分布式数据库复制实施策略中的冲突预防和解决

复制是分布式数据库实施策略中的重要一种，它能大大提高各结点的自治性，同时保证各结点数据副本之间的松散一致性，然而各结点自主的数据操作之间很可能发生冲突。针对这种情况，提出了设计分布式数据库时就积极地采取措施尽可能预防冲突发生；当冲突发生时，采用合理的策略来解决冲突。最后，以SQL Server2000为例来说明这种思想的具体应用。     

分布式数据库系统中数据一致性维护方法

讨论了在分布式数据系统中，对于各个数据库副本维护数据一致性的问题，介绍了Oracle8i数据库系统中数据复制的基本概念，基本原理，复制配置以及数据复制的基本配置和实现方法。     

分布式数据库系统的数据一致性研究

分布式数据库是数据在物理上分布而在逻辑上统一的数据库,如何维护其数据一致性是一个关键的技术问题.分析引起分布式数据库系统数据不一致的主要原因,研究分布式数据库数据一致性的基本原理,结合具体实例阐述基于ADO.Net实现分布式数据库系统数据一致性的有效方法.     

基于全局目录的分布式数据库数据一致性算法

针对分布式数据库中数据的分布性、事务执行的分布性和一些不可预测的软件错误和硬件故障等原因导致的数据不一致性问题,指出解决这些问题尚存在的困难,分析了消息队列法、事务控制法、复制控制法等分布式数据库中维护数据一致性的三种主要方法的缺点。在全局目录和分布式两阶段提交协议的基础上,提出了基于全局目录的分布式数据库数据一致性控制算法。该算法增强了分布式数据库中数据的一致性,节省了网络带宽,也提高了事务处理能力。     

WCSR:一个弱一致性的复制数据库系统

介绍了一个弱一致性的复制数据库系统ＷＣＳＲ。ＷＣＳＲ系统支持服务的移动性与断接,采用Ｒｅａｄ－Ａｎｙ－Ｗｒｉｔｅ－Ａｎｙ复制范型,通过周期同步方式维护系统的一致性,     

分布式数据库一致性维护算法

提出了一种维护分布式数据库的算法,克服了其他算法通信开销大、事务平均响应时间长、数据版本多等问题。该算法能保证原子数据的一致性,减少网络中的通信量,避免死锁的发生。     

基于Oracle高级复制的分布式数据库系统应用研究

该文以CIMS工程应用为背景,介绍了一种运用Oracle高级复制技术实现企业远程信息分布式处理的方案;详细讨论了实现中的数据一致性问题,并提出了通过设置手动复制、合理设置自动复制周期解决数据弱一致性和处理时间滞后问题的方法,以及基于分组方法解决各种数据冲突的实现策略。     

一种维护实时数据库一致性的新方法

本文研究了实时数据库中的一致性要求及现有并发控制技术的缺陷 ,进而提出一种对由现有调度技术生成的事务调度队列进行调整以保证实时数据库外部一致性要求 ,从而获得更佳性能的方法     

分布式数据库系统一致性方法

本文首先对分布式系统进行了概括的描述，包括分布式结构与集中式结构的主要差别，分布式系统的主要优点，以及分布式系统要解决的主要问题—一致性和透明性。文章第二部分讨论了两种一致性方法：两阶段提交和复制服务器。两阶段提交通过事务完整性维护数据一致性。复制服务器是一种解决维护分布式数据和管理分布式事务的固有问题的革命性方法。既适应分布式环境的实现，也满足用户在可用性，对信息立即访问，以及场地自治等方面的要求。     

一种基于数据相关性的优化数据一致性维护方法

针对数据一致性中的数据相关性问题,提出一种优化的数据一致性维护方法.在该方法中,数据对象按固定大小分块,并以数据块作为数据管理的基本单位;数据更新利用Bloom filter技术压缩表示,并进行双路径传播;发起方和协商方在一致性维护过程中,分别调用各自的协商算法检测和解决更新冲突;动态数据管理算法调节数据更新过程中的动态数据块变化,对数据块进行合并或分解.模拟测试结果表明,在选取适当范围内的分块大小时,该方法在一致性维护开销、动态性和鲁棒性方面均具有较好的性能.文中给出了选定适当分块大小的指导性方法.     

