Full MariaDB database restore maybe required

Title: Full MariaDB database restore maybe required
Author: Thomas Deutschmann <whissi@gentoo.org>
Posted: 2021-11-23
Revision: 1
News-Item-Format: 2.0
Display-If-Installed: dev-db/mariadb
Display-If-Installed: sys-cluster/galera

On 2021-11-21, keywords for dev-db/mariadb:10.6 were removed to
address a file collision with dev-db/mariadb-connector-c. This
unintentionally triggered a version downgrade for users who had
successfully upgraded to dev-db/mariadb:10.6 already. [Link 1].

However, downgrades are not supported in MySQL/MariaDB [Link 2].

In case you already fully upgraded to MariaDB 10.6 (which includes
executing mysql_upgrade command) and unintentionally downgraded your
MariaDB instance afterwards during the time window when keywords were
removed, you maybe experiencing different problems:

At best, your unwanted downgraded MariaDB instance prevented startup
so all you have to do is upgrade to MariaDB 10.6 again to resume

In case previous MariaDB version was able to start, you are encouraged
to do a full backup as soon as possible using mysqldump command and
manually restore each database ("logical downgrade") to prevent any
data corruption.

Depending on used feature set and from which version you upgraded,
it is maybe required to do a full restore from a previous backup before
MariaDB 10.6 upgrade to restore services and prevent any data loss or
future runtime errors.

In case you are using MariaDB in a cluster and/or Galera setup you
probably have to rebuild the entire cluster in case the upgrade to
MariaDB 10.6 was already replicated (using pt-table-checksum from
dev-db/percona-toolkit can help you to validate your cluster).

Keep in mind that due to the downgrade, point-in-time recovery may
not be available to the extent that you are used to.

Link 1: https://bugs.gentoo.org/825234

Link 2: https://mariadb.com/kb/en/downgrading-between-major-versions-of-mariadb/