V. Server Programming
    This part is about extending the server functionality with
    user-defined functions, data types, triggers, etc.  These are
    advanced topics which should probably be approached only after all
    the other user documentation about PostgreSQL has
    been understood.  Later chapters in this part describe the server-side
    programming languages available in the
    PostgreSQL distribution as well as
    general issues concerning server-side programming languages.  It
    is essential to read at least the earlier sections of Chapter 33 (covering functions) before diving into the
    material about server-side programming languages.