Validation concurrency control protocol in parallel real-time database systems

In parallel real-time database systems, concurrency control protocols must satisfy time constraints as well as the integrity constraints. The authors present a validation concurrency control(VCC) protocol, which can enhance the performance of real-time concurrency control mechanism by reducing the number of transactions that might miss their deadlines, and compare the performance of validation concurrency control protocol with that of HP2PL(High priority two phase locking) protocol and OCC-TI-WAIT-50(Optimistic concurrency control-time interval-wait-50) protocol under shared-disk architecture by simulation. The simulation results reveal that the protocol the author presented can effectively reduce the number of transactions restarting which might miss their deadlines and performs better than HP2PL and OCC-TI-WAIT-50. It works well when arrival rate of transaction is lesser than threshold. However, due to resource contention the percentage of missing deadline increases sharply when arrival rate is greater than the threshold.

Weak Serializable Concurrency Control in Distributed Real-Time Database Systems

Most of the proposed concurrency control protocols for real time database systems are based on serializability theorem. Owing to the unique characteristics of real time database applications and the importance of satisfying the timing constraints of transactions, serializability is too strong as a correctness criterion and not suitable for real time databases in most cases. On the other hand, relaxed serializability including epsilon serializability and similarity serializability can allow more real time transactions to satisfy their timing constraints, but database consistency may be sacrificed to some extent. We thus propose the use of weak serializability(WSR) that is more relaxed than conflicting serializability while database consistency is maintained. In this paper, we first formally define the new notion of correctness called weak serializability. After the necessary and sufficient conditions for weak serializability are shown, corresponding concurrency control protocol WDHP(weak serializable distributed high priority protocol) is outlined for distributed real time databases, where a new lock mode called mask lock mode is proposed for simplifying the condition of global consistency. Finally, through a series of simulation studies, it is shown that using the new concurrency control protocol the performance of distributed real time databases can be greatly improved.

Nested Transaction Concurrency Control in Parallel Real-Time Dat-abases

An integrated method for concurrency control in parallel real-time databases has been proposed in this paper. The nested transaction model has been investigated to offer more atomic execution units and finer grained control within in a transaction. Based on the classical nested locking protocol and the speculative concurrency control approach, a two-shadow adaptive concurrency control protocol, which combines the Sacrifice based Optimistic Concurrency Control (OPT-Sacrifice) and High Priority two-phase locking (HP2PL) algorithms together to support both optimistic and pessimistic shadow of each sub-transaction, has been proposed to increase the likelihood of successful timely commitment and to avoid unnecessary replication overload.

A solution for concurrency control and long transaction management in SDBMS

The problem of long transactions is a significant problem in spatial database. The checkout mechanism and multi version mechanism are two kind methods of solving the problem of long transactions. In this paper, we present a Shallow Version Management mechanism to realize multi version mechanism in spatial database. And we introduced a increment storage and dynamic version views building method to improve efficiency of storing and consulting. We also illuminate how to resolve the problem of long transaction concurrency control in spatial database by using multi version mechanism. At the end of this paper, we introduce some required means to version management in spatial database, like converge, compress and delete.

CRF:A Scheduling of Multi-Granularity Locks in Object-Oriented Database Systems

This paper introduces a multi-granularity locking model (MGL) for concurrency control in object-oriented database system briefiy, and presents a MGL model formally. Four lockingscheduling algorithms for MGL are proposed in the paper. The ideas of single queue scheduling(SQS) and dual queue scheduling (DQS) are proposed and the algorithm and the performance evaluation for these two scheduling are presented in some paper. This paper describes a new idea of thescheduling for MGL, compatible requests first (CRF). Combining the new idea with SQS and DQS,we propose two new scheduling algorithms called CRFS and CRFD. After describing the simulationmodel, this paper illustrates the comparisons of the performance among these four algorithms. Asshown in the experiments, DQS has better performance than SQS, CRFD is better than DQS, CRFSperforms better than SQS, and CRFS is the best one of these four scheduling algorithms.

