Cost-based optimization of decision support queries using transient-views

Abstract

Next generation decision support applications, besides being capable of processing huge amounts of data, require the ability to integrate and reason over data from multiple, heterogeneous data sources. Often, these data sources differ in a variety of aspects such as their data models, the query languages they support, and their network protocols. Also, typically they are spread over a wide geographical area. The cost of processing decision support queries in such a setting is quite high. However, processing these queries often involves redundancies such as repeated access of same data source and multiple execution of similar processing sequences. Minimizing these redundancies would significantly reduce the query processing cost. In this paper, we (1) propose an architecture for processing complex decision support queries involving multiple, heterogeneous data sources; (2) introduce the notion of transient-views - materialized views that exist only in the context of execution of a query - that is useful for minimizing the redundancies involved in the execution of these queries; (3) develop a cost-based algorithm that takes a query plan as input and generates an optimal "covering plan", by minimizing redundancies in the original plan; (4) validate our approach by means of an implementation of the algorithms and a detailed performance study based on TPC-D benchmark queries on a commercial database system; and finally, (5) compare and contrast our approach with work in related areas, in particular, the areas of answering queries using views and optimization using common sub-expressions. Our experiments demonstrate the practicality and usefulness of transient-views in significantly improving the performance of decision support queries. © 1998 ACM.