移动分布式实时数据库系统的事务处理

提出DMVOCC-MDA协议处理移动分布式实时事务。协议采用多版本乐观方法,使用多版本动态调整串行次序技术。移动分布式事务局部有效性确认分为2个阶段:第1阶段在移动主机上进行,使用向后有效性确认机制,对服务器上个广播周期提交事务进行有效性确认;第2阶段在服务器上进行,通过局部有效性确认的移动事务,提交到服务器进行局部最终有效性确认。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。移动只读事务能无阻塞提交,降低移动只读事务的响应时间,消除移动只读事务和移动更新事务的冲突,避免不必要的移动事务重启动。在移动主机上及早地检测数据冲突,节省处理和通信资源。实验结果表明,DMVOCC-MDA协议与其他协议相比,错过率和重启动率低,提交率和吞吐量高。

Transaction processing in mobile distributed real-time database systems

DMVOCC-MDA(Distributed multiversion optimistic concurrency control with multiversion dynamic adjustment) protocol was presented for processing mobile distributed real-time transaction.In the protocol,multiversion optimistic concurrency control method was adopted.Technique of multiversion dynamic adjustment of serialization order was used.Local validation of mobile distributed transactions was performed in two phases.In the first phase,local validation was performed at mobile host(MH),and carried out against committed transactions at the server in the last broadcast cycle by using backward validation mechanism.In the second phase,local final validation was performed at the server.Transactions that survive in local validation must be submitted to the server for local final validation.In global validation distributed update transactions have to be checked to ensure the distributed serialization in all participants.Mobile read-only transactions can be committed with no-blocking.Respond time of mobile read-only transactions is greatly improved.Data conflicts can be eliminated between mobile read-only transactions and mobile update transactions.Unnecessary restarts of mobile transactions are avoided.The data conflict is early detected in MH.Processing and communication resources are saved.The simulation results show that the new protocol proposed has lower missing rate and restart rate,and higher commit rate and throughput compared with other protocols.