Re: BUG #16497: old and new pg_controldata WAL segment sizes areinvalid or do not match

On Thu, Jun 18, 2020 at 10:18:21AM -0400, Jeff Janes wrote:
> On Thu, Jun 18, 2020 at 4:05 AM Michael Paquier <michael@paquier.xyz> wrote:
> 
>     On Wed, Jun 17, 2020 at 09:00:23PM +0000, PG Bug reporting form wrote:
>     > I am facing error during upgrade from postgresql -11 to 12.
>     > can you please suggest what is solution.
> 
>     As the error message is telling, you need to make the WAL segment
>     sizes of the old and new clusters match.  This can be defined at
>     server initialization time using initdb with a default of 16MB, so
>     that's not a bug from us, but something you need to take care of
>     within your upgrade process.
> 
> 
> Since wal-segsize is changeable with pg_resetwal since v11, and pg_upgrade is
> already calling pg_resetwal, shouldn't pg_upgrade ideally just deal with this
> situation automatically by allowing the upgrade to also change this value,
> rather than forcing the user to make them match manually?

Uh, well, pg_upgrade is very conservative and fails if anything looks
odd, like different WAL sizes.  Since pg_upgrade doesn't even copy the
WAL from the old server, I am not sure why we require the WAL segment
size to match, but it might be so we can run pg_upgrade on replicas.

The bottom line is that pg_upgrade is complex enough, and having it try
to do more is not a wise approach.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EnterpriseDB                             https://enterprisedb.com

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