1. A method comprising: accessing a certain query and a control parameter, wherein the certain query comprises two or more certain disjunctive predicates, and wherein the control parameter indicates a certain procedure of a plurality of alternative stored procedures for expanding queries comprising disjunctive predicates into semantically equivalent candidate queries comprising combinations of subqueries; based at least in part on the control parameter, selecting the certain procedure to expand the certain query into one or more certain semantically equivalent candidate queries, wherein each of the one or more certain semantically equivalent candidate queries, if executed, would collect results from a different combination of two or more subqueries; causing evaluation of the certain query and each of the one or more certain semantically equivalent candidate queries, and, based at least in part on the evaluation, selecting a particular query of the one or more certain semantically equivalent candidate queries or the certain query; causing execution of a transformed query that is based at least in part on the particular query; wherein the method is performed by one or more computing devices.