基于动态探针的分布式死锁预防策略

数据库系统中事务死锁的检测和预防,对提高系统并发性和整体性能具有重要意义。在研究了现有的分布式数据库系统死锁预防策略的基础上,利用创建动态探针(DP)技术,提出了一种改进的死锁预防策略。该DP方法在创建探针后将其发往可能产生死锁的节点,接收到探针后,根据节点信息与探针所包含信息的比较结果,可以判断是否有死锁发生,从而达到预防死锁的目的。分析表明,该方法提高了死锁预防的有效性和系统资源的利用率。     

CAN总线中非周期信息的随机动态优先级调度

针对CAN总线中非周期信息传输的“死锁”现象,利用动态优先级提升机制中消息在发送队列的位置随等待时间动态改变的思想,对非周期性信息的传输采用基于随机数的动态优先级调度策略,以解决CAN总线中非周期信息传输的“死锁”问题。     

分布式OS中处理死锁两种方法

本文扼要介绍和剖析了分布式 OS 中解决死锁问题的两种方法:时间戳定序方法和集中式及层次式死锁检测方法。前者是基于死锁预防的,后者则是基于死锁检测的。     

一种改进型优先级天花板协议设计与实现

分析了嵌入式操作系统μC/OS-II产生的优先级反转问题及缺陷,提出了一种改进型优先级天花板协议,给出了协议的原理,该协议可以解决优先级反转问题,具有预防系统死锁等特点,并介绍了“修改μC/OS-II内核以实现改进型优先级天花板协议”的思想和方法。     

优先级反转和死锁的资源管理模式研究与实现

为了抑制优先级反转现象,采用优先级继承协议来解决优先级反转现象,在此协议中不能避免系统死锁现象的发生。分析了死锁现象产生的原因的,在优先级继承协议基础上提出了优先级反转和死锁问题的资源管理模式,采用排序锁定共享资源的方法,使共享资源按照SourceID由低到高的共享顺序依次被访问。理论证明该方法在一定程度上抑制优先级反转且避免了死锁现象的发生,通过实验结果表明了解决优先级反转和死锁的资源管理模式的正确性与可行性。     

分布式数据库系统的动态负载平衡策略及算法设计

随着网络中数据库应用的发展，使得分布式数据库系统的负载平衡问题突显出来。目前大多数分布式数据库管理系统没有负责平衡功能，其负载平衡依赖于操作系统的负载平衡机制来解决，这样带来的问题是系统负载的评价粒度细小和负载转移的开销增加。讨论了动态负载平衡策略的要素，针对分布式数据库系统的负载平衡问题，提出了以事务队列长度作为负载评价标准，并给出了一个动态负载平衡策略及算法。     

ADA—DDBMS中的并发控制

并发控制是ＤＤＢＭＳ（分布式数据库管理系统）中事务管理的重要功能．本文介绍了一种基于封锁的积极方法与消极方法相结合的并发控制策略．它根据全系统实际运行的即时状态，动态地决定对事务采取的执行策略，大大减少了积极封锁所易产生的死锁情况，同时又改善了消极封锁效率低的问题．     

一种多agent系统中死锁问题的解决策略

多agent系统注重agent之间的相互协作,但是在进行信息传递的过程中不可避免地会出现死锁.文章针对这一问题,结合文献[1]的有关思想,对死锁产生的条件进行了分析,讨论了死锁过程中可能出现的各种情况,利用个体agent的行为的独立性的以及多agent之间的相互依赖关系,采用消息传递和信息存储数据链等技术给出了死锁预防策略以及死锁消除策略,从而有效地对死锁情况进行预防和消除.     

一种多agent系统中死锁问题的解决策略

多agent系统注重agent之间的相互协作,但是在进行信息传递的过程中不可避免地会出现死锁。文章针对这一问题,结合文献[1]的有关思想,对死锁产生的条件进行了分析,讨论了死锁过程中可能出现的各种情况,利用个体agent的行为的独立性的以及多agent之间的相互依赖关系,采用消息传递和信息存储数据链等技术给出了死锁预防策略以及死锁消除策略,从而有效地对死锁情况进行预防和消除。     

基于阻塞调度的优先级反转解决策略

目前通常采用优先级上限协议解决策略,但该协议的系统资源利用率较低。针对该问题,深入分析了优先级反转的必要条件并提出了一种新的阻塞调度算法,能有效的避免优先级反转和检测死锁现象,同时具有较高的资源利用率和较广的适用范围。     

The Performance of Alternative Strategies for Dealing with Deadlocks in Database Management Systems

There is growing evidence that, for a fairly wide variety of database workloads and system configurations, locking is the concurrency control strategy of choice. With locking, of course, comes the possibility of deadlocks. Although the database literature is full of algorithms for dealing with deadlocks, very little in the way of practical performance information is available to a database system designer faced with the decision of choosing a good deadlock resolution strategy. This paper is an attempt to bridge this gap in our understanding of the behavior and performance of alternative deadlock resolution strategies. We employ a simulation model of a database environment to study the relative performance of several strategies based on deadlock detection, several strategies based on deadlock prevention, and a strategy based on timeouts. We show that the choice of the best deadlock resolution strategy depends upon the level of data contention, the resource utilization levels, and the types of transactions. We provide guidelines for selecting a deadlock resolution strategy for different operating regions.     

