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. In this paper, we develop real-time variants of a representative set of classical B-tree ICC protocols and, using a detailed simulation model, compare their performance for real-time transactions with firm deadlines. We also present and evaluate a new real-time ICC protocol called GUARD-link that augments 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. The performance metrics used in evaluating the ICC protocols are the percentage of transactions that miss their deadlines and the fairness with respect to transaction type and size. Our experimental results show that the performance characteristics of the real-time version of an ICC protocol could be significantly different from the performance of the same protocol in a conventional (nonreal-time) database system. In particular, B-link protocols, which are reputed to provide the best overall performance in conventional database systems, perform poorly under heavy real-time loads. The new GUARD-link 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 mechanism. In fact, GUARD-link provides close to ideal fairness in most environments. These and other results presented here represent the first work in the area of real-time index concurrency contro