Date: Wed, 13 Dec 2017 10:04:57 -0500
From: Stephen Frost <sfrost@snowman.net>
To: David Steele <david@pgmasters.net>
Cc: Andres Freund <andres@anarazel.de>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>,
	Michael Paquier <michael.paquier@gmail.com>
Subject: Re: PATCH: Exclude unlogged tables from base backups
Message-ID: <20171213150456.GI4628@tamriel.snowman.net>
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David,

* David Steele (david@pgmasters.net) wrote:
> On 12/12/17 8:48 PM, Stephen Frost wrote:
> > I don't think there is, because, as David points out, the unlogged
> > tables are cleaned up first and then WAL replay happens during recovery,
> > so the init fork will cause the relation to be overwritten, but then
> > later the logged 'drop table' and subsequent re-use of the relfilenode
> > to create a new table (or persistence change) will all be in the WAL and
> > will be replayed over top and will take care of this.
>=20
> Files can be copied in any order, so if an OID is recycled the backup
> could copy its first, second, or nth incarnation.  It doesn't really
> matter since all of it will be clobbered by WAL replay.
>=20
> The new base backup code just does the non-init fork removal in advance,
> following the same rules that would apply on recovery given the same
> file set.

Just to be clear- the new base backup code doesn't actually *do* the
non-init fork removal, it simply doesn't include the non-init fork in
the backup when there is an init fork, right?

We certainly wouldn't want a basebackup actually running around removing
the main fork for unlogged tables on a running and otherwise healthy
system. ;)

Thanks!

Stephen

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