Supported databases are H2 and MySQL(including MariaDB, Amazon Aurora DB for MySQL...). For production workloads, use MySQL / MariaDB.
To use MySQL, install the MySQL Database Plugin to load the MySQL driver.
Note that PostgreSQL 10+ support is experimental(2019-05). To use PostgreSQL, install the PostgreSQL Plugin to load the PostgreSQL driver.
If empty, then a non production grade H2 embedded database will be used.