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 tables and indexes have access methods. The requirements for table
   and index access methods are discussed in detail in Chapter 60 and
   Chapter 61 respectively.
  
Table 51.3. pg_am Columns
| Column Type Description | 
|---|
| 
        Row identifier | 
| 
        Name of the access method | 
| 
        OID of a handler function that is responsible for supplying information about the access method | 
| 
        
        | 
    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 9.68.