Dynamic Real-Time Optimistic Concurrency Control

In a recent study, we have shown that in real-time database systems that discard late transactions, optimistic concurrency control outperforms locking. Although the optimistic algorithm used in that study, OPT-BC, did not factor in transaction deadlines in making data conflict resolution decisions, it still outperformed a deadline-cognizant locking algorithm. In this paper, we discuss why adding deadline information to optimistic algorithms is a non-trivial problem, and describe some alternative methods of doing so. We present a new real-time optimistic concurrency control algorithm, WAlT-50, that monitors transaction conflict states and gives precedence to urgent transactions in a controlled manner. WAIT-50 is shown to provide significant performance gains over OPT-BC under a variety of operating conditions and workloads.