How to fix corrupted database?

[Patrick Gerlier]

Hi all,

Using Digikam 8.6.0 under Fedora 42 with KDE Plasma desktop

I revived a photo archive put on sleep several years ago. Therefore my 
computer underwent several major upgrades in the mean time, i.e. last 
time I opened this archive was done under an older release. Digikam 
crashes in segfault after "Loading albums" step. When launched from the 
terminal, I get:

digikam.dnnmodelmanager: Cannot find DNN models path
digikam.dnnmodelmanager: Cannot find DNN models path
qt.multimedia.ffmpeg: Using Qt multimedia with FFmpeg version 7.1.1 GPL 
version 3 or later
digikam.dnnmodelmanager: Cannot find DNN models path
digikam.dnnmodelmanager: Cannot find DNN models path
digikam.dnnmodelmanager: Cannot find DNN models path
kf.xmlgui: Unhandled container to remove :  Digikam::DigikamApp
Segmentation fault (core dumped)

It is very likely that I manipulated the photo directory outside 
Digikam, because I reconfigured my computer several times.

When I peek into the database, I see many NULL fields in the 'album' 
column of 'images' table. Some of them correspond to albums I decided to 
make an independent collection under a separate database (though the 
images should have also disappeared because the files are no longer 
present).

I first suspected an issue with removable media which were indexed by 
Digikam, but this does not seem to be the case. I also questioned the 
use of UUID in 'albumroots' table because my disks were reformatted and 
data reloaded "as is" without activating Digikam. I change 'uuid=…' to 
'path=…' without effect (I worked on a copy of the DB).

Digikam operates as expected on other databases. I started a separate 
collection and everything works fine though there are also NULL 'album' 
columns (in relatively low numbers) despite the fact that the photos 
where all managed inside Digikam.

I have written a small quick'n'dirty Django-based database browser to 
see the extent of the damage (within my limited understanding of the DB 
schema, ignoring tags presently). Surprisingly, my browser displays 
pictures and data without problem. Note that this browser is purely 
"passive". It does not try to reconstruct a structure; it only queries 
the DB in read-only mode, ignoring NULL columns (thus ignoring possible 
duplicates resulting from external manipulation).

All data seem to be there.

Since the collection holds 10k+ images (and a very sophisticated 
tree-like tag structure), I'd like to recover the database because it is 
quite impossible to re-enter data, some of them being the result of 
time-consuming historical research (XIX century photos) without backup 
outside Digikam DBs.

Since Digikam segfaults, I can't access the Tools>Maintenance menu command.

How can I proceed?

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