Active Real-time Database Systems Research Articles

Transaction processing in distributed active real-time database systems

An active real-time database system (ARTDBS) is designed to provide timely response to the critical situations that are defined on database states. Although a number of studies have already addressed various issues in ARTDBSs, little attention has been paid to scheduling transactions in a distributed ARTDBS environment. In this paper, 2 An earlier version of this paper appears in the Proceedings of the Second International Workshop on Active, Real-Time and Temporal Database Systems. 2 we describe a detailed performance model of a distributed ARTDBS and investigate various performance issues in time-cognizant transaction processing in ARTDBSs. The experiments conducted evaluate the performance under various types of active workload and different distributed transaction-processing architectures. The performance metric used in the evaluations is the fraction of transactions that violate their timing constraints. We also describe and evaluate a nested transaction execution scheme that improves the real-time performance under high levels of active workload.

Integrating temporal, real-time, an active databases

To meet the needs of many real-world control applications, concepts from Temporal, Real-Time, and Active Databases must be integrated: Since the system's data is supposed to reflect the environment being controlled, they must be updated frequently to maintain temporal validity; Many activities, including those that perform the updates, work under time constraints; The occurrence of events, for example, emergency events, trigger actions. In these systems, meeting timeliness , predictability , and QoS guarantee requirements — through appropriate resource and overload management — become very important. So, algorithms and protocols for concurrency control, recovery, and scheduling are needed. These algorithms must exploit semantics of the data and the transactions to be responsive and efficient. Whereas time cognizant scheduling, concurrency control and conflict resolution have been studied in the literature, recovery issues have not. We have developed strategies for data placement at the appropriate level of memory hierarchy, for avoiding undoing/redoing by exploiting data/transaction characteristics, and for placing logs at the appropriate level in the memory hierarchy. Another issue that we have studied deals with the assignment of priority to transactions in active real-time database systems. We are also studying concurrency control for temporal and multi-media data. We have built RADEx, a simulation environment to evaluate our solutions.

DeeDS towards a distributed and 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 must 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, firm or soft deadlines, and how transient overloads may be resolved by substituting transactions by computationally cheaper ones. The rationale for a loosely coupled general purpose event monitoring facility, that works 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 efficient by employing methods such as main memory resident data, full replication, eventual consistency, and prevention of global deadlocks.