一种实时数据库事务处理策略的应用

通过对实时事务特点的分析和对实时数据库中事务处理策略的研究，提出了一种把优先级分配策略与定时调度策略相结合的实时事务调度策略，并融合快照机制与优先级分配策略建立了一种新的基于乐观法的并发控制策略。将这种策略应用于一个实时系统的实时数据库，系统的性能和稳定性明显提高。实验结果表明所给出的新策略及方法的正确性和有效性。     

实时数据库事务的研究与实现

根据设计的实时数据库操作类型,对实时事务进行了分类,时间性是实时事务重要属性,提供了实时事务的时间性、原子性、并发性以及优先级分配的策略,对实时事务进行有效的调度。     

运行时间自适应的事务调度算法

实时数据库中是基于事务的不同优先级进行事务的调度,所以事务优先级的确定对实时数据库的效率有着至关重要的作用。本文讨论了一个运行时间自适应的事务调度算法,对算法思想和调度策略进行了深入的研究。该算法事务的估计运行时间与CPU时钟无关,具有自适应的能力,并且可以得到周期性事务的准确运行时间,对于周期性事务比例比较高的应用系统非常适合。     

一种改进的实时事务调度策略

文中提出一种改进的实时事务调度策略，由改进的优先级分配机制ＨＡＥＤ和相应的实时并发控制算法两部分组成。针对嵌套事务模型，提出了一种子事务截止期的分配方法。最后对改进策略进行了性能模拟。模拟结果表明，改进策略的系统性能在一定程度上优于原有的调度策略。     

一种新的实时事务处理策略及应用

通过对实时事务处理策略的研究,提出一种改进型事务处理策略,将时标调度策略和传统的优先级分配策略进行结合处理不同类型的实时事务,并将快照服务用于并发控制协议中.测试表明,这种处理策略能提升系统的性能.     

区分移动实时事务关键性的并发控制策略

在移动实时数据库系统中,事务的关键性代表实时事务的时间紧迫性,由于实时事务的紧迫程度不同,为了保证事务的时间正确性,因而有必要区分事务的关键性提出相应的并发控制策略。该文按满足截止时间的重要性将实时事务分为软、硬事务加以研究,在此基础上分别提出了三种区分事务关键性的优先级并发控制策略,对三种优先级策略进行了性能比较并提出了改进方法。研究结果表明,将实时事务按关键性分类有利于设计事务优先级分派及调度策略。     

区分移动实时事务关键性的并发控制策略

在移动实时数据库系统中,事务的关键性代表实时事务的时间紧迫性,由于实时事务的紧迫程度不同,为了保证事务的时间正确性,因而有必要区分事务的关键性提出相应的并发控制策略。该文按满足截止时间的重要性将实时事务分为软、硬事务加以研究,在此基础上分别提出了三种区分事务关键性的优先级并发控制策略,对三种优先级策略进行了性能比较并提出了改进方法。研究结果表明,将实时事务按关键性分类有利于设计事务优先级分派及调度策略。     

实时数据库缓冲区管理算法的设计和实现

分析了实时数据库的事务特征,对以往的研究成果进行了总结,以满足事务的按时完成比率（Success Ratio）为目标,为实时系统设计了一种使用反馈控制思想的基于优先级的实时数据库缓冲区管理算法FCLRU2dl,并将该算法与常用的实时数据库事务调度算法和并发控制策略配合进行了测试和评估,证明了算法的优越性。实验中得到的另一个结论是在特定的事务调度算法和并发控制策略下,实时数据库不需要全部位于内存中,可以不是内存数据库。     

小卫星地面自动测试系统中实时数据库事务优先级分配算法

小卫星自动化测试是提高测试效率、缩短研制周期、降低研制成本和保证可靠性的重要手段. 针对测试数据量大、类型复杂和实时性要求高等特点, 设计了小卫星自动测试系统实时数据库方案. 建立测试数据相关的实时数据库事务调度模型, 并在该模型基础上设计了异常数据优先的事务优先级分配算法(Abnormal datafirst, ADF). 最后应用数学仿真验证了ADF分配算法的执行效率、正确性和有效性. 本文建立的事务调度模型和优先级分配算法兼顾测试数据自身特点和实时性要求, 尤其注重异常数据的处理, 从而提高了测试的全面性和准确性.     

实时数据库的事务调度策略分析

实时数据库系统的事务调度策略是系统用来处理实时事务的调度方法.基于调度事务的不同类别产生各异的策略,分析目前各类事务调度策略的优缺点及适应类型,提出新的定时调度和传统的优先级调度相结合的想法.     

