where the dropped column's data type was
   later dropped, and so there is no <structname>pg_type</structname> row anymore.
   <structfield>attlen</structfield> and the other fields can be used
   to interpret the contents of a row of the table.
  </para>
 </sect1>


 <sect1 id="catalog-pg-authid">
  <title><structname>pg_authid</structname></title>

  <indexterm zone="catalog-pg-authid">
   <primary>pg_authid</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_authid</structname> contains information about
   database authorization identifiers (roles).  A role subsumes the concepts
   of <quote>users</quote> and <quote>groups</quote>.  A user is essentially just a
   role with the <structfield>rolcanlogin</structfield> flag set.  Any role (with or
   without <structfield>rolcanlogin</structfield>) can have other roles as members; see
   <link linkend="catalog-pg-auth-members"><structname>pg_auth_members</structname></link>.
  </para>

  <para>
   Since this catalog contains passwords, it must not be publicly readable.
   <link linkend="view-pg-roles"><structname>pg_roles</structname></link>
   is a publicly readable view on
   <structname>pg_authid</structname> that blanks out the password field.
  </para>

  <para>
   <xref linkend="user-manag"/> contains detailed information about user and
   privilege management.
  </para>

  <para>
   Because user identities are cluster-wide,
   <structname>pg_authid</structname>
   is shared across all databases of a cluster: there is only one
   copy of <structname>pg_authid</structname> per cluster, not
   one per database.
  </para>

  <table>
   <title><structname>pg_authid</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolname</structfield> <type>name</type>
      </para>
      <para>
       Role name
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolsuper</structfield> <type>bool</type>
      </para>
      <para>
       Role has superuser privileges
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolinherit</structfield> <type>bool</type>
      </para>
      <para>
       Role automatically inherits privileges of roles it is a
       member of
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolcreaterole</structfield> <type>bool</type>
      </para>
      <para>
       Role can create more roles
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolcreatedb</structfield> <type>bool</type>
      </para>
      <para>
       Role can create databases
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolcanlogin</structfield> <type>bool</type>
      </para>
      <para>
       Role can log in. That is, this role can be given as the initial
       session authorization identifier.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolreplication</structfield> <type>bool</type>
      </para>
      <para>
       Role is a replication role. A replication role can initiate replication
       connections and create and