Bug#986975: libgdal28: please add Breaks: libgdal20

[Dennis Filder]

X-Debbugs-CC: d.filder at web.de

On Wed, May 19, 2021 at 06:49:10PM +0200, Sebastiaan Couwenberg wrote:

> PostGIS databases have never been able to be migrated during a
> distribution upgrade. You've always needed to recreate the databases in
> the new cluster.

/usr/share/doc/postgresql-common/README.md.gz talks about how
postgresql under Debian strives for co-installability of old and new
versions so that you can migrate your databases /after/ upgrading
Debian.  As it stands now you are only able to dump the postgis
databases while you're still on Buster.  After the upgrade to Bullseye
you won't be able to dump them anymore since postgresql-11-postgis-2.5
will be removed.  The error message I get when trying to dump a
database from the old 11 cluster is:

  pg_dump: error: query failed: ERROR:  could not access file "$libdir/postgis-2.5": No such file or directory

Is that fact communicated somewhere?  Or are postgis users just
expected to know this?  I ask because I didn't know this, despite
doing quite a bit of reading in preparation for the upgrade.  None of
the postgresql-*-postgis-* packages have a README.Debian that could
mention that unlike with vanilla postgres DBs pre-distupgrade DB dumps
are necessary for postgis-enabled ones.  Consequently I assumed I'd be
able to do the migration after the upgrade to Bullseye since apt
showed me that the postgresql-11-* packages were left installed as
holdovers.

If pre-distupgrade DB dumps are expected, I feel like that should be
communicated somewhere where it cannot be missed.

Regards,
Dennis.