Date: Wed, 16 Nov 2016 09:36:51 -0500
From: Stephen Frost <sfrost@snowman.net>
To: Gunnar Nick Bluth <gunnar.bluth@pro-open.de>
Cc: pgsql-docs@postgresql.org
Subject: Re: Missing important information in backup.sgml
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Gunnar, all,

* Gunnar "Nick" Bluth (gunnar.bluth.extern@elster.de) wrote:
> Am 16.11.2016 um 11:37 schrieb Gunnar "Nick" Bluth:
> > I ran into this issue (see patch) a few times over the past years, and
> > tend to forget it again (sigh!). Today I had to clean up a few hundred
> > GB of unarchived WALs, so I decided to write a patch for the
> > documentation this time.
>=20
> Uhm, well, the actual problem was a stale replication slot... and
> tomatoes on my eyes, it seems ;-/. Ashes etc.!
>=20
> However, I still think a warning on (esp. rsync's) RCs >=3D 128 is worth
> considering (see -v2 attached).

Frankly, I wouldn't suggest including such wording as it would imply
that using a bare rsync command is an acceptable configuration of
archive_command.  It isn't.  At the very least, a bare rsync does
nothing to ensure that the WAL has been fsync'd to permanent storage
before returning, leading to potential data loss due to the WAL
segment being removed by PG before the new segment has been permanently
stored.

The PG documentation around archive command is, at best, a starting
point for individuals who wish to implement their own proper backup
solution, not as examples of good practice for production environments.

Thanks!

Stephen

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