| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Craig Ringer <craig(dot)ringer(at)2ndquadrant(dot)com> |
| Cc: | 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 02:04:29 |
| Message-ID: | 8786.1493949869@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
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.
regards, tom lane
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