Adaptive trade‐off between consistency and performance in data replication

Replication is widely adopted in modern Internet applications and distributed systems to improve the reliability and performance. Though maintaining the strong consistency among replicas can guarantee the correctness of application behaviors, however, it will affect the application performance at the same time because there is a well‐known trade‐off between consistency and performance. Many real‐world applications favoring performance often choose to enforce weak consistency. Although there has been some work on flexible configuration of consistency, most focuses on design or deployment time. As the system settings constantly change during runtime, the tuning of the consistency‐performance trade‐off needs to be handled dynamically. Failing to do that will cause either underestimation or overestimation of the consistency and performance that can be achieved. Existing work does not well support the dynamic tuning of the aforementioned trade‐off in runtime, which is mainly because of the lack of an appropriate quantitative model of consistency and performance. In this work, based on our previous effort on the quantitative model of consistency and latency, we design a replication protocol, CC‐Paxos, to achieve an adaptive trade‐off between consistency and performance according to application preferences and runtime information. By design, CC‐Paxos is not bound to any specific underlying data stores. We have implemented CC‐Paxos and applied it to MySQL databases. And real experiments both within a data center and across data centers show that CC‐Paxos not only can dynamically adjust the delivered consistency in return for ensured performance but also outperforms MySQL Cluster in the case of strong consistency guarantee. Copyright © 2016 John Wiley & Sons, Ltd.     

移动计算环境下数据复制一致性研究

通过对移动计算环境下已复制数据一致性的研究,提出了一种新的数据复制控制协议。该协议对已复制数据库对象的读操作或写操作等临时信息进行探索,使单副本可串行化和最终一致性两个标准可以同时得到保证。文章最后还对协议的正确性进行了分析。     

保证多volume数据一致性的远程复制机制

提出了一种保证多 volume数据一致性的远程复制机制。其借鉴数据库系统中事务处理的基本思想 ,将多个 volume中相关联的更新作为一个原子事件向远程端复制,分析实现中如数据打包、故障恢复策略、I/O合并等关键问题 ,并给出了具体的实现方法。该远程复制机制解决了在基于存储层或基于逻辑卷方式下的大规模数据复制应用中,保证一组具有相关性数据在复制中的一致性和可用性问题。     

远程复制系统数据一致性研究与实现

针对远程数据复制容灾系统中的数据一致性问题,提出了保证数据一致性和视图一致性并优化系统性能的实现思想,即使用日志卷记录用户请求顺序,通过保持主、从两端数据卷上数据块的更新顺序来保证数据一致性,对于不同的数据类型采用不同的传输方法。论述了它的组织结构、实现流程以及关键技术。     

Local tests for consistency of support hyperplane data

Support functions and samples of convex bodies in R ⁿ are studied with regard to conditions for their validity or consistency. Necessary and sufficient conditions for a function to be a support function are reviewed in a general setting. An apparently little known classical such result for the planar case due to Rademacher and based on a determinantal inequality is presented and a generalization to arbitrary dimensions is developed. These conditions are global in the sense that they involve values of the support function at widely separated points. The corresponding discrete problem of determining the validity of a set of samples of a support function is treated. Conditions similar to the continuous inequality results are given for the consistency of a set of discrete support observations. These conditions are in terms of a series of local inequality tests involving only neighboring support samples. Our results serve to generalize existing planar conditions to arbitrary dimensions by providing a generalization of the notion of nearest neighbor for plane vectors which utilizes a simple positive cone condition on the respective support sample normals.This work partially supported by the Center for Intelligent Control Systems under the U.S. Army Research Office Grant DAAL03-92-G-0115, the Office of Naval Research under Grant N00014-91-J-1004, and the National Science Foundation under Grant MIP-9015281.Partially supported by the National Science Foundation under grant IRI-9209577 and by the U.S. Army Research Office under grant DAAL03-92-G-0320     

