基于功能替代的实时事务调度

Scheduling Real-Time Transactions Based on Functional Alternation Characteristics

实时数据库事务除满足一般的一致性 (完整性 )限制外必须满足时限 ,故高成功率的调度策略是系统的关键 .该文提出了一种基于功能替代性的事务模型 ,它定义事务为若干任务 (事务步 )的集合 ,每个任务又由若干功能等价的子事务组成 ,在每个任务 (事务步 )中取一个子事务就组成该事务的一个替代 ,该模型具有较强的描述能力 .文章研究了事务预分析的策略与方法 ,分析了事务的可调度性 ,在此基础上 ,给出了相应的调度策略与方法 ,替代成为事务调度和并发控制的基本单位 ,一个替代成功执行则该事务可提交 ,但某替代夭折时还可选另外的替代 ,只有当全部替代都失败或超过 (或必定会超过 )截止期时 ,该事务才夭折 .事务的替代特性使事务的执行有多条路径 ,提高了事务的适应能力和应变能力 ,从而提高了事务的成功率 .文章还针对一个实验系统进行了模拟实验与性能分析 .

A scheduling strategy with high success ratio is essential to the RTDBS since the real-time transaction has to follow the constraints of the timing as well as the conventional consistency or integrity. This paper focuses on a transaction model based-on function alternative, which defines the real-time transaction as a set of function steps composed of sub-transaction with function equivalence and one alternative of the transaction is formed when a sub-transaction is given by the transaction step. This model is strong with describing capability. This paper is centered around the research on the strategy and method of transaction pre-analysis as well as the schedulability, on which some related strategies and methods are given, which include that alternatives are the basic unit of schedule and concurrency control. Once an alternative completes, the real-time transaction succeeds, and if one alternative fails, another alternative will be chosen to run. Only if all the alternatives failed or noosed the deadline, the transaction would die. The alternative makes it possible for the transaction to execute by quite a few ways and improves its adaptability and success-ratio. This paper also deals with a simulated experiment and analysis on its performance for an experimental system.