From: | tgl(at)postgresql(dot)org (Tom Lane) |
---|---|
To: | pgsql-committers(at)postgresql(dot)org |
Subject: | pgsql: Add some defenses against constant-FALSE outer join conditions. |
Date: | 2008-08-17 19:40:11 |
Message-ID: | 20080817194011.9D669755315@cvs.postgresql.org |
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Lists: | pgsql-committers |
Log Message:
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Add some defenses against constant-FALSE outer join conditions. Since
eval_const_expressions will generally throw away anything that's ANDed with
constant FALSE, what we're left with given an example like
select * from tenk1 a where (unique1,0) in (select unique2,1 from tenk1 b);
is a cartesian product computation, which is really not acceptable.
This is a regression in CVS HEAD compared to previous releases, which were
able to notice the impossible join condition in this case --- though not in
some related cases that are also improved by this patch, such as
select * from tenk1 a left join tenk1 b on (a.unique1=b.unique2 and 0=1);
Fix by skipping evaluation of the appropriate side of the outer join in
cases where it's demonstrably unnecessary.
Modified Files:
--------------
pgsql/src/backend/optimizer/path:
joinrels.c (r1.93 -> r1.94)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/joinrels.c?r1=1.93&r2=1.94)
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