Hi,

What is the error message from MySQL when you go back to the prior version?

Depending on the error, it is probably possible to simply remove the logfiles before restarting the old version.  I don't have an ubuntu DVD on hand and am on slow internet so I can't test right now.

On Wed, Oct 16, 2019 at 10:15 AM bapt x <baptx.is@gmail.com> wrote:

You said "This step is not necessary when upgrading to MariaDB 10.2.5 or later." and in my case, I was upgrading to mariadb-server 10.3.17, so I guess I should not need "set global innodb_fast_shutdown=0;"?

Can someone reproduce the issue with Ubuntu 19.04 on VirtualBox?

On Wed, 16 Oct 2019 at 11:05, Gordan Bobic <gordan.bobic@gmail.com> wrote:

I'm not sure if you accidentally omitted it, but the part I was referring to is documented here:

https://mariadb.com/kb/en/library/upgrading-from-mariadb-101-to-mariadb-102/

Specifically:

Set innodb_fast_shutdown to 0. It can be changed dynamically with SET GLOBAL. For example:
SET GLOBAL innodb_fast_shutdown=0;

• This step is not necessary when upgrading to MariaDB 10.2.5 or later.

Can you confirm this is reproducible if you:

MariaDB> set global innodb_fast_shutdown=0;

# systemctl stop mariadb

# rm /var/lib/mysql/ib_logfile*

and then do the package upgrade and restart?

Can you back up the full data set (or snapshot it)?

If so, remove the ib_logfile* files and see if that lets you start up mysqld? Failing that, you may have to crank up innodb_force_recover=6 (because this is level to avoid redo log replay), and then mysqldump the data. You will lose any recent transactions that haven't made it from the transaction log to the tablespaces.

On Wed, Oct 16, 2019 at 9:46 AM bapt x <baptx.is@gmail.com> wrote:

@Andrei all the error messages I found were included in my original email, let me know how I can provide additional information if no one can reproduce the problem.
I forgot to include maria-discuss@lists.launchpad.net, you can see my reply below.

---------- Forwarded message ---------
From: bapt x <baptx.is@gmail.com>
Date: Wed, 16 Oct 2019 at 10:35
Subject: Re: [Maria-discuss] database corrupted when switching from MySQL to MariaDB on Ubuntu 19.04
To: Gordan Bobic <gordan.bobic@gmail.com>

Thanks for the information. It looks like I did everything properly since I was able to reproduce the problem several times with a clean install of Ubuntu 19.04 on VirtualBox. I think if someone else tries the steps I explained, he can reproduce the problem. Now it would be nice to know if there is a way to recover the data. If MariaDB was able to corrupt the data, there should be a way to reverse engineer the process and restore the data. Maybe a developer that knows well MariaDB upgrade system has a solution.

On Wed, 16 Oct 2019 at 10:23, Gordan Bobic <gordan.bobic@gmail.com> wrote:

I don't know if it is recoverable but it sounds like you missed the step of always needing a full, clean shutdown between upgrades with innodb_fast_shutdown=0. Then you can delete ib_logfile*, and upgrade.

On Wed, 16 Oct 2019, 09:19 bapt x, <baptx.is@gmail.com> wrote:

Hello,

On Ubuntu 19.04, which uses packages mariadb-server 10.3.17 and
mysql-server 5.7.27, I noticed that if I wanted to switch from MySQL to
MariaDB, the database is corrupted and there is a complete data loss
even if I switch back to MySQL.
In the previous version of Ubuntu, switching from MySQL to MariaDB did
not manage to import data automatically (unlike Debian) but at least it
created a backup of the data in /var/lib/mysql-5.7/ folder which is not
done anymore.

Here is the error message I saw during install when trying to use the
database corrupted by MariaDB and switching back to MySQL:
"MySQL has been frozen to prevent damage to your system. Please see
/etc/mysql/FROZEN for help."

And in /var/log/mysql/error.log:
"[ERROR] InnoDB: Unsupported redo log format. The redo log was created
with MariaDB 10.3.17. Please follow the instructions at
http://dev.mysql.com/doc/refman/5.7/en/upgrading-downgrading.html"

I was able to reproduce the issue with a clean installation of Ubuntu
19.04 in VirtualBox.

Do you know where the problem comes from and if it is possible to fix
the binary data from /var/lib/mysql/ to make it work with either MySQL
or MariaDB?
It looks like MariaDB tried to convert the data ("[ERROR] InnoDB:
Unsupported redo log format") but now it fails with both MySQL and MariaDB.
Is it possible to revert the changes done by MariaDB to make the data
work again with MySQL? (and then do a proper backup with mysqldump)

Thanks.

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