Protocols for Deadlock Detection in Distributed Database Systems

In distributed databases, deadlocks may occur due to conflicts in data file lockings A system is in a deadlock if and only if there is a directed cycle in its demand graph. However, due to the inherent communication delay in a distributed system, it is not easy to construct a consistent demand graph for a distributed system. In this paper, three deadlock detection protocols are discussed. The first protocol uses two communication phases. The second protocol uses a single communication phase. Based on the second protocol, a one-phase hierarchical deadlock detection protocol is developed.     

Locking and Deadlock Detection in Distributed Data Bases

This paper descrbes two protocols for the detection of deadlocks in distributed data bases–a hierarchically organized one and a distributed one. A graph model which depicts the state of execution of all transactions in the system is used by both protocols. A cycle in this graph is a necessary and sufficient condition for a deadlock to exist. Nevertheless, neither protocol requires that the global graph be built and maintained in order for deadlocks to be detected. In the case of the hierarchical protocol, the communications cost can be optimized if the topology of the hierarachy is appropriately chosen.     

On Characterization and Correctness of Distributed Deadlock Detection

Distributed deadlock detection requires identifying the presence of certain properties in the global state of distributed systems. Distributed deadlock detection is complicated due to the lack of both global memory and a common physical clock, and due to unpredictable message delays. We characterize the formation and detection of distributed deadlocks in terms of the contents of local memory of distributed nodes/sites. We describe how the interaction between deadlock detection and deadlock resolution can lead to the detection of false deadlocks that are impossible to avoid due to inherent system limitations. We define shadow, phantom, and pseudo deadlocks in the proposed framework. We give examples of existing incorrect deadlock detection algorithms to illustrate how they violate the developed requirements for distributed deadlock detection. The characterization provides an insight into the properties of distributed deadlocks, expresses inherent limitations of distributed deadlock detection, and yields new correctness criteria for distributed deadlock detection algorithms.     

Comments on "Protocols for Deadlock Detection in Distributed Database Systems"

The two-phase deadlock detection protocol in the above paperl detects false deadlocks. This is contrary to what the authors claim. The false detection o. f deadlocks is shown using a counterexample.     

FC3D: flow control-based distributed deadlock detection mechanism for true fully adaptive routing in wormhole networks

Two general approaches have been proposed for deadlock handling in wormhole networks. Traditionally, deadlock-avoidance strategies have been used. In this case, either routing is restricted so that there are no cyclic dependencies between channels or cyclic dependencies between channels are allowed provided that there are some escape paths to avoid deadlock. More recently, deadlock recovery strategies have begun to gain acceptance. These strategies allow the use of unrestricted fully adaptive routing, usually outperforming deadlock avoidance techniques. However, they require a deadlock detection mechanism and a deadlock recovery mechanism that is able to recover from deadlocks faster than they occur. In particular, progressive deadlock recovery techniques are very attractive because they allocate a few dedicated resources to quickly deliver deadlocked messages, instead of killing them. Unfortunately, distributed deadlock detection is usually based on crude time-outs, which detect many false deadlocks. As a consequence, messages detected as deadlocked may saturate the bandwidth offered by recovery resources, thus degrading performance. Additionally, the threshold required by the detection mechanism (the time-out) strongly depends on network load, which is not known in advance at the design stage. This limits the applicability of deadlock recovery on actual networks. We propose a novel distributed deadlock detection mechanism that uses only local information, detects all the deadlocks, considerably reduces the probability of false deadlock detection over previously proposed techniques, and is not significantly affected by variations in message length and/or message destination distribution.     

Asynchronous operations in distributed concurrency control

Distributed locking is commonly adopted for performing concurrency control in distributed systems. It incorporates additional steps for handling deadlocks. This activity is carried out by methods based on wait-for-graphs or probes. The present study examines detection of conflicts based on enhanced local processing for distributed concurrency control. In the proposed "edge detection" approach, a graph-based resolution of access conflicts has been adopted. The technique generates a uniform wait-for precedence order at distributed sites for transactions to execute. The earlier methods based on serialization graph testing are difficult to implement in a distributed environment. The edge detection approach is a fully distributed approach. It presents a unified technique for locking and deadlock detection exercises. The technique eliminates many deadlocks without incurring message overheads.     

On Concurrency Control in Multidatabase Systems with an Extended Transaction Model

A major concurrency control problem that we have to cope in multidatabase systems is the global deadlock detection and resolution problem. This detection must take into account the autonomy of local systems, which make impossible the visibility of the state of local transactions. A well-known approach to detect such deadlocks, called potential global deadlocks, is one based on the potential conflict graph (PCG) appropriate for the multidatabase transaction model with a global commit protocol. This classical transaction model is very constraining for applications manipulating great volumes of information, and where subtransaction terminations (commit or abort) of global transactions are not totally dependant. In this paper we present an effective potential global deadlock characterization, and an efficient potential global deadlock detection algorithm, in multidatabase systems with an extended transaction model more suited for such applications.     