Deadlock detection in distributed database systems: a new algorithm and a comparative performance analysis

This paper attempts a comprehensive study of deadlock detection in distributed database systems. First, the two predominant deadlock models in these systems and the four different distributed deadlock detection approaches are discussed. Afterwards, a new deadlock detection algorithm is presented. The algorithm is based on dynamically creating deadlock detection agents (DDAs), each being responsible for detecting deadlocks in one connected component of the global wait-for-graph (WFG). The DDA scheme is a “self-tuning” system: after an initial warm-up phase, dedicated DDAs will be formed for “centers of locality”, i.e., parts of the system where many conflicts occur. A dynamic shift in locality of the distributed system will be responded to by automatically creating new DDAs while the obsolete ones terminate. In this paper, we also compare the most competitive representative of each class of algorithms suitable for distributed database systems based on a simulation model, and point out their relative strengths and weaknesses. The extensive experiments we carried out indicate that our newly proposed deadlock detection algorithm outperforms the other algorithms in the vast majority of configurations and workloads and, in contrast to all other algorithms, is very robust with respect to differing load and access profiles. Received December 4, 1997 / Accepted February 2, 1999     

分布式系统死锁的预防、避免和检测

分布式系统涉及到资源和数据的高度共享,从而可能引发死锁。分布式系统的死锁是由于资源和通讯产生的。从分布式系统死锁产生的条件,解决策略,以及分布式系统中死锁预防、避免和检测的各种算法进行了具体阐述。     

移动Agent系统的一种分布式死锁检测方案

传统的分布式死锁解决方案不适合于实体在网络中自由移动的MAS系统.本文描述了一种移动Agent系统的分布式死锁算法,使用专职Agent从事死锁检测和解决.该方案的特点是地点参考、拓扑独立、容错、异步操作.文中建立了StochasticPetri Net模型,并使用仿真试验给出它和Diffusion Computation算法的性能比较.     

A performance study of deadlock prevention algorithms in a distributed file system

This paper describes an implementation and performance evaluation of different deadlock prevention algorithms. A deadlock prevention algorithm ensures that deadlock will never happen. The algorithms for deadlock prevention are proposed and implemented in a locally distributed system. A number of experiments were executed in a distributed system for various lengths of file operation and different numbers of files. The performance of the system and of each algorithm is evaluated and discussed. Some general results are derived for a single-host and a distributed system.     

Sufficient condition for a communication deadlock and distributeddeadlock detection

The necessary and sufficient condition for deadlock in a distributed system and an algorithm for detection of a distributed deadlock based on the sufficient condition are formulated. The protocol formulated, checks all wait-for contiguous requests in one iteration. A cycle is detected when a query message reaches the initiator. A wait-for cycle is only the necessary condition for the distributed deadlock. A no-deadlock message is expected by the query initiator to infer a deadlock-free situation if at least one wait-for cycle is present. A no-deadlock message is issued by a dependent (query intercessor) that is not waiting-for. No no-deadlock message implies a deadlock, and processes listed in the received query messages are the processes involved in a distributed deadlock. Properties of the protocol are discussed. The authors show that a replication of a requested higher-priority (or older) process can prevent a distributed deadlock (in a continuous deadlock treatment). A replication is shown to recover (in a periodical deadlock handling) a sequence of processes from an indefinite wait-die scheme     

选举策略在分布式系统死锁避免中的应用

将单机系统或集中式系统中的死锁避免策略移植到分布式需要面临并发性和冲突问题的解决。本文通过分析二阶段锁的机制,引入了一种应用选举策略来幽雅地解决分布式系统中死锁避免所碰到问题的算法。     

Mobile agent-enabled framework for structuring and building distributed systems on the internet

Mobile agent has shown its promise as a powerful means to complement and enhance existing technology in various application areas. In particular, existing work has demonstrated that MA can simplify the development and improve the performance of certain classes of distributed applications, especially for those running on a wide-area, heterogeneous, and dynamic networking environment like the Internet. In our previous work, we extended the application of MA to the design of distributed control functions, which require the maintenance of logical relationship among and/or coordination of proc- essing entities in a distributed system. A novel framework is presented for structuring and building distributed systems, which use cooperating mobile agents as an aid to carry out coordination and cooperation tasks in distributed systems. The framework has been used for designing various distributed control functions such as load balancing and mutual ex- clusion in our previous work. In this paper, we use the framework to propose a novel ap- proach to detecting deadlocks in distributed system by using mobile agents, which dem- onstrates the advantage of being adaptive and flexible of mobile agents. We first describe the MAEDD (Mobile Agent Enabled Deadlock Detection) scheme, in which mobile agents are dispatched to collect and analyze deadlock information distributed across the network sites and, based on the analysis, to detect and resolve deadlocks. Then the design of an adaptive hybrid algorithm derived from the framework is presented. The algorithm can dynamically adapt itself to the changes in system state by using different deadlock detec- tion strategies. The performance of the proposed algorithm has been evaluated using simulations. The results show that the algorithm can outperform existing algorithms that use a fixed deadlock detection strategy.     

A partially distributed deadlock detection algorithm

In this paper, a partially distributed deadlock detection algorithm [PDDDA] with multiple outstanding requests is presented for use in distributed database systems. This algorithm allows a process to request many resources simultaneously and uses a central controller for detecting multisite deadlocks. The detection of local deadlocks and the maintenance of local deadlock information are performed at each of the local sites. This partially distributed algorithm alleviates the problem of congestion at the central controller in a centralized algorithm and needs fewer messages and smaller storage space than a fully decentralized algorithm. A set of criteria for comparing deadlock detection algorithms are also given and then used to compare PDDDA with a fully decentralized algorithm proposed by Isloor and Marsland.Research reported herein was supported by US Army CECOM, Ft. Monmouth, New Jersey, under Contract No. DAAB07-83-K-K542. The views, opinions, and/or findings contained in this paper are those of the authors and should not be construed as an official Deportment of the Army position, policy or decision.