 <sect1 id="functions-info">
  <title>System Information Functions and Operators</title>

   <para>
    The functions described in this section are used to obtain various
    information about a <productname>PostgreSQL</productname> installation.
   </para>

  <sect2 id="functions-info-session">
   <title>Session Information Functions</title>

  <para>
   <xref linkend="functions-info-session-table"/> shows several
   functions that extract session and system information.
  </para>

  <para>
   In addition to the functions listed in this section, there are a number of
   functions related to the statistics system that also provide system
   information. See <xref linkend="monitoring-stats-functions"/> for more
   information.
  </para>

   <table id="functions-info-session-table">
    <title>Session Information Functions</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>current_catalog</primary>
        </indexterm>
        <function>current_catalog</function>
        <returnvalue>name</returnvalue>
       </para>
       <para role="func_signature">
        <indexterm>
         <primary>current_database</primary>
        </indexterm>
        <function>current_database</function> ()
        <returnvalue>name</returnvalue>
       </para>
       <para>
        Returns the name of the current database.  (Databases are
        called <quote>catalogs</quote> in the SQL standard,
        so <function>current_catalog</function> is the standard's
        spelling.)
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>current_query</primary>
        </indexterm>
        <function>current_query</function> ()
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Returns the text of the currently executing query, as submitted
        by the client (which might contain more than one statement).
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>current_role</primary>
        </indexterm>
        <function>current_role</function>
        <returnvalue>name</returnvalue>
       </para>
       <para>
        This is equivalent to <function>current_user</function>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>current_schema</primary>
        </indexterm>
        <indexterm>
         <primary>schema</primary>
         <secondary>current</secondary>
        </indexterm>
        <function>current_schema</function>
        <returnvalue>name</returnvalue>
       </para>
       <para role="func_signature">
        <function>current_schema</function> ()
        <returnvalue>name</returnvalue>
       </para>
       <para>
        Returns the name of the schema that is first in the search path (or a
        null value if the search path is empty).  This is the schema that will
        be used for any tables or other named objects that are created without
        specifying a target schema.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>current_schemas</primary>
        </indexterm>
        <indexterm>
         <primary>search path</primary>
         <secondary>current</secondary>
        </indexterm>
        <function>current_schemas</function> ( <parameter>include_implicit</parameter> <type>boolean</type> )
        <returnvalue>name[]</returnvalue>
       </para>
       <para>
        Returns an array of the names of all schemas presently in the
        effective search path, in their priority order.  (Items in the current
        <xref linkend="guc-search-path"/> setting that do not correspond to
        existing, searchable schemas are omitted.)  If the Boolean argument
        is <literal>true</literal>, then implicitly-searched system schemas
        such as <literal>pg_catalog</literal> are included in the result.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>current_user</primary>
        </indexterm>
        <indexterm>
         <primary>user</primary>
         <secondary>current</secondary>
        </indexterm>
        <function>current_user</function>
        <returnvalue>name</returnvalue>
       </para>
       <para>
        Returns the user name of the current execution context.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>inet_client_addr</primary>
        </indexterm>
        <function>inet_client_addr</function> ()
        <returnvalue>inet</returnvalue>
       </para>
       <para>
        Returns the IP address of the current client,
        or <literal>NULL</literal> if the current connection is via a
        Unix-domain socket.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>inet_client_port</primary>
        </indexterm>
        <function>inet_client_port</function> ()
        <returnvalue>integer</returnvalue>
       </para>
       <para>
        Returns the IP port number of the current client,
        or <literal>NULL</literal> if the current connection is via a
        Unix-domain socket.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>inet_server_addr</primary>
        </indexterm>
        <function>inet_server_addr</function> ()
        <returnvalue>inet</returnvalue>
       </para>
       <para>
        Returns the IP address on which the server accepted the current
        connection,
        or <literal>NULL</literal> if the current connection is via a
        Unix-domain socket.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>inet_server_port</primary>
        </indexterm>
        <function>inet_server_port</function> ()
        <returnvalue>integer</returnvalue>
       </para>
       <para>
        Returns the IP port number on which the server accepted the current
        connection,
        or <literal>NULL</literal> if the current connection is via a
        Unix-domain socket.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_backend_pid</primary>
        </indexterm>
        <function>pg_backend_pid</function> ()
        <returnvalue>integer</returnvalue>
       </para>
       <para>
        Returns the process ID of the server process attached to the current
        session.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_blocking_pids</primary>
        </indexterm>
        <function>pg_blocking_pids</function> ( <type>integer</type> )
        <returnvalue>integer[]</returnvalue>
       </para>
       <para>
        Returns an array of the process ID(s) of the sessions that are
        blocking the server process with the specified process ID from
        acquiring a lock, or an empty array if there is no such server process
        or it is not blocked.
       </para>
       <para>
        One server process blocks another if it either holds a lock that
        conflicts with the blocked process's lock request (hard block), or is
        waiting for a lock that would conflict with the blocked process's lock
        request and is ahead of it in the wait queue (soft block).  When using
        parallel queries the result always lists client-visible process IDs
        (that is, <function>pg_backend_pid</function> results) even if the
        actual lock is held or awaited by a child worker process.  As a result
        of that, there may be duplicated PIDs in the result.  Also note that
        when a prepared transaction holds a conflicting lock, it will be
        represented by a zero process ID.
       </para>
       <para>
        Frequent calls to this function could have some impact on database
        performance, because it needs exclusive access to the lock manager's
        shared state for a short time.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_conf_load_time</primary>
        </indexterm>
        <function>pg_conf_load_time</function> ()
        <returnvalue>timestamp with time zone</returnvalue>
       </para>
       <para>
        Returns the time when the server configuration files were last loaded.
        If the current session was alive at the time, this will be the time
        when the session itself re-read the configuration files (so the
        reading will vary a little in different sessions).  Otherwise it is
        the time when the postmaster process re-read the configuration files.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_current_logfile</primary>
        </indexterm>
        <indexterm>
         <primary>Logging</primary>
         <secondary>pg_current_logfile function</secondary>
        </indexterm>
        <indexterm>
          <primary>current_logfiles</primary>
          <secondary>and the pg_current_logfile function</secondary>
        </indexterm>
        <indexterm>
         <primary>Logging</primary>
         <secondary>current_logfiles file and the pg_current_logfile
         function</secondary>
        </indexterm>
        <function>pg_current_logfile</function> ( <optional> <type>text</type> </optional> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Returns the path name of the log file currently in use by the logging
        collector.  The path includes the <xref linkend="guc-log-directory"/>
        directory and the individual log file name.  The result
        is <literal>NULL</literal> if the logging collector is disabled.
        When multiple log files exist, each in a different
        format, <function>pg_current_logfile</function> without an argument
        returns the path of the file having the first format found in the
        ordered list: <literal>stderr</literal>,
        <literal>csvlog</literal>, <literal>jsonlog</literal>.
        <literal>NULL</literal> is returned if no log file has any of these
        formats.
        To request information about a specific log file format, supply
        either <literal>csvlog</literal>, <literal>jsonlog</literal> or
        <literal>stderr</literal> as the
        value of the optional parameter. The result is <literal>NULL</literal>
        if the log format requested is not configured in
        <xref linkend="guc-log-destination"/>.
        The result reflects the contents of
        the <filename>current_logfiles</filename> file.
       </para>
       <para>
        This function is restricted to superusers and roles with privileges of
        the <literal>pg_monitor</literal> role by default, but other users can
        be granted EXECUTE to run the function.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_loaded_modules</primary>
        </indexterm>
        <function>pg_get_loaded_modules</function> ()
        <returnvalue>setof record</returnvalue>
        ( <parameter>module_name</parameter> <type>text</type>,
        <parameter>version</parameter> <type>text</type>,
        <parameter>file_name</parameter> <type>text</type> )
       </para>
       <para>
        Returns a list of the loadable modules that are loaded into the
        current server session.  The <parameter>module_name</parameter>
        and <parameter>version</parameter> fields are NULL unless the
        module author supplied values for them using
        the <literal>PG_MODULE_MAGIC_EXT</literal> macro.
        The <parameter>file_name</parameter> field gives the file
        name of the module (shared library).
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_my_temp_schema</primary>
        </indexterm>
        <function>pg_my_temp_schema</function> ()
        <returnvalue>oid</returnvalue>
       </para>
       <para>
        Returns the OID of the current session's temporary schema, or zero if
        it has none (because it has not created any temporary tables).
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_is_other_temp_schema</primary>
        </indexterm>
        <function>pg_is_other_temp_schema</function> ( <type>oid</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Returns true if the given OID is the OID of another session's
        temporary schema.  (This can be useful, for example, to exclude other
        sessions' temporary tables from a catalog display.)
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_jit_available</primary>
        </indexterm>
        <function>pg_jit_available</function> ()
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Returns true if a <acronym>JIT</acronym> compiler extension is
        available (see <xref linkend="jit"/>) and the
        <xref linkend="guc-jit"/> configuration parameter is set to
        <literal>on</literal>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_numa_available</primary>
        </indexterm>
        <function>pg_numa_available</function> ()
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Returns true if the server has been compiled with <acronym>NUMA</acronym> support.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_listening_channels</primary>
        </indexterm>
        <function>pg_listening_channels</function> ()
        <returnvalue>setof text</returnvalue>
       </para>
       <para>
        Returns the set of names of asynchronous notification channels that
        the current session is listening to.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_notification_queue_usage</primary>
        </indexterm>
        <function>pg_notification_queue_usage</function> ()
        <returnvalue>double precision</returnvalue>
       </para>
       <para>
        Returns the fraction (0&ndash;1) of the asynchronous notification
        queue's maximum size that is currently occupied by notifications that
        are waiting to be processed.
        See <xref linkend="sql-listen"/> and <xref linkend="sql-notify"/>
        for more information.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_postmaster_start_time</primary>
        </indexterm>
        <function>pg_postmaster_start_time</function> ()
        <returnvalue>timestamp with time zone</returnvalue>
       </para>
       <para>
        Returns the time when the server started.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_safe_snapshot_blocking_pids</primary>
        </indexterm>
        <function>pg_safe_snapshot_blocking_pids</function> ( <type>integer</type> )
        <returnvalue>integer[]</returnvalue>
       </para>
       <para>
        Returns an array of the process ID(s) of the sessions that are blocking
        the server process with the specified process ID from acquiring a safe
        snapshot, or an empty array if there is no such server process or it
        is not blocked.
       </para>
       <para>
        A session running a <literal>SERIALIZABLE</literal> transaction blocks
        a <literal>SERIALIZABLE READ ONLY DEFERRABLE</literal> transaction
        from acquiring a snapshot until the latter determines that it is safe
        to avoid taking any predicate locks.  See
        <xref linkend="xact-serializable"/> for more information about
        serializable and deferrable transactions.
       </para>
       <para>
        Frequent calls to this function could have some impact on database
        performance, because it needs access to the predicate lock manager's
        shared state for a short time.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_trigger_depth</primary>
        </indexterm>
        <function>pg_trigger_depth</function> ()
        <returnvalue>integer</returnvalue>
       </para>
       <para>
        Returns the current nesting level
        of <productname>PostgreSQL</productname> triggers (0 if not called,
        directly or indirectly, from inside a trigger).
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>session_user</primary>
        </indexterm>
        <function>session_user</function>
        <returnvalue>name</returnvalue>
       </para>
       <para>
        Returns the session user's name.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>system_user</primary>
        </indexterm>
        <function>system_user</function>
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Returns the authentication method and the identity (if any) that the
        user presented during the authentication cycle before they were
        assigned a database role. It is represented as
        <literal>auth_method:identity</literal> or
        <literal>NULL</literal> if the user has not been authenticated (for
        example if <link linkend="auth-trust">Trust authentication</link> has
        been used).
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>user</primary>
        </indexterm>
        <function>user</function>
        <returnvalue>name</returnvalue>
       </para>
       <para>
        This is equivalent to <function>current_user</function>.
       </para></entry>
      </row>
     </tbody>
    </tgroup>
   </table>

