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Optimal Top-Down Join Enumeration (extended version) (2007)
BibTeX
@MISC{Dehaan07optimaltop-down,
author = {David E. Dehaan and Frank Wm. Tompa},
title = {Optimal Top-Down Join Enumeration (extended version)},
year = {2007}
}
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Abstract
Most contemporary database systems perform cost-based join enumeration using some variant of System-R’s bottomup dynamic programming method. The notable exceptions are systems based on the top-down transformational search of Volcano/Cascades. As recent work has demonstrated, bottom-up dynamic programming can attain optimality with respect to the shape of the join graph; no comparable results have been published for transformational search. However, transformational systems leverage benefits of top-down search not available to bottom-up methods. In this paper we describe a top-down join enumeration algorithm that is optimal with respect to the join graph. We present performance results demonstrating that a combination of optimal enumeration with search strategies such as branch-and-bound yields an algorithm significantly faster than those previously described in the literature. Although our algorithm enumerates the search space top-down, it does not rely on transformations and thus retains much of the architecture of traditional dynamic programming. As such, this work provides a migration path for existing bottom-up optimizers to exploit top-down search without drastically changing to the transformational paradigm.
Keyphrases
optimal top-down join enumeration join graph top-down search bottom-up dynamic programming search strategy system-r bottomup dynamic programming method volcano cascade cost-based join enumeration comparable result search space top-down branch-and-bound yield top-down join enumeration algorithm recent work bottom-up method transformational system leverage benefit optimal enumeration contemporary database system transformational search top-down transformational search transformational paradigm traditional dynamic programming bottom-up optimizers migration path present performance result notable exception
