A hybrid petri-net model of grid workflow

In order to effectively control the random tasks submitted and executed in grid workflow, a grid workflow model based on hybrid petri-net is presented. This model is composed of random petri-net, colored petri-net and general petri-net. Therein random petri-net declares the relationship between the number of grid users＇ random tasks and the size of service window and computes the server intensity of grid system. Colored petri-net sets different color for places with grid services and provides the valid interfaces for grid resource allocation and task scheduling. The experiment indicated that the model presented in this letter could compute the valve between the number of users＇ random tasks and the size of grid service window in grid workflow management system.     

MapReduce模型的调度及容错机制研究

MapReduce是一种并行编程模型,可以用来处理和生成大量数据集。它的调度以及容错机制是模型的重要一部分。通过对MapReduce模型的执行过程进行分析,提取得到其上面的调度以及容错模型。并将P2P模型中常用的调度思想使用于MapReduce调度模型上,对原来的调度机制和容错机制做一定的修改。     

Reliability analysis of real-time fault-tolerant task models

One notable advantage of Model-Driven Architecture (MDA) method is that software developers could do sufficient analysis and tests on software models in the design phase, which helps construct high confidence on the expected software behaviors and performance, especially for safety-critical real-time software. Most existing literature of reliability analysis ignores the effects from those deadline requirements of tasks which are critical properties for real-time software and thus cannot be ignored. Considering the contradictory relationship between the deadline requirements and time costs of fault tolerance in real-time tasks, in this paper, we present a novel reliability model, which takes schedulability as one of the major factors affecting the reliability, to analyze reliability of the task execution model in real-time software design phase. The tasks in this reliability model has no restrictions on their distributions and thus could be distributed on a multiprocessor or on a distributed system. Furthermore, the tasks also define arrival rates of faults and fault-tolerant mechanisms to model the occurrences of non-permanent faults and the corresponding time costs of fault handling. By analyzing the probability of tasks still being schedulable in the worst-case execution scenario with faults occurring, reliability and schedulability are combined into an unified analysis framework, and two algorithms for reliability analysis are given. To make this reliability model more pragmatic, we also present an estimation technique for estimating the fault arrival rate of each task. We show through two case studies respectively the detailed derivation process under static-priority scheduling in a multiprocessor system and in the design process of avionics software, and then analyze the factors affecting the reliability analysis by setting up simulation experiments. When no assumptions of fault occurrences made on the task model, this reliability model regresses to a generic schedulability model.     

Reliability and Performance of Star Topology Grid Service With Precedence Constraints on Subtask Execution

The paper considers grid computing systems with star architectures in which the resource management system (RMS) divides service tasks into subtasks, and sends the subtasks to different specialized resources for execution. To provide the desired level of service reliability, the RMS can assign the same subtasks to several independent resources for parallel execution. Some subtasks cannot be executed until they have received input data, which can be the result of other subtasks. This imposes precedence constraints on the order of subtask execution. The service reliability & performance indices are introduced, and a fast numerical algorithm for their evaluation given any subtask distribution is suggested. Illustrative examples are presented.     

树形网格自适应调度模型研究

提出一种基于树形计算网格的自适应调度模型,实现对小粒度独立任务和用户大作业的自适应最优调度.通过对网格环境的实时检测,给出了基于节点负载状况、节点任务执行时间和任务特性的自适应调度算法.实验证明该任务调度模型在负载平衡和容错方面具有良好的性能.     

Optimal Resource Allocation for Maximizing Performance and Reliability in Tree-Structured Grid Services

The paper considers a grid computing systems in which the resource management systems (RMS) can divide service tasks into execution blocks (EB), and send these blocks to different resources. To provide a desired level of service reliability, the RMS can assign the same EB to several independent resources for parallel (redundant) execution. According to the optimal schedule for service task partition, and distribution among resources, one can achieve the greatest possible expected service performance (i.e. least execution time), or reliability. For solving this optimization problem, the paper suggests an algorithm that is based on graph theory, Bayesian approach, and the evolutionary optimization approach. A virtual tree-structure model is constructed in which failure correlation in common communication channels is taken into account. Illustrative examples are presented.     

