Re: Consistent PITR backup

On Thu, 2007-10-11 at 16:37 +0200, Thomas Karcher wrote:
> Hi Tom,
>
> > > My idea is now: When doing a consistent PITR backup, extend the
> > > documented steps between 4 (pg_stop_backup()) and 5 (wait for archived
> > > WAL file) with a busy wait on pg_xlog/archive_status/*.ready files - as
> > > soon as no .ready files are there anymore, the archiver has done its
> > > work, and I can safely backup the archived WAL files in order to have a
> > > really consistent backup.
> > If the database is busy, you might never see an instant where there are
> > no .ready files. Certainly it's possible that this approach will
> > archive many more segments than you need.
>
> I see - but the risk for never seeing an instant without .ready files is
> relatively slow, I hope. And compared to the risk of not having a
> consistent backup, I could live with having backed up more WAL files
> than I actually would have needed.

There will be gaps, otherwise the archiver will never catch up over
time, but its hard to say when those might be.

> > > Is that right? Or is there an easier way to do it?
> > I believe the intended way to do this is to look at pg_stop_backup's
> > return value to determine the last segment you need to archive.
>
> Thank you - I saw that, but I didn't have a clue about how to determine
> the WAL filename in which this segment is to be found ...

Look at pg_stop_backup() in the docs.

--
Simon Riggs
2ndQuadrant http://www.2ndQuadrant.com