Privacy Loss in Distributed Constraint Reasoning: A Quantitative Framework for Analysis and its Applications

It is critical that agents deployed in real-world settings, such as businesses, offices, universities and research laboratories, protect their individual users’ privacy when interacting with other entities. Indeed, privacy is recognized as a key motivating factor in the design of several multiagent algorithms, such as in distributed constraint reasoning (including both algorithms for distributed constraint optimization (DCOP) and distributed constraint satisfaction (DisCSPs)), and researchers have begun to propose metrics for analysis of privacy loss in such multiagent algorithms. Unfortunately, a general quantitative framework to compare these existing metrics for privacy loss or to identify dimensions along which to construct new metrics is currently lacking. This paper presents three key contributions to address this shortcoming. First, the paper presents VPS (Valuations of Possible States), a general quantitative framework to express, analyze and compare existing metrics of privacy loss. Based on a state-space model, VPS is shown to capture various existing measures of privacy created for specific domains of DisCSPs. The utility of VPS is further illustrated through analysis of privacy loss in DCOP algorithms, when such algorithms are used by personal assistant agents to schedule meetings among users. In addition, VPS helps identify dimensions along which to classify and construct new privacy metrics and it also supports their quantitative comparison. Second, the article presents key inference rules that may be used in analysis of privacy loss in DCOP algorithms under different assumptions. Third, detailed experiments based on the VPS-driven analysis lead to the following key results: (i) decentralization by itself does not provide superior protection of privacy in DisCSP/DCOP algorithms when compared with centralization; instead, privacy protection also requires the presence of uncertainty about agents’ knowledge of the constraint graph. (ii) one needs to carefully examine the metrics chosen to measure privacy loss; the qualitative properties of privacy loss and hence the conclusions that can be drawn about an algorithm can vary widely based on the metric chosen. This paper should thus serve as a call to arms for further privacy research, particularly within the DisCSP/DCOP arena.     

一种动态分布式约束优化问题协同求解算法

多Agent协作过程中的许多问题都可在分布式约束优化问题(DCOP)框架下建模,但多局限于规划问题,且一般需Agent具有完全、准确收益函数.针对DCOP局限性,定义动态分布式约束优化问题(DDCOP),分析求解它的两个关键操作:Exploration和Exploitation,提出基于混沌蚂蚁的DDCOP协同求解算法(CA-DDCOP).该算法借鉴单只蚂蚁的混沌行为和蚁群的自组织行为,实现Exploration和Exploitation,根据玻尔兹曼分布,建立平衡Exploration和Exploitation的协同方法.通过多射频多信道无线AdHoc网络的信道分配验证该算法的有效性.     

Methods of resource management in problem-oriented computing environment

One of the important classes of computational problems is problem-oriented workflow applications executed in distributed computing environment. A problem-oriented workflow application can be represented by a directed graph whose vertices are tasks and arcs are data flows. For a problem-oriented workflow application, we can get a priori estimates of the task execution time and the amount of data to be transferred between the tasks. A distributed computing environment designed for the execution of such tasks in a certain subject domain is called problem-oriented environment. To efficiently use resources of the distributed computing environment, special scheduling algorithms are applied. Nowadays, a great number of such algorithms have been proposed. Some of them (like the DSC algorithm) take into account specific features of problem-oriented workflow applications. Others (like Min–Min algorithm) take into account many-core structure of nodes of the computational network. However, none of them takes into account both factors. In this paper, a mathematical model of problem-oriented computing environment is constructed, and a new problem-oriented scheduling (POS) algorithm is proposed. The POS algorithm takes into account both specifics of the problem-oriented jobs and multi-core structure of the computing system nodes. Results of computational experiments comparing the POS algorithm with other known scheduling algorithms are presented.     

A dominant predecessor duplication scheduling algorithm for heterogeneous systems

This paper proposes a new duplication-based task scheduling algorithm for distributed heterogeneous computing (DHC) systems. For such systems, many researchers have focused on solving the NP-complete problem of scheduling directed acyclic task graphs to minimize the makespan. However, the heterogeneity of computational resources and communication mechanisms poses some major obstacles to achieving high parallel efficiency. This paper proposes a heuristic strategy called the Dominant Predecessor Duplication (DPD) scheduling algorithm, which allows for system heterogeneities and communication bandwidth to exploit the potential of parallel processing. This algorithm can improve system utilization and avoid redundant resource consumption, resulting in better schedules. Experimental results show that the system heterogeneities and program structures of applications affect scheduling performance, and that our presented algorithm is better able to avoid these problems than those presented in previous literature. Here, we show that our algorithm can be applied to design efficient distributed systems to overcome performance bottlenecks caused by system heterogeneities.

