Integrating Fixed Priority and Static Scheduling to Maintain External Consistency

Data in hard real-time databases has not only to be logically consistent but has also to be fresh enough in order to be used as an acceptable approximation of associated real-world values. Such external consistency can be achieved, if we use transactions to repeatedly generate new values before the previous ones get out of date. A so-called age constraint is imposed on these transactions. While deadline monotonic scheduling is a usually choice for scheduling subject to age constraints, we propose a static (cyclic) scheduler and show its quality, analytically and by performance evaluation. We continue showing how the received cyclic schedule – which we prefer for time-triggered traffic – can be integrated into overall deadline monotonic scheduling – which is advisable for the eventtriggered part of the database traffic.