Date: Wed, 24 Mar 2021 12:58:15 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Andrew Dunstan <andrew@dunslane.net>,
	Dilip Kumar <dilipbalaut@gmail.com>,
	Alvaro Herrera <alvherre@alvh.no-ip.org>,
	Andres Freund <andres@anarazel.de>,
	Tomas Vondra <tomas.vondra@2ndquadrant.com>,
	Alexander Korotkov <a.korotkov@postgrespro.ru>,
	David Steele <david@pgmasters.net>,
	Ildus Kurbangaliev <i.kurbangaliev@gmail.com>,
	Dmitry Dolgov <9erthalion6@gmail.com>,
	pgsql-hackers@lists.postgresql.org
Subject: Re: [HACKERS] Custom compression methods
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On Wed, Mar 24, 2021 at 01:30:26PM -0400, Robert Haas wrote:
> On Wed, Mar 24, 2021 at 1:24 PM Justin Pryzby <pryzby@telsasoft.com> wrote:
> > I think it's not specific to pg_upgrade, but any pg_dump |pg_restore.
> >
> > The analogy with tablespaces is restoring from a cluster where the tablespace
> > is named "vast" to one where it's named "huge".  I do this by running
> > PGOPTIONS=-cdefault_tablespace=huge pg_restore --no-tablespaces
> >
> > So I thinks as long as --no-toast-compression does the corresponding thing, the
> > "restore with alternate compression" case is handled fine.
> 
> I think you might be missing the point. If you're using pg_dump and
> pg_restore, you can pass --no-toast-compression if you want. But if

Actually, I forgot that pg_restore doesn't (can't) have --no-toast-compression.
So my analogy is broken.

> you're using pg_upgrade, and it's internally calling pg_dump
> --binary-upgrade, then you don't have control over what options get
> passed. So --no-toast-compression is just fine for people who are
> dumping and restoring, but it's no help at all if you want to switch
> TOAST compression methods while doing a pg_upgrade. However, what does
> help with that is sticking with what Tom committed before rather than
> changing to what he's proposing now.

I don't know what/any other cases support using pg_upgrade to change stuff like
the example (changing to lz4).  The way to do it is to make the changes either
before or after.  It seems weird to think that pg_upgrade would handle that.

I'm going to risk making the analogy that it's not supported to pass
--no-tablespaces from pg_upgrade to pg_dump/restore.  It certainly can't work
for --link (except in the weird case that the dirs are on the same filesystem).  

-- 
Justin