Date: Fri, 23 Apr 2021 16:26:17 -0700
From: Andres Freund <andres@anarazel.de>
To: Justin Pryzby <pryzby@telsasoft.com>
Cc: pgsql-hackers@postgresql.org, Peter Geoghegan <pg@bowt.ie>
Subject: Re: Testing autovacuum wraparound (including failsafe)
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 <20210423230812.GN7256@telsasoft.com>
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Hi,

On 2021-04-23 18:08:12 -0500, Justin Pryzby wrote:
> On Fri, Apr 23, 2021 at 01:43:06PM -0700, Andres Freund wrote:
> > 2) FAILSAFE_MIN_PAGES is 4GB - which seems to make it infeasible to test the
> >    failsafe mode, we can't really create 4GB relations on the BF. While
> >    writing the tests I've lowered this to 4MB...
> 
> > For 2), I don't really have a better idea than making that configurable
> > somehow?
> 
> Does it work to shut down the cluster and create the .0,.1,.2,.3 segments of a
> new, empty relation with zero blocks using something like truncate -s 1G ?

I'd like this to be portable to at least windows - I don't know how well
that deals with sparse files. But the bigger issue is that that IIRC
will trigger vacuum to try to initialize all those pages, which will
then force all that space to be allocated anyway...

Greetings,

Andres Freund