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Fix cost_mergejoin's failure to adjust for rescanning of non-unique merge join

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keys when considering a semi or anti join.  This requires estimating the
selectivity of the merge qual as though it were a regular inner join condition.
To allow caching both that and the real outer-join-aware selectivity, split
RestrictInfo.this_selec into two fields.

This fixes one of the problems reported by Kevin Grittner.
This commit is contained in:
Tom Lane
2009-02-06 23:43:24 +00:00
parent c87c31f10b
commit c473d92351
9 changed files with 86 additions and 53 deletions
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30
src/backend/optimizer/path/clausesel.c
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@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.96 2009/01/01 17:23:43 momjian Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.97 2009/02/06 23:43:23 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -516,21 +516,34 @@ clause_selectivity(PlannerInfo *root,
/*
* If the clause is marked redundant, always return 1.0.
*/
if (rinfo->this_selec > 1)
if (rinfo->norm_selec > 1)
return (Selectivity) 1.0;
/*
* If possible, cache the result of the selectivity calculation for
* the clause. We can cache if varRelid is zero or the clause
* contains only vars of that relid --- otherwise varRelid will affect
* the result, so mustn't cache.
* the result, so mustn't cache. Outer join quals might be examined
* with either their join's actual jointype or JOIN_INNER, so we need
* two cache variables to remember both cases. Note: we assume the
* result won't change if we are switching the input relations or
* considering a unique-ified case, so we only need one cache variable
* for all non-JOIN_INNER cases.
*/
if (varRelid == 0 ||
bms_is_subset_singleton(rinfo->clause_relids, varRelid))
{
/* Cacheable --- do we already have the result? */
if (rinfo->this_selec >= 0)
return rinfo->this_selec;
if (jointype == JOIN_INNER)
{
if (rinfo->norm_selec >= 0)
return rinfo->norm_selec;
}
else
{
if (rinfo->outer_selec >= 0)
return rinfo->outer_selec;
}
cacheable = true;
}
@@ -753,7 +766,12 @@ clause_selectivity(PlannerInfo *root,
/* Cache the result if possible */
if (cacheable)
rinfo->this_selec = s1;
{
if (jointype == JOIN_INNER)
rinfo->norm_selec = s1;
else
rinfo->outer_selec = s1;
}
#ifdef SELECTIVITY_DEBUG
elog(DEBUG4, "clause_selectivity: s1 %f", s1);