移动实时事务预留广播空间的验证协议

在无线数据广播环境中,从移动客户机到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信环境.本文提出一种可变乐观并发控制协议,服务器周期性向移动客户机广播数据对象,同时把一个广播周期分成若干个子周期,在两个连续的子周期间,一个保留空间被预留来存放服务器更新事务在第一个子周期开始后修改的所有数据对象,移动只读事务通过比较服务器更新事务提交的写集合和自己读集合来自主进行一致性验证,如果只读事务不能通过部分验证,它不会被草率地夭折并重新启动,相反,应用一个改进的向前验证策略,帮助移动只读事务争取更多提交机会.最后,本文进行充分的实验对提出的算法性能进行了评价.

Validation Protocol for Mobile Real-time Transaction Based on Reserved Broadcast Space

In a wireless data broadcast environment, there is a limited upstream bandwidth from mobile clients to the fixed database server. Traditional concurrency protocols are unsuitable in such an asymmetric communication environment. In this paper, we introduce a variant of the optimistic concurrency control protocols. The fixed database server broadcasts data objects to mobile clients periodically. The broadcast cycle is divided into multiple sub-cycles. Between two sub-cycles, there is a reserved space to accomodate identities for all the data objects which are updated by transactions in the server after the first sub-cycle begins. A read-only mobile transaction can validate its consistency autonomously by comparing its read-set with the committed write-set of the update transactions. If a read-only transaction cannot pass the partial validation, it is not simply aborted and restarted. Instead, an enhanced forward validation policy is applied , which help read-only transactions have more chances to commit. Extensive experiments are conducted to evaluate the performance of the proposed algorithms.