Re: Should we add GUCs to allow partition pruning to be disabled?

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>
Cc: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Should we add GUCs to allow partition pruning to be disabled?
Date: 2018-05-24 16:34:28
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On Wed, May 2, 2018 at 07:49:42PM -0700, David G. Johnston wrote:
> On Wednesday, May 2, 2018, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> wrote:
> Robert Haas wrote:
> > On Wed, May 2, 2018 at 9:28 AM, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
> wrote:
> > > I admit I am more concerned about the possibility of bugs than I am
> > > about providing a performance-related tool.
> >
> > I agree that if partition pruning has bugs, somebody might want to
> > turn it off.  On the other hand, when they do, there's a good chance
> > that they will lose so much performance that they'll still be pretty
> > sad.  Somebody certainly could have a workload where the pruning
> > helps, but by a small enough amount that shutting it off is
> > acceptable.  But I suspect that's a somewhat narrow target.
> >
> > I'm not going to go to war over this, though.  I'm just telling you
> > what I think.
> Well, we didn't have a GUC initially, evidently because none of us
> thought that this would be a huge problem.  So maybe you're both right
> and it's overkill to have it.  I'm not set on having it, either.  Does
> anybody else have an opinion?
> I toss my +1 to removing it altogether.

+1 We are terrible at removing old GUCs and having it around means
everyone has to decide if they need to change it, so having it is not a
zero cost.

Bruce Momjian <bruce(at)momjian(dot)us>

+ As you are, so once was I. As I am, so you will be. +
+ Ancient Roman grave inscription +

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