基于时间戳的并行实时事务调度策略

传统并行事务处理方法不适用于实时数据库，对几种相关事务调度策略进行比较，提出一种基于时间戳的并行实时事务调度策略TS-PRTTS(Timestamp based Parallel Real-Time Transaction Scheduling)，采用M／G／1队列模型，利用时间戳控制子事务同步．实验证明，该策略能较好协调同步控制与通信代价矛盾，在系统负荷较重以及数据倾斜、访问倾斜问题较突出时具有良好的性能。     

一种移动实时事务调度策略

支持无线网络断接和提高实时事务的成功率是移动计算环境下实时事务处理要解决的两个主要问题。本文首先提出了一个优先级分配策略，它考虑了无线网络断接性；然后提出了一个冲突事务定义，它减小了事务冲突的概率；最后给出一个基于此的避免冲突的事务调度策略，它使事务调度和并发控制高度集成，降低了系统的事务管理开销，提高
高了事务成功率。     

Scheduling Value-Based Nested Transactions in Distributed Real-Time Database Systems

Many noticeable studies have focussed on scheduling flat transactions in a distributed real-time database system (RTDBS). However, a nested transaction model has been widely adopted in many real-life applications such as Internet stock trading systems and telecommunications. This work concerns efficiently scheduling real-time nested transactions in a distributed RTDBS. A new real-time scheduler called flexible high reward for nested transactions (FHRN) is proposed. FHRN consists of (1) FHRN_p ¹ policy to schedule real-time nested transactions and (2) 2PL_HPN to resolve the concurrent data-accessing problem among interleaved nested transactions. Simulation results show that FHRN outperforms these existent real-time schedulers such as random priority (RP), earliest deadline (ED), highest value (HV), hierarchical earliest deadline (HED), and highest reward and urgency (HRU) when an application requires a nested transaction model.     

实时事务调度及静态可调度性分析

在类似闭环控制的硬实时数据库应用环境,实时事务具有一定的静态可预报性,其中实时事务的可调度性分析是维护实时数据库时间正确性的基础.通过利用抢占阈值,提出了一种新的实时事务处理模型,它集成了CPU调度和数据调度,实现离线并发控制,具有单阻塞的特征与好的静态可预测性,并有利于降低事务系统的负载和改善可调度性.进一步由此建立了实时事务的静态可调度性分析模型以及求最优可行调度的整数规划模型,该模型有利于达到实时事务调度的整体优化.     

Prescheduling policy for real-time concurrency control: A performance evaluation

A new priority management policy, aprescheduling policy, is proposed. This policy can be applied on any conventional concurrency control protocol to schedule a real-time transaction. Costly preemption is avoided by the prescheduling policy, and parsing dataset of a transaction is not needed. Three widely used conventional concurrency control protocols (dynamic two-phase locking, basic timestamp ordering, and optimistic) are incorporated with the prescheduling policy to form three real-time concurrency control protocols. Performance of the three protocols is evaluated from three different viewpoints: database management systems, protocols, and transaction. From a database management system viewpoint, we show the prescheduling policy can improve the performance of protocols by raising thevalid ratio and reducingrestart counts. In general, two-phase locking with the prescheduling policy performs the best in most cases and yields the best choice for concurrency control in a real-time application. Deciding factors that affect performance of each protocol are identified from protocol viewpoint. Some suggestions are given for writing a timely transaction from the aspect of transaction viewpoint.     

Scheduling transactions with temporal constraints: exploiting data semantics

In this paper, issues involved in the design of a real-time database which maintains data temporal consistency are discussed. The concept of data-deadline is introduced and time cognizant transaction scheduling policies are proposed. Informally, data-deadline is a deadline assigned to a transaction due to the temporal constraints of the data accessed by the transaction. Further, two time cognizant forced wait policies which improve performance significantly by forcing a transaction to delay further execution until a new version of sensor data becomes available are proposed. A way to exploit temporal data similarity to improve performance is also proposed. Finally, these policies are evaluated through detailed simulation experiments. The simulation results show that taking advantage of temporal data semantics in transaction scheduling can significantly improve the performance of user transactions in realtime database systems. In particular, it is demonstrated that under the forced wait policy, the performance can be improved significantly. Further improvements result by exploiting data similarity.     

Priority Scheduling of Transactions in Distributed Real-Time Databases

One of the most important issues in the design of distributed real-time database system (DRTDBS) is transaction scheduling which consists of two parts: priority scheduling and real-time concurrency control. In the past studies, mostly, these issues are studied separately although they have a very close interaction with each other. In this paper, we propose new priority assignment policies for DRTDBS and study their impact on two typical real-time concurrency control protocols (RT-CCPs), High Priority Two Phase Locking (HP-2PL) and Optimistic Concurrency Control with Broadcast Commit (OCC-BC). Our performance results show that many factors, such as data conflict resolution, degree of data contention and transaction restarts, that are unique to database systems, have significant impact on the performance of the policies which in turn affect the performance of the real-time concurrency control protocols. OCC-BC is more affected by the priority assignment policies than HP-2PL owing to the late detection of conflict. In the design of priority assignment policies, we have found that neither the purely deadline driven policies nor data contention driven policies are suitable for DRTDBS. Our proposed policy, the Mixed Method (MM), which considers both transaction timeliness and data contention, outperforms other policies over a wide range of system parameter settings.     

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。