The Liferay portal server uses a relational database to store configuration and state, such as portlet preferences, user permissions, system settings, and more.
By default, Liferay uses Hypersonic (HSQL), which is an embedded database running inside the Java virtual machine. HSQL is useful for standing up a Liferay instance very quickly, but must NOT be used in production due to performance issues and its inability to support clustered Liferay instances.