A Real-Time Locking Protocol

When a database system is used in a real-time application, the concurrency control protocol must not only satisfy the consistency of shared data but also observe the priorities of the transactions. This is because priority scheduling is a commonly used method. In this paper, we examine a prioritydriven two-phase lock protocol called the read/write priority ceiling protocol. We show that this protocol leads to freedom from mutual deadlock. In addition, a high-priority transaction can be blocked by lower priority transactions for at most the duration of a single embedded transaction. These properties can be used by schedulability analysis to guarantee that a set of periodic transactions using this protocol can always meet their deadlines. Finally, we examine the performance of this protocol for randomly arriving transactions using simulation studies. © 1991 IEEE