Measuring the Complexity of Join Enumeration in Query Optimization.
Kiyoshi Ono, Guy M. Lohman:
Measuring the Complexity of Join Enumeration in Query Optimization.
VLDB 1990: 314-325@inproceedings{DBLP:conf/vldb/OnoL90,
author = {Kiyoshi Ono and
Guy M. Lohman},
editor = {Dennis McLeod and
Ron Sacks-Davis and
Hans-J{\"o}rg Schek},
title = {Measuring the Complexity of Join Enumeration in Query Optimization},
booktitle = {16th International Conference on Very Large Data Bases, August
13-16, 1990, Brisbane, Queensland, Australia, Proceedings},
publisher = {Morgan Kaufmann},
year = {1990},
isbn = {1-55860-149-X},
pages = {314-325},
ee = {db/conf/vldb/OnoL90.html},
crossref = {DBLP:conf/vldb/90},
bibsource = {DBLP, http://dblp.uni-trier.de}
}
Abstract
Since relational database management systems typically support only diadic join operators as primitive operations, a query optimizer must choose the "best" sequence of two-way joins to achieve the N-way join of tables requestedby a query.
The computational complexity of this optimization process is dominated by the number of such possible sequences that must be evaluated by the optimizer.
This paper describes and measures the performance of the Starburst join enumerator, which can parameterically adjust for each query the space of join sequences that are evaluated by the optimizer to allow or disallow (1) composite tables (i.e., tables that are themselves the result of a join) as the inner operand of a join and (2) joins between two tables having no join predicate linkingthem (i.e., Cartesian products).
To limit the size of their optimizer's search space, most earlier systems excluded both of these types of plans, which can execute significantly faster for some queries.
By experimentally varying the parameters of the Starburst join enumerator, we have validated analytic formulas for the number of join sequences under a variety of conditions, and have proven their dependence upon the "shape" of the query.
Specifically,"linear" queries, in which tables are connectcd by binary predicates in a straight line, can be optimized in polynomial time. Hence the dynamicprogramming techniques of System R and R* can still be used to optimize linearqueries of as many as 100 tables in a reasonable amount of time!
Copyright © 1990 by the VLDB Endowment.
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Online Paper
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Printed Edition
Dennis McLeod, Ron Sacks-Davis, Hans-Jörg Schek (Eds.):
16th International Conference on Very Large Data Bases, August 13-16, 1990, Brisbane, Queensland, Australia, Proceedings.
Morgan Kaufmann 1990, ISBN 1-55860-149-X
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Copyright © Tue Mar 16 02:22:01 2010
by Michael Ley (ley@uni-trier.de)