Divide and conquer: A basis for augmenting a conventional query optimizer with multiple query-processing capabilities

摘要

An approach for adding a new component without radically changing an existing single-query optimizer (SQO) is proposed. A new way of organizing the strategy space of a set of queries being optimized is proposed for developing a multiple-query optimizer (MQO) architecture. The architecture relies on the generation of two strategy spaces using subsumption and equivalence of subexpressions at the logical level. Heuristics for pruning the space of multistrategies are also presented. It is shown that the partitioned organisation of the strategy space not only reduces the size of the strategy space but also lends itself to division of labor, thereby leading to a simpler MQO design. Clear separation of the module specific to multistrategy generation provides an easy migration path from SQOs to MQOs. In the decomposition algorithm, selections are propagated down the operator tree (counterintuitively) enabling the detection and creation of larger common subexpressions.