Priority scheduling of transactions in distributed real-time databases

One of the most important issues in the design of distributed real-time dat abase system (DRTDBS) is transaction scheduling which consists of two parts : priority scheduling and real-time concurrency control. In the past studie s, mostly, these issues are studied separately although they have a very cl ose interaction with each other. In this paper, we propose new priority ass ignment policies for DRTDBS and study their impact on two typical real-time concurrency control protocols (RT-CCPs), High Priority Two Phase Locking ( HP-2PL) and Optimistic Concurrency Control with Broadcast Commit (OCC-BC). Our performance results show that many factors, such as data conflict resol ution, degree of data contention and transaction restarts, that are unique to database systems, have significant impact on the performance of the poli cies which in turn affect the performance of the real-time concurrency cont rol protocols. OCC-BC is more affected by the priority assignment policies than HP-2PL owing to the late detection of conflict. In the design of prior ity assignment policies, we have found that neither the purely deadline dri ven policies nor data contention driven policies are suitable for DRTDBS. O ur proposed policy, the Mixed Method (MM), which considers both transaction timeliness and data contention, outperforms other policies over a wide ran ge of system parameter settings.