The iRODS metadata catalog is installed and managed by separate plugins. iRODS has PostgreSQL, MySQL, and Oracle database plugins available and tested.
The particular type of database is encoded in /etc/irods/server_config.json with the following directive:
"technology" : "postgres",
This is populated by the setup_irods.py script on configuration.
To implement a new database plugin, a developer will need to provide implementations for all of the plugin operations and GenQuery.