Identifying Robust Plans through Plan Diagram Reduction

Harish, D and Darera, Pooja N and Haritsa, Jayant R (2008) Identifying Robust Plans through Plan Diagram Reduction. In: Proc. of 34th Intl. Conf. on Very Large Data Bases (VLDB), Auckland, New Zealand, Auckland.

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Abstract

Estimates of predicate selectivities by database query optimizers often differ significantly from those actually encountered during query execution, leading to poor plan choices and inflated response times. In this paper, we investigate mitigating this problem by replacing selectivity error-sensitive plan choices with alternative plans that provide robust performance. Our approach is based on the recent observation that even the complex and dense "plan diagrams" associated with industrial-strength optimizers can be efficiently reduced to "anorexic" equivalents featuring only a few plans, without materially impacting query processing quality. Extensive experimentation with a rich set of TPC-H and TPC-DS-based query templates in a variety of database environments indicate that plan diagram reduction typically retains plans that are substantially resistant to selectivity errors on the base relations. However, it can sometimes also be severely counter-productive, with the replacements performing much worse. We address this problem through a generalized mathematical characterization of plan cost behavior over the parameter space, which lends itself to efficient criteria of when it is safe to reduce. Our strategies are fully non-invasive and have been implemented in the Picasso optimizer visualization tool.

Item Type:	Conference Paper
Publisher:	ACM Press
Additional Information:	Copyright of this article belongs to ACM Press.
Department/Centre:	Division of Electrical Sciences > Computer Science & Automation Division of Interdisciplinary Sciences > Supercomputer Education & Research Centre
Date Deposited:	23 Sep 2011 09:14
Last Modified:	23 Sep 2011 09:14
URI:	http://eprints.iisc.ac.in/id/eprint/40713

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