Dynamic real-time optimistic concurrency control

The authors (1990) 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. A discussion is presented of why adding deadline information to optimistic algorithms is a nontrivial problem, and some alternative methods of doing so are described. A new real-time optimistic concurrency control algorithm, WAIT-50, is presented 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