Roam: A Scalable Replication System for Mobility

Nomadic users require replication to store copies of critical data on their mobile machines while disconnected or poorly connected. Existing replication services do not provide all classes of mobile users with the capabilities they require, which include: the ability for direct synchronization between any two replicas, support for large numbers of replicas, and detailed control over what files reside on their local (mobile) replica. Mobile users must adapt their behavior to match the level of service provided by today's replication systems, thereby hindering mobility and costing additional time, money, and systems management. Roam is a replication system designed to satisfy the requirements of the mobile user. Roam is based on the Ward Model, a replication architecture for mobile environments. Using the Ward Model and new distributed algorithms, Roam provides a scalable replication solution for the mobile user. We describe the motivation, design, and implementation of Roam and report its performance.     

一种适应性复制协议的研究与设计

传统的复制协议往往对如何适应遗留系统和引入复制技术对系统性能造成的影响方面考虑不够深入.本文在分析传统复制协议的基础上,提出了一种新协议.其设计采用复制实例数目可动态伸缩的逻辑令牌环结构,因而在满足可用性需求的前提下,可支持不同分布系统对适应性的需求,同时保证引入复制技术后系统的性能.文中详细论述了相应的系统模型和服务请求的处理,并通过与几种典型的传统复制协议的比较,证明了该协议的可行性.     

Replication Requirements in Mobile Environments

Replication is extremely important in mobile environments because nomadic users require local copies of important data. However, today's replication systems are not mobile-ready. Instead of improving the mobile user's environment, the replication system actually hinders mobility and complicates mobile operation. Designed for stationary environments, the replication services do not and cannot provide mobile users with the capabilities they require. Replication in mobile environments requires fundamentally different solutions than those previously proposed, because nomadicity presents a fundamentally new and different computing paradigm. Here we outline the requirements that mobility places on the replication service, and briefly describe ROAM, a system designed to meet those requirements.     

Replication enabled distributed cache invalidation method: replication enabled distributed cache management system for wireless mobile networks

This work proposes a replication scheme that is implemented on top of a previously proposed system for MANETs that cache submitted queries in special nodes, called query directories, and uses them to locate the data (responses) that are stored in the nodes that first request them, called caching nodes. The system, which was named distributed cache invalidation method (DCIM), includes client‐based mechanisms for keeping the cached data consistent with the data source. In this work, we extend DCIM to handle cache replicas inside the MANET. For this purpose, we utilize a push‐based approach within the MANET to propagate the server updates to replicas inside the network. The result is a hybrid approach that utilizes the benefits of pull approaches for client server communication and those of push approaches inside the network between the replicas. The approach is analyzed analytically, and the appropriate number of replicas is obtained, where it was concluded that full replication of the indices of data items at the query directory and two‐partial replication of the data items themselves makes most sense. Simulation results based on ns2 demonstrate the ability of the added replication scheme to lower delays and improve hit ration at the cost of mild increases in overhead traffic. Copyright © 2013 John Wiley & Sons, Ltd.     

一个视频网格系统的副本策略

文章在分析了目前流行的一些视频点播负载均衡技术的优缺点上,提出结合有效的副本策略、流言协议和超节点等相关技术,构建了一个视频网格系统的副本策略模型,并分析了此模型的整个视频点播过程和节目副本在节点间的传播情况。最后,对中心骨干网络和相关节点进行了一系列的实验模拟,证实了模型系统的可行性及其带来的好处。     

一种面向负载平衡的主动复制技术

针对主动复制容错技术中存在资源浪费及请求响应时间长的问题,提出了一种适用于请求-状态相关及请求-状态无关的系统模型、面向负载平衡的主动复制技术。容错组成员都能根据当前的负载信息列表决定是否执行接收到的请求,只有负载最轻的成员执行当前请求。组中各成员同时执行不同的请求,并直接返回请求响应结果,从而在充分利用主动复制技术中,在引入冗余资源的基础上缩短了请求的平均响应时间。实验结果显示,该技术能缩短请求的平均响应时间,提高系统运行效率;在请求-状态相关的系统模型下,请求的平均响应时间跟与状态相关的请求数目成正比。     

一种基于访问频率的非结构化P2P复制策略

旨在通过数据复制来提高非结构化P2P系统的数据访问效能,提出了基于访问频率的复制策略—AFRE算法,该算法通过赋予不同时间片的访问记录不同的权重,计算数据的局部访问频率,并将适量的数据副本放置到节点度较大的节点.实验证明,提出的复制策略在副本总数明显减少的情况下,能够获得较好的平均查询长度及优于其他常用复制策略的查询成功率.     