   <note>
    <para>
     <function>current_catalog</function>,
     <function>current_role</function>,
     <function>current_schema</function>,
     <function>current_user</function>,
     <function>session_user</function>,
     and <function>user</function> have special syntactic status
     in <acronym>SQL</acronym>: they must be called without trailing
     parentheses.  In PostgreSQL, parentheses can optionally be used with
     <function>current_schema</function>, but not with the others.
    </para>
   </note>

   <para>
    The <function>session_user</function> is normally the user who initiated
    the current database connection; but superusers can change this setting
    with <xref linkend="sql-set-session-authorization"/>.
    The <function>current_user</function> is the user identifier
    that is applicable for permission checking. Normally it is equal
    to the session user, but it can be changed with
    <xref linkend="sql-set-role"/>.
    It also changes during the execution of
    functions with the attribute <literal>SECURITY DEFINER</literal>.
    In Unix parlance, the session user is the <quote>real user</quote> and
    the current user is the <quote>effective user</quote>.
    <function>current_role</function> and <function>user</function> are
    synonyms for <function>current_user</function>.  (The SQL standard draws
    a distinction between <function>current_role</function>
    and <function>current_user</function>, but <productname>PostgreSQL</productname>
    does not, since it unifies users and roles into a single kind of entity.)
   </para>

  </sect2>

  <sect2 id="functions-info-access">
   <title>Access Privilege Inquiry Functions</title>

  <indexterm>
   <primary>privilege</primary>
   <secondary>querying</secondary>
  </indexterm>

  <para>
   <xref linkend="functions-info-access-table"/> lists functions that
   allow querying object access privileges programmatically.
   (See <xref linkend="ddl-priv"/> for more information about
   privileges.)
   In these functions, the user whose privileges are being inquired about
   can be specified by name or by OID
   (<structname>pg_authid</structname>.<structfield>oid</structfield>), or if
   the name is given as <literal>public</literal> then the privileges of the
   PUBLIC pseudo-role are checked.  Also, the <parameter>user</parameter>
   argument can be omitted entirely, in which case
   the <function>current_user</function> is assumed.
   The object that is being inquired about can be specified either by name or
   by OID, too.  When specifying by name, a schema name can be included if
   relevant.
   The access privilege of interest is specified by a text string, which must
   evaluate to one of the appropriate privilege keywords for the object's type
   (e.g., <literal>SELECT</literal>).  Optionally, <literal>WITH GRANT
   OPTION</literal> can be added to a privilege type to test whether the
   privilege is held with grant option. Also, multiple privilege types can be
   listed separated by commas, in which case the result will be true if any of
   the listed privileges is held. (Case of the privilege string is not
   significant, and extra whitespace is allowed between but not within
   privilege names.)
   Some examples:
<programlisting>
SELECT has_table_privilege('myschema.mytable', 'select');
SELECT has_table_privilege('joe', 'mytable', 'INSERT, SELECT WITH GRANT OPTION');
</programlisting>
  </para>

   <table id="functions-info-access-table">
    <title>Access Privilege Inquiry Functions</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>has_any_column_privilege</primary>
        </indexterm>
        <function>has_any_column_privilege</function> (
          <optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
          <parameter>table</parameter> <type>text</type> or <type>oid</type>,
          <parameter>privilege</parameter> <type>text</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Does user have privilege for any column of table?
        This succeeds either if the privilege is held for the whole table, or
        if there is a column-level grant of the privilege for at least one
        column.
        Allowable privilege types are
        <literal>SELECT</literal>, <literal>INSERT</literal>,
        <literal>UPDATE</literal>, and <literal>REFERENCES</literal>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>has_column_privilege</primary>
        </indexterm>
        <function>has_column_privilege</function> (
          <optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
          <parameter>table</parameter> <type>text</type> or <type>oid</type>,
          <parameter>column</parameter> <type>text</type> or <type>smallint</type>,
          <parameter>privilege</parameter> <type>text</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Does user have privilege for the specified table column?
        This succeeds either if the privilege is held for the whole table, or
        if there is a column-level grant of the privilege for the column.
        The column can be specified by name or by attribute number
        (<structname>pg_attribute</structname>.<structfield>attnum</structfield>).
        Allowable privilege types are
        <literal>SELECT</literal>, <literal>INSERT</literal>,
        <literal>UPDATE</literal>, and <literal>REFERENCES</literal>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>has_database_privilege</primary>
        </indexterm>
        <function>has_database_privilege</function> (
          <optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
          <parameter>database</parameter> <type>text</type> or <type>oid</type>,
          <parameter>privilege</parameter> <type>text</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Does user have privilege for database?
        Allowable privilege types are
        <literal>CREATE</literal>,
        <literal>CONNECT</literal>,
        <literal>TEMPORARY</literal>, and
        <literal>TEMP</literal> (which is equivalent to
        <literal>TEMPORARY</literal>).
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>has_foreign_data_wrapper_privilege</primary>
        </indexterm>
        <function>has_foreign_data_wrapper_privilege</function> (
          <optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
          <parameter>fdw</parameter> <type>text</type> or <type>oid</type>,
          <parameter>privilege</parameter> <type>text</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Does user have privilege for foreign-data wrapper?
        The only allowable privilege type is <literal>USAGE</literal>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>has_function_privilege</primary>
        </indexterm>
        <function>has_function_privilege</function> (
          <optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
          <parameter>function</parameter> <type>text</type> or <type>oid</type>,
          <parameter>privilege</parameter> <type>text</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Does user have privilege for function?
        The only allowable privilege type is <literal>EXECUTE</literal>.
       </para>
       <para>
        When specifying a function by name rather than by OID, the allowed
        input is the same as for the <type>regprocedure</type> data type (see
        <xref linkend="datatype-oid"/>).
        An example is:
<programlisting>
SELECT has_function_privilege('joeuser', 'myfunc(int, text)', 'execute');
</programlisting>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>has_language_privilege</primary>
        </indexterm>
        <function>has_language_privilege</function> (
          <optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
          <parameter>language</parameter> <type>text</type> or <type>oid</type>,
          <parameter>privilege</parameter> <type>text</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Does user have privilege for language?
        The only allowable privilege type is <literal>USAGE</literal>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>has_largeobject_privilege</primary>
        </indexterm>
        <function>has_largeobject_privilege</function> (
          <optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
          <parameter>largeobject</parameter> <type>oid</type>,
          <parameter>privilege</parameter> <type>text</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Does user have privilege for large object?
        Allowable privilege types are
        <literal>SELECT</literal> and <literal>UPDATE</literal>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>has_parameter_privilege</primary>
        </indexterm>
        <function>has_parameter_privilege</function> (
          <optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
          <parameter>parameter</parameter> <type>text</type>,
          <parameter>privilege</parameter> <type>text</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Does user have privilege for configuration parameter?
        The parameter name is case-insensitive.
        Allowable privilege types are <literal>SET</literal>
        and <literal>ALTER SYSTEM</literal>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>has_schema_privilege</primary>
        </indexterm>
        <function>has_schema_privilege</function> (
          <optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
          <parameter>schema</parameter> <type>text</type> or <type>oid</type>,
          <parameter>privilege</parameter> <type>text</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Does user have privilege for schema?
        Allowable privilege types are
        <literal>CREATE</literal> and
        <literal>USAGE</literal>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>has_sequence_privilege</primary>
        </indexterm>
        <function>has_sequence_privilege</function> (
          <optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
          <parameter>sequence</parameter> <type>text</type> or <type>oid</type>,
          <parameter>privilege</parameter> <type>text</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Does user have privilege for sequence?
        Allowable privilege types are
        <literal>USAGE</literal>,
        <literal>SELECT</literal>, and
        <literal>UPDATE</literal>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>has_server_privilege</primary>
        </indexterm>
        <function>has_server_privilege</function> (
          <optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
          <parameter>server</parameter> <type>text</type> or <type>oid</type>,
          <parameter>privilege</parameter> <type>text</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Does user have privilege for foreign server?
        The only allowable privilege type is <literal>USAGE</literal>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>has_table_privilege</primary>
        </indexterm>
        <function>has_table_privilege</function> (
          <optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
          <parameter>table</parameter> <type>text</type> or <type>oid</type>,
          <parameter>privilege</parameter> <type>text</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Does user have privilege for table?
        Allowable privilege types
        are <literal>SELECT</literal>, <literal>INSERT</literal>,
        <literal>UPDATE</literal>, <literal>DELETE</literal>,
        <literal>TRUNCATE</literal>, <literal>REFERENCES</literal>,
        <literal>TRIGGER</literal>, and <literal>MAINTAIN</literal>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>has_tablespace_privilege</primary>
        </indexterm>
        <function>has_tablespace_privilege</function> (
          <optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
          <parameter>tablespace</parameter> <type>text</type> or <type>oid</type>,
          <parameter>privilege</parameter> <type>text</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Does user have privilege for tablespace?
        The only allowable privilege type is <literal>CREATE</literal>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>has_type_privilege</primary>
        </indexterm>
        <function>has_type_privilege</function> (
          <optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
          <parameter>type</parameter> <type>text</type> or <type>oid</type>,
          <parameter>privilege</parameter> <type>text</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Does user have privilege for data type?
        The only allowable privilege type is <literal>USAGE</literal>.
        When specifying a type by name rather than by OID, the allowed input
        is the same as for the <type>regtype</type> data type (see
        <xref linkend="datatype-oid"/>).
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_has_role</primary>
        </indexterm>
        <function>pg_has_role</function> (
          <optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
          <parameter>role</parameter> <type>text</type> or <type>oid</type>,
          <parameter>privilege</parameter> <type>text</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Does user have privilege for role?
        Allowable privilege types are
        <literal>MEMBER</literal>, <literal>USAGE</literal>,
        and <literal>SET</literal>.
        <literal>MEMBER</literal> denotes direct or indirect membership in
        the role without regard to what specific privileges may be conferred.
        <literal>USAGE</literal> denotes whether the privileges of the role
        are immediately available without doing <command>SET ROLE</command>,
        while <literal>SET</literal> denotes whether it is possible to change
        to the role using the <literal>SET ROLE</literal> command.
        <literal>WITH ADMIN OPTION</literal> or <literal>WITH GRANT
        OPTION</literal> can be added to any of these privilege types to
        test whether the <literal>ADMIN</literal> privilege is held (all
        six spellings test the same thing).
        This function does not allow the special case of
        setting <parameter>user</parameter> to <literal>public</literal>,
        because the PUBLIC pseudo-role can never be a member of real roles.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>row_security_active</primary>
        </indexterm>
        <function>row_security_active</function> (
          <parameter>table</parameter> <type>text</type> or <type>oid</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Is row-level security active for the specified table in the context of
        the current user and current environment?
       </para></entry>
      </row>
     </tbody>
    </tgroup>
   </table>

