Re: What's our minimum supported Python version?

tl;dr I think requiring support of Python 3.9 for PG18 would probably
be reasonable and save us a bunch of maintenance burden over the next
5 years.

On Tue, 22 Apr 2025 at 21:41, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Yeah, that. The distros that are still shipping older Pythons
> are LTS distros where part of the deal is that the vendor
> is supposed to back-patch security fixes, even if the upstream
> has moved on. Maybe a particular vendor is falling down on that
> job, but it's not for us to rate their performance. So I don't
> buy that "but security!" is a good argument here.

I totally agree that "security" is not the discussion that we should
be having here. I think the Python version decision (or really any
minimum version decision) should be based on some analysis of costs to
us for maintaining support vs benefits to the users.

I'm pretty sure most users of RHEL expect most modern software not to
compile/work completely effortlessly on their distros without some
effort on their part or on the part of RHEL packagers. That's kinda
what you're signing up for if you choose a distro like that.

It might very well be that supporting Python 3.6 does not require many
code changes. But it's so old that installing it on most of the recent
OSes is not trivial, e.g. uv does not support installing it[1]. By
saying we support it, it means that all developers need to go through
serious hoops to be able to test that their python scripts work
correctly on their own machines. And given our own support policy,
we'd probably have to do that for 5 more years (unless we want to
change supported python versions in minor PG releases, which I highly
doubt we want).

So that leaves the question, how much are we actually helping users by
spending all that effort on keeping support for old Python versions?
Based on the Red Hat docs, it's pretty easy to install newer Python3
versions on RHEL8. Depending on the X in RHEL 8.X you can install
different Python3 versions from the official repos[2]. And based on
the official RHEL EOL policy[3], only RHEL 8.4, 8.6, 8.8 and 8.10 are
still getting some level of support. With 8.4 and 8.6 only getting the
final level of support called "Update Services for SAP Solutions", and
with 8.8 reaching that same final support level before PG18 is
released (and 8.4 becoming unsupported before PG18).

Based on that information (only taking into account only RHEL8, not
other distros). It seems like we could at least bump the minimum
Python support to Python 3.9, which is the newest python that's
installable in RHEL 8.4 and 8.6. Anyone that's running a RHEL version
that's still supported by Red Hat can then simply do "yum install
python39" and run the tests (assuming we set up meson/autoconf to
correctly detect the "python3.9" binary).

I'd even be curious how much resistance we'd get from RHEL users if
we'd bump the Python requirement for PG18 to Python 3.12, which is the
newest version that RHEL 8.10 supports. RHEL 8.10 is the only RHEL 8
version that is getting regular support from Red Hat.

(Full disclosure: I've used close to EOL versions of RHEL7
professionally, and I hated every second it. I constantly felt like I
was walking through a software museum. Having to work around bugs that
had been fixed for ages in upstream)

Looking a little further than RHEL:
- Ubuntu 20.04 can easily install Python3.9 from the official package
repos. Currently this is still supported by Cristoph his pgdg repos,
but looks like that support might be removed before PG18 given it's
transition to "Expanded Security Maintenance" next month.
- Ubuntu 22.04 can easily install Python3.11 from the official package
repos. Still has full upstream support for 2 years.
- Debian Bullseye (EOL in 1.5 years) can only install Python3.9 from
the official package repos.
- Debian Bookworm (EOL in 3 years) has Pytho
- Python 3.8 itself is declared EOL by upstream
- Python 3.10 will be declared EOL by upstream around the release of PG19

Based on all this info, I think that it sounds quite reasonable to
start requiring Python3.9 for PG18. And for PG19 we could probably
start requiring Python3.11

[1]: https://github.com/astral-sh/uv/issues/9833
[2]: https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/8/html/configuring_basic_system_settings/installing-and-using-dynamic-programming-languages_configuring-basic-system-settings#assembly_installing-and-using-python_installing-and-using-dynamic-programming-languages
[3]: https://access.redhat.com/support/policy/updates/errata#RHEL8_Planning_Guide

P.S. I CC-ed Devrim and Christoph, for insights into this from the
packagers perspective.