Comment 20 for bug 1290717

OK, figured it out myself:

$ mysql --socket=/tmp/akonadi-${USER}.rp6WPG/mysql.socket
mysql> use akonadi
mysql> DELETE FROM PartTable WHERE name = 'GID';
mysql> quit
Bye
$ akonadictl start

That helped and akonadi database migration was successfully completed. KMail is now working again.

P.S. Nota, that exact name of your akonadi mysqld instance temporary socket file will be different, use the following command to find it out:

$ ps aux | grep mysqld

Then look for the line in the output with the following parameter: --datadir=/home/$USER/.local/share/akonadi/db_data/. Copy the --socket= parameter from the same line to start mysql textmode client above.