  <para>
   <xref linkend="functions-aclitem-op-table"/> shows the operators
   available for the <type>aclitem</type> type, which is the catalog
   representation of access privileges.  See <xref linkend="ddl-priv"/>
   for information about how to read access privilege values.
  </para>

    <table id="functions-aclitem-op-table">
     <title><type>aclitem</type> Operators</title>
     <tgroup cols="1">
      <thead>
       <row>
        <entry role="func_table_entry"><para role="func_signature">
         Operator
        </para>
        <para>
         Description
        </para>
        <para>
         Example(s)
        </para></entry>
       </row>
      </thead>

      <tbody>
       <row>
        <entry role="func_table_entry"><para role="func_signature">
         <indexterm>
          <primary>aclitemeq</primary>
         </indexterm>
         <type>aclitem</type> <literal>=</literal> <type>aclitem</type>
         <returnvalue>boolean</returnvalue>
        </para>
        <para>
         Are <type>aclitem</type>s equal?  (Notice that
         type <type>aclitem</type> lacks the usual set of comparison
         operators; it has only equality.  In turn, <type>aclitem</type>
         arrays can only be compared for equality.)
        </para>
        <para>
         <literal>'calvin=r*w/hobbes'::aclitem = 'calvin=r*w*/hobbes'::aclitem</literal>
         <returnvalue>f</returnvalue>
        </para></entry>
       </row>

       <row>
        <entry role="func_table_entry"><para role="func_signature">
         <indexterm>
          <primary>aclcontains</primary>
         </indexterm>
         <type>aclitem[]</type> <literal>@&gt;</literal> <type>aclitem</type>
         <returnvalue>boolean</returnvalue>
        </para>
        <para>
         Does array contain the specified privileges?  (This is true if there
         is an array entry that matches the <type>aclitem</type>'s grantee and
         grantor, and has at least the specified set of privileges.)
        </para>
        <para>
         <literal>'{calvin=r*w/hobbes,hobbes=r*w*/postgres}'::aclitem[] @&gt; 'calvin=r*/hobbes'::aclitem</literal>
         <returnvalue>t</returnvalue>
        </para></entry>
       </row>

       <row>
        <entry role="func_table_entry"><para role="func_signature">
         <type>aclitem[]</type> <literal>~</literal> <type>aclitem</type>
         <returnvalue>boolean</returnvalue>
        </para>
        <para>
         This is a deprecated alias for <literal>@&gt;</literal>.
        </para>
        <para>
         <literal>'{calvin=r*w/hobbes,hobbes=r*w*/postgres}'::aclitem[] ~ 'calvin=r*/hobbes'::aclitem</literal>
         <returnvalue>t</returnvalue>
        </para></entry>
       </row>
      </tbody>
     </tgroup>
    </table>

   <para>
    <xref linkend="functions-aclitem-fn-table"/> shows some additional
    functions to manage the <type>aclitem</type> type.
   </para>

   <table id="functions-aclitem-fn-table">
    <title><type>aclitem</type> Functions</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>acldefault</primary>
        </indexterm>
        <function>acldefault</function> (
          <parameter>type</parameter> <type>"char"</type>,
          <parameter>ownerId</parameter> <type>oid</type> )
        <returnvalue>aclitem[]</returnvalue>
       </para>
       <para>
        Constructs an <type>aclitem</type> array holding the default access
        privileges for an object of type <parameter>type</parameter> belonging
        to the role with OID <parameter>ownerId</parameter>.  This represents
        the access privileges that will be assumed when an object's
        <acronym>ACL</acronym> entry is null. (The default access privileges
        are described in <xref linkend="ddl-priv"/>.)
        The <parameter>type</parameter> parameter must be one of
        'c' for <literal>COLUMN</literal>,
        'r' for <literal>TABLE</literal> and table-like objects,
        's' for <literal>SEQUENCE</literal>,
        'd' for <literal>DATABASE</literal>,
        'f' for <literal>FUNCTION</literal> or <literal>PROCEDURE</literal>,
        'l' for <literal>LANGUAGE</literal>,
        'L' for <literal>LARGE OBJECT</literal>,
        'n' for <literal>SCHEMA</literal>,
        'p' for <literal>PARAMETER</literal>,
        't' for <literal>TABLESPACE</literal>,
        'F' for <literal>FOREIGN DATA WRAPPER</literal>,
        'S' for <literal>FOREIGN SERVER</literal>,
        or
        'T' for <literal>TYPE</literal> or <literal>DOMAIN</literal>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>aclexplode</primary>
        </indexterm>
        <function>aclexplode</function> ( <type>aclitem[]</type> )
        <returnvalue>setof record</returnvalue>
        ( <parameter>grantor</parameter> <type>oid</type>,
        <parameter>grantee</parameter> <type>oid</type>,
        <parameter>privilege_type</parameter> <type>text</type>,
        <parameter>is_grantable</parameter> <type>boolean</type> )
       </para>
       <para>
        Returns the <type>aclitem</type> array as a set of rows.
        If the grantee is the pseudo-role PUBLIC, it is represented by zero in
        the <parameter>grantee</parameter> column.  Each granted privilege is
        represented as <literal>SELECT</literal>, <literal>INSERT</literal>,
        etc (see <xref linkend="privilege-abbrevs-table"/> for a full list).
        Note that each privilege is broken out as a separate row, so
        only one keyword appears in the <parameter>privilege_type</parameter>
        column.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>makeaclitem</primary>
        </indexterm>
        <function>makeaclitem</function> (
          <parameter>grantee</parameter> <type>oid</type>,
          <parameter>grantor</parameter> <type>oid</type>,
          <parameter>privileges</parameter> <type>text</type>,
          <parameter>is_grantable</parameter> <type>boolean</type> )
        <returnvalue>aclitem</returnvalue>
       </para>
       <para>
        Constructs an <type>aclitem</type> with the given properties.
        <parameter>privileges</parameter> is a comma-separated list of
        privilege names such as <literal>SELECT</literal>,
        <literal>INSERT</literal>, etc, all of which are set in the
        result.  (Case of the privilege string is not significant, and
        extra whitespace is allowed between but not within privilege
        names.)
       </para></entry>
      </row>
     </tbody>
    </tgroup>
   </table>

  </sect2>

  <sect2 id="functions-info-schema">
   <title>Schema Visibility Inquiry Functions</title>

  <para>
   <xref linkend="functions-info-schema-table"/> shows functions that
   determine whether a certain object is <firstterm>visible</firstterm> in the
   current schema search path.
   For example, a table is said to be visible if its
   containing schema is in the search path and no table of the same
   name appears earlier in the search path.  This is equivalent to the
   statement that the table can be referenced by name without explicit
   schema qualification.  Thus, to list the names of all visible tables:
<programlisting>
SELECT relname FROM pg_class WHERE pg_table_is_visible(oid);
</programlisting>
   For functions and operators, an object in the search path is said to be
   visible if there is no object of the same name <emphasis>and argument data
   type(s)</emphasis> earlier in the path.  For operator classes and families,
   both the name and the associated index access method are considered.
  </para>

   <indexterm>
    <primary>search path</primary>
    <secondary>object visibility</secondary>
   </indexterm>

   <table id="functions-info-schema-table">
    <title>Schema Visibility Inquiry Functions</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_collation_is_visible</primary>
        </indexterm>
        <function>pg_collation_is_visible</function> ( <parameter>collation</parameter> <type>oid</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Is collation visible in search path?
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_conversion_is_visible</primary>
        </indexterm>
        <function>pg_conversion_is_visible</function> ( <parameter>conversion</parameter> <type>oid</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Is conversion visible in search path?
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_function_is_visible</primary>
        </indexterm>
        <function>pg_function_is_visible</function> ( <parameter>function</parameter> <type>oid</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Is function visible in search path?
        (This also works for procedures and aggregates.)
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_opclass_is_visible</primary>
        </indexterm>
        <function>pg_opclass_is_visible</function> ( <parameter>opclass</parameter> <type>oid</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Is operator class visible in search path?
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_operator_is_visible</primary>
        </indexterm>
        <function>pg_operator_is_visible</function> ( <parameter>operator</parameter> <type>oid</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Is operator visible in search path?
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_opfamily_is_visible</primary>
        </indexterm>
        <function>pg_opfamily_is_visible</function> ( <parameter>opclass</parameter> <type>oid</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Is operator family visible in search path?
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_statistics_obj_is_visible</primary>
        </indexterm>
        <function>pg_statistics_obj_is_visible</function> ( <parameter>stat</parameter> <type>oid</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Is statistics object visible in search path?
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_table_is_visible</primary>
        </indexterm>
        <function>pg_table_is_visible</function> ( <parameter>table</parameter> <type>oid</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Is table visible in search path?
        (This works for all types of relations, including views, materialized
        views, indexes, sequences and foreign tables.)
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_ts_config_is_visible</primary>
        </indexterm>
        <function>pg_ts_config_is_visible</function> ( <parameter>config</parameter> <type>oid</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Is text search configuration visible in search path?
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_ts_dict_is_visible</primary>
        </indexterm>
        <function>pg_ts_dict_is_visible</function> ( <parameter>dict</parameter> <type>oid</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Is text search dictionary visible in search path?
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_ts_parser_is_visible</primary>
        </indexterm>
        <function>pg_ts_parser_is_visible</function> ( <parameter>parser</parameter> <type>oid</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Is text search parser visible in search path?
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_ts_template_is_visible</primary>
        </indexterm>
        <function>pg_ts_template_is_visible</function> ( <parameter>template</parameter> <type>oid</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Is text search template visible in search path?
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_type_is_visible</primary>
        </indexterm>
        <function>pg_type_is_visible</function> ( <parameter>type</parameter> <type>oid</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Is type (or domain) visible in search path?
       </para></entry>
      </row>
     </tbody>
    </tgroup>
   </table>

