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From: Peter Geoghegan <pg@bowt.ie>
Date: Fri, 23 Apr 2021 19:42:30 -0700
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Subject: Re: Testing autovacuum wraparound (including failsafe)
To: Andres Freund <andres@anarazel.de>
Cc: PostgreSQL Hackers <pgsql-hackers@postgresql.org>
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On Fri, Apr 23, 2021 at 7:33 PM Andres Freund <andres@anarazel.de> wrote:
> Check it every so often, independent of whether there are indexes or
> dead tuples? Or just check it at the boundaries.

I think that the former suggestion might be better -- I actually
thought about doing it that way myself.

The latter suggestion sounds like you're suggesting that we just check
it at the beginning and the end in all cases (we do the beginning in
all cases already, but now we'd also do the end outside of the loop in
all cases). Is that right? If that is what you meant, then you should
note that there'd hardly be any check in the one-pass case with that
scheme (apart from the initial check that we do already). The only
work we'd be skipping at the end (in the event of that check
triggering the failsafe) would be heap truncation, which (as you've
pointed out yourself) doesn't seem particularly likely to matter.

-- 
Peter Geoghegan