Bypassing Joins in Disjunctive Queries.

@inproceedings{DBLP:conf/vldb/SteinbrunnPMK95,
  author    = {Michael Steinbrunn and
               Klaus Peithner and
               Guido Moerkotte and
               Alfons Kemper},
  editor    = {Umeshwar Dayal and
               Peter M. D. Gray and
               Shojiro Nishio},
  title     = {Bypassing Joins in Disjunctive Queries},
  booktitle = {VLDB'95, Proceedings of 21th International Conference on Very
               Large Data Bases, September 11-15, 1995, Zurich, Switzerland},
  publisher = {Morgan Kaufmann},
  year      = {1995},
  isbn      = {1-55860-379-4},
  pages     = {228-238},
  ee        = {db/conf/vldb/SteinbrunnPMK95.html},
  crossref  = {DBLP:conf/vldb/95},
  bibsource = {DBLP, http://dblp.uni-trier.de}
}

Abstract

The bypass technique, which was formerly restricted to selections only [KMPS94], is extended to join operations. Analogous to the selection case, the join operator may generate two outputstreams-the join result and its complement-whose subsequent operator sequence is optimized individually. By extending the bypass technique to joins, several problems have to be solved. (1) An algorithm for exhaustive generation of the search space for bypass plans has to be developed. (2) The search space for bypass plans is quite large. Hence, partial exploration strategies still resulting in sufficiently efficient plans have to be developed. (3) Since the complement of a join can be very large, those cases where the complement can be restricted to the complement of the semijoin have to be detected. We attack all three problems. Especially, we present an algorithm generating the optimal bypass plan andone algorithm producing near optimal plans exploring the search space onlypartially.

As soon as disjunctions occur, bypassing results in savings. Since the join operator is often more expensive than the selection, the savings for bypassing joins are even higher than those for selections only. We give a quantitative assessment of these savings on the basis of some example queries. Further, we evaluate the performance of the two bypass plan generating algorithms.

Copyright © 1995 by the VLDB Endowment. Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial advantage, the VLDB copyright notice and the title of the publication and its date appear, and notice is given that copying is by the permission of the Very Large Data Base Endowment. To copy otherwise, or to republish, requires a fee and/or special permission from the Endowment.

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