Upgrading Between Major MariaDB Versions

MariaDB is designed to allow easy upgrades. You should be able to trivially upgrade from ANY earlier MariaDB version to the latest one (for example MariaDB 5.5.x to MariaDB 10.5.x), usually in a few seconds. This is also mainly true for any MySQL version < 8.0 to MariaDB 10.4 and up.

Upgrades are normally easy because:

All MariaDB table data files are backward compatible
The MariaDB connection protocol is backward compatible. You don't normally need to upgrade any of your old clients to be able to connect to a newer MariaDB version.
The MariaDB slave can be of any newer version than the master.

MariaDB Corporation regularly runs tests to check that one can upgrade from MariaDB 5.5 to the latest MariaDB version without any trouble. All older versions should work too (as long as the storage engines you were using are still around).

Note that if you are using MariaDB Galera Cluster, you have to follow the Galera upgrading instructions!

Requirements for Doing an Upgrade Between Major Versions

Go through the individual version upgrade notes (listed below) to look for any major changes or configuration options that have changed.
Ensure that the target MariaDB version supports the storage engines you are using. For example, in 10.5 TokuDB is not supported.
Backup the database (just in case). At least, take a copy of the mysql data directory with mysqldump --add-drop-table mysql as most of the upgrade changes are done there (adding new fields and new system tables etc).
Ensure that the innodb_fast_shutdown variable is not 2 (fast crash shutdown) or 3. The default of this variable is 1. The safest option for upgrades is 0, but the shutdown time may be notably larger with 0 than for 1 as there are a lot more cleanups done for 0.
innodb_force_recovery must be less than 3.
Cleanly shutdown of the server. This is necessary because even if data files are compatible between versions, recovery logs may not be.

Note that rpms don't support upgrading between major versions, only minor like 10.4.1 to 10.4.2. If you are using rpms, you should de-install the old MariaDB rpms and install the new MariaDB rpms before running mysql_upgrade. Note that when installing the new rpms, mysql_upgrade may be run automatically. There is no problem with running mysql_upgrade many times.

Recommended Steps

If you have a master-slave setup, first upgrade one slave and when you have verified that the slave works well, upgrade the rest of the slaves (if any). Then upgrade one slave to master, upgrade the master, and change the master to a slave.

If you don't have a master-slave setup, then take a backup, shutdown MariaDB and do the upgrade.

Step by step instructions for upgrades

Upgrade MariaDB binaries and libraries, preferably without starting MariaDB.
If the MariaDB server process, mysqld or mariadbd was not started as part of the upgrade, start it by executing mysqld --skip-grant-tables. This may produce some warnings about some system tables not being up to date, but you can ignore these for now as mysql_upgrade will fix that.
Run mysql_upgrade
Restart MariaDB server.

Work Done by mysql_upgrade

The main work done when upgrading is done by running mysql_upgrade. The main things it does are:

Updating the system tables in the mysql database to the newest version. This is very quick.
mysql_upgrade also runs mysqlcheck --check-upgrade to check if there have been any collation changes between the major versions. This recreates indexes in old tables that are using any of the changed collations. This can take a bit of time if there are a lot of tables or there are many tables which used the changed collation. The last time a collation changed was in MariaDB/MySQL 5.1.23.

Post Upgrade Work

Check the MariaDB error log for any problems during upgrade. If there are any warnings in the log files, do you best to get rid of them!

The common warnings/errors are:

Using obsolete options. If this is the case, remove them from your my.cnf files.

Check the manual for new features that have been added since your last MariaDB version.
Test that your application works as before. The main difference from before is that because of optimizer improvements your application should work better than before, but in some rare cases the optimizer may get something wrong. In this case, you can try to use explain, optimizer trace or optimizer_switch to fix the queries.

If Something Goes Wrong

First, check the MariaDB error log to see if you are using configure options that are not supported anymore.
Check the upgrade notices for the MariaDB release that you are upgrading to.
File an issue in the MariaDB bug tracker so that we know about the issue and can provide a fix to make upgrades even better.
Add a comment to this manual entry for how we can improve it.

Disaster Recovery

In the unlikely event something goes wrong, you can try the following:

Remove the InnoDB tables from the mysql data directory. They are:
- gtid_slave_pos
- innodb_table_stats
- innodb_index_stats
- transaction_registry
Move the mysql data directory to mysql-old and run mysql_install_db to generate a new one.
After the above, you have to add back your old users.
When done, delete the mysql-old data directory.

Downgrading

MariaDB server is not designed for downgrading. That said, in most cases, as long as you haven't run any ALTER TABLE or CREATE TABLE statements and you have a mysqldump of your old mysql database , you should be able to downgrade to your previous version by doing the following:

Do a clean shutdown. For this special case you have to set innodb_fast_shutdown to 0,before taking down the new MariaDB server, to ensure there are no redo or undo logs that need to be applied on the downgraded server.
Delete the tables in the mysql database (if you didn't use the option --add-drop-table to mysqldump)
Delete the new MariaDB installation
Install the old MariaDB version
Start the server with mysqld --skip-grant-tables
Install the old mysql database
Execute in the mysql client FLUSH PRIVILEGES