A Two-Level Distributed Detection Algorithm of AND/OR Deadlocks

Numerous algorithms on distributed deadlock detection in distributed systems have been proposed for various deadlock models such as the AND model, OR model, and AND/OR model. This paper describes a new distributed algorithm for the AND/OR model by two levels of deadlock detection procedures. In every deadlock model, the existence of a cycle in a wait-for graph is a necessary condition. At the first level of our algorithm, a wait-for cycle is detected with a very simple operation. If no cycle is found, a deadlock does not exist. In this level, deadlocks consisting of AND-requested nodes are detected, and for the cycle of AND- and OR-requested nodes, an initiator is elected and the second-level algorithm is initiated by the initiator. The second-level algorithm uses the deadlock detection method of Herman and Chandy, but the communication cost is reduced even in the worst case because the second-level operation can be initiated by only qualified initiators.     

Backward validation of communicating complex state machines in web services environments

Communicating Finite State Machines (CFSM) lack the high level syntactic and structural abstractions of Communicating Complex State Machines (CCSM), such as nesting and encapsulation, to model highly complex protocols that are likely to arise in web services environments. The incorporation of these features in a protocol specification model would require the design of a new validation technique to efficiently check for protocol errors, such as deadlocks and non-reachable transitions. A reachability graph is used to represent the execution states of the protocol and to verify their consistency. In this paper, we propose a new validation technique for protocols modeled with complex FSM, called RLRA (Reverse Leaping Reachability Analysis), which enables the detection of all deadlock errors. It is a backtracking approach, which first identifies an initial set of suspected states, those possibly containing deadlocks, then refines this set to those likely to cause deadlock, and finally backtracks through the graph while checking for errors until the root state of the protocol is reached. Leap graphs are employed to prune the number of execution states examined, and thereby mitigate the combinatorial explosion of the state space. Extensive tests and comparisons were performed, which show the effectiveness of our technique.     

基于锁增广分段图的多线程程序死锁检测

死锁是并行程序常见的缺陷之一,动态死锁分析方法根据程序运行轨迹构建锁图、分段图等模型来检测死锁.然而,锁图及其现有的各种变型无法区分同一循环中锁授权语句的多次执行,扩展锁图中记录的锁集无法捕捉线程曾经持有而又随后释放的锁信息,分段图无法刻画锁的获取和释放操作与线程启动操作耦合而导致的段间依赖关系.上述问题导致了多种死锁...     

容错的分布式系统通用死锁模型检测解除算法

分布式系统技术为采用低成本购建高性能系统提供了有效的途径,但是由于资源的分配与需求可能产生冲突,造成系统中发生死锁,导致系统运行陷入停滞.在不可靠的分布式系统中,故障会干扰正常的死锁检测,但现有的死锁检测算法不具有容错功能.对失效形式进行了归类,提出一个容错的死锁检测解除算法.算法建立在通用的AND-OR模型基础上,采用扩散计算和集中规约方式,不仅能够检测到死锁,而且能给出死锁环的全部成员.若死锁拓扑处于静态且为环状,算法的消息复杂度的上限为e n-1,时间复杂度为d,其中e为死锁等待图中边的个数,n和d为构成死锁环的节点的个数,分析表明算法性能等于或优于同类算法.     

A distributed deadlock resolution algorithm for the AND model

Previous proposals for Distributed Deadlock Detection/Resolution algorithms for the AND model have the main disadvantage of resolving false deadlocks, that is, nonexisting or currently being resolved deadlocks. This paper provides an algorithm free of false deadlock resolutions, A simple specification for a safe deadlock resolution algorithm is introduced, and the new distributed solution is developed in a hierarchical fashion from its abstract specification. The algorithm is probe-based, uses node priorities, and coordinates the actions of resolvers so that false deadlocks are not resolved. The solution is formally proven correct by using the input-output Automata Model. Finally, a study about the liveness of the algorithm is provided     

A cost-effective approach to deadlock handling in wormhole networks

Wormhole networks have traditionally used deadlock avoidance strategies. More recently, deadlock recovery strategies have begun to gain acceptance. In particular, progressive deadlock recovery techniques allocate a few dedicated resources to quickly deliver deadlocked packets. Deadlock recovery is based on the assumption that deadlocks are rare; otherwise, recovery techniques are not efficient. Measurements of deadlock occurrence frequency show that deadlocks are highly unlikely when enough routing freedom is provided. However, networks are more prone to deadlocks when the network is close to or beyond saturation, causing some network performance degradation. Similar performance degradation behavior at saturation was also observed in networks using deadlock avoidance strategies. In this paper, we take a different approach to handling deadlocks and performance degradation. We propose the use of an injection limitation mechanism that prevents performance degradation near the saturation point and, at the same time, reduces the probability of deadlock to negligible values. We also propose an improved deadlock detection mechanism that uses only local information, detects all deadlocks, and considerably reduces the probability of false deadlock detection over previous proposals. In the rare case when impending deadlock is detected, our proposal consists of using a simple recovery technique that absorbs the deadlocked message at the current node and later reinjects it for continued routing toward its destination. Performance evaluation results show that our new approach to handling deadlock is more efficient than previously proposed techniques     

