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From: Peter Geoghegan <pg@bowt.ie>
Date: Thu, 9 Dec 2021 13:12:50 -0800
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Subject: Re: do only critical work during single-user vacuum?
To: John Naylor <john.naylor@enterprisedb.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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On Thu, Dec 9, 2021 at 1:04 PM Peter Geoghegan <pg@bowt.ie> wrote:
> On Thu, Dec 9, 2021 at 11:28 AM John Naylor
> <john.naylor@enterprisedb.com> wrote:
> > Now that we have a concept of a fail-safe vacuum, maybe it would be
> > beneficial to skip a vacuum in single-user mode if the fail-safe
> > criteria were not met at the beginning of vacuuming a relation.
>
> Obviously the main goal of the failsafe is to not get into this
> situation in the first place. But it's still very reasonable to ask
> "what happens when the failsafe even fails at that?". This was
> something that we considered directly when working on the feature.

Oh, I think I misunderstood. Your concern is for the case where the
DBA runs a simple "VACUUM" in single-user mode; you want to skip over
tables that don't really need to advance relfrozenxid, automatically.

I can see an argument for something like that, but I think that it
should be a variant of VACUUM. Or maybe it could be addressed with a
better user interface; single-user mode should prompt the user about
what exact VACUUM command they ought to run to get things going.

-- 
Peter Geoghegan