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From: Masahiko Sawada <sawada.mshk@gmail.com>
Date: Tue, 21 Dec 2021 16:56:07 +0900
Message-ID: 
 <CAD21AoAXHZ0J-Xd0RfP_VpkUnGv0G_gCbwt3aCuy6weOKNaHNw@mail.gmail.com>
Subject: Re: do only critical work during single-user vacuum?
To: Peter Geoghegan <pg@bowt.ie>
Cc: Andres Freund <andres@anarazel.de>, "Bossart,
 Nathan" <bossartn@amazon.com>,
	John Naylor <john.naylor@enterprisedb.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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On Tue, Dec 21, 2021 at 1:53 PM Peter Geoghegan <pg@bowt.ie> wrote:
>
> On Mon, Dec 20, 2021 at 8:40 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> > BTW a vacuum automatically enters failsafe mode under the situation
> > where the user has to run a vacuum in the single-user mode, right?
>
> Only for the table that had the problem. Maybe there are no other
> tables that a database level "VACUUM" will need to spend much time on,
> or maybe there are, and they will make it take much much longer (it
> all depends).
>
> The goal of the patch is to make sure that when we're in single user
> mode, we'll consistently trigger the failsafe, for every VACUUM
> against every table -- not just the table (or tables) whose
> relfrozenxid is very old. That's still naive, but much less naive than
> simply telling users to VACUUM the whole database in single user mode
> while vacuuming indexes, etc.

I understand the patch, thank you for the explanation!

I remember Simon proposed a VACUUM command option[1], called
FAST_FREEZE, to turn off index cleanup and heap truncation. Now that
we have failsafe mechanism probably we can have a VACUUM command
option to turn on failsafe mode instead.

Regards,

[1] https://commitfest.postgresql.org/32/2908/

-- 
Masahiko Sawada
EDB:  https://www.enterprisedb.com/