MariaDB is not supported by Confluence. Confluence's internal code as well as third party plugins assume you are using a supported database.

The reason that we do not support MariaDB is because we did not test our product with this type of database. Because of this, there might be several compatibility issues within the usage of Confluence and MariaDB. A number of problems can occur when using MariaDB.

The term "unsupported" means that we may not be able to help you in troubleshooting issues within your instance should it presents any problem.

If you are interested in future MariaDB support for Confluence, please watch:  CONF-29060 - Getting issue details... STATUS

Resolution

Install a supported database