Strategies for resolving inter-class data conflicts in mixed real-time database systems

Although many efficient concurrency control protocols have been proposed for real-time database systems, they are mainly designed for the systems with a single type of real-time transactions. Their performance objective is usually to minimize the number of deadline missing of soft real-time transactions or to guarantee the deadline satisfaction of hard real-time transactions. Due to the very different performance requirements of hard and soft real-time transactions, existing realtime concurrency control protocols may not be suitable to Mixed Real-time Database Systems (MRTDBS), where different types of real-time transactions, and even non-real-time transactions, may co-exist in the systems. In this paper, we propose strategies for resolving data conflicts between different types of transactions in a MRTDBS so that the performance requirements of each individual transaction type can be satisfied and, at the same time, the overall system performance can be improved. The performance of the proposed strategies is evaluated and compared with a real-time optimistic approach, which has been shown to give a better performance than the lock-based protocols for soft and firm real-time transactions. The performance of our proposed conflict resolution methods has also been investigated in a more realistic environment in which the number of priority levels supported in the system is limited, and some of the data may be resided on the disk.