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In cost_mergejoin, the early-exit effect should not apply to the
outer side of an outer join. Per andrew@supernews.
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@ -49,7 +49,7 @@
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/optimizer/path/costsize.c,v 1.140 2005/03/27 23:53:02 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/optimizer/path/costsize.c,v 1.141 2005/04/04 01:43:12 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -917,16 +917,17 @@ cost_mergejoin(MergePath *path, Query *root)
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rescanratio = 1.0 + (rescannedtuples / inner_path_rows);
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/*
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* A merge join will stop as soon as it exhausts either input stream.
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* Estimate fraction of the left and right inputs that will actually
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* need to be scanned. We use only the first (most significant) merge
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* clause for this purpose.
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* A merge join will stop as soon as it exhausts either input stream
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* (unless it's an outer join, in which case the outer side has to be
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* scanned all the way anyway). Estimate fraction of the left and right
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* inputs that will actually need to be scanned. We use only the first
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* (most significant) merge clause for this purpose.
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*
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* Since this calculation is somewhat expensive, and will be the same for
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* all mergejoin paths associated with the merge clause, we cache the
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* results in the RestrictInfo node.
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*/
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if (mergeclauses)
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if (mergeclauses && path->jpath.jointype != JOIN_FULL)
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{
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firstclause = (RestrictInfo *) linitial(mergeclauses);
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if (firstclause->left_mergescansel < 0) /* not computed yet? */
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@ -946,10 +947,14 @@ cost_mergejoin(MergePath *path, Query *root)
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outerscansel = firstclause->right_mergescansel;
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innerscansel = firstclause->left_mergescansel;
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}
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if (path->jpath.jointype == JOIN_LEFT)
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outerscansel = 1.0;
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else if (path->jpath.jointype == JOIN_RIGHT)
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innerscansel = 1.0;
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}
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else
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{
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/* cope with clauseless mergejoin */
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/* cope with clauseless or full mergejoin */
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outerscansel = innerscansel = 1.0;
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}
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