文档介绍：在值域内容许的偏差。
移动实时数据库系统中不同类型的事务错过截止期对系统性能影响是不同的:硬
实时事务错过截止期会导致系统性能严重降低;而软实时事务出现少量的错过截止期
却能够容忍。与此相应它们带给系统的价值也不同,所以系统对具有不同价值的事务
实行差分服务,以此减少事务对系统资源的竞争。不仅如此文章中还引入不精确计算
技术调度事务,其实现方法是把一个复杂嵌套事务建模成一个必要部分和若干可选部
分,当完成一个事务所有的可选部分代价太大时,系统可以选择只执行该事务的必要
部分。而且,由于移动实时数据库系统中大多数事务都是复杂的嵌套事务,传统调度
策略都已不太适用。因此论文也提出了新的基于触发机制的事务调度算法,即通过反
馈控制架构实现的 RODDFTS 与 RODBFTS 两种算法。这两种算法都属于递归算法,
且都是在遍历数据对象的有向非循环图的基础上提出。通过仿真实验评估,两种算法
使系统的性能参数均不超过数据库管理员预置的两种状态(稳态和暂态)的参考值,
从而使得系统的综合性能得以提高。
关键词:移动实时数据库系统,服务质量,数据新鲜度,反馈控制,事务错过截
止期比率,不精确计算,能耗
II
Abstract
With the extending of mobile real-time database systems applications in merce
and traffic controlling, the timing constraints of data objects in these applications are
growing higher and higher. And these applications require database systems to reflect the
current data objects state using the freshest data value before the objects status in physical
world change. At the same time the transactions in mobile real-time database systems have
strict timing constraints and must mitted in their deadlines, otherwise it will lead to a
heavy damage even catastrophe. The objective of a mobile real-time database system is not
system throughout but the ratio of transactions that meet their timing constraint. Thus we
must resolve the academic and technical problems about the data models, transaction models,
and priority assignment and schedule strategies of the mobile real-time transactions.
Conventional scheduling methods of transaction in database systems are not suitable to
mobile real-time applications because they don’t consider the timing constraints of data
objects and transactions.
The unpredictable system workload and even possible overloading, the limited system
resources are the problems which must be resolved in mobile real-time applications. It is
impossible to meet the various requirements of performance because of the limit constraints
of system resources. Many scholars proposed imp