Date: Mon, 27 Jun 2022 14:36:09 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, Peter Geoghegan <pg@bowt.ie>,
	John Naylor <john.naylor@enterprisedb.com>,
	pgsql-hackers@lists.postgresql.org,
	Hannu Krosing <hannuk@google.com>
Subject: Re: do only critical work during single-user vacuum?
Message-ID: <20220627193609.GB19662@telsasoft.com>
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On Thu, Feb 03, 2022 at 01:05:50PM -0500, Robert Haas wrote:
> On Thu, Dec 9, 2021 at 8:56 PM Andres Freund <andres@anarazel.de> wrote:
> > I think we should move *away* from single user mode, rather than the
> > opposite. It's a substantial code burden and it's hard to use.
> 
> Yes. This thread seems to be largely devoted to the topic of making
> single-user vacuum work better, but I don't see anyone asking the
> question "why do we have a message that tells people to vacuum in
> single user mode in the first place?". It's basically bad advice,

> The correct thing to do would be to remove
> the hint as bad advice that we never should have offered in the first
> place. And so here. We should not try to make vacuum in single
> user-mode work better or differently, or at least that shouldn't be
> our primary objective. We should just stop telling people to do it. We
> should probably add messages and documentation *discouraging* the use
> of single user mode for recovering from wraparound trouble, exactly
> the opposite of what we do now. There's nothing we can do in
> single-user mode that we can't do equally well in multi-user mode. If
> people try to fix wraparound problems in multi-user mode, they still
> have read-only access to their database, they can use parallelism,
> they can use command line utilities like vacuumdb, and they can use
> psql which has line editing and allows remote access and is a way
> nicer user experience than running postgres --single. We need a really
> compelling reason to tell people to give up all those advantages, and
> there is no such reason. It makes just as much sense as telling people
> to deal with wraparound problems by angering a live anaconda.

By chance, I came across this prior thread which advocated the same thing in a
initially (rather than indirectly as in this year's thread).

https://www.postgresql.org/message-id/flat/CAMT0RQTmRj_Egtmre6fbiMA9E2hM3BsLULiV8W00stwa3URvzA%40mail.gmail.com
|We should stop telling users to "vacuum that database in single-user mode"