| From: | Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> |
|---|---|
| To: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
| Cc: | David Fetter <david(at)fetter(dot)org>, Claudio Freire <klaussfreire(at)gmail(dot)com>, Craig Ringer <craig(at)2ndquadrant(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Merlin Moncure <mmoncure(at)gmail(dot)com>, Andreas Karlsson <andreas(at)proxel(dot)se>, Andrew Dunstan <andrew(dot)dunstan(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Subject: | Re: CTE inlining |
| Date: | 2017-05-03 17:44:17 |
| Message-ID: | CAFj8pRC5T-ucUeiP4dgqO0FXS7wuGDQMdUDKX10kgW1RmXMO=w@mail.gmail.com |
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| Lists: | pgsql-hackers |
2017-05-03 19:33 GMT+02:00 Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>:
> David Fetter wrote:
>
> > When we add a "temporary" GUC, we're taking on a gigantic burden.
> > Either we support it forever somehow, or we put it on a deprecation
> > schedule immediately and expect to be answering questions about it for
> > years after it's been removed.
> >
> > -1 for the GUC.
>
> Absolutely.
>
> So ISTM we have three choices:
>
> 1) we switch unmarked CTEs as inlineable by default in pg11. What seems
> likely to happen for a user that upgrades to pg11 is that 5 out of 10
> CTE-using queries are going to become faster than with pg10, and they
> are going to be happy; 4 out of five are going to see no difference, but
> they didn't have to do anything about it; and the remaining query is
> going to become slower, either indistinguishably so (in which case they
> don't care and they remain happy because of the other improvements) or
> notably so, in which case they can easily figure where to add the
> MATERIALIZED option and regain the original performance.
>
>
> 2) unmarked CTEs continue to be an optimization barrier, but we add
> "WITH INLINED" so that they're inlineable. Some users may wonder about
> it and waste a lot of time trying to figure out which CTEs to add it to.
> They see a benefit in half the queries, which makes them happy, but they
> are angry that they had to waste all that time on the other queries.
>
>
> 3) We don't do anything, because we all agree that GUCs are not
> suitable. No progress. No anger, but nobody is happy either.
>
yes, these variants are all.
@2 is only little bit better than bad @3 - is not nice to have default
behave different than any other and than what 90% developers expects.
Regards
Pavel
>
> --
> Álvaro Herrera https://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
>
>
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