[postgis-users] Newest PostGIS code with old PostgreSQL major versions

[Jeremy Schneider]

Hello,

I would like to learn more about how the PostGIS development community
thinks about old major versions of PostgreSQL.

Specifically, I'm curious to hear a little more elaboration on this part
of the PostGIS policy:

> We may on occasion introduce compile support for a newer PostgreSQL
> major version in the previous micro version to allow easier PostgreSQL
> pg_upgrade migrations. ... While the PostGIS version may work on lower
> versions of PostgreSQL, GEOS, GDAL, and Proj, enhanced features may be
> disabled on the lower versions.

https://postgis.net/eol_policy/

I also notice that the support matrix says:

> As a general rule, the PostGIS Project Steering committee tries to
> maintain support of PostGIS for at least two versions of PostgreSQL.

https://trac.osgeo.org/postgis/wiki/UsersWikiPostgreSQLPostGIS

I see that PostGIS maintains stable branches for a number of years. I
can't quite tell, but the statements above read to me like the latest
versions of PostGIS aren't really tested with old versions of
PostgreSQL. It sounds like you introduce compiler support for the
purpose of upgrades, but the PostGIS development community doesn't spend
much effort looking at PostGIS 3.1 on PostgreSQL 10 (for example) -
beyond making sure it compiles successfully.

If I'm reading this right, then when a heavy PostgreSQL v10 user loads
the latest PostGIS code across wide fleets of PostgreSQL v10 systems,
then they should expect to be on the cutting edge of that configuration,
and they would likely be the first reporters of issues unique to running
the latest PostGIS release on old PostgreSQL code.

It might be "safer" for them to stick with PostGIS 2.4 stable releases
on their PostgreSQL 10 fleet, and upgrade PostGIS around the same time
as when they upgrade to the latest major version of PostgreSQL? (Which
should happen within the next year, since PG 10 only has about a year of
official lifetime remaining, similar to PostGIS 2.4.)

But maybe I'm reading too much into this policy and the maintenance of
stable branches, and maybe the PostGIS community would encourage
everyone to run the latest available PostGIS major version even on very
old versions of PostgreSQL? Also, the actual risk of issues with running
recent PostGIS code against really old PostgreSQL versions might not be
that high in practice.

I'm a bit out of my depth here, and I'm looking for thoughts from folks
who know a bit more about this than me.  :)

Thanks,
Jeremy

-- 
Jeremy Schneider
Database Engineer
Amazon Web Services

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