Low-latency, concurrent checkpointing for parallel programs

Presents the results of an implementation of several algorithms for checkpointing and restarting parallel programs on shared-memory multiprocessors. The algorithms are compared according to the metrics of overall checkpointing time, overhead imposed by the checkpointer on the target program, and amount of time during which the checkpointer interrupts the target program. The best algorithm measured achieves its efficiency through a variation of copy-on-write, which allows the most time-consuming operations of the checkpoint to be overlapped with the running of the program being checkpointed     

VMckpt:lightweight and live virtual machine checkpointing

Recent advance of virtualization technology provides a new approach to check-point/restart at the virtual machine(VM) level.In contrast to traditional process-level checkpointing,checkpointing at the virtualization layer brings up several advantages,such as compatibility,transparence,flexibility and simplicity.However,because the virtualization layer has little semantic knowledge about the operation system and the applications running atop,VM-layer checkpointing requires saving the entire operating system state rather than a single process.The overhead may render the approach impractical.To reduce the size of VM checkpoint,in this paper we propose a page eviction scheme and an incremental checkpointing mechanism to avoid saving unnecessary VM pages in the checkpoint.To keep the system online transparently,we propose a live checkpointing mechanism by saving the memory image in a copy-on-write(COW) manner.We implement the performance optimization mechanisms in a prototype system,called VMckpt.Experimental results with a group of representative applications show that our page eviction scheme and incremental checkpointing can significantly reduce the checkpoint file size by up to 87% and shorten the total checkpointing/restart time by a factor of up to 71%,in comparison with the Xens default checkpointing mechanism.The observed application downtimes due to checkpointing can be reduced to as small as 300 ms.     

Nonblocking checkpointing for optimistic parallel simulation: description and an implementation

Describes a nonblocking checkpointing mode in support of optimistic parallel discrete event simulation. This mode allows real concurrency in the execution of state saving and other simulation specific operations (e.g, event list update, event execution) with the aim of removing the cost of recording state information from the completion time of the parallel simulation application. We present an implementation of a C library supporting nonblocking checkpointing on a myrinet based cluster, which demonstrates the practical viability of this checkpointing mode on standard off-the-shelf hardware. By the results of an empirical study on classical parameterized synthetic benchmarks, we show that, except for the case of minimal state granularity applications, nonblocking checkpointing allows improvement of the speed of the parallel execution, as compared to commonly adopted, optimized checkpointing methods based on the classical blocking mode. A performance study for the case of a personal communication system (PCS) simulation is additionally reported to point out the benefits from nonblocking checkpointing for a real world application.     

Adaptive Remus: adaptive checkpointing for Xen-based virtual machine replication

With the ever increasing dependence on computers and networks, many systems are required to be continuously available in order to fulfil their mission. Virtualization technology enables high availability to be offered in a convenient, cost-effective manner: with the encapsulation provided by virtual machines (VMs), entire systems can be replicated transparently in software, obviating the need for expensive fault-tolerant hardware. Remus is a VM replication mechanism for the Xen hypervisor that provides high availability despite crash failures. Replication is performed by checkpointing the VM at fixed intervals. However, there is an antagonism between processing and communication regarding the optimal checkpoint interval: while longer intervals benefit processor-intensive applications, shorter intervals favour network-intensive applications. Thus, any chosen interval may not always be suitable for the hosted applications, limiting Remus usage in many scenarios. This work introduces Adaptive Remus, a proposal for adaptive checkpointing in Remus that dynamically adjusts the replication frequency according to the characteristics of running applications. Experimental results indicate that our proposal improves performance for applications that require both processing and communication, without harming applications that use only one type of resource.     

