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Re: Backup of live database

From: Steve Holdoway <steve(dot)holdoway(at)firetrust(dot)com>
To: pgsql-admin(at)postgresql(dot)org
Subject: Re: Backup of live database
Date: 2008-01-16 10:30:30
Message-ID: 20080116233030.c1adbcb1.steve.holdoway@firetrust.com (view raw or flat)
Thread:
Lists: pgsql-admin
You can be absolutely certain that the tar backup of a file that's changed is a complete waste of time. Because it changed while you were copying it. 

Steve.
On Wed, 16 Jan 2008 10:24:00 +0200
"Brian Modra" <epailty(at)googlemail(dot)com> wrote:

> Sorry to be hammering this point, but I want to be totally sure its OK,
> rather than 5 months down the line attempt to recover, and it fails...
> 
> Are you absolutely certain that the tar backup of the file that changed, is
> OK? (And that even if that file is huge, tar has managed to save the file as
> it was before it was changed - otherwise I'm afraid that the first part of
> the file is saved to tar, and then the file is modified, and the last part
> of the file is saved to tar from the point it was modified - and so
> therefore not consistent with the first part... And therefore the file has
> lost its integrity, so even a WAL restore won't help because the base files
> themselves are corrupt in the tar file?
> 
> On 16/01/2008, Joshua D. Drake <jd(at)commandprompt(dot)com> wrote:
> >
> > Brian Modra wrote:
> > > The documentation about WAL says that you can start a live backup, as
> > > long as you use WAL backup also.
> > > I'm concerned about the integrity of the tar file. Can someone help me
> > > with that?
> >
> > If you are using point in time recovery:
> >
> > http://www.postgresql.org/docs/8.2/static/continuous-archiving.html
> >
> > You do not have to worry about it.
> >
> > Joshua D. Drake
> >
> >
> >
> >
> >
> >
> > >
> > > On 16/01/2008, *Joshua D. Drake* <jd(at)commandprompt(dot)com
> > > <mailto:jd(at)commandprompt(dot)com>> wrote:
> > >
> > >     Brian Modra wrote:
> > >      > Hi,
> > >      > If tar reports that a file was modified while it was being
> > archived,
> > >      > does that mean that the file was archived correctly, or is it
> > >     corrupted
> > >      > in the archive?
> > >      > Does tar take a snapshot of the file so that even if it is
> > >     modified, at
> > >      > least the archive is safe?
> > >
> > >     You can not use tar to backup postgresql if it is running.
> > >
> > >     http://www.postgresql.org/docs/8.2/static/backup.html
> > >     <http://www.postgresql.org/docs/8.2/static/backup.html>
> > >
> > >     Sincerely,
> > >
> > >     Joshua D. Drake
> > >
> > >      > Thanks
> > >      >
> > >      > --
> > >      > Brian Modra   Land line: +27 23 5411 462
> > >      > Mobile: +27 79 183 8059
> > >      > 6 Jan Louw Str, Prince Albert, 6930
> > >      > Postal: P.O. Box 2, Prince Albert 6930
> > >      > South Africa
> > >
> > >
> > >
> > >
> > > --
> > > Brian Modra   Land line: +27 23 5411 462
> > > Mobile: +27 79 183 8059
> > > 6 Jan Louw Str, Prince Albert, 6930
> > > Postal: P.O. Box 2, Prince Albert 6930
> > > South Africa
> >
> >
> 
> 
> -- 
> Brian Modra   Land line: +27 23 5411 462
> Mobile: +27 79 183 8059
> 6 Jan Louw Str, Prince Albert, 6930
> Postal: P.O. Box 2, Prince Albert 6930
> South Africa
> 


-- 
Steve Holdoway <steve(dot)holdoway(at)firetrust(dot)com>

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