Distributed scheduling for disconnected cooperation

Ability to cooperate on common tasks in a distributed setting is key to solving a broad range of computation problems ranging from distributed search such as SETI to distributed simulation and multi-agent collaboration. In such settings there exists a trade-off between computation and communication: both resources must be managed to decrease redundant computation and to ensure efficient computational progress. This paper deals with scheduling issues for distributed collaboration. Specifically, we examine the extreme situation where initially collaboration must occur without communication. That is, we consider the extent to which efficient collaboration is possible if all resources are directed to computation at the expense of communication. The results summarized here precisely characterize the ability of distributed agents to collaborate on a known collection of independent tasks by means of local scheduling decisions that require no communication and that achieve low redundancy in task executions. Such scheduling solutions exhibit an interesting connection between the distributed collaboration problem and the design theory. The lower bounds presented here along with the randomized and deterministic schedule constructions show the limitations on such low-redundancy cooperation and show that schedules with near-optimal redundancy can be efficiently constructed by processors working in isolation. The work of G. Malewicz was done when he was a Ph.D. student at the University of Connecticut, and in part during a visit to the Specification and Algorithm Research Department, AT&T Shannon Lab, and the Supercomputing Technologies Group, Massachusetts Institute of Technology. Parts of this article appeared in a preliminary form in the Proceedings of the 14th International Symposium on Distributed Computing [24], Springer LNCS Vol. 1914, pp. 119–133, in the Proceedings of the 8th International Colloquium on Structural Information and Communication Complexity [23], and the doctoral thesis of the first author.     

DRT-UNIX系统的任务调度

任务调度是分布式实时系统的核心问题之一.文章概述了实时系统的任务调度,结合DRT-UNIX系统的实际情况,提出了一种任务调度算法,并对算法的优点进行了分析.     

Solving distributed FMS scheduling problems subject to maintenance: Genetic algorithms approach

In general, distributed scheduling problem focuses on simultaneously solving two issues: (i) allocation of jobs to suitable factories and (ii) determination of the corresponding production scheduling in each factory. The objective of this approach is to maximize the system efficiency by finding an optimal planning for a better collaboration among various processes. This makes distributed scheduling problems more complicated than classical production scheduling ones. With the addition of alternative production routing, the problems are even more complicated. Conventionally, machines are usually assumed to be available without interruption during the production scheduling. Maintenance is not considered. However, every machine requires maintenance, and the maintenance policy directly affects the machine's availability. Consequently, it influences the production scheduling. In this connection, maintenance should be considered in distributed scheduling. The objective of this paper is to propose a genetic algorithm with dominant genes (GADG) approach to deal with distributed flexible manufacturing system (FMS) scheduling problems subject to machine maintenance constraint. The optimization performance of the proposed GADG will be compared with other existing approaches, such as simple genetic algorithms to demonstrate its reliability. The significance and benefits of considering maintenance in distributed scheduling will also be demonstrated by simulation runs on a sample problem.     

On the convergence of the holistic analysis for EDF distributed systems

Dynamic scheduling techniques, and EDF (Earliest Deadline First) in particular, have demonstrated their ability to increase the schedulability of real time systems compared to fixed-priority scheduling. In distributed systems, the scheduling policies of the processing nodes tend to be the same as in stand-alone systems and, although few EDF networks exist, it is foreseen that dynamic scheduling will gradually develop into real-time networks. There are some response time analysis techniques for EDF scheduled distributed systems, mostly derived from the holistic analysis developed by Spuri. A major factor influencing the response time is the release jitter of each task, which is the maximum variation suffered by the release time of the task jobs. The convergence of the holistic analysis in the context of EDF distributed systems with shared resources had not been studied until now. There is a circular dependency between the task release jitter values, response times and the preemption level ceilings of shared resources. In this paper we present an extension of Spuri’s algorithm and we demonstrate that its iterative formulas are non-decreasing, even in the presence of shared resources. This result enables us to assert that the new algorithm converges towards a solution for the response times of the tasks and messages in a distributed system.¹     

