Weak Serializable Concurrency Control in Real-time Broadcast Environments

Given the asymmetric communication capabilities in mobile real-time environments, traditional serializability-based approaches are too restrictive, unnecessary, and impractical. The new notion of correctness called weak serializability is given. After the necessary and sufficient conditions for weak serializability are shown, corresponding concurrency control protocol based on this criterion is outlined for real-time broadcast environments. The simulation results confirmed that the proposed techniques help mobile transactions to meet their deadlines and improve query response time.

Quasi Serializable Concurrency Control in Distributed Real-Time Database Systems

This paper formally defines and analyses the new notion of correctness called quasi serializability, and then outlines corresponding concurrency control protocol QDHP for distributed real-time databases. Finally, through a series of simulation studies, it shows that using the new concurrency control protocol the performance of distributed real-time databases can be much improved.

Scheduling transactions in mobile distributed real-time database systems

A DMVOCC-MVDA （distributed multiversion optimistic concurrency control with multiversion dynamic adjustment） protocol was presented to process mobile distributed real-time transaction in mobile broadcast environments. At the mobile hosts, all transactions perform local pre-validation. The local pre-validation process is carried out against the committed transactions at the server in the last broadcast cycle. Transactions that survive in local pre-validation must be submitted to the server for local final validation. The new protocol eliminates conflicts between mobile read-only and mobile update transactions, and resolves data conflicts flexibly by using multiversion dynamic adjustment of serialization order to avoid unnecessary restarts of transactions. Mobile read-only transactions can be committed with no-blocking, and respond time of mobile read-only transactions is greatly shortened. The tolerance of mobile transactions of disconnections from the broadcast channel is increased. In global validation mobile distributed transactions have to do check to ensure distributed serializability in all participants. The simulation results show that the new concurrency control protocol proposed offers better performance than other protocols in terms of miss rate, restart rate, commit rate. Under high work load （think time is ls） the miss rate of DMVOCC-MVDA is only 14.6%, is significantly lower than that of other protocols. The restart rate of DMVOCC-MVDA is only 32.3%, showing that DMVOCC-MVDA can effectively reduce the restart rate of mobile transactions. And the commit rate of DMVOCC-MVDA is up to 61.2%, which is obviously higher than that of other protocols.

实时广播环境中的分布式校验并发控制机制

本文设计了一种新的分布式阶段校验的移动实时事务并发控制协议 :校验任务由移动客户机与服务器共同分担、允许获得更高的并发度、可更早的检测到数据冲突以减少处理与通讯资源的浪费 .性能实验结果表明 ,新协议有效可行。

数据广播环境下移动实时事务的有效并发控制

在无线数据广播环境下,从移动客户机到数据库服务器的上行带宽非常有限。传统的并发控制协议不适合这种不对称通讯环境。本文结合乐观并发控制协议和时标排序协议提出一种并发控制协议。只读事务满足弱一致性,包含所有更新事务和一个移动只读事务的可串行化图是非循环的。使用本文提出的并发控制协议,移动只读事务能够自主执行,移动更新事务能够较早地检测到数据冲突。模拟试验显示,我们提出的协议相对其它已经存在的并发控制协议来说,能够更好地满足事务截止期。

实时广播环境中的弱可串行化并发控制

1.引言 随着便携计算机及无线通讯技术的快速发展,移动计算已经成为现实,其中主要采用数据广播方法进行数据发布.广播模式的一个显著特征是通讯的不对称性,即下行带宽比上行带宽宽很多.

数据广播中т-可串行化移动实时事务并发控制

研究了实时数据广播环境中的一致性维护问题。由于广播环境的非对称通讯特性,传统可串行化并发控制方法过于严格而不必要;现有放松可串行化方法都会导致数据库受限不一致、使各个用户读取受限不一致数据。提出了使用т-可串行化并发控制,首先形式化定义了т-可串行化正确性准则,证明了它虽比传统可串行化宽松但能始终保证数据一致性,使各个用户始终读取一致性数据,进而给出了相应的并发控制协议。实验结果表明,新协议可显著降低平均响应时间,使更多移动实时事务满足截止期要求。

广播环境中的Q可串行化实时并发控制

研究了实时广播中的数据一致性问题。传统冲突可串行化并发控制协议对非对称通信的广播环境来说过于严格且不必要。为此,提出使用Q可串行化形式化定义了Q可串行化,证明了它虽比传统冲突可串行化宽松但能始终保证数据一致性,基于可动态调整串行化顺序的时标段排序方法给出了相应的并发控制协议。实验结果表明新协议可显著降低平均响应时间,使更多移动实时事务满足截止期要求。

广播环境中的移动实时事务并发控制

研究了实时数据广播中的一致性问题 .由于广播环境的通信不对称性 ,传统的可串行化并发控制协议显得过于严格、不必要、不可行 .为此 ,提出使用伪可串行化并发控制 :形式化定义了伪可串行化的概念 ,证明了它虽比传统可串行化宽松但能保证数据一致性 ,给出了相应的并发控制协议 .实验结果表明 :新协议可显著降低平均响应时间 。