Thank you everybody for your suggestions.
So, to summarize - we can run pg_upgrade from 8.3 to 9.4 (in place), fix app related issues (if any), then migrate to a version more recent than 9.6, either through pg_basebackup or through logical replication (if we would upgrade to version 10).
First step requires downtime. Second does not. Correct?
-Julie
From: Tom Lane <tgl@sss.pgh.pa.us>
Sent: Wednesday, December 4, 2019 5:28 AM
To: Stephen Frost <sfrost@snowman.net>
Cc: Laurenz Albe <laurenz.albe@cybertec.at>; Michael Paquier <michael@paquier.xyz>; Julie Nishimura <juliezain@hotmail.com>; pgsql-general@lists.postgresql.org <pgsql-general@lists.postgresql.org>; pgsql-general <pgsql-general@postgresql.org>
Subject: Re: upgrade and migrate
Stephen Frost <sfrost@snowman.net> writes:
> * Laurenz Albe (laurenz.albe@cybertec.at) wrote:
>> Right, Slony is the way to go, since pg_upgrade doesn't support 8.3.
>> I would upgrade to a version more recent than 9.6.
> So... there's a bit of history here. pg_upgrade in 9.4 actually does
> support upgrading from 8.3.X. Support for upgrading from 8.3 was
> removed in 2209b3923a7afe0b6033ecfea972219df252ca8e.
Yeah. Also note that 8.3 to 9.6-or-newer is going to be a pretty
huge jump in terms of minor compatibility issues (have you read
all the relevant release notes?). So there's something to be said
for breaking this down into two steps: update to 9.4, test/fix
your applications against that, then make a second jump to something
current. Each of those jumps could be handled by the respective
version of pg_upgrade. I concur with Laurenz's advice that stopping
at 9.6 is probably not your best choice for a migration today.
regards, tom lane