Architectures and Monitoring Techniques for Active Databases: An Evaluation

The need for active capability for non-traditional applications and its concomitant bene ts are well-established. Although the event-based technique for monitoring conditions (leading to the integrated architecture) is the most versatile of all the techniques, from a practical viewpoint there is a need for enhancing pre-existing non-active DBMSs to support active capability. The set of techniques that can be used for providing this add-on active capability (leading to the layered architecture) imposes limitations on the active capability that can be supported. Insights into the details of techniques as well as their impact on the architecture entails a better design that meets the active database objectives. This paper identi es a repertoire of techniques for condition monitoring and discusses their suitability to di erent architectures. This paper argues that from a pragmatic viewpoint, both layered and integrated approaches to support active capability need to be pursued. Then it compares polling and event-based or asynchronous monitoring techniques using an implementation of avors on Symbolics. The focus of this comparison is on: techniques, performance, in uence of implementation strategies on performance, and identi cation of opportunities for optimization.