   <para>
    All these functions require object OIDs to identify the object to be
    checked.  If you want to test an object by name, it is convenient to use
    the OID alias types (<type>regclass</type>, <type>regtype</type>,
    <type>regprocedure</type>, <type>regoperator</type>, <type>regconfig</type>,
    or <type>regdictionary</type>),
    for example:
<programlisting>
SELECT pg_type_is_visible('myschema.widget'::regtype);
</programlisting>
    Note that it would not make much sense to test a non-schema-qualified
    type name in this way &mdash; if the name can be recognized at all, it must be visible.
   </para>

  </sect2>

  <sect2 id="functions-info-catalog">
   <title>System Catalog Information Functions</title>

  <para>
   <xref linkend="functions-info-catalog-table"/> lists functions that
   extract information from the system catalogs.
  </para>

   <table id="functions-info-catalog-table">
    <title>System Catalog Information Functions</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry id="format-type" xreflabel="format_type" role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>format_type</primary>
        </indexterm>
        <function>format_type</function> ( <parameter>type</parameter> <type>oid</type>, <parameter>typemod</parameter> <type>integer</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Returns the SQL name for a data type that is identified by its type
        OID and possibly a type modifier.  Pass NULL for the type modifier if
        no specific modifier is known.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_basetype</primary>
        </indexterm>
        <function>pg_basetype</function> ( <type>regtype</type> )
        <returnvalue>regtype</returnvalue>
       </para>
       <para>
        Returns the OID of the base type of a domain identified by its
        type OID.  If the argument is the OID of a non-domain type,
        returns the argument as-is.  Returns NULL if the argument is
        not a valid type OID.  If there's a chain of domain dependencies,
        it will recurse until finding the base type.
       </para>
       <para>
        Assuming <literal>CREATE DOMAIN mytext AS text</literal>:
       </para>
       <para>
        <literal>pg_basetype('mytext'::regtype)</literal>
        <returnvalue>text</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry id="pg-char-to-encoding" role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_char_to_encoding</primary>
        </indexterm>
        <function>pg_char_to_encoding</function> ( <parameter>encoding</parameter> <type>name</type> )
        <returnvalue>integer</returnvalue>
       </para>
       <para>
        Converts the supplied encoding name into an integer representing the
        internal identifier used in some system catalog tables.
        Returns <literal>-1</literal> if an unknown encoding name is provided.
       </para></entry>
      </row>

