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1.
封锁与可串行化调度是数据库并发操作采取的两种主要措施。判断一个调度是否可串行化调度的最有效方法是两段锁协议。但是,一方面,事务遵守两段锁协议只是可串行化调度的充分条件而不是必要条件;另一方面,遵守两段锁协议的事务仍可能发生死锁。文中给出了一种算法,利用该算法,不仅可判断出一个调度是否为可串行化调度,而且可判断出该调度是否会发生死锁。  相似文献   

2.
二维协同工作空间的并发操作加锁协议   总被引:2,自引:0,他引:2  
提出一种用于在二维工作空间中协同作业的并发操作加锁协议和相应的锁调度算法,协议采用悲观锁,以抽象的二维空间为并发操作的对象,支持任意锁粒度,具有无死锁性质.加锁协议和算法存一个实时分布式协同绘图系统中实现.协议的实现采用多Agent系统模型。将面向Agent的程序设计中Agent的情绪值的概念用于控制锁的释放和调度,支持并发操作者之间的主动协同和细粒度感知.  相似文献   

3.
叙述了关系型数据库管理系统中的事务管理和基于锁的事务并发控制方法。详细介绍了事务的串行化调度方法中的锁技术和锁协议,并深入讨论了锁的管理、死锁处理、幻影问题和其它加锁过程中可能出现的一些问题。  相似文献   

4.
2PL协议的Petri网模型   总被引:1,自引:0,他引:1  
2PL协议是目前并发事务数据库广泛采用以保证并发调度正确性的封锁协议,该文给出了2PL协议的Petri网模型,并利用该模型给出可预防死锁的封锁序列。  相似文献   

5.
XML数据库并发控制机制的研究   总被引:2,自引:0,他引:2  
刘波  张春海  李华 《计算机工程与应用》2005,41(21):198-201,205
并发控制是改善数据库系统事务性能的最重要的机制,多用户事务并发问题在XML原型数据库领域是一个难点。通过一种类XPath数据模型,定义基于此模型的几种XML数据库操作。在此基础上,提出一种基于XPath的锁协议(XPL)以及锁模型,并验证在此锁协议机制下的调度是可串行性调度,从而实现了XML原型数据库的多用户事务并发控制。最后通过实验对XPL协议的并发性能进行测试和分析。  相似文献   

6.
本文用带抑制/容许弧的增广有色Petri网构建一类带封锁机制的数据库并发控制模型,此模型适用于描述多个事务访问多个共享资源。其中采用了2PL协议解决了数据库中并发所引起的数据不一致性,并采取了FIFO策略避免了2PL协议引起的活锁问题,且给出死锁检测方法。  相似文献   

7.
本文通过分析并发控制中的几种锁模型及其在分布式环境下的拓展,提出了一种基于加锁粒度的分布式高优先级两段锁模型。在该模型中,引入一种加锁检测机制,通过该机制可以确定哪些冲突事务可以通过降低加锁粒度来解决冲突。同时提出了该模型的算法。该算法在避免死锁、提高事务的并发度上有很大的改善。  相似文献   

8.
为满足移动自组网(MANETS)多级事务处理的安全性和并发性要求,将多版本两段锁协议运用到MANETS多级事务中。该协议有效地解决了由于竞争产生的错误的事务调度以及安全问题。模拟仿真结果表明,多版本两段锁协议在延迟截至时间率和重启动率方面比单一的多版本协议或者单一的两段锁协议都要低。  相似文献   

9.
通过分析数据仓库体系结构中并发控制导致的数据的不一致性,提出了解决并发控制的动态加锁粒度的两段锁协议。  相似文献   

10.
多版本两段锁MV2PL协议是集中式和分布式数据库中广泛采用的并发控制方法。文中对传统的多版本两段锁MV2PL协议进行了优化,提出了一种更适合数据库的事务执行方法。  相似文献   

