The Pega Platform requires Java user-defined functions (UDFs). To work with PostgreSQL, UDFs require the PL/Java add-on for PostgreSQL and a new dedicated schema. The new schema, called SQLJ, is defined for the Pega Platform database.
Provided the Pega 7.3.1 installation guide with postgre. This may help you.
As far as I know the Amazon RDS service does not allow installation of user-defined functions (UDFs).Because we do not have access to the operating system which is required to add PL/Java to PostgreSQL, we cannot install traditional UDFs on Amazon RDS (PostgreSQL). I am looking for workaround like PL/V8 instead of pl/java otherwise we need to complete the installation without UDF.