Re: Postgres restart in the middle of exclusive backup and the presence of backup_label file

From: David Steele <david(at)pgmasters(dot)net>
To: Nathan Bossart <nathandbossart(at)gmail(dot)com>, Chapman Flack <chap(at)anastigmatix(dot)net>
Cc: Stephen Frost <sfrost(at)snowman(dot)net>, pgsql-hackers(at)lists(dot)postgresql(dot)org
Subject: Re: Postgres restart in the middle of exclusive backup and the presence of backup_label file
Date: 2022-03-08 21:09:50
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On 3/8/22 14:01, Nathan Bossart wrote:
> On Wed, Mar 02, 2022 at 02:23:51PM -0500, Chapman Flack wrote:
>> I did not notice this earlier (sorry), but there seems to remain in
>> backup.sgml a programlisting example that shows a psql invocation
>> for pg_backup_start, then a tar command, then another psql invocation
>> for pg_backup_stop.
>> I think that was only workable for the exclusive mode, and now it is
>> necessary to issue pg_backup_start and pg_backup_stop in the same session.
>> (The 'touch backup_in_progress' business seems a bit bogus now too,
>> suggesting an exclusivity remembered from bygone days.)
>> I am not sure what a workable, simple example ought to look like.
>> Maybe a single psql script issuing the pg_backup_start and the
>> pg_backup_stop, with a tar command in between with \! ?
>> Several bricks shy of production-ready, but it would give the idea.
> Another option might be to just remove this section. The top of the
> section mentions that this is easily done using pg_basebackup with the -X
> parameter. The bottom part of the section includes more complicated steps
> for when "more flexibility in copying the backup files is needed..."
> AFAICT the more complicated strategy was around before pg_basebackup, and
> the pg_basebackup recommendation was added in 2012 as part of 920febd.
> Thoughts?

This makes sense to me. I think pg_basebackup is far preferable to doing
anything like what is described in this section. Unless you are planning
to do something fancy (parallelization, snapshots, object stores, etc.)
then pg_basebackup is the way to go.


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