Robust Real - Timeindex Concurrency Controls

Real-time database systems are expected to rely heavily on indexes to speed up data access and thereby help more transactions meet their deadlines. Accordingly, high-performance index concurrency control (ICC) protocols are required to prevent contention for the index from becoming a bottleneck. We took a rst step towards achieving this objective in a recent simulation-based study that evaluated the performance of a representative set of B-tree ICC protocols for real-time applications with rm deadlines. A load-adaptive variant of the B-link protocol, called LAB-link, was found to provide the best real-time performance in that study. In this paper, we extend and improve on this prior research in several ways: First, we present a new real-time ICC protocol calledAED-link, which employs an adaptive feedback-based admission control mechanism. Our results show that it provides signi cantly better and more robust performance than LAB-link. Second, we make a detailed study of the fairness characteristics of the ICC protocols. Our results indicate that AED-link provides almost ideal fairness for a wide range of workloads. Third, we explicitly model the \undos" of index actions of aborted transactions. An unexpected and interesting result here is that performing undos usually has only marginal adverse impact on real-time performance and can, in a few scenarios, actually result in better performance. Finally, we model the performance e ects of range index operations whereas the previous study was limited to point index operations. 1