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...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。展开更多
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 sa...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.展开更多
文摘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。
文摘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.
