一种分布式实时数据库提交协议

A Commit Protocol in Distributed Real-Time Databases

传统的事务提交协议不适合实时环境的需要 ,并且文献中现有的几个实时提交协议限制了实时事务执行的并发度 ,影响了实时事务的定时限制 .该文针对分布式实时数据库系统的提交处理提出了 2 SC协议 ,它增加了事务执行的并发度且有助于事务截止期的满足 .文中首先提出了一个分布式实时事务经历模型 ,着重讨论了事务因为冲突操作而引起的提交依赖和夭折依赖 .然后给出了 2 SC(双空间提交 )协议规则 ,根据该协议分布式实时事务的提交处理在两个空间中完成 :结点的局部事务空间和系统的全局事务空间 .在局部事务空间中 ,当处于准备状态的参与者夭折时 ,仅仅夭折其夭折依赖集中的事务而不会夭折其提交依赖集中的事务 ;在适当的条件下 ,处于准备状态的参与者允许其它事务访问其锁住的数据 .在全局事务空间中 ,参与者能够在进入准备之前主动夭折 ,即当一个事务在进入准备状态之前就超过了截止期 ,其协调者和所有的参与者都将“寂寞死”.接着该文证明了 2 SC协议的正确性 ,即确保分布式事务提交的原子性 ,同时分析了该协议固有的优点比如提高事务执行的并发度和减缓事务的串联夭折等 .并且 2 SC协议能够和现有的并发控制协议有机地结合在一起 ,确保分布式实时事务可串行化和提交的原子性 .最后通过一个模拟实验证?

Traditional transaction commit protocols are unsuitable in the real time context. And the few real time commit protocols proposed in the literatures restrict the concurrency of transaction execution and affect timing properties of transactions. This paper proposes the 2SC commit protocol for distributed real time database systems, which can increase the concurrency of transactions and help to meet real time transactions' deadlines. In the paper, a history model of distributed real time transactions is presented, and commit dependencies and abort dependencies between transactions by conflicting operations are described. The paper gives the 2SC (double space commit) protocol rules, in which distributed real time transaction commit processing is conducted in two spaces: The local transaction space at a node and the global transaction space for the system. In the local transaction space, when a participator in preparing (to commit) is aborted, only the transactions in its abort dependency set, but not in its commit dependency set, are aborted. A preparing participator allows its locked data to be accessed by other transactions in a certain conditions. In the global transaction space, a participator can actively abort only before entering its preparing phase. Once a transaction misses its deadline before entering its preparing phase, the coordinator and all the participators will 'silently kill'. The paper proves the correctness of the 2SC protocol, commit atomicity of distributed real time transactions and analyzes its advantages: improving the concurrency and decreasing cascading aborts. Furthermore, 2SC protocol can incorporate with existing concurrency control strategies to ensure both serializability and commit atomicity of distributed real time transactions, and the performance, as shown in the experimental system, is better than that of the HOPT protocol.