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From: Jens Wilke <jens.wilke@affinitas.de>
Organization: Affinitas GmbH
To: pgsql-admin@postgresql.org
Subject: Re: upgrade postgres 8.1.21 to version 8.3.6
Date: Tue, 13 Jul 2010 12:58:01 +0200
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Am Dienstag 13 Juli 2010 11:30:20 schrieb Silvio Brandani:
> We need to upgrade the postgres running on our production system under
> Red Hat Enterprise Linux Server release 5.1  from version 8.1.21 to
> version 8.3.6.

Have a look here:
http://wiki.postgresql.org/wiki/RPM_Installation#How_do_I_perform_a_major_upgrade.3F
You should test the restore of your dump on another port or maschine first.
this might be of interest for you as well:
http://blog.endpoint.com/2010/01/postgres-upgrades-ten-problems-and.html

> Which is the best practice to execute such upgrade with possible
> rollback operation 

Do a filesystem backup.
You should test the restore of your dump on another port or maschine first.

> to gain in 3/4 hour this job ??

That depends on your hardware.

Jens