Deeds: a D Istributed Active Real-time Database System

DeeDS combines active database functionality with critical timing constraints and integrated system monitoring. Since the reactive database mechanisms, or rule management system, must meet critical deadlines, we m ust employ methods that make triggering of rules and execution of actions predictable. We will focus on the scheduling issues associated with dynamic scheduling of workloads where the triggered transactions have hard, rm or soft deadlines, and how transient o verloads may be resolved by substituting transactions by computationally cheaper ones. The rationale for a loosely coupled general purpose event monitoring facility, t h a t w orks in tight connection with the scheduler, is presented. For performance and predictability, the scheduler and event monitor are executing on a separate CPU from the rest of the system. Real-time database accesses in DeeDS are made predictable and ecient b y employing methods such as main memory resident data, full replication, eventual consistency, and prevention of global deadlocks. Authors are listed in alphabetical order.