Re: [HACKERS] Incrementally Updated Backup

> On Tue, 2006-09-19 at 12:13 -0400, Tom Lane wrote:

> Also, I'm not sold that the concept is even useful. Apparently the idea
> is to offload the expense of taking periodic base backups from a master
> server, by instead backing up a PITR slave's fileset --- which is fine.

Good. That's the key part of the idea and its a useful one, so I was
looking to document it for 8.2

I thought of this idea separately, then, as usual, realised that this
idea has a long heritage: Change Accumulation has been in production use
with IMS for at least 20 years.

> But why in the world would you want to stop the slave to do it? ISTM
> we would want to arrange things so that you can copy the slave's files
> while it continues replicating, just as with a standard base backup.

You can do that, of course, but my thinking was that people would regard
the technique as "unsupported", so I added a quick flag as a prototype.

On Tue, 2006-09-19 at 12:13 -0400, Tom Lane wrote:

> This patch has obviously been thrown together with no thought and even
> less testing. It breaks the normal case (I think the above if-test is
> backwards), and I don't believe that it works for the advertised purpose
> either (because nothing gets done to force a checkpoint before aborting,
> thus the files on disk are not up to date with the end of WAL).

Yes, it was done very quickly and submitted to ensure it could be
considered yesterday for inclusion. It was described by me as rushed,
which it certainly was because of personal time pressure yesterday: I
thought that made it clear that discussion was needed. Heikki mentions
to me it wasn't clear, so those criticisms are accepted.

On Tue, 2006-09-19 at 16:05 +0100, Heikki Linnakangas wrote:
> Simon Riggs wrote:
> > +
> > + if (startupAfterRecovery)
> > + ereport(ERROR,
> > + (errmsg("recovery ends normally with startup_after_recovery=false")));
> > +
>
> I find this part of the patch a bit ugly.

Me too.

Overall, my own thoughts and Tom's and Heikki's comments indicate I
should withdraw the patch rather than fix it. Patch withdrawn.

Enclose a new doc patch to describe the capability, without s/w change.

--
Simon Riggs
EnterpriseDB http://www.enterprisedb.com