The Pervasive Workflow: A Decentralized Workflow System Supporting Long-Running Transactions

Workflow technologies are becoming pervasive in that they enable the execution of business processes in distributed and ubiquitous computing environments. As long-running transactions, the execution of workflows in environments without dedicated infrastructures raises transactional requirements due to the dynamicity of resources available to run a workflow instance and the integration of relaxed atomicity constraints at both design and instantiation time. In this paper, we propose an adaptive transactional protocol for the pervasive workflow model developed in a previous work to support the execution of business processes in the pervasive setting. The execution of this protocol takes place in two phases. First, candidate business partners are assigned to tasks using an algorithm wherein the selection process is based on both functional and transactional requirements. The workflow execution further proceeds through a hierarchical coordination protocol managed by the workflow initiator and controlled based on a decision table computed as an outcome of the business partner assignment procedure. The resulting workflow execution is compliant with the defined consistency requirements, and the coordination decisions depend on the transactional characteristics offered by the partners assigned to each task. An implementation of our theoretical results relying on ontology Web Language for Series and Business Process Execution Language technologies is further detailed as a proof of concept.     

A Fault Tolerant Doubly Fed Induction Generator Wind Turbine Using a Parallel Grid Side Rectifier and Series Grid Side Converter

With steadily increasing wind turbine penetration, regulatory standards for grid interconnection have evolved to require that wind generation systems ride-through disturbances such as faults and support the grid during such events. Conventional modifications to the doubly fed induction generation (DFIG) architecture for providing ride-through result in compromised control of the turbine shaft and grid current during fault events. A DFIG architecture in which the grid side converter is connected in series as opposed to parallel with the grid connection has shown improved low voltage ride through but poor power processing capabilities. In this paper, a unified DFIG wind turbine architecture which employs a parallel grid side rectifier and series grid side converter is presented. The combination of these two converters enables unencumbered power processing and robust voltage disturbance ride through. A dynamic model and control structure for this architecture is developed. The operation of the system is illustrated using computer simulations.     

面向智能电网架空线的传感器故障容忍机制

在配用电网络全网的监控过程中,杆塔等设施的状态监测与故障容忍成为电力系统亟待解决的问题。现有的监控系统由于网络线性拓扑结构等限制,故障发生时无法及时维护,影响到电力生产业务,易造成电力重大事故。该文面向利用传感器监控电网架空线的背景,提出一个针对传感器部署的故障容忍机制。首先,依据N-x原则等,最小化冗余备份节点和无线模块的数量,达到成本最小化的目的。其次,综合考虑时延约束、N-x原则的数量约束等构建数学优化模型。基于该模型,利用聚类合并思想,构建了一个面向智能电网架空线的传感器故障容忍机制。最后,仿真实验证明,以此机制部署的传感器监测网络能够在成本最小化的基础上,有效地容忍故障。     

具有自律特征的网络故障管理框架

自律计算是IT研究的一个热点，它旨在设计出一种具有自我配置、自我优化、自我恢复和自我保护的计算机系统，使系统能够根据管理员给定的高层次目标进行自我管理。文章根据基本的控制理论．结合IBM提出的自律计算模型，将基于反馈的反应式控制和基于前馈的预测式控制相结合，运用于网络故障管理系统中，提出了一个具有自律特征的网络故障管理框架。最后，根据该故障管理系统的实现经验，分析了框架实现中的关键技术。     

动态工作流的进化策略

大型分布式系统工作流具有动态、分布、松散耦合特点。系统在维护工作流正常运行同时,还能根据实时情况分析,对工作流进行在线进化,从而构造更优流模型。对原工作流定义进行了可行替换集扩展,并给出了兼顾组合预算、任务时限以及服务信用等各因数的综合评分函数,对XML标准流日志进行在线应用挖掘,由管理Agent对工作流重新配置,实现流中变迁的替换、归并和分裂等进化操作,使其保持综合评分最优,为虚拟企业工作流管理提供进化支持。     

