In this work we propose and assess a novel technique, called bypass processing, for optimizing the evaluation of disjunctive queries in object-oriented database systems. In the object-oriented data model, selection predicates often contain terms whose evaluation cost varies tremendously; e.g., the evaluation cost of a user-defined function may be orders of magnitude more expensive than an attribute access (and comparison). The idea of bypass processing consists of avoiding the evaluation of such expensive terms whenever the outcome of the entire selection predicate can already be deduced by testing other, less expensive terms. In order to validate the viability of bypass evaluation, we extend a previously developed optimizer architecture and incorporate three alternative optimization algorithms for generating bypass processing plans and-for comparison purpose-one algorithm for generating conventional query evaluation plans. The optimizer is assessed with respect to running time and quality of the obtained query evaluation plans on a (generated) set of queries.
Ulrike Peiker, Martin Griebl