ForgeRock OpenIDM 4 uses OrientDB as its default datastore, which is good for learning and evaluation, but not suitable for a Production environment. In an earlier post on this space, we looked at the Configuration of MySQL database as the repository for OpenIDM 4. Picking up from there, because a site that I know of uses PostgreSQL instead of MySQL, made a quick demonstration on setting up OpenIDM 4 with PostgreSQL.
Related ForgeRock Documentation:
Setting up OpenIDM with PostgreSQL