自适应区间配置在关联规则并行采掘中的作用

现行的采掘关联规则的并行算法基于经典的层次算法.该方法在每一次重复扫描数据库时都需要一次同步,这种同步运算对于共享内存多处理器并行机来说极大地降低了采掘性能,这种低效主要源于对共享的I/O通道的竞争.该文提出了在共享内存多处理机上采掘关联规则的异步算法APM.在APM中,所有参与计算的处理器能独立地产生备选集和计算支持度.而且,APM所需的扫描数据库的次数比层次方法所需的更少.该文还提出了一种增强APM的技术,使得该算法的性能对于数据分布更具有鲁棒性.文中实现了APM的变种算法,还实现了Apriori的并行版本Count Distribution算法.在SGI Power Challenge SMP并行机上,进行了性能分析,结果表明所提出的异步算法APM具有更好的性能和可扩展性.     

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.     

Oracle高级复制技术及其实现

数据复制技术是在分布式数据库环境中复制和维护数据库对象的重要技术。本文介绍了Oracle数据复制技术及其实现过程,并举一实例介绍了如何在实际应用中使用该技术。     

Efficient Integration of Compiler-Directed Cache Coherence and Data Prefetching

Cache coherence enforcement and memory latency reduction and hiding are very important and challenging problems in the design of large-scale distributed shared-memory (DSM) multiprocessors. We propose an integrated approach to solve these problems through a compiler-directed cache coherence scheme called the Cache Coherence with Data Prefetching (CCDP) scheme. The CCDP scheme enforces cache coherence by prefetching the potentially stale references in a parallel program. It also prefetches the non-stale references to hide their memory latencies. To optimize the performance of the CCDP scheme, some prefetch hardware support is provided to efficiently handle these two forms of data prefetching operations. We also developed the compiler techniques utilized by the CCDP scheme for stale reference detection, prefetch target analysis, and prefetch scheduling. We evaluated the performance of the CCDP scheme via execution-driven simulations of several numerical applications from the SPEC CFP95 and the Perfect benchmark suites. The simulation results show that the CCDP scheme provides significant performance improvements for the applications studied, comparable to that obtained with a full-map hardware cache coherence scheme.     

Collective communication: theory,practice, and experience

We discuss the design and high‐performance implementation of collective communications operations on distributed‐memory computer architectures. Using a combination of known techniques (many of which were first proposed in the 1980s and early 1990s) along with careful exploitation of communication modes supported by MPI, we have developed implementations that have improved performance in most situations compared to those currently supported by public domain implementations of MPI such as MPICH. Performance results from a large Intel Xeon/Pentium 4 (R) processor cluster are included. Copyright © 2007 John Wiley & Sons, Ltd.     

嵌套的计算系统进程级自适应抗衰重启策略研究及模型分析

执行细粒度的进程级软件抗衰可以进一步降低抗衰成本，提高软件可靠性。本文针对软件系统中进程间交互频繁多变且交互关系难以判定的特点，分析进程间控制、调用及数据访问的关系，重新定义了进程重启相关度，提出了自适应进程相关拓扑图的算法理论，从而制定了嵌套的进程级软件抗衰重启策略，并在此基础上构建了策略实施模型，从而为全面实现智能化的软件系统细粒度软件抗衰提供了支持。     

Adaptive locks: Combining transactions and locks for efficient concurrency

Transactional memory is being advanced as an alternative to traditional lock-based synchronization for concurrent programming. Transactional memory simplifies the programming model and maximizes concurrency. At the same time, transactions can suffer from interference that causes them to often abort, from heavy overheads for memory accesses, and from expressiveness limitations (e.g., for I/O operations). In this paper we propose an adaptive locking technique that dynamically observes whether a critical section would be best executed transactionally or while holding a mutex lock. The critical new elements of our approach include the adaptivity logic and cost–benefit analysis, a low-overhead implementation of statistics collection and adaptive locking in a full C compiler, and an exposition of the effects on the programming model. In experiments with both micro and macrobenchmarks we found adaptive locks to consistently match or outperform the better of the two component mechanisms (mutexes or transactions). Compared to either mechanism alone, adaptive locks often provide 3-to-10x speedups. Additionally, adaptive locks simplify the programming model by reducing the need for fine-grained locking: with adaptive locks, the programmer can specify coarse-grained locking annotations and often achieve fine-grained locking performance due to the transactional memory mechanisms.     

多副本分布式事务处理关键技术及典型数据库系统综述

数据复制是分布式数据库提高可用性的重要手段,通过在不同区域放置数据库的部分副本,还可以提高本地读写操作的响应速度,增加副本数量也会提升读负载的线性扩展能力.考虑到这些优良特性,近年来国内外都出现了众多多副本分布式数据库系统,包括Google Spanner、CockroachDB、TiDB、OceanBase等一系列主流的工业界系统,也出现了包括Calvin、Aria、Berkeley Anna等一系列优秀的学术界系统.然而,多副本数据库带来诸多收益的同时,也带来了一致性维护、跨节点事务、事务隔离等一系列挑战.总结分析现有的复制架构、一致性维护策略、跨节点事务并发控制等技术,对比几个代表性多副本数据库系统之间在分布式事务处理方面上的差异与共同点,并在阿里云环境下搭建跨区域的分布式集群环境,对几个代表性系统的分布式事务处理能力进行了实验测试分析.     

Sybase Replication Server12.0的复制服务器技术研究及应用

介绍了分布式数据库数据复制的概念和方法，着重探讨了Sybase Replication Server12.0复制服务器机制的基本原理和主要功能，给出了一个基于异构数据类型支持（HDS）的应用实例。     

分布式数据库的复制和分片

通过对集中式数据库和分布式数据库进行比较,指出集中式数据库在存储能力、访问速度等方面存在的问题;对分布式数据库中的数据复制和分片的概念、原则、方法进行了详细的论述;最后对数据复制和分片要解决的关键问题进行了分析。     

分布式数据库的复制和分片

该文通过对集中式数据库和分布式数据库进行比较,指出集中式数据库在存储能力,访问速度等方面存在的问题,对分布式数据库中的数据复制和分片的概念,原则,方法进行详细的论述,最后,对数据复制和分片要解决的关键问题进行分析。     

数据分布型sort-first并行图形绘制系统的研究与实现

sort-first体系结构常用来构建高性能并行图形绘制系统,基于immediate-mode的数据集中型Sort-first系统,对网络带宽高度依赖,网络带宽和归属计算易成为系统瓶颈,提出了一个基于retain-mode的数据分布型并行绘制系统,工作原理是将几何数据分布于绘制结点,并利用帧间相似性动态调整绘制结点上的数据分布以适应视角的改变,有效地降低了数据分布所需的传输开销,系统利用Cell结构来控制并行粒度,实验结果显示能以相对较低的并行开销实现高分辨率显示和并行加速。     

分布式数据库的复制和分片

该文通过对集中式数据库和分布式数据库进行比较,指出集中式数据库在存储能力,访问速度等方面存在的问题,对分布式数据库中的数据复制和分片的概念,原则,方法进行详细的论述,最后,对数据复制和分片要解决的关键问题进行分析。     

电厂数据多级复制与集成系统的设计与实现

为获取信息系统的实时数据,实现跨分区网络的实时数据复制与集成,研究复杂网络环境下企业异构数据库平台之间的实时数据复制与集成方法,提出与应用无关的多级异步数据复制与集成方案。分析结果表明,根据该方案建立的复制系统可节约开发成本,适用于多种网络环境。     

LAURIN: A Distributed Digital Library of Newspaper Clippings

Among the wide range of digital libraries, an interesting, yet quite neglected, subclass is constituted by those exclusively dealing with newspaper clippings. Compared with book–oriented digital libraries, clipping libraries are more difficult to seize, since they are wide and unstructured, and the subjects and content of a clipping are completely heterogeneous. LAURIN is an EU–funded project involving seventeen participants from several countries, including two software companies and a large group of libraries, whose main purpose is to set up a network of digitalized newspaper clipping archives that can be easily accessed through the Internet, for searching and retrieving clippings. The project also provides the libraries with models and methodologies to be used for scanning, digitalizing, storing, indexing, and making accessible newspaper clippings. This paper concentrates on the main architectural features of the LAURIN distributed system, exposing the peculiarities deriving from the diverse users and tasks it supports.     