Quasi serializable concurrency control in mobile broadcast environments

The problem of maintaining data consistency in mobile broadcast environments is researched. Quasi serializability is formally defined and analyzed at first. It was shown that quasi serializability is less stringent than serializability when database consistency is maintained for transactions. Then, corresponding concurrency control protocol that supports both update transactions and read-only transactions is outlined for mobile broadcast environments. Finally, the simulation results confirmed that the proposed protocol could improve the response time significantly.

Concurrency Control of Single-Level Transaction in WHYMX Object-Oriented Database System

The data model of WHYMX complicates transaction management. Traditional locking method is not powerful enough to solve the new problem of concurrency control of WHYMX's transaction. This paper presents a number of concurrency control algorithms based on the extended locking method.

Design and Implementation of a Concurrency Control Mechanism in an Object-Oriented Database System

This paper presents a practical concurrency control mechanism - ObjectLockingin OODBMS. Object-Locking can schedule transactions, each of themcan be considered as a sequence of high level operations defined on classes. Bythe properties of parallelity and coatativity between high level operations,proper lock modes for each operation are desigued and the compatibility matrixis constructed. With these lock modes, phatoms are kept away from databasesand a high degree of concurrency is achieved.

基于锁避免的事务内阻塞分析与调度策略

在现代教育环境中,高效且可靠的数据管理系统对于在线教育平台和学生信息管理系统的运行至关重要.随着教育数据量的持续增长和多用户访问频率的提高,数据库系统面临并发冲突操作带来的高吞吐要求的挑战.在众多并发控制策略中,基于锁的控制策略是数据库系统中常用的策略之一,然而,由于锁造成的阻塞会影响数据库中事务并发执行的性能.现有的工作主要通过调度事务间执行顺序或优化存储过程等方法减少锁竞争.为了进一步提升事务吞吐,本文基于锁避免进行事务内的阻塞分析和代价建模,并提出事务内调度策略,通过对工作负载的阻塞分析预估调度代价,然后根据一定规则在事务内部有限程度地交换操作顺序,减少锁阻塞造成的延迟,从而提高性能.最后,通过对比传统的调度策略,验证了提出的调度策略对吞吐的提升及对事务平均延迟的降低的效果.

TRANSACTION MANAGEMENT IN DISTRIBUTED DATABASE SYSTEM C-POREL

This paper covers the transaction management of C-POREL, i. e. the distributed rela-tional data base management system on a microcomputer network. Presented in the pa-per are the concurrency control strategy of transactions in C-POREL, the mechanism ofthe local and global recovery, the reliable state control protocol RSC for getting the ro-bustness of the network and the protocol for processing distributed multisite transactions,and the outline of the architecture of the transaction manager TM of C-POREL.

支持复杂应用的工作流并发控制机制

针对复杂应用领域工作流的特点 ,提出了一种确保工作流并发执行正确性的方法·首先定义任务冲突 ,冲突类别 ,同名共享锁和同名互斥锁的概念 ,而后给出了一种基于这些概念扩展的工作流并发控制机制·在这种并发调度机制中 ,由于充分考虑了不同工作流执行的并发控制 ,同一工作流不同实例之间执行的并发控制等工作流并发特点 ,使该并发机制能够确保复杂应用环境中多工作流多实例并发执行的正确性·

移动数据库系统乐观事务处理策略

在移动数据库系统中 ,计算平台的移动性、频繁的断接性以及长事务等特性使得传统的事务处理模式不再适用 .为了解决移动数据库中的事务处理问题 ,提出了一种新的移动事务处理模型——乐观两阶段提交移动事务模型 ( O2 PC-MT) .该模型采用乐观并发控制与两阶段提交协议相结合的方法 ,对移动事务的长事务特性提供了灵活与有效的支持 ;此外 ,该模型允许移动计算机分多次发送事务操作 ,且在事务执行的过程中可以任意移动 ,从而提供了对交互式事务及随意移动性的支持 .实验结果表明 ,与基于两段锁协议及其变形的其它移动事务处理模型相比 ,O2

