Re: tar error, in pg_start_backup()

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Magnus Hagander <magnus(at)hagander(dot)net>
Cc: raghavendra t <raagavendra(dot)rao(at)gmail(dot)com>, pgsql-general <pgsql-general(at)postgresql(dot)org>
Subject: Re: tar error, in pg_start_backup()
Date: 2010-04-20 13:50:20
Message-ID: 201004201350.o3KDoKR02633@momjian.us
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Magnus Hagander wrote:
> .
>
> On Fri, Apr 16, 2010 at 11:55 AM, raghavendra t
> <raagavendra(dot)rao(at)gmail(dot)com> wrote:
> > Hi All,
> >
> > For?some setups reason, i started taking Hot backup. In this course I have first issued pg_start_backup('backup') and went to the data directory for backing up in OS format using the command "tar -cf backup.tar? /data" . When i issued this command , tar was generating some errors as show below.
> >
> > bash-3.00# tar -cf 16aprilstandby.tar /db-data/
> > tar: Removing leading `/' from member names
> > tar: /db-data/base/24643/151667: file changed as we read it
> > tar: /db-data/base/24643/151764.2: file changed as we read it
> > tar: /db-data/base/24643/151766: file changed as we read it
> > tar: /db-data/base/24643/151768: file changed as we read it
> > tar: /db-data/base/66412/151969: file changed as we read it
> >
> > After sometime tar has ended and i also issued pg_stop_backup() and i continued the process.
> >
> > My question here is, is this errors generated by tar are to worrisome or whats happening in the backend.
> > Is "tar" file is safewell to use. Could you please tell me.
>
> Those are not errors, they are warnings. As long as you use
> pg_start_backup() and pg_stop_backup() before and after the tar, they
> are perfectly harmless, and can be ignored.

Yes, and the manual does mention this issue:

http://developer.postgresql.org/pgdocs/postgres/continuous-archiving.html#BACKUP-BASE-BACKUP

Some file system backup tools emit warnings or errors if the files they
are trying to copy change while the copy proceeds. When taking a base
backup of an active database, this situation is normal and not an error.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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