DCSP和DCOP求解研究进展

分布式约束满足问题（DCSP）和分布式约束最优问题（DCOP）的研究是分布式人工智能领域的基础性工作。本文首先介绍了卿和DCOP的形式化描述及对实际应用问题的建模方法。在DCSP和DCOP的求解中，通常对问题要进行限制和要求，同时要满足分布性、异步性、局部性、完备性的原则。异步回溯（ABT）、异步弱承诺搜索（AWC）和分布式逃逸（DB）算法是求解DCSP的有代表性的算法；DCSP算法对DCOP求解产生了影响，但由DCSP一般化到DCOP的算法，仅适用于解决部分特定的问题，DCOP的最优、异步算法有异步分布式约束最优算法（A—dopt）和最优异步部分交叉算法（OptAPO）。本文讨论了上述算法的性能。相关的研究工作在多局部变量的处理、超约束DCSP、算法性能度量、通信的保密等方面进行了扩充，在对问题本身的研究、建模方法学、算法、与其他方法的结合以及拓展应用领域等方面仍有许多问题需要进一步研究。     

分布事务处理中的资源管理

1 引言在分布事务处理环境中,资源管理器(数据库管理系统,可靠消息队列以及事务性文件系统等是最常见的资源管理器)扮演着数据管理的核心作用,因此,分布事务处理中的资源管理的研究显得极为重要。     

Benchmarking hybrid algorithms for distributed constraint optimisation games

In this paper, we consider algorithms for distributed constraint optimisation problems (DCOPs). Using a potential game characterisation of DCOPs, we decompose eight DCOP algorithms, taken from the game theory and computer science literatures, into their salient components. We then use these components to construct three novel hybrid algorithms. Finally, we empirical evaluate all eleven algorithms, in terms of solution quality, timeliness and communication resources used, in a series of graph colouring experiments. Our experimental results show the existence of several performance trade-offs (such as quick convergence to a solution, but with a cost of high communication needs), which may be exploited by a system designer to tailor a DCOP algorithm to suit their mix of requirements.     

Resource-aware hybrid scheduling algorithm in heterogeneous distributed computing

Today, almost everyone is connected to the Internet and uses different Cloud solutions to store, deliver and process data. Cloud computing assembles large networks of virtualized services such as hardware and software resources. The new era in which ICT penetrated almost all domains (healthcare, aged-care, social assistance, surveillance, education, etc.) creates the need of new multimedia content-driven applications. These applications generate huge amount of data, require gathering, processing and then aggregation in a fault-tolerant, reliable and secure heterogeneous distributed system created by a mixture of Cloud systems (public/private), mobile devices networks, desktop-based clusters, etc. In this context dynamic resource provisioning for Big Data application scheduling became a challenge in modern systems. We proposed a resource-aware hybrid scheduling algorithm for different types of application: batch jobs and workflows. The proposed algorithm considers hierarchical clustering of the available resources into groups in the allocation phase. Task execution is performed in two phases: in the first, tasks are assigned to groups of resources and in the second phase, a classical scheduling algorithm is used for each group of resources. The proposed algorithm is suitable for Heterogeneous Distributed Computing, especially for modern High-Performance Computing (HPC) systems in which applications are modeled with various requirements (both IO and computational intensive), with accent on data from multimedia applications. We evaluate their performance in a realistic setting of CloudSim tool with respect to load-balancing, cost savings, dependency assurance for workflows and computational efficiency, and investigate the computing methods of these performance metrics at runtime.     

Distributed Constraint Optimization Problems: Review and perspectives

Intelligent agents is a research area of the Artificial Intelligence intensely studied since the 1980s. Multi-agent systems represent a powerful paradigm of analyzing, projecting, and developing complex systems. One of the main difficulties in modeling a multi-agent system is defining the coordination model, due to the autonomous behavior of the agents. Distributed Constraint Optimization Problems (DCOP) have emerged as one of most important formalisms for coordination and distributed problem solving in multi-agent systems and are capable of modeling a large class of real world problems naturally. This work aims to provide an overview and critical review of DCOP, addressing the most popular methods and techniques, the evolution and comparison of algorithms, and future perspectives on this promising research area.     

Node and Link Allocation in Network Virtualization Based on Distributed Constraint Optimization

Virtual Networks (VNs) offer a flexible and economic approach to deploy customer suited networks. However, defining how resources of a physical network are used to support VNs requirements is a NP-hard problem. For this reason, heuristics have been used on mapping of virtual networks. Although heuristics do not ensure the optimal solution, they implement fast solutions and showed satisfactory results. This work presents a modeling of the node and link allocation problem using Distributed Constraint Optimization Problem (DCOP) with factor graphs, which is a formalism widely used in real distributed optimization problems. In our approach, we use the max-sum algorithm to solve the DCOP. Correctness criteria for this approach are discussed and verifications are conducted through model checking.     

