型

针对目前现有的OLAP查询机制,讨论了一种新的模型——统计树。这种模型可以应用到OLAP中,并能够有效提高OLAP查询多维数据的速度。     

网络相关媒体流缓存管理策略NRC

Internet网络上媒体流的应用受限于应用时的网络状况，如时延、包丢失率等．本文研究通过在网络边缘处设置缓存代理来减小这些影响，提出一种新的缓存管理算法NRC，即接入媒体流服务时，用户以两种方式获取媒体流对象：一部分对象内容从代理缓存中获取，而另一部分对象内容则直接从流媒体源服务器处传输而来；从而加速媒体流接入服务，提高媒体流服务质量,算法同网络特性和媒体流特性相关．最后仿真实验证实同网络和流媒体特性相关的缓存管理算法NRC可以很好地减少服务延迟和提高媒体流的总体服务质量．     

一种Internet上流媒体代理高速缓存的框架

文章采用代理高速缓存技术解决Internet上流媒体传输时瓶颈带宽对传输质量的影响，分析了现有Web缓存技术用于音频、视频等连续媒体对象的不足，提出了一种新的流媒体代理高速缓存的框架，讨论了框架中各模块实现的关键技术。     

动态更新实物化视图以提高OLAP查询效率

在数据仓库系统中,OLAP查询一般都涉及多表连接和分组聚集两部分操作,提高这些查询的性能成为提高OLAP响应速度的关键。利用实物化视图,可以准确地计算并保存表连接或聚集等耗时较多的操作的结果。研究基于查询频率的实物化视图的更新算法,可以使实物化视图得到最大效率的使用,明显地缩短查询的响应时间,从而提高OLAP的查询效率。     

基于J2EE平台集群服务的分布式缓存队列模型

集群缓存足提高J2FE(Java 2 Entcrprisc Edition)应用程序可扩展性能的关键技术,但目前J2EE提供的集群技术对于集群缓存的性能处理还存在一定的不足,该文在分析、12EE集群缓存技术的应用基础上,提出一种分布式缓存队列模型,可以有效地解决集群中的可靠性、可扩展性和失败转发等问题。实验表明,采用分布式缓存队列模型能提高集群的访问效率,是一种可行的解决方案。     

基于流行度预测的互联网+电视节目缓存调度算法

针对互联网+电视平台为提高热点节目命中率而过渡消耗存储空间的问题,提出一种基于流行度预测的节目缓存调度算法PPRA(popularity prediction replication algorithm).首先,在对实际测量数据进行统计与分析的基础上,使用随机森林(random forests, RF)算法构建节目流行度预测模型.同时,针对所选特征存在的“维数灾难”问题,利用主成分分析法(principal component analysis, PCA)实施特征降维处理,以实现视频流行度预测值的快速计算.然后基于节目流行度预测数据调度缓存中的节目.最后以某广电运营商130万用户120 d的收视数据为例,对PPRA算法进行实验.实验结果表明,在保证一定缓存命中率前提下,与LRU,LFU算法相比,PPRA算法仅需30%的存储空间,可有效降低互联网+电视平台的建设成本.     

Caching Scheme Could Boost Developing World's Internet Access

Topics include a caching scheme that could improve Internet access in the developing world, a software tool that eliminates computer freezes, and gender-recognition software that promises to make advertising more effective.     

Designing Efficient and Robust Caching Algorithms for Streaming-on-Demand Services on the Internet

Content Delivery Networks (CDN) have been used on the Internet to cache media content so as to reduce the load on the original media server, network congestion, and latency. Due to the large size of media content compared to normal web objects, current caching algorithms used in the Internet are no longer suitable. This paper presents a high-performance prefetch system that accommodates user time-varying behavior. A hybrid caching technique, which combines prefetch and replacement algorithms, is also introduced. The robustness of the cache system against imperfect user request information is evaluated using three request noise models. Two prefetch performance indices are also presented to help content administrators in deciding when to update the user request profile for caching algorithms.     

SProxy: A Caching Infrastructure to Support Internet Streaming

Many algorithmic efforts have been made to address technical issues in designing a streaming media caching proxy. Typical of those are segment-based caching approaches that efficiently cache large media objects in segments which reduces the startup latency while ensuring continuous streaming. However, few systems have been practically implemented and deployed. The implementation and deployment efforts are hindered by several factors: 1) streaming of media content in complicated data formats is difficult; 2) typical streaming protocols such as RTP often run on UDP; in practice, UDP traffic is likely to be blocked by firewalls at the client side due to security considerations; and 3) coordination between caching discrete object segments and streaming continuous media data is challenging. To address these problems, we have designed and implemented a segment-based streaming media proxy, called SProxy. This proxy system has the following merits. First, SProxy leverages existing Internet infrastructure to address the flash crowd. The content server is now free of the streaming duty while hosting streaming content through a regular Web server. Thus, UDP based streaming traffic from SProxy suffers less dropping and no blocking. Second, SProxy streams and caches media objects in small segments determined by the object popularity, causing very low startup latency, and significantly reducing network traffic. Finally, prefetching techniques are used to pro-actively preload uncached segments that are likely to be used soon, thus providing continuous streaming. SProxy has been extensively tested and we show that it provides high quality streaming delivery in both local area networks and wide area networks (e.g., between Japan and the U.S.).     