基于optorsim的网格作业调度和数据复制策略仿真

利用网格仿真软件optorsim，在不同的数据网格场景中测试研究了几种作业调度和数据复制策略对网格的影响。结果表明作业调度和数据复制策略的选择对网格资源利用率和平均作业执行时间的影响很大。     

数据复制在水利领域中的应用研究

在简要说明数据复制技术定义与特点的基础上,针对国家水利行业管理部门地理上的分布造成各个管辖区域的水利数据呈现出分散的现状,利用Oracle10g高级复制服务器,为水利资源数据分中心数据库数据维护管理系统设计了一种新的复制模型,该模型将多宿主复制模式与快照复制模式进行了有机的结合.实验结果表明,新的混合复制模型避免了传统...     

一种基于纠删码的分布式存储容灾的设计与实现

在广域的文件存储系统中,每一个节点的可用性是至关重要的,这就需要在该系统中引入一定的冗余来提高每个存储节点的可用性以对存储的数据起到保护的作用。传统的冗余方式是完全复制,但随着副本个数的增加,该机制在存储空间上的浪费暴露无遗,而且在一定程度上这对整个系统性能的提高几乎没有帮助。本丈提出一种基于纠删码的分布式网络容灾模型,在空间冗余度和性能上均优于传统的存储模型。     

HLR Replication Protocols for Global Mobility Management in PCS Networks

The new trend for PCS networks is to provide mobile users with large-scalemobile capability across many service areas. In this scenario, global databasemanagement for PCS networks has become an increasingly important researchissue.In this paper, we examined two replicated database strategies,single-replica (SR) and multiple-replica (MR), for large-scalemobility of per-user data management in personal communicationnetworks. The SR strategy uses a single replica approach of HLR.The MR strategy replicates the per-user data of HLR in manyregions. The two strategies are based a partial replicationscheme, and a primary copy method is used to maintain replicas'consistency. Our numerical results show that the MR strategyoutperforms the SR strategy in most situations; however, it may beworse when the probability of a mobile user visiting a foreignregion is high and the query rates from other foreign regions arelow. Additionally, the number of replicas should be compact in theMR strategy in order to achieve a reasonable query response time.Therefore, we propose an adaptive multiple replication protocol tochoose a suitable replication strategy and to decide the optimizednumber of replicas.     

高精度微结构聚合物光栅的复制技术

光栅复制是降低光栅制造成本,提高产量的一条有效途径。研究了利用紫外压印技术复制微结构光栅的方法。使用玻璃基底矩形浮雕结构的微结构光栅作为母光栅,给出了利用聚二甲基硅氧烷(PDMS)制作光栅模具和在光敏聚合物材料上复制微结构光栅的详细过程。经过优化工艺条件,成功地复制了一系列不同周期和开口比的微结构光栅,测试了复制光栅和母光栅的衍射图像和0级与±1级的衍射强度,结果表明,复制光栅和母光栅的衍射图像与光强分布基本一致。     

实体鉴别与复制鉴别

受理鉴别和彩信鉴别,就可以满足交易和网络的基本安全需要,但不能彻底解决复制攻击问题,特别是在网络安全上又多了一个防Do S攻击的问题。为此,CPK鉴别系统将受理鉴别划分为离线鉴别和在线鉴别,以在线鉴别对付对门户（网站、服务器）的复制攻击和Do S攻击。     

Optimal Replication for a Specific System Objective

This paper defines component replication as the concept of using two or more i.i.d. components at a specific location in a system design. Both parallel and series physical connections are used to place replicate components into a system. The choice of parallel or series depends upon why the components are being made replicate and is complicated by the fact that a component might be used for several functions. A given physical connection can be logically in series for some situations and logically in parallel for others. Reducing system unavailability is one important use of component replication. The mathematical models relating replication and unavailability are often complex, and casual inspection does not reveal which components should be replicated to reduce unavailability. This paper develops a method for determining which components can be replicated (and how) for the greatest unavailability reduction. The method was used to study three system designs. For each design it was possible to identify several components which could be replicated with an associated reduction in unavailability at reasonable cost. In addition it was possible to demonstrate or confirm that replicating most components does not reduce unavailability. Applying this method helps the designer develop insight concerning the role of replication (in a system design) without complex calculations and interpretations.     

