A Chase Too Far

In a previous paper* we proposed a novel method for generating alternative query plans that uses chasing (and back-chasing) with logical constraints. The method brings together use of indexes, use of materialized views, semantic optimization and join elimination (minimization). Each of these techniques is known separately to be beneficial to query optimization. The novelty of our approach is in allowing these techniques to interact systematically, e.g. non-trivial use of indexes and materialized views may be enabled only by semantic constraints. We have implemented our method for a variety of schemas and queries. We examine how far we can push the method in terms of complexity of both schemas and queries. We propose a technique for reducing the size of the search space by "stratifying" the sets of constraints used in the (back)chase. The experimental results demonstrate that our method is practical (i.e., feasible and worthwhile).