11.
移动实时嵌套事务的并发控制   总被引:5,自引:0,他引:5  
廖国琼  刘云生  杨进才 《计算机学报》2003,26(10):1326-1331
在移动计算环境中,事务移动性和无线网络固有的缺陷使得传统分布式实时事务管理机制不足以支持移动实时事务的执行,故有必要为移动实时事务研究新的事务处理机制以提高其成功率.该文着重研究移动实时事务的并发控制机制.首先,该文给出了一个考虑事务定时限制以及移动性的嵌套事务模型.然后,为减少移动分布式环境中解决数据冲突的开销,该文研究了一种结合优先级夭折和优先级继承的基于封锁的并发控制协议PAI-2PL.当高优先级事务被低优先级事务阻塞时,对于相同家族事务,采用优先级继承方法解决冲突;而对于不同家族事务,则夭折重启低优先级事务.另外,为减少由于断接所引起的无效阻塞,PAI-2PL允许低优先级事务夭折处于断接状态的高优先级事务.通过性能测试,表明所提出的事务模型及并发控制机制能提高实时事务的成功率.  相似文献   

12.
在实时主动数据库中,事务不仅有时间约束,而且事务执行可能触发其它事务执行。传统并发控制协议不适应于实时主动数据库系统。该文研究了实时主动数据库事务执行模式,提出了有效性检查并发控制协议。协议使用动态调整串行次序策略,避免不必要的事务重启动。通过仿真模拟与HP2PL协议和OCC-TI-WAIT-50协议进行了比较。结果表明,该协议能有效地降低事务延误截止时间率和事务重启动率,性能优于HP2PL和OCC-TI-WAIT-50协议。  相似文献   

13.
Lam  Kam-Yiu  Hung  Sheung-Lun  Son  Sang H. 《Real-Time Systems》1997,13(2):141-166
The use of Static Two Phase Locking Protocols (S2PL) for concurrency control in real-time database systems (RTDBS) has received little attention in the past. Actually, real-time S2PL (RT-S2PL) protocols do possess some desirable features making them suitable for RTDBS, especially for distributed real-time database systems (DRTDBS) in which remote locking is required and distributed deadlock is possible. In this paper, different RT-S2PL protocols are proposed. They differ in their methods of reducing the blocking time of higher priority transactions. Their performance is studied and compared with a real-time dynamic two phase locking protocol (RT-D2PL), called Hybrid Two Phase Locking (Hb2PL). The impact of different system and workload parameters, such as mean inter-arrival time of transactions, number of remote lock requests of a transaction, communication overhead for sending messages, and database size on their performance have been examined. The performance results indicate that the RT-S2PL protocols are suitable for DRTDBS in which the proportion of local locks of a transaction is small and the communication overhead for locking is high.  相似文献   

14.
李龙  欧阳松 《计算机工程》2008,34(18):154-156
P2P网络是当前网络研究的热点之一,被认为是构建下一代网络的基础。该文基于混合式结构的P2P网络提出一种事务管理策略。该策略利用P2P网络中的超级节点处理能力强的特点,由超级节点管理普通节点上的事务调度。普通节点检查事务之间的冲突并向超级节点发送事务冲突消息。超级节点根据冲突消息确定事务之间的依赖关系,合理调度事务。并对提出的事务管理模型进行论证和仿真。  相似文献   

15.
介绍了几种用于RTDBS(实时数据库系统)中的并发控制模型以及它们在分布式环境下(DRTDBS)的拓展。根据DHP-2PL提出一种改进的并发控制模型。在该模型中,引入优先级分配机制和加锁检测机制。通过这两种机制可更好地协调DRTDBS中一致性与截止期的关系,同时也解决了DHP-2PL中事务高重启率的问题。  相似文献   

16.
2PL并发控制的研究与实现探析   总被引:4,自引:1,他引:4  
将数据库技术分别与面向对象技术(OO)和实时系统(RTS)等技术结合,在传统的2PL基础上提出了改进办法,实现OODBS中的资料一致性处理,在实时数据库系统中,建议使用一种新的协议:锁全写(2PL-LW)解决死锁,为在RTDBS系统中实现对事务处理提供了可行的并发控制调度方案。  相似文献   