Providing Transactional Properties for Migrating Workflows

Current workflow management systems have several limitations that need to be addressed by the research community. This paper deals with two of them: the lack of flexibility necessary in a changing business environment, and the lack of transactional guarantees for workflow applications.To handle the dynamic character of current business environments and processes, we have proposed the Migrating Workflow Model. A migrating workflow transfers its code (specification) and its execution state to a site, negotiates a service to be executed on its behalf, receives the results, and moves on. The next place visited by the workflow, and the next service requested, is determined by both the objectives of the process and the results of the current requests.The transactional properties are addressed by merging of the Migrating Workflow Model with a Transactional Workflow Model, in which the workflow designer has the ability of specifying, independently, the task coordination requirements, the failure atomicity requirements, and the execution atomicity requirements. The result, described in this paper, is a migrating workflow model endowed with transactional properties that guarantee the correct execution of workflow applications in the presence of failures and in the presence of concurrent access to shared data.     

UniFAFF: a unified framework for implementing autonomic fault management and failure detection for self‐managing networks

Today's network management, as known within the Fault, Configuration, Accounting, Performance, Security (FCAPS) management framework, is moving towards the definition and implementation of ‘self‐managing’ network functions, with the aim of eliminating or drastically reducing human intervention in some of the complex aspects or daunting tasks of network management. The fault management plane of the FCAPS framework deals with the following functions: fault detection, fault diagnosis, localization or isolation, and fault removal. Task automation is at the very heart of self‐managing (autonomic) nodes and networks, meaning that all functions and processes related to fault management must be automated as much as possible within the functionalities of self‐managing (autonomic) nodes and networks, in order for us to talk about autonomic fault management. At this point in time there are projects calling for implementing new network architectures that are flexible to support on‐demand functional composition for context‐ or situation‐aware networking. A number of such projects have started, under the umbrella of the so‐called clean‐slate network designs. Therefore, this calls for open frameworks for implementing self‐managing (autonomic) functions across each of the traditional FCAPS management planes. This paper presents a unified framework for implementing autonomic fault management and failure detection for self‐managing networks, a framework we are calling UniFAFF. Copyright © 2008 John Wiley & Sons, Ltd.     

Modeling reflex-healing autonomy for large-scale embedded systems

High-energy physics experiments require an extraordinary amount of real-time computation, and the computers implementing the online data processing must be very reliable because of the large cost associated with operating the facilities and the potential for loss of irreplaceable data. Conventional redundancy-based fault tolerance and adaptive approaches are not appropriate because of the tremendous system cost (fault tolerance is limited to a maximum of 10% overhead). In this work, we developed a framework for building robust embedded systems, which utilizes an autonomic reflex-healing approach to achieve fault tolerance. Components of the framework implement user-defined failure adaptation strategies within the context of a large-scale embedded environment. The tools embrace a model-based approach combining design specification and code-generation for both simulation and system implementation. In this paper we present the concepts and entities of the reflex and healing framework.     

基于高效负载均衡的网络任务分配技术

针对传统的网格在分配任务的过程中,当多任务发生竞争的时候,由于多条路径的任务负载不均衡,造成传输速度慢的问题,提出一种基于遗传算法负载均衡的网格工作流算法.通过模拟自然界的生物进化过程对任务空间进行随机化搜索,根据预定任务的适应度函数,并用全局并行搜索方式找到最优节点,避免了传统方法的负载不均衡问题.实验证明,该算法实现了负载的快速均衡,提高了网格工作流系统的工作效率.     

