Migrating from 8.3 to 8.4 on the same server

In the documentation under the heading "Migration Between Releases" we
read:

<<It is also possible to use replication methods, such as Slony, to
create a slave server with the updated version of PostgreSQL. The slave
can be on the same computer or a different computer. [...] Such a
switch-over results in only several seconds of downtime for an upgrade. >>

In the section "Warm Standby Servers for High Availability" it says:

<< For testing purposes, it is possible to run both primary and standby
servers on the same system. >>

Although this section does not use the term Point-In-Time Recovery, I
understand this is what it refers to.  Could the WAL/PITR method then be
used to upgrade from 8.3 to 8.4 on the same server and avoid having the
significant downtime of dump/restore?

If so, I understand the two servers would have to run on different
ports.  Are there any other issues/traps to be aware of?

--

Thank you,

Lewis Kapell
Computer Operations
Seton Home Study School