Bug#986975: libgdal28: please add Breaks: libgdal20

[Dennis Filder]

Hi,

as stated in #988722 during my upgrade to Bullseye I could not cleanly
migrate a postgresql cluster with a table using features from the
postgis extension.  Apparently the reason is that
postgresql-11-postgis-2.5 and postgresql-13-postgis-3 are currently
not co-installable because some dependencies of the latter are in
conflict with dependencies of the former (but to migrate a cluster you
need both).  One is libhdf5-103-1 (which has a Breaks/Replaces on
libhdf5-103) which #988722 covers and which the postgresql team is
aware of.  Another is gdal-data 3.2.1+dfsg-1 (but also 3.2.2+dfsg-1)
which defines a Depends: on libgdal28, but also a Breaks: on libgdal20
(<< 2.5.0~) introduced with commit a029936[1].
postgresql-11-postgis-2.5 depends on libgdal20 2.4.0, but I don't
think they've realized this yet.

I tried to bring this to the attention of Julien Cristau (who
reassigned #988722 to hdf5) yesterday, but so far he hasn't reacted.
I'd also like a second opinion/confirmation for how big of a problem
this actually is.  And if you deem it a problem could you make the
postgresql team aware of this?

Do you remember why you added that Breaks:?  And if it was due to
upstream changes does that mean that postgis-enabled clusters are
essentially unmigratable unless you dump them in full before starting
the upgrade?  Because if so, this should be mentioned in the Bullseye
release notes.

Regards,
Dennis.

1: https://salsa.debian.org/debian-gis-team/gdal/-/commit/a029936168d5b164c5943ebdcd97b417a1751829