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Don't try to remove duplicate OR-subclauses in create_bitmap_subplan and

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make_restrictinfo_from_bitmapqual.  The likelihood of finding duplicates
seems much less than in the AND-subclause case, and the cost much higher,
because OR lists with hundreds or even thousands of subclauses are not
uncommon.  Per discussion with Ilia Kantor and andrew@supernews.
This commit is contained in:
Tom Lane
2005-10-13 00:06:46 +00:00
parent 23e2f9ebf7
commit 1e9a6ba5e6
2 changed files with 24 additions and 16 deletions
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20
src/backend/optimizer/util/restrictinfo.c
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@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/util/restrictinfo.c,v 1.39 2005/07/28 20:26:21 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/util/restrictinfo.c,v 1.40 2005/10/13 00:06:46 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -123,9 +123,13 @@ make_restrictinfo_from_bitmapqual(Path *bitmapqual,
List *withoutris = NIL;
/*
* Here, we detect both obvious redundancies and qual-free subplans.
* A qual-free subplan would cause us to generate "... OR true ..."
* which we may as well reduce to just "true".
* Here, we only detect qual-free subplans. A qual-free subplan would
* cause us to generate "... OR true ..." which we may as well reduce
* to just "true". We do not try to eliminate redundant subclauses
* because (a) it's not as likely as in the AND case, and (b) we might
* well be working with hundreds or even thousands of OR conditions,
* perhaps from a long IN list. The performance of list_append_unique
* would be unacceptable.
*/
foreach(l, opath->bitmapquals)
{
@@ -144,12 +148,12 @@ make_restrictinfo_from_bitmapqual(Path *bitmapqual,
return NIL;
}
/* Create AND subclause with RestrictInfos */
withris = list_append_unique(withris,
make_ands_explicit(sublist));
withris = lappend(withris,
make_ands_explicit(sublist));
/* And one without */
sublist = get_actual_clauses(sublist);
withoutris = list_append_unique(withoutris,
make_ands_explicit(sublist));
withoutris = lappend(withoutris,
make_ands_explicit(sublist));
}
/*