DB running on MySQL v 5.7.21 on localhost.
Upon opening DigiKam, I get an information box about initializing the database and it runs for several minutes. At the end of that, I get an error message about a failure to update the database schema from v8 to v9. Enabling the general log allows me to follow along with what is running on the DB side of things and trying the upgrade/open digiKam several times proved a consistent failure. Immediately (sub 2 seconds) upon attempting to run:
ALTER TABLE ImageTagProperties MODIFY COLUMN value LONGTEXT CHARACTER SET utf8 COLLATE utf8_general_ci
an error of some kind was thrown and a Rollback of the DB began.
The end result of this is that I'm unable to open digiKam and it has become unusable for me.
Please try with last 5.9.0 AppImage linux bundle, to see if problem is reproducible :
You can also replace the dbconfig.xml as described in the double bug report.
*** This bug has been marked as a duplicate of bug 388977 ***
Not reproducible with 7.0.0 beta1.