Mutable checkpoints: a new checkpointing approach for mobilecomputing systems

Mobile computing raises many new issues such as lack of stable storage, low bandwidth of wireless channel, high mobility, and limited battery life. These new issues make traditional checkpointing algorithms unsuitable. Coordinated checkpointing is an attractive approach for transparently adding fault tolerance to distributed applications since it avoids domino effects and minimizes the stable storage requirement. However, it suffers from high overhead associated with the checkpointing process in mobile computing systems. Two approaches have been used to reduce the overhead: First is to minimize the number of synchronization messages and the number of checkpoints; the other is to make the checkpointing process nonblocking. These two approaches were orthogonal previously until the Prakash-Singhal algorithm combined them. However, we found that this algorithm may result in an inconsistency in some situations and we proved that there does not exist a nonblocking algorithm which forces only a minimum number of processes to take their checkpoints. In this paper; we introduce the concept of “mutable checkpoint,” which is neither a tentative checkpoint nor a permanent checkpoint, to design efficient checkpointing algorithms for mobile computing systems. Mutable checkpoints can be saved anywhere, e.g., the main memory or local disk of MHs. In this way, taking a mutable checkpoint avoids the overhead of transferring large amounts of data to the stable storage at MSSs over the wireless network. We present techniques to minimize the number of mutable checkpoints. Simulation results show that the overhead of taking mutable checkpoints is negligible. Based on mutable checkpoints, our nonblocking algorithm avoids the avalanche effect and forces only a minimum number of processes to take their checkpoints on the stable storage     

FINE: A Fully Informed aNd Efficient communication-induced checkpointing protocol for distributed systems

Communication-Induced Checkpointing (CIC) protocols are classified into two categories in the literature: Index-based and Model-based. In this paper, we discuss two data structures being used in these two kinds of CIC protocols, and their different roles in helping the checkpointing algorithms to enforce Z-cycle Free (ZCF) property. Then, we present our Fully Informed aNd Efficient (FINE) communication-induced checkpointing algorithm, which not only has less checkpointing overhead than the well-known Fully Informed (FI) CIC protocol proposed by Helary et al. but also has less message overhead. Performance evaluation indicates that our protocol performs better than many of the other existing CIC protocols.     

Boundary, Purpose, and Values in Work-Domain Models: Models of Naval Command and Control

This paper presents an application of work-domain analysis (WDA) to the domain of the command and control of a multipurpose naval frigate—the Canadian Halifax Class frigate. This represents an application of this approach to a real system and, to the authors' knowledge, is the most extensive WDA of a naval work domain. In particular, and in contrast to other applications of cognitive work analysis, the authors extended the basic WDA framework to handle a multipurpose, loosely bound work domain. In addition, the naval domain is value driven, and this affects naval decision making. Values were incorporated as a social organizational analysis into the work-domain model and were represented as a type of soft constraint. A total of 38 submodels of the work domain were developed, whose primary models are discussed in this paper. From these models, 132 information requirements were extracted, substantiating that WDA is a worthwhile technique for supporting interface design. This paper makes a theoretical contribution by extending the WDA framework and a practical contribution by demonstrating the usefulness of the framework in a real design context. This paper concentrates on presenting WDA as a process, not as a finished product, showing intermediate levels of models and the design requirements that can be extracted from the early stages of the WDA.     

Software Reliability Models: Assumptions, Limitations, and Applicability

A number of analytical models have been proposed during the past 15 years for assessing the reliability of a software system. In this paper we present an overview of the key modeling approaches, provide a critical analysis of the underlying assumptions, and assess the limitations and applicability of these models during the software development cycle. We also propose a step-by-step procedure for fitting a model and illustrate it via an analysis of failure data from a medium-sized real-time command and control software system.     

Multireceiver Authentication Codes: Models, Bounds, Constructions, and Extensions

Multireceiver authentication codes allow one sender to construct an authenticated message for a group of receivers such that each receiver can verify authenticity of the received message. In this paper, we give a formal definition of multireceiver authentication codes, derive information theoretic and combinatorial lower bounds on their performance, and give new efficient and flexible constructions for such codes. Finally, we extend the basic model to the case that multiple messages are sent and the case that the sender can be any member of the group.     

Replication in Distributed Systems: Models,Methods, and Protocols

Programming and Computer Software - Data replication is used to enhance the reliability, availability, and throughput of database systems at a price of increased complexity and cost of data...     

