A technique for constructing highly available services

This paper describes a general method for constructing a highly available service for use in a distributed system. It gives a specific implementation of the method and proves the implementation correct. The service consists of replicas that reside at several different locations in a network. It presents its clients with a consistent view of its state, but the view may contain old information. Clients can indicate how recent the information must be. The method can be used in applications satisfying certain semantic constraints. For applications that can use it, the method performs better than other replication techniques.This research was supported in part by the Advanced Research Projects Agency of the Department of Defense, monitored by the Office of Naval Research under Contract No. N00014-83-K.-0125, by the National Science Foundation under Grant No. DCR-8503662, and by the HTI Postdoctoral Fellowship.     

一种直觉模糊熵的构造方法

针对直觉指数所表征的中立证据中支持与反对的程度呈均衡状态时无法表述的问题,提出一种直觉模糊熵的构造方法.首先基于均衡状态假设,揭示了影响直觉模糊熵大小的3个相互作用因素之间的内部关系,给出了直觉模糊熵的几何解释;然后分析了满足直觉模糊熵的直观约束条件,给出一种直觉模糊熵的公理化定义,揭示了直觉模糊熵最小值计算性质;最后通过算例分析比较,验证了所提出方法的正确性、合理性和有效性.     

A highly available local leader election service

We define the highly available local leader election problem (G. LeLann, 1977), a generalization of the leader election problem for partitionable systems. We propose a protocol that solves the problem efficiently and give some performance measurements of our implementation. The local leader election service has been proven useful in the design and implementation of several fail-aware services for partitionable systems     

Using NUMA interconnects for highly available filers

The paper discusses the clustered failover configuration which connects two independent file-server appliances via a nonuniform-memory-access network. Combining NUMA interconnects and a proprietary, log-structured file system results in file service that survives hardware faults with minimal disruption to clients     

Dependency-aware maintenance for highly available service-oriented grid

When the scale of computational system grow from a single machine to a Grid with potentially thousands of heterogeneous nodes, the interdependencies among the resources and software components make management and maintenance activities much more complicated. One of the most important challenges to overcome is how to balance maintenance of the system and the global system availability. In this paper, a novel mechanism is proposed, the Cobweb Guardian, which provides solutions not only to reduce the effects of maintenance but to remove the effects of dependencies on system availability due to deployment dependencies, invocation dependencies, and environment dependencies. By using the Cobweb Guardian, Grid administrators can execute the maintenance tasks safely at runtime whilst ensuring high system availability. The results of our evaluations show that our proposed dependency-aware maintenance mechanism can significantly increase the throughput and the availability of the whole system at runtime.     

A process partitioning technique for constructing decentralized web service compositions

Web service compositions have been widely applied in different applications. A service composition is usually implemented in either a centralized or decentralized manner. Compared with the centralized service composition, the decentralized composition has no central control component, and components interact with each other directly, thereby achieving better performance. Process partitioning is a technique to divide a process into multiple parts and has been shown that it can be successfully applied to decentralizing process-driven service compositions. This paper proposes a new process partitioning technique for constructing decentralized service compositions. The proposed technique, which is based on typed digraphs and a graph transformation technique, is used for exploring available process partitioning solutions. For applications, this paper discusses the topology and interaction features about the partitioning solutions and summarizes a ranking method for them. Three experiments are conducted to evaluate the proposed methods in this paper. Experimental results show that the proposed methods can be applied in constructing decentralized service compositions effectively. In addition, the results also show that the decentralized compositions can have lower average response times and higher throughputs than the corresponding centralized compositions in the experiments.     

A parallel pruning technique for highly asymmetric assignmentproblems

We introduce a new two-phase technique to solve highly asymmetric assignment problems. In the first phase, the assignment problem is decomposed into subproblems which are solved in parallel. The first phase is used to exclude certain suboptimal assignments from consideration in the second phase. In the second phase, the optimal assignment is finalized. We show that the two-phase algorithm can reduce the theoretical time bound for solving an n×k assignment problem (nk/_n     

一种Windows Services进程控制方法的探讨与实现

Win32平台下的Windows Services是一种强大的后台程序管理模式。如果将服务程序要执行的内容与服务程序剥离写成若干单独的可执行程序,而只在服务程序里面生成它们的进程,则不但可以实现后台程序的开机启动,还可以更加有效地管理它们。     

Scheduling highly available applications on cloud environments

Cloud computing is becoming a popular solution for storing data and executing applications due to its on-demand pay-per-use policy that allows access to virtually unlimited resources. In this frame applications such as those oriented towards Web 2.0 begin to be migrated on cloud systems. Web 2.0 applications are usually composed of several components that run indefinitely and need to be available to end users throughout their execution life cycle. Their availability strongly depends on the number of resource failures and on the variation in user hit rate. These problems are usually solved through scaling. A scaled application can span its components on several nodes. Hence if one or more nodes fail it could become unavailable. Therefore we require a method of ensuring the application’s functionality despite the number of node failures. In this paper we propose to build highly available applications, i.e., systems with low downtimes, by taking advantage of the component based architecture and of the application scaling property. We present a solution to finding the optimal number of component types needed on nodes so that every type is present on every allocated node. Furthermore nodes cannot exceed a maximum threshold and the total running cost of the applications needs to be minimized. A sub-optimal solution is also given. Both solutions rely on genetic algorithms to achieve their goals. The efficiency of the sub-optimal algorithm is studied with respect to its success rate, i.e., probability of the schedule to provide highly available applications in case all but one node fail. Tests performed on the sub-optimal algorithm in terms of node load, closeness to the optimal solution and success rate prove the algorithm’s efficiency.     

Supporting highly manageable Web services

This paper focuses on the management aspects of Web service provision. We argue that support for manageability has to be considered at the design stage if services are to be capable of delivering high levels of quality of service for their users. Examples of the problems caused by lack of manageability include maintenance operations that necessitate service downtime, or difficulties in ensuring consistency of information. We categorise management issues into those concerning a site as a whole and those pertaining to individual services. Our approach to site management supports the arbitrary distribution of services to machines, allowing the optimum cost/performance configuration to be selected. Services can be easily migrated between machines, resulting in sites that scale, both in terms of the number of services and the number of users. Service management issues may be generalised as supporting evolution, for example, supporting changes to the functionality, the presentation logic, and the overall look and feel of a service. Our approach, based on the separation of functionality and presentation, allows such changes to be performed on-line and ensures that updates are reflected consistency across the various pages of a service, or across services. This approach also facilitates the development of services that utilise dynamic content for service customisations, such as tailoring a service to match the profile of users. Furthermore, all management operations are available through Web-based interfaces, making them accessible to a broad range of users, not only specialist system administrators.     

Pattern based configuration generation for highly available COTS components based systems

ContextService availability is an important quality factor that distinguishes between providers. High availability is achieved when the service is available at least 99.999% of the time. The Service Availability Forum has defined several middleware services, among them the Availability Management Framework (AMF) aims at ensuring the high availability of services provided by applications under its control. AMF requires a configuration. The design of an AMF configuration is complex and error prone. For improving the quality of such configurations, an automated generation technique has been proposed in the literature. However, this technique may generate several configurations among which some may not meet the required level of availability. Therefore, the generated configurations are evaluated using availability analysis tools to select an appropriate one for deployment.ObjectiveInstead of generating configurations, analyze them and select one that meets the required level of availability if any, we target directly configurations that are estimated to satisfy the required level of availability.MethodWe investigated the different aspects/attributes of an AMF configuration that may affect service recovery when a failure happens to come up with configuration design patterns and integrate them into an enhanced configuration generation technique.ResultsA set of configuration design patterns and two lightweight methods for availability estimation have been defined. These configuration design patterns and analysis methods are embedded into an enhanced configuration generation technique to target only the configurations that are estimated to satisfy the required level of availability or the configuration that is the closest to the required level of availability when it is not possible to meet the requirements.ConclusionWe conclude it is possible to target directly the best configurations in terms of estimated availability using configuration design patterns and estimation methods. The enhanced configuration generation technique is less resource and time consuming than related approaches.     

