A concurrency control algorithm for firm real-time database systems

Abstract

Unlike a conventional database system, whose main objective is to provide fast average response time, Real-time database systems (RTDBS) may be evaluated based on how often transactions miss their deadline, the average lateness or tardiness of late transactions, the cost incurred in transactions missing their deadlines. Therefore, in RTDBS, transactions should be scheduled according to their criticalness and the tightness of their deadlines, even if this means sacrificing fairness and system throughput. And it always must guarantee preceding process of a high priority transaction (HPT) as the 2PL-HP (two phase locking with high priority) method. 2PL-HP resolves a conflict through aborting or blocking of a low priority transaction (LPT). If HPT is eliminated in a system because of its deadline missing, an unnecessary aborting or blocking of LPT is occurred. To resolve the problem, AVCC (alternate version concurrency control) algorithm that outperforms 2PL-HP was proposed. However, AVCC must always create the alternative version and have additionally a technique to manage complex alternative versions. In this paper, we propose a new efficient scheduling algorithm, called Multi-level EFDF that combines EFDF (earliest feasible deadline first) and Multilevel Queue scheduling algorithm very ably, and a concurrency control algorithm, called 2PL-FT that prevents wastes of needless resources and eliminates an unnecessary aborting or blocking of LPT. We show through the performance evaluation that our algorithm achieves good performance over the other existing methods proposed earlier. © Springer-Verlag Berlin Heidelberg 2003.