基于层次结构的远程数据复制系统

针对传统的集中式复制结构存在的单点瓶颈和扩展性差等不足，提出了基于层次化结构的数据复制系统。通过将复制节点之间的拓扑结构抽象为图，提出了使用最小代价树的方式对节点进行组织。通过将数据由树根逐层扩散复制到树叶，使得在保证数据一致性的同时，分散了主节点的负荷。最后分析了使用复制数据进行灾难恢复的过程，并通过原型实验对集中式与层次化复制结构进行了比较。     

基于分区的无线传感网节点复制攻击检测方法

 无线传感器网络部署在敌方区域时,节点可能被俘获,其信息被复制并散布到网络中进行破坏活动.这种攻击隐蔽,破坏力较强.本文提出了基于分区的节点复制攻击检测方法,通过将部署区域分区,并建立基于跳数的坐标,可有效检测节点复制攻击.仿真实验表明:本方法耗能少,效率高且无需辅助节点.     

广电CRM应急系统设计与实现

广电业务随着互联网的发展,企业运作越依赖于IT架构,对信息系统运作的稳定性和可靠性的要求就越高,业务连续性将是最重要的竞争力.为保证24×7运营,除灾难恢复外,还需要制定业务连续综合计划.保证高度可用性和连续运营能力是企业成功的关键.企业需保证系统关键应用和数据受到保护并处于可用状态,发生停机或灾难后运营可以继续.通过利用底层数据复制技术和逻辑复制技术构建的应急系统,切换回切时长在1 min以内,保障了业务连续性,对用户无感知.     

Static Replication Strategies for Content Availability in Vehicular Ad-hoc Networks

This study investigates replication strategies for reducing latency to desired content in a vehicular peer-to-peer network. We provide a general constrained optimization formulation for efficient replication and study it via analysis and simulations employing a discrete random walk mobility model for the vehicles. Our solution space comprises of a family of popularity based replication schemes each characterized by an exponent n. We find that the optimal replication exponent depends significantly on factors such as the total system storage, data item size, and vehicle trip duration. With small data items and long client trip durations, n ∼ 0.5 i.e., a square-root replication scheme provides the lowest aggregate latency across all data item requests. However, for short trip durations, n moves toward 1, making a linear replication scheme more favorable. For larger data items and long client trip durations, we find that the optimal replication exponent is below 0.5. Finally, for these larger data items, if the client trip duration is short, the optimal replication exponent is found to be a function of the total storage in the system. Subsequently, the above observations are validated with two real data sets: one based on a city map with freeway traffic information and the other employing encounter traces from a bus network.     

P2P网络中基于语义组的自适应资源预测复制算法

在众多P2P资源搜索技术中,基于热点资源复制的搜索被重点关注。本文在考虑节点语义的情况下,基于ARIMA预测模型提出了自适应热点资源复制方法(semantic-aware replication based on ARIMA,SARA)。SARA充分考虑了无结构P2P网络中语义拓扑结构的特性,引入ARIMA预测模型,对于可能出现的热点资源提前进行副本复制。实验表明,SARA有效地避免了不必要的副本复制浪费,减小了复制开销,同时保证了较高的副本查询效率。     

移动数据库中数据复制同步处理策略分析

在实际的数据系统运行过程中,关联事务结果集会出现模型结合方面的问题,所以需要通过算法的更新来促进数据库的稳定运行。有关研究结果显示,数据库中的数据复制同步处理和常规的数据复制处理,有着实质性的区别,关联事务结果集模型会在信息化的基础上对移动事物进行优先处理,这样会有效的改善移动复制的结果,减少复制同步处理过程中存在的各种空间消耗问题。文章指出,更新算法在使用的过程中,会显著地提高数据处理和传输的效果,保证客户动态的可操控性。