Re: [HACKERS] Incrementally Updated Backup

On Wed, Sep 20, 2006 at 05:50:48PM -0400, Tom Lane wrote:
> "Jim C. Nasby" <jim@nasby.net> writes:
> > My thought is that in many envoronments it would take much beefier
> > hardware to support N postmasters running simultaneously than to cycle
> > through them periodically bringing the backups up-to-date.
>
> How you figure that?  The cycling approach will require more total I/O
> due to extra page re-reads ... particularly if it's built on a patch
> like this one that abandons work-in-progress at arbitrary points.
>
> A postmaster running WAL replay does not require all that much in the
> way of CPU resources.  It is going to need I/O comparable to the gross
> I/O load of its master, but cycling isn't going to reduce that at all.

True, but running several dozen instances on a single machine will
require a lot more memory (or, conversely, each individual database gets
a lot less memory to use).

Of course, this is all hand-waving right now... it'd be interesting to
see which approach was actually better.
--
Jim Nasby                                            jim@nasby.net
EnterpriseDB      http://enterprisedb.com      512.569.9461 (cell)