A Probe-Based Technique to Optimize Join Queries in Distributed Internet Databases

An adaptive probe-based optimization technique is developed and demonstrated in the context of an Internet-based distributed database environment. More and more common are database systems which are distributed across servers communicating via the Internet where a query at a given site might require data from remote sites. Optimizing the response time of such queries is a challenging task due to the unpredictability of server performance and network traffic at the time of data shipment; this may result in the selection of an expensive query plan using a static query optimizer. We constructed an experimental setup consisting of two servers running the same database management system connected via the Internet. Concentrating on join queries, we demonstrate how a static query optimizer might choose an expensive plan by mistake. This is due to the lack of a priori knowledge of the run-time environment, inaccurate statistical assumptions in size estimation, and neglecting the cost of remote method invocation. These shortcomings are addressed collectively by proposing a probing mechanism. An implementation of our run-time optimization technique for join queries was constructed in the Java language and incorporated into an experimental setup. The results demonstrate the superiority of our probe-based optimization over a static optimization. Received 6 February 1999 / Revised 15 February 2000 / Accepted 10 May 2000     

Policies for cyberspace — Illegal content on the Internet

Current estimates suggest that by the year 2000 some 200 million users will be logged on to the Internet worldwide. But this is not a passive medium for the user simply to observe. Each individual has the opportunity to establish their own presence on the Net. Unless prevented from doing so, either by technological control or regulation, the individual is free to access and publish what they like.     

Answers to Queries to Internet: An Optimal Generation Strategy

Representation of the answers to a query to Internet as a list of hypertext references to found objects is studied. Optimization of the strategy for choosing between static and dynamic references by criteria of server performance and reliability of information on an object is investigated. A probabilistic model is developed. Two strategies providing 100% reliability and admitting obsolete information with some probability are designed. Formulas for choosing a strategy are derived. Examples are given to illustrate their application to exponential distributions admitting an analytical solution. More complex distributions require the application of numerical methods of inverse Laplace transformation, integration, and optimization.     

网上银行的安全问题及对策

网上银行以网络技术为手段,向客户提供信息服务和金融交易服务,是一种新兴的银行服务模式,给用户办理银行业务提供了快捷和便利。通过对网上银行发展的现状和存在的安全问题进行分析,提出了解决网上银行安全问题的对策建议,旨在促进网上银行健康有序地发展。     

基于OLAP的网络广告投放分析系统的设计与实现*

随着Internet的普及,网络广告以其独特的优势成为企业参与市场经济竞争的重要手段。如何分析广告的市场与受众,从而有针对性地投放广告,是现代企业信息化管理的必然选择。以OLAP体系结构为基础,设计并实现了一个网络广告投放分析系统,详细介绍了其设计思想和体系结构,并对系统的各部分功能进行了分析,还就一些具体的实际问题提出了解决方案。     

Caching for Web Searching

Abstract. We study Web Caching when the input sequence is a depth first search traversal of some tree. There are at least two good motivations for investigating tree traversal as a search technique on the WWW: First, empirical studies of people browsing and searching the WWW have shown that user access patterns commonly are nearly depth first traversals of some tree. Secondly (as we will show in this paper), the problem of visiting all the pages on some WWW site using anchor clicks (clicks on links) and back button clicks—by far the two most common user actions—reduces to the problem of how best to cache a tree traversal sequence (up to constant factors). We show that for tree traversal sequences the optimal offline strategy can be computed efficiently. In the bit model, where the access time of a page is proportional to its size, we show that the online algorithm LRU is (1 + 1/ɛ) -competitive against an adversary with unbounded cache as long as LRU has a cache of size at least (1+ ɛ) times the size of the largest item in the input sequence. In the general model, where pages have arbitrary access times and sizes, we show that in order to be constant competitive, any online algorithm needs a cache large enough to store Ω(log n) pages; here n is the number of distinct pages in the input sequence. We provide a matching upper bound by showing that the online algorithm Landlord is constant competitive against an adversary with an unbounded cache if Landlord has a cache large enough to store the Ω(log n) largest pages. This is further theoretical evidence that Landlord is the ``right' algorithm for Web Caching.     

ICN中的一种协作缓存机制

为了克服现有 Internet 架构存在的众所周知的缺点,未来网络的研究成为热点.ICN(information-centric networking)在众多新架构中正逐渐被公认为最有前途的方案.它把传输的内容缓存到沿途的节点.高效的缓存机制是它的一个重要研究方面.为此,提出了一种在分布式缓存机制中嵌入中心式缓存决策的机制(content-aware placement,discovery and replacement,简称APDR),它把内容的放置、发现、替换统一起来考虑,实现内容的有序缓存,提高网络的性能.APDR的主要思想是：Interest报文除了携带对内容的请求以外,还收集沿途各节点对该内容的潜在需求、空闲缓存等信息,使得Interest的汇聚点和目的地节点可以据此计算出一个缓存方案,并把该方案附加在Data报文上,通知返程途中的某些节点缓存该内容并设置指定的缓存时间.在多种实验条件下对APDR进行了仿真验证,结果表明,APDR 可以改善网络性能,包括缓存命中率、接入代价、替换数量、转发效率以及缓存鲁棒性等;而且APDR的额外开销也不大.     

基于NOMA-MEC的车联网任务卸载、迁移与缓存策略

在移动边缘计算(MEC)与非正交多路接入(NOMA)技术相结合的车联网系统中,针对用户处理计算密集型和时延敏感型任务时面临的高时延问题,提出了一种基于博弈论和Q学习的任务卸载、迁移与缓存优化策略.首先,对基于NOMA-MEC的车联网任务卸载时延、迁移时延与缓存时延进行建模;其次,采用合作博弈算法获得最优用户分组,以实现...