移动分布式实时数据库中并发控制框架

A Framework for Concurrency Control in Mobile Distributed Real-time Database Systems

在移动分布式数据库系统中采用三层结构,提出了DMVOCC-DA-2PLV(Distributed Multiversion Opti mis-tic Concurrency Control-Dynamic Adjust ment of Serialization Order-Two-Phase Local Validation)协议处理移动分布式实时事务。移动实时事务处理分两阶段进行。第一阶段在移动主机(MHs)上处理,并进行局部部分有效性检查性确认,使用向后有效性确认机制,与在服务器提交事务进行有效性确认。及早地检测数据冲突,节省了处理和通信资源。第二阶段在服务器处理,通过局部部分有效性确认的事务,提交到服务器进行局部最终有效性确认。协议消除了移动只读事务和移动更新事务的冲突,使用多版本动态调整串行次序技术,避免了不必要的事务重启动。如果移动只读事务所有读数据项通过局部部分向后有效性确认,则可提交,大大降低了移动只读事务的响应时间。在全局有效性确认中对分布更新事务进行检查,以保证分布串行性。通过模拟仿真,对DMVOCC-DA-2PV协议进行了性能测试,并与DTO-2PC和DHP-2PL进行了比较。实验结果表明DMVOCC-DA-2PV并发控制协议要优于其它协议。

Mobile distributed real-database systems （MI）RTDBS） are viewed as three-tier architecture. This paper presents DMVOCC-DA-2PLV （Distributed Multiversion Optimistic Concurrency Control with Dynamic Adjustment using Two-Phase Local Validation） protocol for proces＇sing mobile distributed real-time transaction in mobile broadcast environments. Mobile real-time transaction processing is performed in two stages. In the first stage transaction processing is performed at MH（Mobile Host）. At MHs all mobile transactions perform local partial backward validation of transactions. The local partial validation process is carried out against committed transactions at the server. Such an early data conflict detect detection feature can save processing and communication resources. In the second stage transaction processing is performed at server. Transactions that survive in local partial backward validation must be submitted to server for local final backward validation. The protocol can eliminate conflicts between mobile read-only and mobile update transactions, and resolve data conflicts flexibly using multiversion dynamic adjustment of serialization order to avoid unnecessary restarts of transactions. For a ready-only transaction at the MH, it can be committed locally if it passes all the local partial backward validation in the course of it execution. Respond time of mobile read-only transactions is greatly improved. In global validation distributed update transactions have to do check to ensure distributed serializability in all participants. The protocol presented is compared with DTO-2PC and D HP-2PL by simulation experiments. The results of experiment show that the new protocol proposed offers better performance in terms of miss rate, restart rate, commit rate and throughput.