人工免疫系统:原理、模型、分析及展望

目前,受生物免疫系统启发而产生的人工免疫系统（Artificial ImmuneSystem,AIS)正在兴起,它作为计算智能研究的新领域,提供了一种强大的信息处理和问题求解范式,该文侧重以AIS的基本原理框架为线索,对其研究状况加以系统综述,首先从AIS的生物原型入手,归纳提炼出其仿生机理,主要包括免疫识别,免疫学习,免疫记忆,克隆选择,个体多样性,分布式和自适应等,进而对几种典型的AIS模型和算法分门别类地进行了细致讨论,随后介绍了AIS在若干具有代表性的领域中的应用情况,最后通过对AIS的特性和存在问题的分析,展望了今后的研究重点和发展趋势。     

Culture, Models, and Games: Incorporating Warfare's Human Dimension

Increasingly, modern conflict and military activity require soldiers to carry out their missions within foreign cultures in which the civilian populace rather than a battlefield becomes the focal point. So, from the commander to the soldier on the street, the warfighter must understand the society's values and the motivations of the groups within it. Gaming can help the military train soldiers for this new type of conflict.     

Robots, Models, and Automation

Low-cost, mass-produced industrial robots could free human workers from the tedium of the assembly line. Such robots may be possible within the next decade.     

Qualitative Models in Computational Simulative Sciences: Representation,Confirmation, Experimentation

The Epistemology Of Computer Simulation (EOCS) has developed as an epistemological and methodological analysis of simulative sciences using quantitative computational models to represent and predict empirical phenomena of interest. In this paper, Executable Cell Biology (ECB) and Agent-Based Modelling (ABM) are examined to show how one may take advantage of qualitative computational models to evaluate reachability properties of reactive systems. In contrast to the thesis, advanced by EOCS, that computational models are not adequate representations of the simulated empirical systems, it is shown how the representational adequacy of qualitative models is essential to evaluate reachability properties. Justification theory, if not playing an essential role in EOCS, is exhibited to be involved in the process of advancing and corroborating model-based hypotheses about empirical systems in ECB and ABM. Finally, the practice of evaluating model-based hypothesis by testing the simulated systems is shown to constitute an argument in favour of the thesis that computer simulations in ECB and ABM can be put on a par with scientific experiments.

     

Disjunctive Stable Models: Unfounded Sets, Fixpoint Semantics, and Computation

Disjunctive logic programs have become a powerful tool in knowledge representation and commonsense reasoning. This paper focuses on stable model semantics, currently the most widely acknowledged semantics for disjunctive logic programs. After presenting a new notion of unfounded sets for disjunctive logic programs, we provide two declarative characterizations of stable models in terms of unfounded sets. One shows that the set of stable models coincides with the family of unfounded-free models (i.e., a model is stable iff it contains no unfounded atoms). The other proves that stable models can be defined equivalently by a property of their false literals, as a model is stable iff the set of its false literals coincides with its greatest unfounded set. We then generalize the well-founded operator to disjunctive logic programs, give a fixpoint semantics for disjunctive stable models and present an algorithm for computing the stable models of function-free programs. The algorithm's soundness and completeness are proved and some complexity issues are discussed.     

SD Models: Super‐Deformed Character Models

Super‐deformed, SD, is a specific artistic style for Japanese manga and anime which exaggerates characters in the goal of appearing cute and funny. The SD style characters are widely used, and can be seen in many anime, CG movies, or games. However, to create an SD model often requires professional skills and considerable time and effort. In this paper, we present a novel technique to generate an SD style counterpart of a normal 3D character model. Our approach uses an optimization guided by a number of constraints that can capture the properties of the SD style. Users can also customize the results by specifying a small set of parameters related to the body proportions and the emphasis of the signature characteristics. With our technique, even a novel user can generate visually pleasing SD models in seconds.     

移动群智感知安全与隐私:模型、进展与趋势

移动群智感知作为一种新兴的物联网感知范式,通过激励现代化智能感知设备获得高质量的感知数据,从而高效地完成大规模且复杂的社会感知任务并服务人类社会.移动群智感知系统由感知用户、感知平台和服务提供商组成,在感知任务执行过程中,感知数据经历感知、上传和交易三个阶段,各阶段均面临多种多样的数据安全和隐私泄露风险,危害感知用户隐私和感知数据安全.首先介绍移动群智感知的系统模型、实际应用场景并给出主要安全研究方法,以感知数据参与感知任务的生命周期为轴线,讨论在感知数据生命周期的三个阶段所面临的安全与隐私威胁;在上述威胁基础上,分别从三个阶段系统阐述现有的数据安全与隐私保护解决方案;最后,从隐私度量、隐私框架、隐私保护和隐私计算等方面探讨进一步的发展趋势与研究方向.