| A number of modern and important applications, such as tele-medicine systems, mobile internet stock trading systems, and traffic information and navigation systems, all require the support of efficient mobile database systems. Concurrency control constitutes an integral part of any transaction processing systems and thus deserves special attention. In this paper, we study concurrency control strategies, especially the optimistic approach, for mobile distributed databases, and postulate a controlled optimistic concurrency control algorithm, called Prudent-Waiting control, to reduce the number of transaction restarts. Our approach is able to reduce such restarts by recognizing more serializable schedules and prudently waiting to commit following the serialization order established. A detailed simulation model of a mobile distributed database has been constructed and a series of experiments have been conducted to evaluate the performance of the proposed approach. The results demonstrate that the new algorithm outperforms the optimistic concurrency control (with broadcast commit) and two-phase locking over a wide range of system workload. |
