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Tweak nestloop costing to weight restart cost of inner path more heavily.
Without this, it was making some pretty silly decisions about whether an expensive sub-SELECT should be the inner or outer side of a join...
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@ -41,7 +41,7 @@
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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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* $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.69 2001/03/22 03:59:34 momjian Exp $
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* $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.70 2001/04/25 22:04:37 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -443,14 +443,22 @@ cost_nestloop(Path *path,
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/* cost of source data */
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/*
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* NOTE: we assume that the inner path's startup_cost is paid once,
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* not over again on each restart. This is certainly correct if the
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* inner path is materialized. Are there any cases where it is wrong?
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* NOTE: clearly, we must pay both outer and inner paths' startup_cost
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* before we can start returning tuples, so the join's startup cost
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* is their sum. What's not so clear is whether the inner path's
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* startup_cost must be paid again on each rescan of the inner path.
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* This is not true if the inner path is materialized, but probably
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* is true otherwise. Since we don't yet have clean handling of the
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* decision whether to materialize a path, we can't tell here which
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* will happen. As a compromise, charge 50% of the inner startup cost
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* for each restart.
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*/
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startup_cost += outer_path->startup_cost + inner_path->startup_cost;
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run_cost += outer_path->total_cost - outer_path->startup_cost;
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run_cost += outer_path->parent->rows *
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(inner_path->total_cost - inner_path->startup_cost);
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if (outer_path->parent->rows > 1)
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run_cost += (outer_path->parent->rows - 1) * inner_path->startup_cost;
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/*
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* Number of tuples processed (not number emitted!). If inner path is
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