Date: Wed, 25 Mar 2026 12:21:00 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Laurenz Albe <laurenz.albe@cybertec.at>
Cc: Nikolay Samokhvalov <nik@postgres.ai>, pgsql-docs@lists.postgresql.org
Subject: Re: [PATCH] Doc: clarify that pg_upgrade statistics transfer works
 cross-version
Message-ID: <acQLbAQntxQzfhtP@momjian.us>
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On Wed, Mar 25, 2026 at 07:03:01AM +0100, Laurenz Albe wrote:
> On Tue, 2026-03-24 at 14:11 -0400, Bruce Momjian wrote:
> > On Tue, Mar 24, 2026 at 05:53:27PM +0100, Laurenz Albe wrote:
> > > Bruce, you are confusing me.  Your first sentence suggests that you
> > > (erroneously) thought that upgrading statistics only works when upgrading
> > 
> > Right.
> > 
> > > *from* v18 or better.  But your last sentence suggests that you'd rather
> > > not add anything to the documentation that could dispel that misconception.
> > 
> > So, we don't normally document cases where a limitation does not exist. 
> > I think the logical place to document this is in the PG 18 release
> > notes.  I am still confused why people, like myself, got this wrong. 
> > What is the source of the confusion?  Just unclear release notes?
> 
> I understand now, thanks.  I agree with you in principle, but I wouldn't
> see that as a hard rule that should stand in the way of clarity.
> 
> Let me quote a precedent from https://www.postgresql.org/docs/current/upgrading.html
> 
>   Minor releases never change the internal storage format and are always
>   compatible with earlier and later minor releases of the same major
>   version number. For example, version 10.1 is compatible with version 10.0
>   and version 10.6.
> 
> To me, that clarifies that there is no limitation to performing minor
> updates with a simple restart.  I think that is useful information.

Right.

> Perhaps you'd feel better if we phrase it as a limitation:
> 
>   Transferring optimizer statistics only work when upgrading to PostgreSQL
>   version v18 or later, but there is no such limitation to the version of
>   the old cluster.
> 
> I like my original suggestion better, though.

Uh, we added the feature in PG 18, so why would we say it only works in
PG 18 --- that is kind of obvious.  I am still asking, why did people,
like me, think it only worked for _old_ PG 18 servers.  If we find where
that was communicated, we can clarify it _there_.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  Do not let urgent matters crowd out time for investment in the future.