pg_am
The catalog pg_am stores information about
relation access methods. There is one row for each access method supported
by the system.
Currently, only indexes have access methods. The requirements for index
access methods are discussed in detail in Chapter 61.
Table 52.3. pg_am Columns
| Name | Type | References | Description |
|---|---|---|---|
oid | oid | Row identifier (hidden attribute; must be explicitly selected) | |
amname | name | Name of the access method | |
amhandler | regproc | | OID of a handler function that is responsible for supplying information about the access method |
amtype | char |
Currently always i to indicate an index access
method; other values may be allowed in future
|
Before PostgreSQL 9.6, pg_am
contained many additional columns representing properties of index access
methods. That data is now only directly visible at the C code level.
However, pg_index_column_has_property() and related
functions have been added to allow SQL queries to inspect index access
method properties; see Table 9.63.