Invariant-based verification of a distributed deadlock detectionalgorithm

It is argued that most previous proposals for distributed deadlock detection are incorrect because they have used informal/intuitive arguments to prove the correctness of their algorithms. Informal and intuitive arguments are prone to errors because of the highly complex nature of distributed deadlock detection/resolution algorithms. The priority-based probe algorithm for distributed deadlock detection and resolution of A.L. Choudhary et al. (1989) is corrected, and it is formally proven that the modified algorithm is correct (i.e., that it does detect all deadlocks and does not report phantom deadlocks). The proof technique is novel in that the authors first abstract the properties of the deadlock detection and resolution algorithm by invariants, and then show that the invariants imply the desired correctness of the algorithm     

Deadlock Models and a General Algorithm for Distributed Deadlock Detection

This paper deals with the problem of deadlock detection in asynchronous message passing systems in a system model that covers unspecified receptions and non-FIFO channels. It presents a hierarchy of deadlock models and deadlock detection problems. It abstracts deadlocks by a general deadlock model that has the same modeling power as the OR-AND model; however, it has much concise expressive power. An abstract general definition of deadlocks in distributed systems is presented that defines deadlocks independently of the underlying deadlock model. This formulation can be used to design a single distributed deadlock detection algorithm which uniformly addresses all deadlocks in the context of various request models such as AND, OR, AND-OR, and k-out-of-n requests. A simple generalized deadlock detection algorithm that uses a circulating token is presented to illustrate the concept. The algorithm is formally described and proven correct. Moreover, possible refinements of the basic solution concerning improvements of token routing and parallel implementation are outlined and evaluated. Extensions to individual and global termination issues are also addressed. Since the proposed deadlock detection algorithm is designed around the abstract definition of deadlocks, it has some very favorable features.     

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。     

Efficient detection and resolution of OR deadlocks in distributed systems

This paper proposes a distributed algorithm for resolving deadlocks under the OR request model. The algorithm builds a distributed spanning tree by propagating probes. An encoding scheme is devised to deduce the ancestor–descendant relationship between tree nodes, so that the initiator of the algorithm collects only non-tree edge information to detect deadlock, whereas the current algorithms require all the edge information for deadlock detection. The proposed algorithm resolves all deadlocks reachable from the initiator. Its performance in terms of number of messages and execution time is better than or comparable to that of the existing algorithms. We further showed through analytic evaluation that the suggested algorithm substantially shortens deadlock detection time.     

A Priority Based Distributed Deadlock Detection Algorithm

Deadlock handling is an important component of transaction management in a database system. In this paper, we contribute to the development of techniques for transaction management by presenting an algorithm for detecting deadlocks in a distributed database system. The algorithm uses priorities for transactions to minimize the number of messages initiated for detecting deadlocks. It does not construct any wait-for graph but detects cycles by an edge-chasing method. It does not detect any phantom deadlock (in the absence of failures), and for the resolution of deadlocks it does not need any extra computation. The algorithm also incorporates a post-resolution computation that leaves information characterizing dependence relations of remaining transactions of the deadlock cycle in the system, and this will help in detecting and resolving deadlocks which may arise in the future. An interesting aspect of this algorithm is that it is possible to compute the exact number of messages generated for a given deadlock configuration. The complexity is comparable to the best algorithm reported. We first present a basic algorithm and then extend it to take into account shared and exclusive lock modes, simultaneous acquisition of multiple locks, and nested transactions.     

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.     

OpenMP Fortran程序中死锁的静态检测

与BARRIER相关的死锁是导致OpenMP程序失效的重要隐患之一.对该类隐患的静态检测有助于在OpenMP程序运行之前提高其正确性.为了便于检测,将这种死锁分为两类.借助搜索与数据流分析分别按照存在性规则和非一致性规则检测第1类和第2类死锁.扩展了传统的控制流图以表示OpenMP程序.对于每个检测到的死锁,通过回溯记录控制流图中相关的路径,并利用静态分支预测量化其严重程度.基于上述思想,实现了一个OpenMP Fortran程序中死锁的静态检测工具C-Checker.实验表明,该工具能有效地检测OpenMP程序中与BARRIER相关的死锁.