Towards highly available and scalable high performance clusters

In recent years, we have witnessed a growing interest in high performance computing (HPC) using a cluster of workstations. This growth made it affordable to individuals to have exclusive access to their own supercomputers. However, one of the challenges in a clustered environment is to keep system failure to the minimum and to achieve the highest possible level of system availability. High-Availability (HA) computing attempts to avoid the problems of unexpected failures through active redundancy and preemptive measures. Since the price of hardware components are significantly dropping, we propose to combine both HPC and HA concepts and layout the design of a HA-HPC cluster, considering all possible measures. In particular, we explore the hardware and the management layers of the HA-HPC cluster design, as well as a more focused study on the parallel-applications layer (i.e. FT-MPI implementations). Our findings show that combining HPC and HA architectures is feasible, in order to achieve HA cluster that is used for High Performance Computing.     

SLDRT: A measurement technique for available bandwidth on multi-hop path with bursty cross traffic

End-to-end available bandwidth is of great importance as a metric that characterizes the network’s dynamic transmitting capability. Most estimation methodologies infer available bandwidth from the relationship between the input inter-packet gaps and those of the output. This paper analyzes the challenges brought by extending the measurement environment to the multi-hop path with bursty cross-traffic. Based on the analysis, a novel probing technique, self-loading decreasing rate train (SLDRT), is proposed. SLDRT measures the available bandwidth by using a single decreasing rate packet train. The special train can efficiently avoid bias caused by multiple sampling. Performance analysis via NS-2 simulations and PlanetLab experiments verify the effectiveness of our method under multi-hop path with the bursty cross traffic environment, and also show that SLDRT estimates available bandwidth more quickly, accurately, and with less measurement overhead than other existing techniques such as pathload and pathChirp.     

A simple method for constructing heptadecagon

It is proved that among the regular polygons with prime edges, only the regular polygons with Fermat prime edges are constructable with compass and straightedge. As 17 is a Fermat prime number, the construction of heptadecagon has been discussing all the time. Many different construction methods are proposed although they are based on the same theory. Simplification of the construction is still a sensible problem. Here, we propose a simple method for constructing regular heptadecagon with the fewest steps. The accumulation of construction errors is also avoided. This method is more applicable than the previous construction.     

Web Services在构建企业信息化平台中的应用研究

企业信息化建设一直是企业比较关心的课题之一,但是随着网络技术和通信技术的飞速发展,在企业内部或不同企业间如何实现信息共享和数据集成,成为构建企业信息化平台中所必须解决的关键问题。讨论了Web Services的基本概念和体系架构,根据Web Services与企业信息化的特点,提出了利用Web Services构建企业信息化平台,并结合企业实际运营中的相关服务,给出了Web Services在构建企业信息化平台中的具体应用。     

一种实用的自动指纹识别完整算法

本文设计并实现了一套完整的指纹图像自动识别算法,该算法首先对指纹图像进行增强包括归一化,分割指纹图像,区分有效区域和无效区域,计算方向图、用方向滤波的方法对指纹图像进行滤波、接着用动态阈值法二值化经过滤波增强的指纹图像,并对二值化图像进行细化及细化后处理,然后提取细化后图像的特征数据,最后将提取的特征数据进行匹配。实验表明该算法运行时间短,识别效率较高,是一种实用的自动指纹识别算法。     

Scalable, secure, and highly available distributed file access

A summary of and historical perspective on work done to implement easy-to-share distributed file systems based on the Unix model are presented. Andrew and Coda are distributed Unix file systems that embody many of the recent advances in solving the problem of data sharing in large, physically dispersed workstation environments. The Andrew architecture is presented, the scalability and security of the system are discussed. The Coda system is examined, with emphasis on its high availability