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

On Jan 14, 2014 2:44 PM, "Andres Freund" <andres(at)2ndquadrant(dot)com> wrote:
>
> 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?

Sure, but as I understand it that's not at all the scenario that the
suggested functionality is for. You can still use rsync for that, I don't
think anybody suggested removing that ability. Replicas weren't the
target...

/Magnus