Re: pg_upgrade: fail early if a tablespace dir already exists for new cluster version

On Wed, Oct 21, 2020 at 06:54:17AM -0500, Justin Pryzby wrote:
> On Tue, Oct 20, 2020 at 09:17:22PM -0400, Tom Lane wrote:
> > Justin Pryzby <pryzby@telsasoft.com> writes:
> > > I wonder if pg_upgrade should try to rmdir() the tablespace dirs before
> > > restoring global objects, allowing it to succeed, rather than just "failing
> > > early".
> > 
> > I'm a little confused about that.  If the directories aren't empty,
> > that will fail,
> 
> You mean rmdir() will fail, returning -1, which my patch will ignore, and the
> pg_upgrade will fail, same as it would have before.  The goal of the patch is
> to improve the "empty" case, only.
> 
> > but if they are, shouldn't the upgrade just work?
> 
> It fails in "Restoring global objects", which runs "CREATE TABLESPACE".
> | errmsg("directory \"%s\" already in use as a tablespace",
> 
> I considered the possibility of changing that, but it seems like this is
> specific to pg_upgrade.  I wouldn't want to change the core server just for
> that, and it has a good reason for failing in that case:
> | * The creation of the version directory prevents more than one tablespace
> | * in a single location.

I think it is best to report an error --- pg_upgrade rarely tries to fix
things because that adds complexity, and perhaps bugs.

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

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