pg_shadow contains information about
   database users.  The name stems from the fact that this table
   should not be readable by the public since it contains passwords.
   pg_user is a publicly readable view on
   pg_shadow that blanks out the password field.
  
   The Administrator's Guide contains detailed
   information about user and permission management.
  
   Because user identities are cluster-wide,
   pg_shadow
   is shared across all databases of a cluster: there is only one
   copy of pg_shadow per cluster, not
   one per database.
  
Table 3-26. pg_shadow Columns
| Name | Type | References | Description | 
|---|
| usename | name |   | User name | 
| usesysid | int4 |   | User id (arbitrary number used to reference this user) | 
| usecreatedb | bool |   | User may create databases | 
| usesuper | bool |   | User is a superuser | 
| usecatupd | bool |   |        User may update system catalogs.  (Even a superuser may not do
       this unless this attribute is true.)
       | 
| passwd | text |   | Password | 
| valuntil | abstime |   | Account expiry time (only used for password authentication) | 
| useconfig | text[] |   | Session defaults for run-time configuration variables |