Re: pgsql: Apply a band-aid fix for the problem that 8.2 and up completely

[Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>]

Gregory Stark <stark(at)enterprisedb(dot)com> writes:
> "Tom Lane" <tgl(at)postgresql(dot)org> writes:
>> Log Message:
>> -----------
>> Apply a band-aid fix for the problem that 8.2 and up completely misestimate
>> the number of rows likely to be produced by a query such as
>> SELECT * FROM t1 LEFT JOIN t2 USING (key) WHERE t2.key IS NULL;

> I'm a little wary of backpatching planner logic changes like this and another
> instance in the past.

I probably wouldn't have even made this patch if 8.2's behavior weren't
so completely broken on an important class of query.  For a significant
number of people, this is a bug fix.

In any case, there have been planner changes much larger than this
committed into the 8.2 branch since release --- both the outer join
rearrangement logic and choose_bitmap_and have needed significant
surgery.

			regards, tom lane