Real-time index concurrency control

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. I n this paper, we develop real-time variants of a representative set of clas sical B-tree ICC protocols and, using a detailed simulation model, compare their performance for real-time transactions with firm deadlines. We also p resent and evaluate a new real-time ICC protocol called GUARD-link that aug ments the classical B-link protocol with a feedback-based admission control mechanism. Both point and range queries, as well as the undos of the index actions of aborted transactions are included in the scope of our study. Th e performance metrics used in evaluating the ICC protocols are the percenta ge of transactions that miss their deadlines and the fairness with respect to transaction type and size. Our experimental results show that the perfor mance characteristics of the real-time version of an ICC protocol could be significantly different from the performance of the same protocol in a conv entional (nonreal-time) database system. In particular, B-link protocols, w hich are reputed to provide the best overall performance in conventional da tabase systems, perform poorly under heavy real-time loads. The new GUARD-l ink protocol, however, although based on the B-link approach, delivers the best performance (with respect to all performance metrics) for a variety of real-time transaction workloads, by virtue of its admission control mechan ism. In fact, GUARD-link provides close to ideal fairness in most environme nts. These and other results presented here represent the first work in the area of real-time index concurrency control.