Re: Incrementally Updated Backups

On Sun, 2010-09-12 at 12:18 +0200, J. Roeleveld wrote:
> On Sunday 12 September 2010 00:43:19 Bruce Momjian wrote:
> > Gabe Nell wrote:
> > > > That section has been removed from the current 9.0 docs because we are
> > > > unsure it works.
> > >
> > > Hmm. So the only way to make a consistent backup from a standby server
> > > is to shut down the standby first? Or is even that problematic?
> > >
> > > Would it change anything if we are able to guarantee that the
> > > filesystem is snapshotted as a point-in-time snapshot by using LVM or
> > > on Amazon EC2 by snapshotting an EBS volume?
> >
> > I believe a snapshot of the standby is fine even if it is running, just
> > like on the master.
>
> How can you ensure the snapshot is in a consistent state if the server is
> running?
>
> If a snapshot is taken between 2 updates in a single transaction, only half of
> this transaction is included in the snapshot.
> I would never take an LVM (or similar) snapshot of an application that can't
> be paused in a way to provide a consistent filesystem.

You need to read up on things like WAL and MVCC.

Joshua D. Drake

>
> --
> Joost
>

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