[Pkg-kde-extras] Bug#895937: database upgrade from schema 8 to 9 fails - workaround

[tv.debian at googlemail.com]

Since Digikam crashes on Mariadb database conversion I tried reverting 
to older Digikam version, but that only gave me an empty view. So the 
database is unusable with the previous Digikam versions.
Restoring a previous database version leads to the same result: failed 
conversion, corruption that makes it unusable with previous Digikam version.

I downloaded the Digikam 5.9 appimage from digikam.org, which fails to 
convert the database too, but doesn't crash. From it I was able to 
migrate the Mariadb database to sqlite (conversion is very slow). Using 
the sqlite was totally impractical due to sluggishness and high system 
load, so I converted it back to "external Mysql" (Mariadb) with the 
exact same settings in database configuration as the previous one 'user, 
db names...).
Again conversion is slow but about twice as fast as the other way round.

Important, once conversion back to Mariadb is complete, and Digikam 
settings have been switched back to external Mysql database, Digikam 
scanned all content but displayed an empty view. I needed to close and 
relaunch before I could see the images.

I can now use Digikam 5.9 from Debian Unstable with the newly converted 
Mariadb external database, I did not notice any data loss, tags are 
intact too..

So problem solved for me, the double database conversion workaround is 
time expensive but works.