Software Engineering Institute

When a database system is used in a real-time application, the concurrency control protocol must satisfy not only the consistency of shared data but also the timing constraints of the application. In this paper, we examine a priority-driven, two-phase lock protocol called the read- or write-priority ceiling protocol. We show that this protocol is free of deadlock, and, in addition, a high-priority transaction can be blocked by lower priority transactions for, at most, the duration of a single embedded transaction. We then evaluate system performance experimentally.