Priority Assignment in Real - Time Active Databases 1 2

Active databases and real-time databases have been important areas of research in the recent past. It has been recognized that many beneets can be gained by integrating active and real-time database technologies. However, there has not been much work done in the area of transaction processing in active real-time databases. This paper deals with an important aspect of transaction processing in active real-time databases, namely the problem of assigning priorities to transactions. In these systems, time-constrained transactions trigger other transactions during their execution. We present three policies for assigning priorities to parent, immediate and deferred transactions executing on a multiprocessor system and then evaluate the policies through simulation. The policies use diierent amounts of semantic information about transactions to assign the priorities. The simulator has been validated against the results of earlier published studies. We conducted experiments in three settings: a task setting, a main memory database setting and a disk resident database setting. Our results demonstrate that dynamically changing the priorities of transactions, depending on their behavior (triggering rules), yields a substantial improvement in the number of triggering transactions that meet their deadline in all three settings.