You might consider using Slony-I to minimize the downtime.
I haven't done an upgrade using, but know that others have, and I've
done the same using eRServer...
The idea is that you set up an 8.0.1 backend, and set up replication
well ahead of time. Replicate from the 7.4 system to the 8.0 one.
It might take several days to get replication up to date if the
databases are large enough, but once they are relatively in sync, they
should stay there pretty easily.
Switching versions is then as easy as using MOVE SET to switch the
origin from the 7.4 system to the 8.0 one. That ou
--
output = reverse("moc.liamg" "@" "enworbbc")
http://linuxdatabases.info/info/versionupgrade.html
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