MIRROR: a state-conscious concurrency control protocol for replicated real-time databases

Data replication can help database systems meet the stringent temporal constraints of current time-critical applications, especially Internet-based services. A prerequisite, however, is the development of high-performance concurrency control mechanisms. We present here a new CC protocol called MIRROR (Managing Isolation in Replicated Real-time Object Repositories), specifically designed for firm-deadline applications operating on replicated real-time databases. MIRROR augments the optimistic two-phase locking (O2PL) algorithm developed for non-real-time databases with a novel and easily implementable state-based conflict resolution mechanism to fine-tune the real-time performance. A simulation-based study of MIRROR's performance against the real-time versions of a representative set of classical protocols shows that (a) the relative performance characteristics of replica concurrency control algorithms in the real-time environment could be significantly different from their performance in a traditional (non-real-time) database system, (b) compared to locking based protocols, MIRROR provides the best performance in replicated environments for real-time applications, and (c) MIRROR's conflict resolution mechanism works almost as well as more sophisticated (and difficult to implement) strategies.