About the Postgres System Catalogs

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 classes 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 3-1. Postgres System Catalogs

Catalog NameDescription
pg_database databases
pg_class classes
pg_attribute class attributes
pg_index secondary indices
pg_proc procedures (both C and SQL)
pg_type types (both base and complex)
pg_operator operators
pg_aggregate aggregates and aggregate functions
pg_am access methods
pg_amop access method operators
pg_amproc access method support functions
pg_opclass access method operator classes

Figure 3-1. The major Postgres system catalogs

The Reference Manual gives a more detailed explanation of these catalogs and their attributes. However, The major Postgres system catalogs shows the major entities and their relationships in the system catalogs. (Attributes that do not refer to other entities are not shown unless they are part of a primary key.) This diagram is more or less incomprehensible until you actually start looking at the contents of the catalogs and see how they relate to each other. For now, the main things to take away from this diagram are as follows: