Deriving deadlines and periods for real-time update transactions

Abstract

Typically, temporal validity of real-time data is maintained by periodic update transactions. In this paper we examine the problem of period and deadline assignment for these update transactions such that (1) these transactions can be guaranteed to complete by their deadlines and (2) the imposed workload is minimized. To this end, we propose a novel approach, named More-Less principle. By applying this principle, updates occur with a period which is more than the period obtained through traditional approaches but with a deadline which is less than the traditional period. We show that the More-Less principle is better than existing approaches in terms of schedulability and the imposed load. We examine the issue of determining the assignment order in which transactions must be considered for period and deadline assignment so that the resulting workloads can be minimized. To this end, the More-Less principle is first examined in a restricted case where the Shortest Validity First (SVF) order is shown to be an optimal solution. We then relax some of the restrictions and show that SVF is an approximate solution which results in workloads that are close to the optimal solution. Our analysis and experiments show that the More-Less principle is an effective design principle that can provide better schedulability and reduce update transaction workload while guaranteeing data validity constraints.