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Fix best_inner_indexscan to return both the cheapest-total-cost and

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cheapest-startup-cost innerjoin indexscans, and make joinpath.c consider
both of these (when different) as the inside of a nestloop join.  The
original design was based on the assumption that indexscan paths always
have negligible startup cost, and so total cost is the only important
figure of merit; an assumption that's obviously broken by bitmap
indexscans.  This oversight could lead to choosing poor plans in cases
where fast-start behavior is more important than total cost, such as
LIMIT and IN queries.  8.1-vintage brain fade exposed by an example from
Chuck D.
This commit is contained in:
Tom Lane
2007-05-22 01:40:33 +00:00
parent 2415ad9831
commit d7153c5fad
5 changed files with 94 additions and 63 deletions
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5
src/backend/nodes/outfuncs.c
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@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.306 2007/04/27 22:05:47 tgl Exp $
* $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.307 2007/05/22 01:40:33 tgl Exp $
*
* NOTES
* Every node type that can appear in stored rules' parsetrees *must*
@@ -1440,7 +1440,8 @@ _outInnerIndexscanInfo(StringInfo str, InnerIndexscanInfo *node)
WRITE_NODE_TYPE("INNERINDEXSCANINFO");
WRITE_BITMAPSET_FIELD(other_relids);
WRITE_BOOL_FIELD(isouterjoin);
WRITE_NODE_FIELD(best_innerpath);
WRITE_NODE_FIELD(cheapest_startup_innerpath);
WRITE_NODE_FIELD(cheapest_total_innerpath);
}
static void