Re: Extending BASE_BACKUP in replication protocol: incremental backup and backup format

On 2014-01-14 14:42:36 +0100, Magnus Hagander wrote:
> On Tue, Jan 14, 2014 at 2:41 PM, Andres Freund <andres(at)2ndquadrant(dot)com>wrote:
>
> > On 2014-01-14 14:40:46 +0100, Magnus Hagander wrote:
> > > On Tue, Jan 14, 2014 at 2:18 PM, Andres Freund <andres(at)2ndquadrant(dot)com
> > >wrote:
> > >
> > > > On 2014-01-14 14:12:46 +0100, Magnus Hagander wrote:
> > > > > Either way - if we can do this in a safe way, it sounds like a good
> > idea.
> > > > > It would be sort of like rsync, except relying on the fact that we
> > can
> > > > look
> > > > > at the LSN and don't have to compare the actual files, right?
> > > >
> > > > Which is an advantage, yes. On the other hand, it doesn't fix problems
> > > > with a subtly broken replica, e.g. after a bug in replay, or disk
> > > > corruption.
> > > >
> > > >
> > > Right. But neither does rsync, right?
> >
> > Hm? Rsync's really only safe with --checksum and with that it definitely
> > should fix those?
> >
> >
> I think we're talking about difference scenarios.

Sounds like it.

> I thought you were talking about a backup taken from a replica, that
> already has corruption. rsync checksums surely aren't going to help with
> that?

I was talking about updating a standby using such an incremental or
differential backup from the primary (or a standby higher up in the
cascade). If your standby is corrupted in any way a rsync --checksum
will certainly correct errors if it syncs from a correct source?

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
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