| From: | Ants Aasma <ants(dot)aasma(at)eesti(dot)ee> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Petr Jelinek <petr(dot)jelinek(at)2ndquadrant(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Adam Brusselback <adambrusselback(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Discussion on missing optimizations |
| Date: | 2017-10-09 14:08:05 |
| Message-ID: | CA+CSw_tAwJD9MXQncwK2_4bhJ+9wN-KsoUQ2sKKwFvChxtE9WQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Sun, Oct 8, 2017 at 7:24 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Petr Jelinek <petr(dot)jelinek(at)2ndquadrant(dot)com> writes:
>> Okay, that makes sense, thanks for explanation. Your patch is the way to
>> go then.
>
> Hearing no further comment, pushed. Thanks for reviewing it.
The tautological col = col comparison on is occasionally used as a
planner "hint" to correct for row count overestimates. Not a great
solution, but PostgreSQL doesn't really have a better way to guide the
planner. Those queries will now have to do something else, like col =
col + 0, which still works.
Regards,
Ants Aasma
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