Abstract: The Web service composition transaction has the characteristic of long execution period, and a global transaction can be divided into multiple distributed sub transactions. Each sub transaction has different significance for the global transaction, as the success or failure of the key sub transaction’s execution will directly lead to the success or failure of the global transaction. On the other hand, some failed transactions have to be compensated, while executing too much compensating transactions will bring huge compensation cost. In the aim of solving these problems, this paper proposes a nested transaction model based on the pivot transaction, and divides transactions in the model into the pivot transactions and the non-pivot transactions, the model contains at least one pivot transaction. And based on this model, this paper presents a pivot transaction priority scheduling (PTPS) algorithm to reduce the number of compensating transactions that is needed to execute while the pivot transaction fails and reduce the compensation cost, by giving priority to execute the pivot transaction.

Key words: transaction model, pivot transaction, scheduling algorithm, transaction compensation, Web service composition

摘要： Web服务组合中的事务具有执行周期长的特性，一个全局事务会被划分为多个分布的子事务。各个子事务对全局事务而言具有不同的重要程度，关键子事务执行的成功与否，直接影响到全局事务执行的成败。另一方面，对某些出现故障的事务需要进行补偿，而执行过多的补偿事务会带来巨大的补偿开销。针对这些问题，提出了一个基于pivot事务的嵌套事务模型，模型中的事务分为pivot事务和非pivot事务，且含有至少一个pivot事务。同时基于该模型，给出了一个pivot事务优先调度（pivot transaction priority scheduling，PTPS）算法，通过优先执行pivot事务，来减少在pivot事务失败时执行的补偿事务数目，降低补偿开销。

关键词: 事务模型, pivot事务, 调度算法, 事务补偿, Web服务组合