Re: pg_upgrade libraries check

On Tue, May 29, 2012 at 04:10:41PM -0400, Tom Lane wrote:
> Hmmm ... that is a good point; right now, there are probably still an
> awful lot of installations that have PL languages installed "bare"
> rather than wrapped in an extension, including all the ones where the
> plpython library has the old name. So a fix that only considers
> extensions doesn't get you out of the plpython problem.
>
> (Eventually I would like to see "CREATE LANGUAGE foo" with no parameters
> redefined as doing "CREATE EXTENSION foo", and doing away with
> pg_pltemplate; but it didn't get done for 9.2.)
>
> Actually, though, I don't see why pg_upgrade couldn't treat PL
> languages, even bare ones, the same way I'm proposing for extensions.
> Right now, it's already the case AFAICS that pg_dump --binary-upgrade
> does not dump PL support functions for PLs listed in pg_pltemplate;
> it just emits the CREATE LANGUAGE command and nothing else. This being
> the case, it's simply wrong for pg_upgrade to be checking shlib names
> for the old support functions, because that has got exactly nothing
> to do with whether the CREATE LANGUAGE command will succeed in the new
> installation. There are at least two ways you could check that
> condition without assuming that the shlib name has stayed the same:
>
> 1. Look for an extension control file for the language name in the new
> installation; if present, assume the proper shlib is installed too.
>
> 2. Look at the pg_pltemplate entries for the language in the new
> database and see if they point to a shlib that exists.
>
> I'd vote for #1 on the grounds that it's simpler and won't break when
> we remove pg_pltemplate. It does assume that packagers of third-party
> PLs have gotten off their duffs and extension-ified their languages.
> I would think that would have been a pretty popular thing to do, though,
> since it so greatly reduces the installation complexity for a language
> not known to pg_pltemplate.

Uh, there is a pg_upgrade C comment on this, so we did discuss it at
some point; see second paragraph:

* In Postgres 9.0, Python 3 support was added, and to do that, a
* plpython2u language was created with library name plpython2.so
* as a symbolic link to plpython.so. In Postgres 9.1, only the
* plpython2.so library was created, and both plpythonu and
* plpython2u pointing to it. For this reason, any reference to
* library name "plpython" in an old PG <= 9.1 cluster must look
* for "plpython2" in the new cluster.
*
* For this case, we could check pg_pltemplate, but that only works
* for languages, and does not help with function shared objects,
* so we just do a general fix.

The bottom line is that already needed function shared objects checking,
so we just wrapped languages into that as well.

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

+ It's impossible for everything to be true. +