三角形网格数据的边缘提取及网格自适应细分

三角形网格数据是数值计算及实际测量中获得的一类主要的不规则网格数据,数据量比较在,结构复杂,因而数据的可视化和分析存在许多困难。如果只将人们有兴趣的数据特征区域提取出来并单独处理（可视化,存储,后处理）,不仅可以减少可视化中的计算了储需求,而且可以为数据场中特征的高级表示,分析提供基础。因此本文讨论三角形网格数据中特征区域边缘的提取算法。我们在三角形网格中引入了邻域的定义,并基于此定义给出网格数据     

透明计算系统端计算机间的数据传送方法

提出一种透明计算系统中端计算机间的数据传送方法,该方法通过将数据传送的控制信息和传送的数据分离,省去数据在网络上的传送过程,从而提高对传送请求的处理速度,减少对相关资源的占用,通过优化服务器对传送请求的调度处理,改善系统整体的响应速度和性能。在基于龙芯平台的透明计算原型系统中实现了上述方法,并作了性能测试和分析,验证了该方法的有效性。     

基于网关模式的数据同步复制的研究与应用

为了满足分布式实时数据库中对关键数据的强一致性和系统中各个节点数据副本的完整性的要求 ,提出了基于网关式的主副本复制技术的方案 ,很好地实现了分布式实时数据库的异地镜像功能。从成功用于电力系统的配调综合自动化管理 (SCADA)系统的实效来看 ,文中所述思想可行 ,整个系统对在传输系统关键数据时能迅速准确同步更新到网络中的各个节点 ,能稳定可靠地长时间运行     

Knowledge transfer in globally distributed teams: the role of transactive memory

This paper explores the role of transactive memory in enabling knowledge transfer between globally distributed teams. While the information systems literature has recently acknowledged the role transactive memory plays in improving knowledge processes and performance in colocated teams, little is known about its contribution to distributed teams. To contribute to filling this gap, knowledge‐transfer challenges and processes between onsite and offshore teams were studied at TATA Consultancy Services. In particular, the paper describes the transfer of knowledge between onsite and offshore teams through encoding, storing and retrieving processes. An in‐depth case study of globally distributed software development projects was carried out, and a qualitative, interpretive approach was adopted. The analysis of the case suggests that in order to overcome differences derived from the local contexts of the onsite and offshore teams (e.g. different work routines, methodologies and skills), some specific mechanisms supporting the development of codified and personalized ‘directories’ were introduced. These include the standardization of templates and methodologies across the remote sites as well as frequent teleconferencing sessions and occasional short visits. These mechanisms contributed to the development of the notion of ‘who knows what’ across onsite and offshore teams despite the challenges associated with globally distributed teams, and supported the transfer of knowledge between onsite and offshore teams. The paper concludes by offering theoretical and practical implications.     

Simulation Studies of Computation and Data Scheduling Algorithms for Data Grids

Data Grids seek to harness geographically distributed resources for large-scale data-intensive problems. Such problems, involving loosely coupled jobs and large data-sets, are found in fields like high-energy physics, astronomy and bioinformatics. A variety of factors need to be considered for effective scheduling of resources in such environments: e.g., resource utilization, response time, global and local allocation policies and scalability. We propose a general and extensible scheduling architecture that addresses these issues. Within this architecture we develop a suite of job scheduling and data replication algorithms that we evaluate using simulations for a wide range of parameters. Our results show that it is important to evaluate the combined effectiveness of replication and scheduling strategies, rather than study them separately. More specifically, we find that scheduling jobs to locations that contain the data they need and asynchronously replicating popular data-sets to remote sites, works rather well.