Re: obsoleting plpython2u and defaulting plpythonu to plpython3u

On Friday, April 27, 2018 5:51:57 PM CEST Tom Lane wrote:
> Note that there's a specific timeline there: they expect PEP 394 to get
> changed not more than 2 years from now.  I am not sure if Red Hat has
> enough pull in the Python community to guarantee that will happen, but
> do you want to bet against it?

Well, also it depends what's meant by "get PEP 394 changed".  My guess is
that distros might well avoid providing /bin/python if that PEP is
a concern..  that's actually typical situation in Fedora even now; python2
package isn't installed by default.  And it can disappear entirely if
that's too expensive for maintenance.

To me, PEP 394 is mostly about python distributors - not about python
projects;  so IMO for PostgreSQL that PEP is a bit orthogonal thing.
For quite some time already, doing 'CREATE EXTENSION plpython' implies at
least some (maybe serious) migration headaches in not so distant future.

> > So that's all great.  There are some opportunities for prep work in the
> > meantime that have been mentioned.
> 
> We should evidently plan on making this stuff happen in v12, or we're
> going to be behind the curve.

Agreed, but I'm still not sure what would be the expected 2->3 migration
path.  If that change happens in PG v12, people will migrate to that from
v11 and there's the trouble.  Would it technically possible to upgrade
such clusters with pg_upgrade when 'plpythonu' silently goes from
'plpython2.so' to 'plpython3.so' behind the scenes?

Or is it expected that people will migrate semi-automatically/manually
from plpython2 to plpython3 on v11 - before hitting pg_upgrade?

Pavel