Scheduling Multi - Class Real - Time Transactions : A Performance Evaluation

than traditional real-time scheduling in the sense that certain aspects of transactions may not integrate well with real-time scheduling. This paper introduces a dynamic admission control and parametrable priority based scheduling algorithm called H/M/L. It is based on the transaction importance, an attribute given by the programmer. We consider a multi-class transaction workload consisting of high, medium, and low importance classes. The H/M/L algorithm makes the transactions with higher importance to be executed first even in overload situations. Simulation results confirm the H/M/L behaviour compared to EDF, an optimal scheduling algorithm. I. RESEARCH CONTEXT ASED on definitions from [1]–[10], we place real-time transactions into three categories: transactions with hard, firm and soft deadlines. A hard deadline transaction has hard timing constraints that must absolutely be met. Firm deadline transactions should also be met but may be missed occasionally, e.g. during transient overloads. A firm transaction that misses its deadline adds no value to the system. Thus, it is discarded as soon as its deadline is missed. A soft transaction is not interrupted once its deadline missed because some systems tolerate imprecise results and less quality of service. Real-time database transactions are usually in either firm deadline or soft deadline class. In this paper, we restrict our attention on real-time database systems that execute firm deadline transactions. Applications include e-commerce applications, stock trading and internet bids. Real-time database systems received a lot of attention the last fifteen years. Many efforts have been made in the design of suitable concurrency and commitment protocols. However, there are few works on transaction scheduling. Indeed, often DBMS do not apply explicit scheduling algorithms. Our transaction model is multi-class, each class representing a different transaction importance. The importance attribute is given by the application developer to indicate how critical to the system is that the transaction meets its deadline. We adopt three levels of importance: high, medium and low. A high importance means that the transaction is critical and should be executed even if other transactions of less importance are discarded. A medium importance means that the transaction should satisfy its deadline. A low importance is the default importance and signifies that a deadline miss for this transaction is tolerated. In this paper we introduce a parametrable algorithm for the scheduling of real-time transactions called H/M/L and present some experiments of H/M/L and EDF, the most famous scheduling algorithm [8]. The related work in real-time transaction …