嵌入式实时数据库事务的并发控制

嵌入式实时数据库系统中的并发控制除保证数据库一致性不被破坏外,还须考虑事务的定时限制及减少解除数据冲突开销。该文讨论了一个基于封锁的、可避免循环夭折的有条件高优先级夭折并发控制协议ACA-HPA-AC,包括其形式化描述、封锁相容矩阵、锁表结构及封锁操作的实现算法。该协议能避免一般高优先级夭折协议中可能出现的循环夭折和无效夭折现象,并已成功应用于嵌入式实时内存数据库系统ARTs-EDB中。

一种面向混合实时事务调度的并发控制协议

首先给出了一个两层结构的混合实时数据库系统模型,其中支持采用非定期任务调度算法来改进系统的性能.进一步,针对这种模型下混合事务的数据一致性问题,提出了一种新的并发控制协议--MCC-DATI.该协议采用动态优先级驱动的调度算法,通过限制非定期的软实时事务对硬实时事务的阻塞时间,保证硬实时事务的可调度性;同时,采用非定期任务调度算法以及基于时间戳间隔的动态串行化顺序调整机制来减少软实时事务的截止期错失率.仿真实验表明,相对于先前的混合事务的并发控制协议,该协议在不同的系统负载与截止期约束下都能够改进系统的性能。

基于混合粒度冲突检测的事务工作流调度算法

事务工作流由若干个平面事务组成,其执行满足松弛原子性.由于组成事务工作流的平面事务具有不同的完成特性,为了防止不可串行化的执行,现有的调度算法通常只允许一个活动工作流执行不可补偿事务,这大大限制了并发度.定义了基于事务类型和事务实例两种粒度的冲突关系,并提出了一种基于这两种粒度冲突检测的调度算法,保证了并发事务工作流的可串行化和可恢复执行.该算法从两个方面提高了并发度:一方面通过事务实例之间(细粒度)的冲突检测减少了工作流冲突的概率;另一方面通过事务类型之间(粗粒度)的冲突预测,允许多个将来不冲突的工作流执行不可补偿事务.

2PL并发控制的研究与实现探析

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系统中实施对事务处理提供了可行的并发控制调度方案。

实时数据库系统中的嵌套事务

传统的原子事务是由一个平坦数据库操作序列组成的，事务的执行具有ＡＣＩＤ（Ａｔｏｍｉｃｉｔｙ，Ｃｏｎｓｉｓｔｅｎｃｙ，Ｉｓｏｌａｔｉｏｎ，Ｄｕｒａｂｉｌｉｔｙ）特性．然而，在实时应用环境下，这些却不太适用．该文提出了一种支持实时应用的嵌套事务模型，给出了嵌套事务的特性及正确性标准。

移动实时嵌套事务的并发控制

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 .

关于实时事务调度中的优先级反转

分析了基于优先级的调度策略中优先级反转产生的原因,并且给出了RTDBS中实时平淡事务和实时嵌套事务的并发控制中优先级反转的解决方法。主要有优先级继承,高优先级夭折,优先级顶,避免优先级反转的多版本协议,基于优先级的时标排序及一些求精的算法。

CCPP: 一个并发C++语言的设计与实现

并发面向对象语言ＣＯＯＬ（ｃｏｎｃｕｒｅｎｔｏｂｊｅｃｔ－ｏｒｉｅｎｔｅｄｌａｎｇｕａｇｅ）是一种有效的并发程序设计语言．本文提出了一种并发对象模型（ＣｏｎｃｕｒｅｎｔＣ＋＋，ＣＣＰＰ）及其语言．在ＣＣＰＰ并发对象模型中，所有对象都是并发对象，对象间的通讯都采用异步消息发送方式．对象间的同步采用“需要时等待”策略，同一对象内并发线程间的同步用路径表达式描述．ＣＣＰＰ语言是对Ｃ＋＋语言的扩充，采用预编译方法实现．