Using Priorities in Concurrency Control for RTDBSs

In a real-time database system, it is difficult to meet all timing constraints due to the consistency requirements of the underlying database. Real-time database transaction scheduling requires the development of efficient concurrency control protocols that try to maximize the number of transactions satisfying their real-time constraints. Therefore transaction priorities should be taken account when making decisions in concurrency control. Although optimistic approach has been shown to be better than locking protocols for RTDBS, it has the problems of unnecessary restarts and heavy restart overhead. In this paper, we propose a new optimistic concurrency control protocol called OCC-PDATI which uses priority information in conflict resolution. In OCC-PDATI number of transaction restarts is minimized by dynamically adjusting the serialization order of the conflicting transactions. Need for dynamic serialization order adjustment is checked and serialization order is updated in the validation phase. This provides more freedom to adjust serialization order of conflicting transactions. OCC-PDATI has several advantages over the other optimistic concurrency control protocols. The protocol maintains all the nice properties with forward validation, high degree of concurrency, free from deadlock, early detection and resolution of conflicts, resulting in both less wasted resources and smaller number of restarts. All of these are important to the performance of RTDBS and contribute to greater chances of meeting transaction deadlines. Performance studies of our protocol has been carried out in RODAIN RTDBMS and the results confirm the believe that OCC-PDATI clearly offers better changes for high priority transactions to complete according to their deadlines.