Upgrade to new version

Hello all!

I would like to ask what would be the best procedure to upgrade to a
new version of PostgreSQL in a production system when there is a 'initdb'
necessary?

Situation:
We are running PostgreSQL in a production system. There are about 1000
selects and about 100 inserts per minute.

To upgrade to PostgreSQL 7.2.3 there is an 'initdb' necessary.

The straight forward approach is to shut down the PostgreSQL server
and restore the saved databases.
But, this approach is not possible for us.

We need a "smooth" switch over with a downtime of maximum 5 minutes.

It is possible to set up an other filesystem and another PostgreSQL server
with another port number to initdb the database and restore the databases
and tables backuped at a given time.
But meanwhile some new inserts (well a lot of them) did happen in the existing
databases.
How should the missed inserts be transferred to the new PostgreSQL server?

What would you recommend for this switch?

Thank you for your discussion!
--
--
Mit freundlichen Gruessen / With best regards
Reiner Dassing