Re: [HACKERS] PATCH: multivariate histograms and MCV lists

From: Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com>
To: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
Cc: David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, Andres Freund <andres(at)anarazel(dot)de>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Mark Dilger <hornschnorter(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [HACKERS] PATCH: multivariate histograms and MCV lists
Date: 2019-02-07 06:41:03
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On Wed, 6 Feb 2019 at 23:44, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
> On 2/6/19 10:59 PM, David Rowley wrote:
> > On Thu, 7 Feb 2019 at 03:16, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> wrote:
> >> I wonder what should we be doing with this series -- concretely, should
> >> the effort concentrate on one of the two patches, and leave the other
> >> for pg13, to increase the chances of the first one being in pg12? I
> >> would favor that approach, since it's pretty late in the cycle by now
> >> and it seems dubious that both will be ready.
> >
> > I mostly have been reviewing the MCV patch with the thoughts that one
> > is better than none in PG12. I don't see any particular reason that
> > we need both in the one release.
> >
> I agree with that, although most of the complexity likely lies in
> integrating the stats into the selectivity estimation - if we get that
> right for the MCV patch, adding histogram seems comparably simpler.
> But yeah, let's focus on the MCV part.

Agreed. I think the overall approach of the MCV patch is sound and
it's getting closer to being committable. David's review comments were
excellent. I'll try to review it as well when you post your next

I have some more fundamental doubts about the histogram patch, to do
with the way it integrates with selectivity estimation, and some vague
half-formed ideas about how that could be improved, but nothing clear
enough that I can express right now.

So yes, let's focus on the MCV patch for now.


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