Scientific Workflow Makespan Minimization in Edge Multiple Service Providers Environment

The edge computing model offers an ultimate platform to support scientific and real-time workflow-based applications over the edge of the network. However, scientific workflow scheduling and execution still facing challenges such as response time management and latency time. This leads to deal with the acquisition delay of servers, deployed at the edge of a network and reduces the overall completion time of workflow. Previous studies show that existing scheduling methods consider the static performance of the server and ignore the impact of resource acquisition delay when scheduling workflow tasks. Our proposed method presented a meta-heuristic algorithm to schedule the scientific workflow and minimize the overall completion time by properly managing the acquisition and transmission delays. We carry out extensive experiments and evaluations based on commercial clouds and various scientific workflow templates. The proposed method has approximately 7.7% better performance than the baseline algorithms, particularly in overall deadline constraint that gives a success rate.

     

An Ant Colony Optimization Approach to a Grid Workflow Scheduling Problem With Various QoS Requirements

Grid computing is increasingly considered as a promising next-generation computational platform that supports wide-area parallel and distributed computing. In grid environments, applications are always regarded as workflows. The problem of scheduling workflows in terms of certain quality of service (QoS) requirements is challenging and it significantly influences the performance of grids. By now, there have been some algorithms for grid workflow scheduling, but most of them can only tackle the problems with a single QoS parameter or with small-scale workflows. In this frame, this paper aims at proposing an ant colony optimization (ACO) algorithm to schedule large-scale workflows with various QoS parameters. This algorithm enables users to specify their QoS preferences as well as define the minimum QoS thresholds for a certain application. The objective of this algorithm is to find a solution that meets all QoS constraints and optimizes the user-preferred QoS parameter. Based on the characteristics of workflow scheduling, we design seven new heuristics for the ACO approach and propose an adaptive scheme that allows artificial ants to select heuristics based on pheromone values. Experiments are done in ten workflow applications with at most 120 tasks, and the results demonstrate the effectiveness of the proposed algorithm.     

水利网格工作流管理系统及其在水污染事件中的应用

针对水利行业对高效能计算力的需求,以工作流作为桥梁,将网格技术引入水利计算中,形成了水利网格工作流管理系统。介绍了水利网格工作流管理系统所应用的关键技术和设计过程,重点阐述了工作流引擎的设计思路,介绍了一种＂基于关键路径的学习型工作流调度算法＂,并以松花江石油污染为假设对系统进行了实验,最后提出了几点改进要求。     

网格环境下信息服务系统的研究

文章基于建立一个网格环境中信息管理机制的思想,首先对网格环境中信息的特点进行了分析,然后根据网格的体系结构及技术规范提出了能够实现网格环境中信息管理的信息服务系统的设计模型,最后给出了该信息服务系统的具体实现。整个信息服务系统设计合理,具有可扩展性,配置简单,具有并发操作的特性,在完成网格环境中和信息管理过程中发挥重要作用。     

SIFT: Design and analysis of a fault-tolerant computer for aircraft control

SIFT (Software Implemented Fault Tolerance) is an ultrareliable computer for critical aircraft control applications that achieves fault tolerance by the replication of tasks among processing units. The main processing units are off-the-shelf minicomputers, with standard microcomputers serving as the interface to the I/O system. Fault isolation is achieved by using a specially designed redundant bus system to interconnect the proeessing units. Error detection and analysis and system reconfiguration are performed by software. Iterative tasks are redundantly executed, and the results of each iteration are voted upon before being used. Thus, any single failure in a processing unit or bus can be tolerated with triplication of tasks, and subsequent failures can be tolerated after reconfiguration. Independent execution by separate processors means that the processors need only be loosely synchronized, and a novel fault-tolerant synchronization method is described. The SIFT software is highly structured and is formally specified using the SRI-developed SPECIAL language. The correctness of SIFT is to be proved using a hierarchy of formal models. A Markov model is used both to analyze the reliability of the system and to serve as the formal requirement for the SIFT design. Axioms are given to characterize the high-level behavior of the system, from which a correctness statement has been proved. An engineering test version of SIFT is currently being built.