Re: upgrade and migrate

On 12/6/19 8:14 AM, Julie Nishimura wrote:
> 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?

Well pg_basebackup is a binary copy so I am pretty sure you cannot use
the copy from an old Postgres version with a new Postgres major version.
I am also pretty sure whatever you do there is going to be some
downtime. Left unsaid to date and relevant to downtime:

1) Space/machines available to juggle multiple Postgres instances?

2) Network proximity of above.

3) Whether it is essential all the databases remain in a single cluster?

>
> -Julie
>
> ------------------------------------------------------------------------
> *From:* Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
> *Sent:* Wednesday, December 4, 2019 5:28 AM
> *To:* Stephen Frost <sfrost(at)snowman(dot)net>
> *Cc:* Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>; Michael Paquier
> <michael(at)paquier(dot)xyz>; Julie Nishimura <juliezain(at)hotmail(dot)com>;
> pgsql-general(at)lists(dot)postgresql(dot)org <pgsql-general(at)lists(dot)postgresql(dot)org>;
> pgsql-general <pgsql-general(at)postgresql(dot)org>
> *Subject:* Re: upgrade and migrate
> Stephen Frost <sfrost(at)snowman(dot)net> writes:
>> * Laurenz Albe (laurenz(dot)albe(at)cybertec(dot)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

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com