Research Of Mixed Real-time Transaction Scheduling Based On Constant Bandwidth Server

Along with rapid development of information technology and internet technology, the application of real-time database with mixed transaction loads becomes extremely common. Transaction processing of real-time database is more complex and difficult than traditional real-time tasks and database transactions, so it must simultaneously implement data consistency (including external consistency, mutual consistency and dynamic consistency) and timing constraint. Therefore, it causes that the structure of traditional transactions be not appropriate for expressing real-time transactions. We have thoroughly discussed the real-time transaction processing, and proposed a transaction model which is suitable for mixed real-time transaction scheduling.A hard real-time transaction, which misses its deadline, may result in great loss even catastrophic, but it is tolerate for a small quantity of soft real-time transactions to miss their deadlines. Therefore, the goal of mixed real-time transaction scheduling should be: guaranteeing each hard real-time transaction can be complete within its deadline, and minimizing the deadline missing rate of soft real-time transactions. Facing the issue of mixed real-time transaction scheduling, we proposed a mixed real-time transaction scheduling model based on CBS.Transaction scheduler is a core of real-time transaction scheduling, and the scheduling work of real-time transactions is done by it. On the basis of studying and researching CBS and EDF algorithm, we have designed transaction scheduler in detail. The scheduler consists of main scheduler, EDF scheduler and CBS scheduler. It can realize scheduling among mixed real-time transactions. On the Concurrency Control of transactions, this article doesn't research thoroughly. According to the comparison of existing Concurrency Control protocols, we selected the MCC-DATI protocol.Based on these above research results, we have realized the mixed real-time transaction scheduling model we had advanced. The simulation test is an important part of real-time transaction scheduling research and performance evaluation, so we did a simulation test of this model. The result of simulation test indicates our model can satisfy the deadline of hard real-time transaction, at the same time the model can reduce the deadline miss ratio of soft real-time transaction deadline. Especially on these transactions whose WCET (Worst Case Execution Time) is hard to be estimated or whose WCET is too long, its performance is better than mixed real-time transaction model based on other algorithms.