数据网格下基于时间戳的副本一致性模型研究

分析了目前数据网格环境下的副本一致性研究现状,提出一种基于时间戳的副本一致性模型（Replica Consistency Model Based on Timestamp,RCMTS）,克服了分布锁带来的时间延迟问题,并在模拟环境OptorSim下与其他几种传统的模型算法进行比较,实验结果表明该模型比传统算法更适合于网格环境中保持副本的一致性。     

Service for consistency management of replicas in data grid

Today, grid technology has evolved to the point where it is no longer a theory but a proven practice. It represents a viable direction for corporations to explore grid computing as an answer to their business needs within tight financial constraints. In general, grids enable the efficient sharing and management of computing resources for the purpose of performing large complex tasks. Data grid provides the data management features to enable data access, synchronization, and distribution of a grid. The main aim here is to ensure a efficient access and quality data, to improve the availability, and be able to continue delivering acceptable services. In such systems, these advantages are not yielded by means others than replication mechanisms. The effective use the replication technique involves several problems, in relation with the problem of the coherence maintenance of replicas. Our contribution consists new service for the consistency management in the data grid. This service combines between pessimistic and optimistic approaches, taking into account benefits of both approaches, to find a compromise between performance and quality. In addition, our service has been extended by a mechanism placement of replicas based on economics model.     

Solutions and debugging for data consistency in multiprocessors with noncoherent caches

We analyze two important problems that arise in shared-memory multiprocessor systems. Thestale data problem involves ensuring that data items in local memory of individual processors are current, independent of writes done by other processors.False sharing occurs when two processors have copies of the same shared data block but update different portions of the block. The false sharing problem involves guaranteeing that subsequent writes are properly combined. In modern architectures these problems are usually solved in hardware, by exploiting mechanisms for hardware controlled cache consistency. This leads to more expensive and nonscalable designs. Therefore, we are concentrating on software methods for ensuring cache consistency that would allow for affordable and scalable multiprocessing systems. Unfortunately, providing software control is nontrivial, both for the compiler writer and for the application programmer. For this reason we are developing a debugging environment that will facilitate the development of compiler-based techniques and will help the programmer to tune his or her application using explicit cache management mechanisms. We extend the notion of a race condition for IBM Shared Memory System POWER/4, taking into consideration its noncoherent caches, and propose techniques for detection of false sharing problems. Identification of the stale data problem is discussed as well, and solutions are suggested.     

混合云环境下利用世系保障数据一致性的研究

混合云环境下,公有云与私有云共同为用户提供服务,公有云中的应用可能需要频繁读取私有云中的数据,通过复制私有云中的副本到公有云中可降低网络开销,但不同云中文件副本的动态更新会导致云中各个副本的不一致性。提出了一致性服务,该服务由一致性维护模块和一致性检测与恢复模块两个部分组成。一致性维护模块通过发送文件的更新消息的方法维护副本的一致,降低了系统的响应时间;一致性检测与恢复模块利用世系的思想,通过对比副本的世系记录来检测副本的一致性,可将副本不一致状态恢复成一致状态。实验证明混合云下利用世系一致性服务是可行的,由此带来的通信和存储开销在可接受范围内。     

基于伪标签一致度的不平衡数据特征选择算法

针对大多数粒计算特征选择算法未考虑数据的类别不平衡性的问题,提出一种融合伪标签策略的类别不平衡数据特征选择算法.首先,为了便于研究类别不平衡数据特征选择算法,重新定义样本和数据集一致度的概念,并设计了相应特征选择的贪婪前向搜索算法;其次,引入伪标签策略以平衡数据的类别分布,并将所学样本的伪标签融入一致性测度中,以构造伪...