On Co-scheduling of Periodic Update and Application Transactions with Fixed Priority Assignment for Real-Time Monitoring

In a real-time database system for detection of critical events,On co-scheduling of periodic update and application transactions with fixed priority assignment for real-time monitoring meeting the deadlines of the application transactions and maintaining the quality of the real-time data objects are two critical issues in ensuring the effectiveness of performing the real-time monitoring tasks. Unfortunately, these two goals conflict with each other and are difficult to be achieved at the same time. To address this update and application transaction co-scheduling problem, in this paper, we propose a fixed priority scheduling algorithm called Periodic Co-Scheduling (PCS). PCS uses periodic update transactions to maintain the temporal validity of real-time data objects. It judiciously decides the priority order among all the update and application transactions so that the constructed co-schedule can satisfy the deadline constraints of all the application transactions while maximizing the qualities of the real-time data objects. The effectiveness of the PCS algorithm is validated through our extensive simulation experiments.

I. Introduction

With the rapid advancements in sensor and wireless communication technologies, various novel pervasive computing applications are emerging such as humanoid robot, wireless body area network [1], [2], smart house and intelligent vehicle. An important function of these applications is to provide a close monitoring on the status of an operation environment so that timely and appropriate responses are generated to react to the critical events occurring in the environment. For example, in a humanoid robot, it needs to continuously collect information about its working environment to decide what to do; In a smart house system, various sensors work together for tracking moving objects and detecting intruders. To support the real-time monitoring functions efficiently, periodic application transactions may be defined according to the specific requirements of the monitoring tasks. Each invocation of an application transaction has a hard deadline on its completion time, and failing to meet the deadlines can result in serious problem and even be catastrophic, e.g., in health monitoring. How to schedule a set of periodic application transactions to meet their deadlines is a typical real-time scheduling problem [3]. However, simply satisfying the real-time constraints of the application transactions are not sufficient to achieve the real-time monitoring functions effectively. Another important issue is how to maintain the temporal validity of the realtime data objects installed in the system so that the application transactions only access to data objects with sufficiently up-to-date quality.