This is true, but you could run the new version on the same server/different
port to the current version, and do a simultaneous dump/restore without
having to use extra disk space, or taking your production database offline -
then you can schedule a time to kill the old one, re-assign the port on the
new one and bring it up - would take about 30 seconds, and this could be
done at a time when traffic was at its lowest.
QUOTE:
Uh, for many sites minutes of downtime would be a huge issue, let alone
hours.
Fortunately, you can use Slony to migrate between versions, greatly
reducing downtime.
END QUOTE
