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Re: [HACKERS] Incrementally Updated Backup

From: "Jim C(dot) Nasby" <jim(at)nasby(dot)net>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org,Heikki Linnakangas <heikki(at)enterprisedb(dot)com>,pgsql-patches(at)postgresql(dot)org
Subject: Re: [HACKERS] Incrementally Updated Backup
Date: 2006-09-20 22:07:29
Message-ID: 20060920220728.GF28987@nasby.net (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patches
On Wed, Sep 20, 2006 at 05:50:48PM -0400, Tom Lane wrote:
> "Jim C. Nasby" <jim(at)nasby(dot)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(at)nasby(dot)net
EnterpriseDB      http://enterprisedb.com      512.569.9461 (cell)

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