8.3. About the PostgreSQL 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 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

Catalog NameDescription
pg_database databases
pg_class tables
pg_attribute table columns
pg_index indexes
pg_proc procedures/functions
pg_type data types (both base and complex)
pg_operator operators
pg_aggregate aggregate functions
pg_am access methods
pg_amop access method operators
pg_amproc access method support functions
pg_opclass access method operator classes

Figure 8-1. The major PostgreSQL system catalogs

The Developer's Guide gives a more detailed explanation of these catalogs and their columns. However, Figure 8-1 shows the major entities and their relationships in the system catalogs. (Columns 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: