Bug#989597: release.debian.org: upgrade issue: non-coinstallability of libgdal20 and libgdal28

[Christoph Berg <myon@debian.org>]

Re: Andreas Beckmann
> So packaging wise this looks good. But I have no idea about the postgresql
> side:
> * how do I get some tables using the postgis extension into the database to
> start with? Is there a package in buster that "does that for me" by just
> installing it (postgis with --install-recommends pulls in
> postgresql-postgis, but does not populate a database)?

sudo -u postgres psql -vON_ERROR_STOP=1 <<EOF
create extension postgis;
create table test (geom geometry);
insert into test values ('POLYGON((1 1,1 2,2 2,2 1,1 1))');
EOF

> * how do I "verify" that? (SELECT foo FROM bar ...)

select * from test;
                                                                                            geom                                                                                            
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
 01030000000100000005000000000000000000F03F000000000000F03F000000000000F03F0000000000000040000000000000004000000000000000400000000000000040000000000000F03F000000000000F03F000000000000F03F

> * how do I correctly migrate the database (with postgis stuff) from 11 to 13

As said in my mail: pg_dumpall, then dist-upgrade, and load the dump
again.

Once gdal is fixed, pg_upgradecluster should work, modulo the problem
I ran into. (I still have to retry it.)

> * how do I verify that it worked ?

Do that select again.

> There should be a real package postgresql-postgis, not a virtual one.

Yes, but in the general case of other PG extension packages which are
usually quite small, I'm reluctant to add yet another micro-package
just for the dependencies. Though maybe that's the way to go...

> PS: @Christoph: In piuparts I'm using this receipe to upgrade postgresql
> clusters after dist-upgrades - is this the correct approach?
> 
>                 echo "Upgrading PostgreSQL Cluster from ${from} to ${to}"
>                 pg_dropcluster ${to} main --stop
>                 pg_upgradecluster -v ${to} ${from} main
>                 echo "Dropping old PostgreSQL ${from} Cluster"
>                 pg_dropcluster ${from} main

Yes. (Though pg_upgradecluster is bad at reporting errors during the
upgrade, so you'd have to check if all tables/data arrived manually.)

Christoph