Having introduced the basic extensibility concepts, we can now
take a look at how the catalogs are actually laid out. You can
skip this section for now, but some later sections will be
incomprehensible without the information given here, so mark
this page for later reference. All system catalogs have names
that begin with pg_. The following tables contain information
that may be useful to the end user. (There are many other system
catalogs, but there should rarely be a reason to query them
directly.) Table 8-1. PostgreSQL System Catalogs |pg_type||data
types (both base and complex)| |pg_amop||access method
operators| |pg_amproc||access method support functions|
|pg_opclass||access method operator classes| In several of the
sections that follow, we will present various join queries on
the system catalogs that display information we need to extend
the system. Looking at this diagram should make some of these
join queries (which are often three- or four-way joins) more
understandable, because you will be able to