| From: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, Julien Rouhaud <rjuju123(at)gmail(dot)com>, Antonin Houska <ah(at)cybertec(dot)at>, Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Ordered Partitioned Table Scans |
| Date: | 2019-03-22 15:48:02 |
| Message-ID: | CANP8+jJ1Z+1aVDUjXWupgEFTKf=cm9NyxZ4aJZ_DHqLPfM2e4Q@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, 22 Mar 2019 at 11:39, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Simon Riggs <simon(at)2ndquadrant(dot)com> writes:
> > I agree that the issue of mixing sorts at various points will make
> nonsense
> > of the startup cost/total cost results.
>
> Right.
>
> > I don't see LIMIT costing being broken as a reason to restrict this
> > optimization. I would ask that we allow improvements to the important use
> > case of ORDER BY/LIMIT, then spend time on making LIMIT work correctly.
>
> There's not time to reinvent LIMIT costing for v12. I'd be happy to
> see some work done on that in the future, and when it does get done,
> I'd be happy to see Append planning extended to allow this case.
> I just don't think it's wise to ship one without the other.
>
I was hoping to motivate you to look at this personally, and soon. LIMIT is
so broken that any improvements count as bug fixes in my book.
--
Simon Riggs http://www.2ndQuadrant.com/
<http://www.2ndquadrant.com/>
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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