基于约束图分片求解DCOP的Agent组织结构

MAS中许多分布式推理问题可以建模为分布式约束优化问题(DCOP),解决DCOP的分布式算法已经成为MAS中的重要基础.已有的Adopt等算法通过对等的Agent之间的平等协商完成求解,强调了异步通信、分布计算与对解质量的保证,在求解问题的组织结构方面仍有改进余地.可以采用一种基于分散与集中相结合的思路,基于对约束图分片的方法及核心结点、通信主干道等概念,构造新颖的Agent组织结构,完成DCOP问题的异步、分布求解.在该组织结构下求解DCOP的算法可在效率、适应动态性方面得到改善,并将一个Agent一个变量和一个Agent多个变量的DCOP求解方法统一起来.     

Approximation algorithms and heuristics for task scheduling in data‐intensive distributed systems

In this work, we are interested in the problem of task scheduling on large‐scale data‐intensive computing systems. In order to achieve good performance, one must construct not only good task schedules but also good data allocation across nodes on the system, since before a task can be executed, it must have access to data distributed on the system. In this article, we present a general formulation of a static problem that combines both scheduling and replication problems in data‐intensive distributed systems. We show that this problem does not admit an approximation algorithm. However, considering a restricted version of the problem that considers some practical constraints, an approximation algorithm can be designed. From a practical perspective, we introduce a novel heuristic for the problem that is based on nodes clustering. We compare the heuristic with two adapted approaches from other works in the literature by computational simulations using an extensive set of instances based on real computer grids. We show that our heuristic often obtains the best solutions and also runs faster than other approaches.     

基于局部并行搜索的分布式约束优化算法框架

针对当前局部搜索算法在求解大规模、高密度的分布式约束优化问题（DCOP）时,求解困难且难以跳出局部最优取得进一步优化等问题,提出一种基于局部并行搜索的分布式约束优化算法框架（LPOS）,算法中agent通过自身的取值并行地搜索局部所有邻居取值来进一步扩大对解空间的搜索,从而避免算法过早陷入局部最优。为了保证算法的收敛性与稳定性,设计了一种自适应平衡因子K来平衡算法对解的开发和继承能力,并在理论层面证明了并行搜索优化算法可以扩大对解空间的搜索,自适应平衡因子K可以实现平衡目的。综合实验结果表明,基于该算法框架的算法在求解低密度和高密度DCOP时性能都优于目前最新的算法。特别是在求解高密度DCOP中有显著的提升。     

分布式任务调度的智能化及其实验系统 KZ2／FRD

在一个大型分布式系统中,传统的调度方法存在着知识的不确定性、不完整性、调度不稳定性和策略单一性等问题.为了解决这些问题,本文提出一个智能分布式任务调度的新方法,并介绍了实验系统KZ2/FRD的实现和性能分析.     

Scheduling in a dynamic heterogeneous distributed system using estimation error

In real-world dynamic heterogeneous distributed systems, allocating tasks to processors can be an inefficient process, due to the dynamic nature of the resources, and the tasks to be processed. The information about these tasks and resources is not known a priori, and thus must be estimated online. We utilize the accuracy of these estimates, and when combined with different objectives, such as minimizing makespan and evenly distributing load, naturally gives rise to a family of four different scheduling algorithms. The algorithms have been implemented on a real-world heterogeneous distributed system with up to 90 processors. A set of real-world problems from the areas of cryptography, bioinformatics, and biomedical engineering were used as a test-set to measure the effectiveness of the scheduling algorithms. We have found that considering estimation error when allocating tasks to processors can provide more efficient solutions, than when estimation error is not considered. We have found that using a simple heuristic, combined with estimation error, can in some cases provide solutions approaching the efficiency of complicated well-known evolutionary algorithms.     

A distributed switch scheduling algorithm

The maximum weight matching algorithm is a high-performance scheduling algorithm for cross-bar switches. It is known that it performs optimally under heavy loads. However, its centralized nature and high computational complexity limit the algorithm’s applicability. This paper presents a randomized algorithm for distributed switch scheduling that is capable of delivering high throughput.