From: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Craig Ringer <craig(dot)ringer(at)2ndquadrant(dot)com>, Joe Conway <mail(at)joeconway(dot)com>, Mario Becroft <mb(at)true(dot)group>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Ilya Shkuratov <motr(dot)ilya(at)ya(dot)ru>, "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Gavin Flower <GavinFlower(at)archidevsys(dot)co(dot)nz>, Andrew Dunstan <andrew(dot)dunstan(at)2ndquadrant(dot)com>, Serge Rielau <serge(at)rielau(dot)com> |
Subject: | Re: CTE inlining |
Date: | 2017-05-05 12:43:33 |
Message-ID: | CAKJS1f-zcdda_6Rskry8cwaVmrmdPg1XBAE40-5+fWHjnwmK=g@mail.gmail.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
On 5 May 2017 at 14:04, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Craig Ringer <craig(dot)ringer(at)2ndquadrant(dot)com> writes:
>> We're carefully maintaining this bizarre cognitive dissonance where we
>> justify the need for using this as a planner hint at the same time as
>> denying that we have a hint. That makes it hard to make progress here.
>> I think there's fear that we're setting some kind of precedent by
>> admitting what we already have.
>
> I think you're overstating the case. It's clear that there's a
> significant subset of CTE functionality where there has to be an
> optimization fence. The initial implementation basically took the
> easy way out by deeming *all* CTEs to be optimization fences. Maybe
> we shouldn't have documented that behavior, but we did. Now we're
> arguing about how much of a compatibility break it'd be to change that
> planner behavior. I don't see any particular cognitive dissonance here,
> just disagreements about the extent to which backwards compatibility is
> more important than better query optimization.
How about we get the ball rolling on this in v10 and pull that part
out of the docs. If anything that'll buy us a bit more wiggle room to
change this in v11.
I've attached a proposed patch.
--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
Attachment | Content-Type | Size |
---|---|---|
doc_caution_about_cte_changes_in_the_future.patch | application/octet-stream | 2.7 KB |
From | Date | Subject | |
---|---|---|---|
Next Message | Alvaro Herrera | 2017-05-05 13:37:09 | Re: Patch - Tcl 8.6 version support for PostgreSQL |
Previous Message | Michael Paquier | 2017-05-05 12:42:57 | Re: password_encryption, default and 'plain' support |