Bypassing Joins in Disjunctive Queries

In this paper we develop a novel optimization strategy for disjunctive queries involving join predicates. This work is an extension of our previously published approach [KMPS94] for optimizing disjunctive selection predicates by generating two output streams from selection operators: a "true"-stream for objects (tuples) satisfying the selection predicate and a "false"-stream for those objects not satisfying the predicate. Then, each stream undergoes an individual, "customized" optimization. Here, we extend the basic idea of [KMPS94] to disjunctive queries with join operators. Analogously to selections, we propose to generate two output streams from a join operator: one "true"-stream for pairs of objects (of the two input streams) that satisfy the join predicate and one "false"- stream for those pairs not satisfying it. In combination with the extended selection predicate processing, this provides a large potential for efficiently evaluating disjunctive queries because it allows to "byp..

Optimizing Disjunctive Queries with Expensive Predicates

In this work, we propose and assess a technique called bypass processing for optimizing the evaluation of disjunctive queries with expensive predicates. The technique is particularly useful for optimizing selection predicates that contain terms whose evaluation costs vary tremendously; e.g., the evaluation of a nested subquery or the invocation of a user-defined function in an object-oriented or extended relational model 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 induced 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. 1 Introduction During the past few years we have witnessed tremendous..