Performance studies of concurrency control algorithms for conventional database systems have shown that, under most operating circumstances, locking protocols outperform optimistic techniques. Real-time database systems have special characteristics - timing constraints are associated with transactions, performance criteria are based on satisfaction of these timing constraints, and scheduling algorithms are priority driven. In light of these special characteristics, results regarding the performance of concurrency control algorithms need to be re-evaluated. We show in this paper that the following parameters of the real-time database system - its policy for dealing with transactions whose constraints are not met, its knowledge of transaction resource requirements, and the availability of resources - have a significant impact on the relative performance of the concurrency control algorithms. In particular, we demonstrate that under a policy that discards transactions whose constraints are not met, optimistic concurrency control outperforms locking over a wide range of system utilization. We also outline why, for a variety of reasons, optimistic algorithms appear well-suited to real-time database systems.
对常规数据库系统的并发控制算法的性能研究表明,在大多数操作情况下,锁定协议的性能优于乐观技术。实时数据库系统具有特殊的特性-时序约束与事务相关联,性能标准基于对这些时序约束的满足,并且调度算法由优先级驱动。鉴于这些特殊特性,需要重新评估与并发控制算法的性能有关的结果。我们在本文中表明,实时数据库系统的以下参数-处理不满足约束的交易的策略,对交易资源要求的了解以及资源的可用性-对相对性能有重大影响并发控制算法。尤其是,我们证明,在丢弃不满足约束的事务的策略下,乐观并发控制的性能优于在广泛的系统利用率上的锁定。我们还概述了为什么出于各种原因,乐观算法似乎非常适合实时数据库系统。 P>
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