17.
Concurrency control (CC) algorithms guarantee the correctness and consistency criteria for concurrent execution of a set of transactions in a database. A precondition that is seen in many CC algorithms is that the writeset (WS) and readset (RS) of transactions should be known before the transaction execution. However, in real operational environments, we know the WS and RS only for a fraction of transaction set before execution. However, optional knowledge about WS and RS of transactions is one of the advantages of the proposed CC algorithm in this paper. If the WS and RS are known before the transaction execution, the proposed algorithm will use them to improve the concurrency and performance. On the other hand, the concurrency control algorithms often use a specific static or dynamic equation in making decision about granting a lock or detection of the winner transaction. The proposed algorithm in this paper uses an adaptive resonance theory (ART)-based neural network for such a decision making. In this way, a parameter called health factor (HF) is defined for transactions that is used for comparing the transactions and detecting the winner one in accessing the database objects. HF is calculated using ART2 neural network. Experimental results show that the proposed neural-based CC (NCC) algorithm increases the level of concurrency by decreasing the number of aborts. The performance of proposed algorithm is compared with strict two-phase locking (S2PL) algorithm, which has been used in most commercial database systems. Simulation results show that the performance of proposed NCC algorithm, in terms of number of aborts, is better than S2PL algorithm in different transaction rates.  相似文献   

18.
In the presence of semantic information, serializability is too strong a correctness criterion and unnecessarily restricts concurrency. Many researchers have investigated the use of semantic information to allow interleaving among transactions which are non-serializable, but which nonetheless preserves the consistency of the database and is acceptable to the users. In this paper we consider a class of schedules, calledconflict-correct schedules, first proposed by Farrag and Özsu, which enlarges upon the class of serializable schedules by taking semantic information of transactions into account. In this paper we show that the problem of recognizing schedules in this class is NP-complete. Thus it is unlikely that there exists an efficient scheduler which accepts the entire class of conflict-correct schedules.This research was partially supported by MICRO grants with IBM and XEROX Corporations.  相似文献   

19.
A lot of research efforts have focused on global serializability, global atomicity, and global deadlocks in multidatabase systems. Surprisingly, however, very few transaction processing model exists that ensures global serializability, global atomicity, and freedom from global deadlocks in a uniform manner. In this paper, we examine previous transaction processing models and propose a new transaction processing model that generates globally serializable and deadlock-free schedules in failure-prone multidatabase systems. A new transaction processing model adopts rigid conflict serializability as a correctness criterion on global serializability, and follows an emulated 2PC, criteria for global commitment, and an abort-based multidatabase recovery scheme for global serializability in failure-prone multidatabase systems. In addition, a deadlock-free policy is suggested where rigid conflict serializability is enforced when each subtransaction, including redo transactions, begins its execution. To practically support a new transaction processing model, Rigid Ticket Ordering (RTO) methods are designed. The proposed transaction processing model has the following improvements: (a) it resolves abnormal direct conflicts identified in this paper, (b) it imposes no restrictions on the execution of local transactions, and (c) it relaxes the restrictions on the execution of global transactions.  相似文献   

20.
A non-two-phase database concurrency control technique is introduced. The technique is deadlock-free, places no restrictions on the structure of the data, never requires data to be reread, never forces a transaction to be rolled back in order to achieve serializability, applies a type of lock conversion, and allows items to be released to subsequent transactions as soon as possible. The method introduced, database flow graph locking (FGL), uses a directed acyclic graph to direct the migration of locks between transactions. Unlike many previous non-two-phase methods, the database need not be structured in any specific fashion. The effect of these changes is that, with the same serializable schedule, FGL obtains a higher degree of concurrency than two-phase locking (2PL). Overhead requirements for database flow graph locking are comparable to those for two-phase locking, with 2PL being better in low conflict situations and FGL better in high conflict  相似文献   

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