Re: Streaming replication upgrade sanity check

On Thu, Mar 11, 2021 at 07:50:16PM -0500, Stephen Frost wrote:
> > So, my thought is to just upgrade the active side as normal, and once
> > that's done and the master is back in use, stop the standby's
> > postgres, call "pg_start_backup(...)" on the master, rsync the changed
> > files from the running master's data dir to the standby's 10.x data
> > directory, call "pg_stop_backup()", migrate the recovery.conf into a
> > postgresql.auto.conf, touch the standby.signal file, and then start
> > the new postgres 13 on the standby. That seems to work, but I want to
> > be sure I'm not just having good luck due to the relatively low
> > activity on my test systems.
>
> Exactly how are you doing this rsync..? A simplistic rsync would end up
> just copying everything over and, as Bruce says later, if you're doing
> that then you might as well just use pg_basebackup or a similar tool to
> do it cleanly. In other words, I don't think that you're actually
> getting the benefit that you think you are with this.. Note that the
> file names are not kept the same after the pg_upgrade...
>
> Also- I don't think you realize how fast the rsync process to update the
> standbys will be. Done correctly, it should be faster than the
> pg_upgrade.. Note that you'll want to make sure you TRUNCATE and

He/she wants to run the standby, I guess in read-only mode, while
pg_upgrade is running, which is why I didn't even bother to mention
that. I think if downtime is the critical for this person, he/she
should be using logical replication for the upgrade. pg_upgrade really
wants full control of the primary/standbys during its operation, and if
you can't do that, pg_upgrade is not the right tool to use.

> unlogged tables before the pg_upgrade, et al, otherwise you'll end up
> rsync'ing those over. Also make sure you haven't got any stray or
> forgotten temp files or other things. Again, done properly, the rsync
> to upgrade the standbys should only be copying the catalog tables
> themselves and it should be quite fast.

Yes, good points.

--
Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EDB https://enterprisedb.com

The usefulness of a cup is in its emptiness, Bruce Lee