Comment 2 for bug 1579708

On Fri, Jun 17, 2016 at 10:49:28AM -0000, Calabacin wrote:
> In my case I had MySQL and wanted to install MariaDB. After using
> MariaDB for some time I decided it was not for me and tried to go back
> to MySQL. That's when hell started. There is no way to recover what I
> had before and everything I try seems to fail. I thought I had it
> finally working but I now get these MySQL crashes all the time.

I'm afraid this expected behaviour. MariaDB is drop-in compatible with
MySQL, but then it changes your database in a way that MySQL does not
understand. You cannot switch back to MySQL after this without
restoring from backup.

I believe our MariaDB packaging warns you of this before you switch. If
it did not, please file a bug against MariaDB. Further, the MySQL
packaging should have stopped you from switching back. The only
supported path is to purge all MySQL/MariaDB -related packages, remove
/etc/mysql and /var/lib/mysql, and either start again or restore from
MySQL (not MariaDB) backup.

Also relevant is bug 1490071. IMHO, there should be a path in packaging
by which the user can use MariaDB but in a different data location so
that going back to MySQL is possible later (albeit by effectively
winding the database back). But this requires extensive work and
coordination and I don't expect to have it ready any time soon.