pg_opclass defines index access method operator classes. Each operator class defines semantics for index columns of a particular datatype and a particular index access method. Note that there can be multiple operator classes for a given datatype/access method combination, thus supporting multiple behaviors.
Operator classes are described at length in the Programmer's Guide.
Table 3-22. pg_opclass Columns
| Name | Type | References | Description |
|---|---|---|---|
| opcamid | oid | pg_am.oid | index access method opclass is for |
| opcname | name | name of this opclass | |
| opcnamespace | oid | pg_namespace.oid | namespace of this opclass |
| opcowner | int4 | pg_shadow.usesysid | opclass owner |
| opcintype | oid | pg_type.oid | type of input data for opclass |
| opcdefault | bool | true if opclass is default for opcintype | |
| opckeytype | oid | pg_type.oid | type of index data, or zero if same as opcintype |
The majority of the information defining an operator class is actually not in its pg_opclass row, but in the associated rows in pg_amop and pg_amproc. Those rows are considered to be part of the operator class definition --- this is not unlike the way that a relation is defined by a single pg_class row, plus associated rows in pg_attribute and other tables.