      <row>
       <entry id="pg-encoding-to-char" role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_encoding_to_char</primary>
        </indexterm>
        <function>pg_encoding_to_char</function> ( <parameter>encoding</parameter> <type>integer</type> )
        <returnvalue>name</returnvalue>
       </para>
       <para>
        Converts the integer used as the internal identifier of an encoding in some
        system catalog tables into a human-readable string.
        Returns an empty string if an invalid encoding number is provided.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_catalog_foreign_keys</primary>
        </indexterm>
        <function>pg_get_catalog_foreign_keys</function> ()
        <returnvalue>setof record</returnvalue>
        ( <parameter>fktable</parameter> <type>regclass</type>,
          <parameter>fkcols</parameter> <type>text[]</type>,
          <parameter>pktable</parameter> <type>regclass</type>,
          <parameter>pkcols</parameter> <type>text[]</type>,
          <parameter>is_array</parameter> <type>boolean</type>,
          <parameter>is_opt</parameter> <type>boolean</type> )
       </para>
       <para>
        Returns a set of records describing the foreign key relationships
        that exist within the <productname>PostgreSQL</productname> system
        catalogs.
        The <parameter>fktable</parameter> column contains the name of the
        referencing catalog, and the <parameter>fkcols</parameter> column
        contains the name(s) of the referencing column(s).  Similarly,
        the <parameter>pktable</parameter> column contains the name of the
        referenced catalog, and the <parameter>pkcols</parameter> column
        contains the name(s) of the referenced column(s).
        If <parameter>is_array</parameter> is true, the last referencing
        column is an array, each of whose elements should match some entry
        in the referenced catalog.
        If <parameter>is_opt</parameter> is true, the referencing column(s)
        are allowed to contain zeroes instead of a valid reference.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_constraintdef</primary>
        </indexterm>
        <function>pg_get_constraintdef</function> ( <parameter>constraint</parameter> <type>oid</type> <optional>, <parameter>pretty</parameter> <type>boolean</type> </optional> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Reconstructs the creating command for a constraint.
        (This is a decompiled reconstruction, not the original text
        of the command.)
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_expr</primary>
        </indexterm>
        <function>pg_get_expr</function> ( <parameter>expr</parameter> <type>pg_node_tree</type>, <parameter>relation</parameter> <type>oid</type> <optional>, <parameter>pretty</parameter> <type>boolean</type> </optional> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Decompiles the internal form of an expression stored in the system
        catalogs, such as the default value for a column.  If the expression
        might contain Vars, specify the OID of the relation they refer to as
        the second parameter; if no Vars are expected, passing zero is
        sufficient.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_functiondef</primary>
        </indexterm>
        <function>pg_get_functiondef</function> ( <parameter>func</parameter> <type>oid</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Reconstructs the creating command for a function or procedure.
        (This is a decompiled reconstruction, not the original text
        of the command.)
        The result is a complete <command>CREATE OR REPLACE FUNCTION</command>
        or <command>CREATE OR REPLACE PROCEDURE</command> statement.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_function_arguments</primary>
        </indexterm>
        <function>pg_get_function_arguments</function> ( <parameter>func</parameter> <type>oid</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Reconstructs the argument list of a function or procedure, in the form
        it would need to appear in within <command>CREATE FUNCTION</command>
        (including default values).
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_function_identity_arguments</primary>
        </indexterm>
        <function>pg_get_function_identity_arguments</function> ( <parameter>func</parameter> <type>oid</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Reconstructs the argument list necessary to identify a function or
        procedure, in the form it would need to appear in within commands such
        as <command>ALTER FUNCTION</command>.  This form omits default values.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_function_result</primary>
        </indexterm>
        <function>pg_get_function_result</function> ( <parameter>func</parameter> <type>oid</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Reconstructs the <literal>RETURNS</literal> clause of a function, in
        the form it would need to appear in within <command>CREATE
        FUNCTION</command>.  Returns <literal>NULL</literal> for a procedure.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_indexdef</primary>
        </indexterm>
        <function>pg_get_indexdef</function> ( <parameter>index</parameter> <type>oid</type> <optional>, <parameter>column</parameter> <type>integer</type>, <parameter>pretty</parameter> <type>boolean</type> </optional> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Reconstructs the creating command for an index.
        (This is a decompiled reconstruction, not the original text
        of the command.)  If <parameter>column</parameter> is supplied and is
        not zero, only the definition of that column is reconstructed.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_keywords</primary>
        </indexterm>
        <function>pg_get_keywords</function> ()
        <returnvalue>setof record</returnvalue>
        ( <parameter>word</parameter> <type>text</type>,
        <parameter>catcode</parameter> <type>"char"</type>,
        <parameter>barelabel</parameter> <type>boolean</type>,
        <parameter>catdesc</parameter> <type>text</type>,
        <parameter>baredesc</parameter> <type>text</type> )
       </para>
       <para>
        Returns a set of records describing the SQL keywords recognized by the
        server.  The <parameter>word</parameter> column contains the
        keyword.  The <parameter>catcode</parameter> column contains a
        category code: <literal>U</literal> for an unreserved
        keyword, <literal>C</literal> for a keyword that can be a column
        name, <literal>T</literal> for a keyword that can be a type or
        function name, or <literal>R</literal> for a fully reserved keyword.
        The <parameter>barelabel</parameter> column
        contains <literal>true</literal> if the keyword can be used as
        a <quote>bare</quote> column label in <command>SELECT</command> lists,
        or <literal>false</literal> if it can only be used
        after <literal>AS</literal>.
        The <parameter>catdesc</parameter> column contains a
        possibly-localized string describing the keyword's category.
        The <parameter>baredesc</parameter> column contains a
        possibly-localized string describing the keyword's column label status.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_partition_constraintdef</primary>
        </indexterm>
        <function>pg_get_partition_constraintdef</function> ( <parameter>table</parameter> <type>oid</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Reconstructs the definition of a partition constraint.
        (This is a decompiled reconstruction, not the original text
        of the command.)
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_partkeydef</primary>
        </indexterm>
        <function>pg_get_partkeydef</function> ( <parameter>table</parameter> <type>oid</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Reconstructs the definition of a partitioned table's partition
        key, in the form it would have in the <literal>PARTITION
        BY</literal> clause of <command>CREATE TABLE</command>.
        (This is a decompiled reconstruction, not the original text
        of the command.)
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_ruledef</primary>
        </indexterm>
        <function>pg_get_ruledef</function> ( <parameter>rule</parameter> <type>oid</type> <optional>, <parameter>pretty</parameter> <type>boolean</type> </optional> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Reconstructs the creating command for a rule.
        (This is a decompiled reconstruction, not the original text
        of the command.)
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_serial_sequence</primary>
        </indexterm>
        <function>pg_get_serial_sequence</function> ( <parameter>table</parameter> <type>text</type>, <parameter>column</parameter> <type>text</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Returns the name of the sequence associated with a column,
        or NULL if no sequence is associated with the column.
        If the column is an identity column, the associated sequence is the
        sequence internally created for that column.
        For columns created using one of the serial types
        (<type>serial</type>, <type>smallserial</type>, <type>bigserial</type>),
        it is the sequence created for that serial column definition.
        In the latter case, the association can be modified or removed
        with <command>ALTER SEQUENCE OWNED BY</command>.
        (This function probably should have been
        called <function>pg_get_owned_sequence</function>; its current name
        reflects the fact that it has historically been used with serial-type
        columns.)  The first parameter is a table name with optional
        schema, and the second parameter is a column name.  Because the first
        parameter potentially contains both schema and table names, it is
        parsed per usual SQL rules, meaning it is lower-cased by default.
        The second parameter, being just a column name, is treated literally
        and so has its case preserved.  The result is suitably formatted
        for passing to the sequence functions (see
        <xref linkend="functions-sequence"/>).
       </para>
       <para>
        A typical use is in reading the current value of the sequence for an
        identity or serial column, for example:
<programlisting>
SELECT currval(pg_get_serial_sequence('sometable', 'id'));
</programlisting>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_statisticsobjdef</primary>
        </indexterm>
        <function>pg_get_statisticsobjdef</function> ( <parameter>statobj</parameter> <type>oid</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Reconstructs the creating command for an extended statistics object.
        (This is a decompiled reconstruction, not the original text
        of the command.)
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_triggerdef</primary>
        </indexterm>
<function>pg_get_triggerdef</function> ( <parameter>trigger</parameter> <type>oid</type> <optional>, <parameter>pretty</parameter> <type>boolean</type> </optional> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Reconstructs the creating command for a trigger.
        (This is a decompiled reconstruction, not the original text
        of the command.)
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_userbyid</primary>
        </indexterm>
        <function>pg_get_userbyid</function> ( <parameter>role</parameter> <type>oid</type> )
        <returnvalue>name</returnvalue>
       </para>
       <para>
        Returns a role's name given its OID.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_viewdef</primary>
        </indexterm>
        <function>pg_get_viewdef</function> ( <parameter>view</parameter> <type>oid</type> <optional>, <parameter>pretty</parameter> <type>boolean</type> </optional> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Reconstructs the underlying <command>SELECT</command> command for a
        view or materialized view.  (This is a decompiled reconstruction, not
        the original text of the command.)
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <function>pg_get_viewdef</function> ( <parameter>view</parameter> <type>oid</type>, <parameter>wrap_column</parameter> <type>integer</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Reconstructs the underlying <command>SELECT</command> command for a
        view or materialized view.  (This is a decompiled reconstruction, not
        the original text of the command.)  In this form of the function,
        pretty-printing is always enabled, and long lines are wrapped to try
        to keep them shorter than the specified number of columns.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <function>pg_get_viewdef</function> ( <parameter>view</parameter> <type>text</type> <optional>, <parameter>pretty</parameter> <type>boolean</type> </optional> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Reconstructs the underlying <command>SELECT</command> command for a
        view or materialized view, working from a textual name for the view
        rather than its OID.  (This is deprecated; use the OID variant
        instead.)
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_index_column_has_property</primary>
        </indexterm>
        <function>pg_index_column_has_property</function> ( <parameter>index</parameter> <type>regclass</type>, <parameter>column</parameter> <type>integer</type>, <parameter>property</parameter> <type>text</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Tests whether an index column has the named property.
        Common index column properties are listed in
        <xref linkend="functions-info-index-column-props"/>.
        (Note that extension access methods can define additional property
        names for their indexes.)
        <literal>NULL</literal> is returned if the property name is not known
        or does not apply to the particular object, or if the OID or column
        number does not identify a valid object.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_index_has_property</primary>
        </indexterm>
        <function>pg_index_has_property</function> ( <parameter>index</parameter> <type>regclass</type>, <parameter>property</parameter> <type>text</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Tests whether an index has the named property.
        Common index properties are listed in
        <xref linkend="functions-info-index-props"/>.
        (Note that extension access methods can define additional property
        names for their indexes.)
        <literal>NULL</literal> is returned if the property name is not known
        or does not apply to the particular object, or if the OID does not
        identify a valid object.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_indexam_has_property</primary>
        </indexterm>
        <function>pg_indexam_has_property</function> ( <parameter>am</parameter> <type>oid</type>, <parameter>property</parameter> <type>text</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Tests whether an index access method has the named property.
        Access method properties are listed in
        <xref linkend="functions-info-indexam-props"/>.
        <literal>NULL</literal> is returned if the property name is not known
        or does not apply to the particular object, or if the OID does not
        identify a valid object.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_options_to_table</primary>
        </indexterm>
        <function>pg_options_to_table</function> ( <parameter>options_array</parameter> <type>text[]</type> )
        <returnvalue>setof record</returnvalue>
        ( <parameter>option_name</parameter> <type>text</type>,
        <parameter>option_value</parameter> <type>text</type> )
       </para>
       <para>
        Returns the set of storage options represented by a value from
        <structname>pg_class</structname>.<structfield>reloptions</structfield> or
        <structname>pg_attribute</structname>.<structfield>attoptions</structfield>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_settings_get_flags</primary>
        </indexterm>
        <function>pg_settings_get_flags</function> ( <parameter>guc</parameter> <type>text</type> )
        <returnvalue>text[]</returnvalue>
       </para>
       <para>
        Returns an array of the flags associated with the given GUC, or
        <literal>NULL</literal> if it does not exist. The result is
        an empty array if the GUC exists but there are no flags to show.
        Only the most useful flags listed in
        <xref linkend="functions-pg-settings-flags"/> are exposed.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_tablespace_databases</primary>
        </indexterm>
        <function>pg_tablespace_databases</function> ( <parameter>tablespace</parameter> <type>oid</type> )
        <returnvalue>setof oid</returnvalue>
       </para>
       <para>
        Returns the set of OIDs of databases that have objects stored in the
        specified tablespace.  If this function returns any rows, the
        tablespace is not empty and cannot be dropped.  To identify the specific
        objects populating the tablespace, you will need to connect to the
        database(s) identified by <function>pg_tablespace_databases</function>
        and query their <structname>pg_class</structname> catalogs.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_tablespace_location</primary>
        </indexterm>
        <function>pg_tablespace_location</function> ( <parameter>tablespace</parameter> <type>oid</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Returns the file system path that this tablespace is located in.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_typeof</primary>
        </indexterm>
        <function>pg_typeof</function> ( <type>"any"</type> )
        <returnvalue>regtype</returnvalue>
       </para>
       <para>
        Returns the OID of the data type of the value that is passed to it.
        This can be helpful for troubleshooting or dynamically constructing
        SQL queries.  The function is declared as
        returning <type>regtype</type>, which is an OID alias type (see
        <xref linkend="datatype-oid"/>); this means that it is the same as an
        OID for comparison purposes but displays as a type name.
       </para>
       <para>
        <literal>pg_typeof(33)</literal>
        <returnvalue>integer</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>COLLATION FOR</primary>
        </indexterm>
        <function>COLLATION FOR</function> ( <type>"any"</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Returns the name of the collation of the value that is passed to it.
        The value is quoted and schema-qualified if necessary.  If no
        collation was derived for the argument expression,
        then <literal>NULL</literal> is returned.  If the argument is not of a
        collatable data type, then an error is raised.
       </para>
       <para>
        <literal>COLLATION FOR ('foo'::text)</literal>
        <returnvalue>"default"</returnvalue>
       </para>
       <para>
        <literal>COLLATION FOR ('foo' COLLATE "de_DE")</literal>
        <returnvalue>"de_DE"</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>to_regclass</primary>
        </indexterm>
        <function>to_regclass</function> ( <type>text</type> )
        <returnvalue>regclass</returnvalue>
       </para>
       <para>
        Translates a textual relation name to its OID.  A similar result is
        obtained by casting the string to type <type>regclass</type> (see
        <xref linkend="datatype-oid"/>); however, this function will return
        <literal>NULL</literal> rather than throwing an error if the name is
        not found.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>to_regdatabase</primary>
        </indexterm>
        <function>to_regdatabase</function> ( <type>text</type> )
        <returnvalue>regdatabase</returnvalue>
       </para>
       <para>
        Translates a textual database name to its OID.  A similar result is
        obtained by casting the string to type <type>regdatabase</type> (see
        <xref linkend="datatype-oid"/>); however, this function will return
        <literal>NULL</literal> rather than throwing an error if the name is
        not found.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>to_regcollation</primary>
        </indexterm>
        <function>to_regcollation</function> ( <type>text</type> )
        <returnvalue>regcollation</returnvalue>
       </para>
       <para>
        Translates a textual collation name to its OID.  A similar result is
        obtained by casting the string to type <type>regcollation</type> (see
        <xref linkend="datatype-oid"/>); however, this function will return
        <literal>NULL</literal> rather than throwing an error if the name is
        not found.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>to_regnamespace</primary>
        </indexterm>
        <function>to_regnamespace</function> ( <type>text</type> )
        <returnvalue>regnamespace</returnvalue>
       </para>
       <para>
        Translates a textual schema name to its OID.  A similar result is
        obtained by casting the string to type <type>regnamespace</type> (see
        <xref linkend="datatype-oid"/>); however, this function will return
        <literal>NULL</literal> rather than throwing an error if the name is
        not found.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>to_regoper</primary>
        </indexterm>
        <function>to_regoper</function> ( <type>text</type> )
        <returnvalue>regoper</returnvalue>
       </para>
       <para>
        Translates a textual operator name to its OID.  A similar result is
        obtained by casting the string to type <type>regoper</type> (see
        <xref linkend="datatype-oid"/>); however, this function will return
        <literal>NULL</literal> rather than throwing an error if the name is
        not found or is ambiguous.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>to_regoperator</primary>
        </indexterm>
        <function>to_regoperator</function> ( <type>text</type> )
        <returnvalue>regoperator</returnvalue>
       </para>
       <para>
        Translates a textual operator name (with parameter types) to its OID.  A similar result is
        obtained by casting the string to type <type>regoperator</type> (see
        <xref linkend="datatype-oid"/>); however, this function will return
        <literal>NULL</literal> rather than throwing an error if the name is
        not found.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>to_regproc</primary>
        </indexterm>
        <function>to_regproc</function> ( <type>text</type> )
        <returnvalue>regproc</returnvalue>
       </para>
       <para>
        Translates a textual function or procedure name to its OID.  A similar result is
        obtained by casting the string to type <type>regproc</type> (see
        <xref linkend="datatype-oid"/>); however, this function will return
        <literal>NULL</literal> rather than throwing an error if the name is
        not found or is ambiguous.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>to_regprocedure</primary>
        </indexterm>
        <function>to_regprocedure</function> ( <type>text</type> )
        <returnvalue>regprocedure</returnvalue>
       </para>
       <para>
        Translates a textual function or procedure name (with argument types) to its OID.  A similar result is
        obtained by casting the string to type <type>regprocedure</type> (see
        <xref linkend="datatype-oid"/>); however, this function will return
        <literal>NULL</literal> rather than throwing an error if the name is
        not found.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>to_regrole</primary>
        </indexterm>
        <function>to_regrole</function> ( <type>text</type> )
        <returnvalue>regrole</returnvalue>
       </para>
       <para>
        Translates a textual role name to its OID.  A similar result is
        obtained by casting the string to type <type>regrole</type> (see
        <xref linkend="datatype-oid"/>); however, this function will return
        <literal>NULL</literal> rather than throwing an error if the name is
        not found.
       </para></entry>
      </row>

      <row>
       <entry id="to-regtype" xreflabel="to_regtype" role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>to_regtype</primary>
        </indexterm>
        <function>to_regtype</function> ( <type>text</type> )
        <returnvalue>regtype</returnvalue>
       </para>
       <para>
        Parses a string of text, extracts a potential type name from it,
        and translates that name into a type OID.  A syntax error in the
        string will result in an error; but if the string is a
        syntactically valid type name that happens not to be found in the
        catalogs, the result is <literal>NULL</literal>.  A similar result
        is obtained by casting the string to type <type>regtype</type>
        (see <xref linkend="datatype-oid"/>), except that that will throw
        error for name not found.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>to_regtypemod</primary>
        </indexterm>
        <function>to_regtypemod</function> ( <type>text</type> )
        <returnvalue>integer</returnvalue>
       </para>
       <para>
        Parses a string of text, extracts a potential type name from it,
        and translates its type modifier, if any.  A syntax error in the
        string will result in an error; but if the string is a
        syntactically valid type name that happens not to be found in the
        catalogs, the result is <literal>NULL</literal>.  The result is
        <literal>-1</literal> if no type modifier is present.
       </para>
       <para>
        <function>to_regtypemod</function> can be combined with
        <xref linkend="to-regtype"/> to produce appropriate inputs for
        <xref linkend="format-type"/>, allowing a string representing a
        type name to be canonicalized.
       </para>
       <para>
        <literal>format_type(to_regtype('varchar(32)'), to_regtypemod('varchar(32)'))</literal>
        <returnvalue>character varying(32)</returnvalue>
       </para></entry>
      </row>
     </tbody>
    </tgroup>
   </table>

  <para>
   Most of the functions that reconstruct (decompile) database objects
   have an optional <parameter>pretty</parameter> flag, which
   if <literal>true</literal> causes the result to
   be <quote>pretty-printed</quote>.  Pretty-printing suppresses unnecessary
   parentheses and adds whitespace for legibility.
   The pretty-printed format is more readable, but the default format
   is more likely to be interpreted the same way by future versions of
   <productname>PostgreSQL</productname>; so avoid using pretty-printed output
   for dump purposes.  Passing <literal>false</literal> for
   the <parameter>pretty</parameter> parameter yields the same result as
   omitting the parameter.
  </para>

  <table id="functions-info-index-column-props">
   <title>Index Column Properties</title>
   <tgroup cols="2">
    <colspec colname="col1" colwidth="1*"/>
    <colspec colname="col2" colwidth="3*"/>
    <thead>
     <row><entry>Name</entry><entry>Description</entry></row>
    </thead>
    <tbody>
     <row>
      <entry><literal>asc</literal></entry>
      <entry>Does the column sort in ascending order on a forward scan?
      </entry>
     </row>
     <row>
      <entry><literal>desc</literal></entry>
      <entry>Does the column sort in descending order on a forward scan?
      </entry>
     </row>
     <row>
      <entry><literal>nulls_first</literal></entry>
      <entry>Does the column sort with nulls first on a forward scan?
      </entry>
     </row>
     <row>
      <entry><literal>nulls_last</literal></entry>
      <entry>Does the column sort with nulls last on a forward scan?
      </entry>
     </row>
     <row>
      <entry><literal>orderable</literal></entry>
      <entry>Does the column possess any defined sort ordering?
      </entry>
     </row>
     <row>
      <entry><literal>distance_orderable</literal></entry>
      <entry>Can the column be scanned in order by a <quote>distance</quote>
      operator, for example <literal>ORDER BY col &lt;-&gt; constant</literal> ?
      </entry>
     </row>
     <row>
      <entry><literal>returnable</literal></entry>
      <entry>Can the column value be returned by an index-only scan?
      </entry>
     </row>
     <row>
      <entry><literal>search_array</literal></entry>
      <entry>Does the column natively support <literal>col = ANY(array)</literal>
      searches?
      </entry>
     </row>
     <row>
      <entry><literal>search_nulls</literal></entry>
      <entry>Does the column support <literal>IS NULL</literal> and
      <literal>IS NOT NULL</literal> searches?
      </entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <table id="functions-info-index-props">
   <title>Index Properties</title>
   <tgroup cols="2">
    <colspec colname="col1" colwidth="1*"/>
    <colspec colname="col2" colwidth="3*"/>
    <thead>
     <row><entry>Name</entry><entry>Description</entry></row>
    </thead>
    <tbody>
     <row>
      <entry><literal>clusterable</literal></entry>
      <entry>Can the index be used in a <literal>CLUSTER</literal> command?
      </entry>
     </row>
     <row>
      <entry><literal>index_scan</literal></entry>
      <entry>Does the index support plain (non-bitmap) scans?
      </entry>
     </row>
     <row>
      <entry><literal>bitmap_scan</literal></entry>
      <entry>Does the index support bitmap scans?
      </entry>
     </row>
     <row>
      <entry><literal>backward_scan</literal></entry>
      <entry>Can the scan direction be changed in mid-scan (to
             support <literal>FETCH BACKWARD</literal> on a cursor without
             needing materialization)?
      </entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <table id="functions-info-indexam-props">
   <title>Index Access Method Properties</title>
   <tgroup cols="2">
    <colspec colname="col1" colwidth="1*"/>
    <colspec colname="col2" colwidth="3*"/>
    <thead>
     <row><entry>Name</entry><entry>Description</entry></row>
    </thead>
    <tbody>
     <row>
      <entry><literal>can_order</literal></entry>
      <entry>Does the access method support <literal>ASC</literal>,
      <literal>DESC</literal> and related keywords in
      <literal>CREATE INDEX</literal>?
      </entry>
     </row>
     <row>
      <entry><literal>can_unique</literal></entry>
      <entry>Does the access method support unique indexes?
      </entry>
     </row>
     <row>
      <entry><literal>can_multi_col</literal></entry>
      <entry>Does the access method support indexes with multiple columns?
      </entry>
     </row>
     <row>
      <entry><literal>can_exclude</literal></entry>
      <entry>Does the access method support exclusion constraints?
      </entry>
     </row>
     <row>
      <entry><literal>can_include</literal></entry>
      <entry>Does the access method support the <literal>INCLUDE</literal>
        clause of <literal>CREATE INDEX</literal>?
      </entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <table id="functions-pg-settings-flags">
   <title>GUC Flags</title>
   <tgroup cols="2">
    <colspec colname="col1" colwidth="1*"/>
    <colspec colname="col2" colwidth="3*"/>
    <thead>
     <row><entry>Flag</entry><entry>Description</entry></row>
    </thead>
    <tbody>
     <row>
      <entry><literal>EXPLAIN</literal></entry>
      <entry>Parameters with this flag are included in
       <command>EXPLAIN (SETTINGS)</command> commands.
      </entry>
     </row>
     <row>
      <entry><literal>NO_SHOW_ALL</literal></entry>
      <entry>Parameters with this flag are excluded from
       <command>SHOW ALL</command> commands.
      </entry>
     </row>
     <row>
      <entry><literal>NO_RESET</literal></entry>
      <entry>Parameters with this flag do not support
      <command>RESET</command> commands.
      </entry>
     </row>
     <row>
      <entry><literal>NO_RESET_ALL</literal></entry>
      <entry>Parameters with this flag are excluded from
       <command>RESET ALL</command> commands.
      </entry>
     </row>
     <row>
      <entry><literal>NOT_IN_SAMPLE</literal></entry>
      <entry>Parameters with this flag are not included in
       <filename>postgresql.conf</filename> by default.
      </entry>
     </row>
     <row>
      <entry><literal>RUNTIME_COMPUTED</literal></entry>
      <entry>Parameters with this flag are runtime-computed ones.
      </entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  </sect2>

  <sect2 id="functions-info-object">
   <title>Object Information and Addressing Functions</title>

  <para>
   <xref linkend="functions-info-object-table"/> lists functions related to
   database object identification and addressing.
  </para>

   <table id="functions-info-object-table">
    <title>Object Information and Addressing Functions</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_acl</primary>
        </indexterm>
        <function>pg_get_acl</function> ( <parameter>classid</parameter> <type>oid</type>, <parameter>objid</parameter> <type>oid</type>, <parameter>objsubid</parameter> <type>integer</type> )
        <returnvalue>aclitem[]</returnvalue>
       </para>
       <para>
        Returns the <acronym>ACL</acronym> for a database object, specified
        by catalog OID, object OID and sub-object ID. This function returns
        <literal>NULL</literal> values for undefined objects.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_describe_object</primary>
        </indexterm>
        <function>pg_describe_object</function> ( <parameter>classid</parameter> <type>oid</type>, <parameter>objid</parameter> <type>oid</type>, <parameter>objsubid</parameter> <type>integer</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Returns a textual description of a database object identified by
        catalog OID, object OID, and sub-object ID (such as a column number
        within a table; the sub-object ID is zero when referring to a whole
        object).  This description is intended to be human-readable, and might
        be translated, depending on server configuration.  This is especially
        useful to determine the identity of an object referenced in the
        <structname>pg_depend</structname> catalog. This function returns
        <literal>NULL</literal> values for undefined objects.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_identify_object</primary>
        </indexterm>
        <function>pg_identify_object</function> ( <parameter>classid</parameter> <type>oid</type>, <parameter>objid</parameter> <type>oid</type>, <parameter>objsubid</parameter> <type>integer</type> )
        <returnvalue>record</returnvalue>
        ( <parameter>type</parameter> <type>text</type>,
        <parameter>schema</parameter> <type>text</type>,
        <parameter>name</parameter> <type>text</type>,
        <parameter>identity</parameter> <type>text</type> )
       </para>
       <para>
        Returns a row containing enough information to uniquely identify the
        database object specified by catalog OID, object OID and sub-object
        ID.
        This information is intended to be machine-readable, and is never
        translated.
        <parameter>type</parameter> identifies the type of database object;
        <parameter>schema</parameter> is the schema name that the object
        belongs in, or <literal>NULL</literal> for object types that do not
        belong to schemas;
        <parameter>name</parameter> is the name of the object, quoted if
        necessary, if the name (along with schema name, if pertinent) is
        sufficient to uniquely identify the object,
        otherwise <literal>NULL</literal>;
        <parameter>identity</parameter> is the complete object identity, with
        the precise format depending on object type, and each name within the
        format being schema-qualified and quoted as necessary. Undefined
        objects are identified with <literal>NULL</literal> values.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_identify_object_as_address</primary>
        </indexterm>
        <function>pg_identify_object_as_address</function> ( <parameter>classid</parameter> <type>oid</type>, <parameter>objid</parameter> <type>oid</type>, <parameter>objsubid</parameter> <type>integer</type> )
        <returnvalue>record</returnvalue>
        ( <parameter>type</parameter> <type>text</type>,
        <parameter>object_names</parameter> <type>text[]</type>,
        <parameter>object_args</parameter> <type>text[]</type> )
       </para>
       <para>
        Returns a row containing enough information to uniquely identify the
        database object specified by catalog OID, object OID and sub-object
        ID.
        The returned information is independent of the current server, that
        is, it could be used to identify an identically named object in
        another server.
        <parameter>type</parameter> identifies the type of database object;
        <parameter>object_names</parameter> and
        <parameter>object_args</parameter>
        are text arrays that together form a reference to the object.
        These three values can be passed
        to <function>pg_get_object_address</function> to obtain the internal
        address of the object.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_object_address</primary>
        </indexterm>
        <function>pg_get_object_address</function> ( <parameter>type</parameter> <type>text</type>, <parameter>object_names</parameter> <type>text[]</type>, <parameter>object_args</parameter> <type>text[]</type> )
        <returnvalue>record</returnvalue>
        ( <parameter>classid</parameter> <type>oid</type>,
        <parameter>objid</parameter> <type>oid</type>,
        <parameter>objsubid</parameter> <type>integer</type> )
       </para>
       <para>
        Returns a row containing enough information to uniquely identify the
        database object specified by a type code and object name and argument
        arrays.
        The returned values are the ones that would be used in system catalogs
        such as <structname>pg_depend</structname>; they can be passed to
        other system functions such as <function>pg_describe_object</function>
        or <function>pg_identify_object</function>.
        <parameter>classid</parameter> is the OID of the system catalog
        containing the object;
        <parameter>objid</parameter> is the OID of the object itself, and
        <parameter>objsubid</parameter> is the sub-object ID, or zero if none.
        This function is the inverse
        of <function>pg_identify_object_as_address</function>.
        Undefined objects are identified with <literal>NULL</literal> values.
       </para></entry>
      </row>
     </tbody>
    </tgroup>
   </table>

   <para>
    <function>pg_get_acl</function> is useful for retrieving and inspecting
    the privileges associated with database objects without looking at
    specific catalogs. For example, to retrieve all the granted privileges
    on objects in the current database:
<programlisting>
postgres=# SELECT
    (pg_identify_object(s.classid,s.objid,s.objsubid)).*,
    pg_catalog.pg_get_acl(s.classid,s.objid,s.objsubid) AS acl
FROM pg_catalog.pg_shdepend AS s
JOIN pg_catalog.pg_database AS d
    ON d.datname = current_database() AND
       d.oid = s.dbid
JOIN pg_catalog.pg_authid AS a
    ON a.oid = s.refobjid AND
       s.refclassid = 'pg_authid'::regclass
WHERE s.deptype = 'a';
-[ RECORD 1 ]-----------------------------------------
type     | table
schema   | public
name     | testtab
identity | public.testtab
acl      | {postgres=arwdDxtm/postgres,foo=r/postgres}
</programlisting>
   </para>

  </sect2>

  <sect2 id="functions-info-comment">
   <title>Comment Information Functions</title>

   <indexterm>
    <primary>comment</primary>
    <secondary sortas="database objects">about database objects</secondary>
   </indexterm>

   <para>
    The functions shown in <xref linkend="functions-info-comment-table"/>
    extract comments previously stored with the <xref linkend="sql-comment"/>
    command.  A null value is returned if no
    comment could be found for the specified parameters.
   </para>

   <table id="functions-info-comment-table">
    <title>Comment Information Functions</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>col_description</primary>
        </indexterm>
        <function>col_description</function> ( <parameter>table</parameter> <type>oid</type>, <parameter>column</parameter> <type>integer</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Returns the comment for a table column, which is specified by the OID
        of its table and its column number.
        (<function>obj_description</function> cannot be used for table
        columns, since columns do not have OIDs of their own.)
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>obj_description</primary>
        </indexterm>
        <function>obj_description</function> ( <parameter>object</parameter> <type>oid</type>, <parameter>catalog</parameter> <type>name</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Returns the comment for a database object specified by its OID and the
        name of the containing system catalog.  For
        example, <literal>obj_description(123456, 'pg_class')</literal> would
        retrieve the comment for the table with OID 123456.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <function>obj_description</function> ( <parameter>object</parameter> <type>oid</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Returns the comment for a database object specified by its OID alone.
        This is <emphasis>deprecated</emphasis> since there is no guarantee
        that OIDs are unique across different system catalogs; therefore, the
        wrong comment might be returned.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>shobj_description</primary>
        </indexterm>
        <function>shobj_description</function> ( <parameter>object</parameter> <type>oid</type>, <parameter>catalog</parameter> <type>name</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Returns the comment for a shared database object specified by its OID
        and the name of the containing system catalog.  This is just
        like <function>obj_description</function> except that it is used for
        retrieving comments on shared objects (that is, databases, roles, and
        tablespaces).  Some system catalogs are global to all databases within
        each cluster, and the descriptions for objects in them are stored
        globally as well.
       </para></entry>
      </row>
     </tbody>
    </tgroup>
   </table>

  </sect2>

  <sect2 id="functions-info-validity">
   <title>Data Validity Checking Functions</title>

   <para>
    The functions shown in <xref linkend="functions-info-validity-table"/>
    can be helpful for checking validity of proposed input data.
   </para>

   <table id="functions-info-validity-table">
    <title>Data Validity Checking Functions</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para>
       <para>
        Example(s)
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_input_is_valid</primary>
        </indexterm>
        <function>pg_input_is_valid</function> (
          <parameter>string</parameter> <type>text</type>,
          <parameter>type</parameter> <type>text</type>
        )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Tests whether the given <parameter>string</parameter> is valid
        input for the specified data type, returning true or false.
       </para>
       <para>
        This function will only work as desired if the data type's input
        function has been updated to report invalid input as
        a <quote>soft</quote> error.  Otherwise, invalid input will abort
        the transaction, just as if the string had been cast to the type
        directly.
        </para>
        <para>
         <literal>pg_input_is_valid('42', 'integer')</literal>
         <returnvalue>t</returnvalue>
        </para>
        <para>
         <literal>pg_input_is_valid('42000000000', 'integer')</literal>
         <returnvalue>f</returnvalue>
        </para>
        <para>
         <literal>pg_input_is_valid('1234.567', 'numeric(7,4)')</literal>
         <returnvalue>f</returnvalue>
       </para></entry>
      </row>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_input_error_info</primary>
        </indexterm>
        <function>pg_input_error_info</function> (
          <parameter>string</parameter> <type>text</type>,
          <parameter>type</parameter> <type>text</type>
        )
        <returnvalue>record</returnvalue>
        ( <parameter>message</parameter> <type>text</type>,
        <parameter>detail</parameter> <type>text</type>,
        <parameter>hint</parameter> <type>text</type>,
        <parameter>sql_error_code</parameter> <type>text</type> )
       </para>
       <para>
        Tests whether the given <parameter>string</parameter> is valid
        input for the specified data type; if not, return the details of
        the error that would have been thrown.  If the input is valid, the
        results are NULL.  The inputs are the same as
        for <function>pg_input_is_valid</function>.
       </para>
       <para>
        This function will only work as desired if the data type's input
        function has been updated to report invalid input as
        a <quote>soft</quote> error.  Otherwise, invalid input will abort
        the transaction, just as if the string had been cast to the type
        directly.
       </para>
       <para>
        <literal>SELECT * FROM pg_input_error_info('42000000000', 'integer')</literal>
        <returnvalue></returnvalue>
<programlisting>
                       message                        | detail | hint | sql_error_code
------------------------------------------------------+--------+------+----------------
 value "42000000000" is out of range for type integer |        |      | 22003
</programlisting>
       </para></entry>
      </row>
     </tbody>
    </tgroup>
   </table>

  </sect2>

  <sect2 id="functions-info-snapshot">
   <title>Transaction ID and Snapshot Information Functions</title>

   <para>
    The functions shown in <xref linkend="functions-pg-snapshot"/>
    provide server transaction information in an exportable form.  The main
    use of these functions is to determine which transactions were committed
    between two snapshots.
   </para>

   <table id="functions-pg-snapshot">
    <title>Transaction ID and Snapshot Information Functions</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>age</primary>
        </indexterm>
        <function>age</function>  ( <type>xid</type> )
        <returnvalue>integer</returnvalue>
       </para>
       <para>
        Returns the number of transactions between the supplied
        transaction id and the current transaction counter.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>mxid_age</primary>
        </indexterm>
        <function>mxid_age</function>  ( <type>xid</type> )
        <returnvalue>integer</returnvalue>
       </para>
       <para>
        Returns the number of multixacts IDs between the supplied
        multixact ID and the current multixacts counter.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_current_xact_id</primary>
        </indexterm>
        <function>pg_current_xact_id</function> ()
        <returnvalue>xid8</returnvalue>
       </para>
       <para>
        Returns the current transaction's ID.  It will assign a new one if the
        current transaction does not have one already (because it has not
        performed any database updates);  see <xref
        linkend="transaction-id"/> for details.  If executed in a
        subtransaction, this will return the top-level transaction ID;
        see <xref linkend="subxacts"/> for details.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_current_xact_id_if_assigned</primary>
        </indexterm>
        <function>pg_current_xact_id_if_assigned</function> ()
        <returnvalue>xid8</returnvalue>
       </para>
       <para>
        Returns the current transaction's ID, or <literal>NULL</literal> if no
        ID is assigned yet.  (It's best to use this variant if the transaction
        might otherwise be read-only, to avoid unnecessary consumption of an
        XID.)
        If executed in a subtransaction, this will return the top-level
        transaction ID.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_xact_status</primary>
        </indexterm>
        <function>pg_xact_status</function> ( <type>xid8</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Reports the commit status of a recent transaction.
        The result is one of <literal>in progress</literal>,
        <literal>committed</literal>, or <literal>aborted</literal>,
        provided that the transaction is recent enough that the system retains
        the commit status of that transaction.
        If it is old enough that no references to the transaction survive in
        the system and the commit status information has been discarded, the
        result is <literal>NULL</literal>.
        Applications might use this function, for example, to determine
        whether their transaction committed or aborted after the application
        and database server become disconnected while
        a <literal>COMMIT</literal> is in progress.
        Note that prepared transactions are reported as <literal>in
        progress</literal>; applications must check <link
        linkend="view-pg-prepared-xacts"><structname>pg_prepared_xacts</structname></link>
        if they need to determine whether a transaction ID belongs to a
        prepared transaction.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_current_snapshot</primary>
        </indexterm>
        <function>pg_current_snapshot</function> ()
        <returnvalue>pg_snapshot</returnvalue>
       </para>
       <para>
        Returns a current <firstterm>snapshot</firstterm>, a data structure
        showing which transaction IDs are now in-progress.
        Only top-level transaction IDs are included in the snapshot;
        subtransaction IDs are not shown;  see <xref linkend="subxacts"/>
        for details.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_snapshot_xip</primary>
        </indexterm>
        <function>pg_snapshot_xip</function> ( <type>pg_snapshot</type> )
        <returnvalue>setof xid8</returnvalue>
       </para>
       <para>
        Returns the set of in-progress transaction IDs contained in a snapshot.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_snapshot_xmax</primary>
        </indexterm>
        <function>pg_snapshot_xmax</function> ( <type>pg_snapshot</type> )
        <returnvalue>xid8</returnvalue>
       </para>
       <para>
        Returns the <structfield>xmax</structfield> of a snapshot.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_snapshot_xmin</primary>
        </indexterm>
        <function>pg_snapshot_xmin</function> ( <type>pg_snapshot</type> )
        <returnvalue>xid8</returnvalue>
       </para>
       <para>
        Returns the <structfield>xmin</structfield> of a snapshot.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_visible_in_snapshot</primary>
        </indexterm>
        <function>pg_visible_in_snapshot</function> ( <type>xid8</type>, <type>pg_snapshot</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Is the given transaction ID <firstterm>visible</firstterm> according
        to this snapshot (that is, was it completed before the snapshot was
        taken)?  Note that this function will not give the correct answer for
        a subtransaction ID (subxid);  see <xref linkend="subxacts"/> for
        details.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_multixact_members</primary>
        </indexterm>
        <function>pg_get_multixact_members</function> ( <parameter>multixid</parameter> <type>xid</type> )
        <returnvalue>setof record</returnvalue>
        ( <parameter>xid</parameter> <type>xid</type>,
        <parameter>mode</parameter> <type>text</type> )
       </para>
       <para>
        Returns the transaction ID and lock mode for each member of the
        specified multixact ID.  The lock modes <literal>forupd</literal>,
        <literal>fornokeyupd</literal>, <literal>sh</literal>, and
        <literal>keysh</literal> correspond to the row-level locks
        <literal>FOR UPDATE</literal>, <literal>FOR NO KEY UPDATE</literal>,
        <literal>FOR SHARE</literal>, and <literal>FOR KEY SHARE</literal>,
        respectively, as described in <xref linkend="locking-rows"/>.  Two
        additional modes are specific to multixacts:
        <literal>nokeyupd</literal>, used by updates that do not modify key
        columns, and <literal>upd</literal>, used by updates or deletes that
        modify key columns.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_multixact_stats</primary>
        </indexterm>
        <function>pg_get_multixact_stats</function> ()
        <returnvalue>record</returnvalue>
        ( <parameter>num_mxids</parameter> <type>integer</type>,
          <parameter>num_members</parameter> <type>bigint</type>,
          <parameter>members_size</parameter> <type>bigint</type>,
          <parameter>oldest_multixact</parameter> <type>xid</type> )
       </para>
       <para>
        Returns statistics about current multixact usage:
        <literal>num_mxids</literal> is the total number of multixact IDs
        currently present in the system, <literal>num_members</literal> is
        the total number of multixact member entries currently present in
        the system, <literal>members_size</literal> is the storage occupied
        by <literal>num_members</literal> in the
        <literal>pg_multixact/members</literal> directory,
        <literal>oldest_multixact</literal> is the oldest multixact ID still
        in use.
       </para>
       <para>
        The function reports statistics at the time it is invoked. Values may
        vary between calls, even within a single transaction.
       </para>
       <para>
        To use this function, you must have privileges of the
        <literal>pg_read_all_stats</literal> role.
       </para></entry>
      </row>
     </tbody>
    </tgroup>
   </table>

   <para>
    The internal transaction ID type <type>xid</type> is 32 bits wide and
    wraps around every 4 billion transactions.  However,
    the functions shown in <xref linkend="functions-pg-snapshot"/>, except
    <function>age</function>, <function>mxid_age</function>, and
    <function>pg_get_multixact_members</function>, use a
    64-bit type <type>xid8</type> that does not wrap around during the life
    of an installation and can be converted to <type>xid</type> by casting if
    required;  see <xref linkend="transaction-id"/> for details.
    The data type <type>pg_snapshot</type> stores information about
    transaction ID visibility at a particular moment in time.  Its components
    are described in <xref linkend="functions-pg-snapshot-parts"/>.
    <type>pg_snapshot</type>'s textual representation is
    <literal><replaceable>xmin</replaceable>:<replaceable>xmax</replaceable>:<replaceable>xip_list</replaceable></literal>.
    For example <literal>10:20:10,14,15</literal> means
    <literal>xmin=10, xmax=20, xip_list=10, 14, 15</literal>.
   </para>

   <table id="functions-pg-snapshot-parts">
    <title>Snapshot Components</title>
    <tgroup cols="2">
    <colspec colname="col1" colwidth="1*"/>
    <colspec colname="col2" colwidth="3*"/>
     <thead>
      <row>
       <entry>Name</entry>
       <entry>Description</entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry><structfield>xmin</structfield></entry>
       <entry>
         Lowest transaction ID that was still active.  All transaction IDs
         less than <structfield>xmin</structfield> are either committed and visible,
         or rolled back and dead.
       </entry>
      </row>

      <row>
       <entry><structfield>xmax</structfield></entry>
       <entry>
         One past the highest completed transaction ID.  All transaction IDs
         greater than or equal to <structfield>xmax</structfield> had not yet
         completed as of the time of the snapshot, and thus are invisible.
       </entry>
      </row>

      <row>
       <entry><structfield>xip_list</structfield></entry>
       <entry>
        Transactions in progress at the time of the snapshot.  A transaction
        ID that is <literal>xmin &lt;= <replaceable>X</replaceable> &lt;
        xmax</literal> and not in this list was already completed at the time
        of the snapshot, and thus is either visible or dead according to its
        commit status.  This list does not include the transaction IDs of
        subtransactions (subxids).
       </entry>
      </row>
     </tbody>
    </tgroup>
   </table>

   <para>
    In releases of <productname>PostgreSQL</productname> before 13 there was
    no <type>xid8</type> type, so variants of these functions were provided
    that used <type>bigint</type> to represent a 64-bit XID, with a
    correspondingly distinct snapshot data type <type>txid_snapshot</type>.
    These older functions have <literal>txid</literal> in their names.  They
    are still supported for backward compatibility, but may be removed from a
    future release. See <xref linkend="functions-txid-snapshot"/>.
   </para>

   <table id="functions-txid-snapshot">
    <title>Deprecated Transaction ID and Snapshot Information Functions</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para></entry>
      </row>
     </thead>

     <tbody>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>txid_current</primary>
        </indexterm>
        <function>txid_current</function> ()
        <returnvalue>bigint</returnvalue>
       </para>
       <para>
        See <function>pg_current_xact_id()</function>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>txid_current_if_assigned</primary>
        </indexterm>
        <function>txid_current_if_assigned</function> ()
        <returnvalue>bigint</returnvalue>
       </para>
       <para>
        See <function>pg_current_xact_id_if_assigned()</function>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>txid_current_snapshot</primary>
        </indexterm>
        <function>txid_current_snapshot</function> ()
        <returnvalue>txid_snapshot</returnvalue>
       </para>
       <para>
        See <function>pg_current_snapshot()</function>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>txid_snapshot_xip</primary>
        </indexterm>
        <function>txid_snapshot_xip</function> ( <type>txid_snapshot</type> )
        <returnvalue>setof bigint</returnvalue>
       </para>
       <para>
        See <function>pg_snapshot_xip()</function>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>txid_snapshot_xmax</primary>
        </indexterm>
        <function>txid_snapshot_xmax</function> ( <type>txid_snapshot</type> )
        <returnvalue>bigint</returnvalue>
       </para>
       <para>
        See <function>pg_snapshot_xmax()</function>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>txid_snapshot_xmin</primary>
        </indexterm>
        <function>txid_snapshot_xmin</function> ( <type>txid_snapshot</type> )
        <returnvalue>bigint</returnvalue>
       </para>
       <para>
        See <function>pg_snapshot_xmin()</function>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>txid_visible_in_snapshot</primary>
        </indexterm>
        <function>txid_visible_in_snapshot</function> ( <type>bigint</type>, <type>txid_snapshot</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        See <function>pg_visible_in_snapshot()</function>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>txid_status</primary>
        </indexterm>
        <function>txid_status</function> ( <type>bigint</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        See <function>pg_xact_status()</function>.
       </para></entry>
      </row>
     </tbody>
    </tgroup>
   </table>

  </sect2>

  <sect2 id="functions-info-commit-timestamp">
   <title>Committed Transaction Information Functions</title>

   <para>
    The functions shown in <xref linkend="functions-commit-timestamp"/>
    provide information about when past transactions were committed.
    They only provide useful data when the
    <xref linkend="guc-track-commit-timestamp"/> configuration option is
    enabled, and only for transactions that were committed after it was
    enabled.  Commit timestamp information is routinely removed during
    vacuum.
   </para>

   <table id="functions-commit-timestamp">
    <title>Committed Transaction Information Functions</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_xact_commit_timestamp</primary>
        </indexterm>
        <function>pg_xact_commit_timestamp</function> ( <type>xid</type> )
        <returnvalue>timestamp with time zone</returnvalue>
       </para>
       <para>
        Returns the commit timestamp of a transaction.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_xact_commit_timestamp_origin</primary>
        </indexterm>
        <function>pg_xact_commit_timestamp_origin</function> ( <type>xid</type> )
        <returnvalue>record</returnvalue>
        ( <parameter>timestamp</parameter> <type>timestamp with time zone</type>,
         <parameter>roident</parameter> <type>oid</type>)
       </para>
       <para>
         Returns the commit timestamp and replication origin of a transaction.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_last_committed_xact</primary>
        </indexterm>
        <function>pg_last_committed_xact</function> ()
        <returnvalue>record</returnvalue>
        ( <parameter>xid</parameter> <type>xid</type>,
        <parameter>timestamp</parameter> <type>timestamp with time zone</type>,
        <parameter>roident</parameter> <type>oid</type> )
       </para>
       <para>
        Returns the transaction ID, commit timestamp and replication origin
        of the latest committed transaction.
       </para></entry>
      </row>
     </tbody>
    </tgroup>
   </table>

  </sect2>

  <sect2 id="functions-info-controldata">
   <title>Control Data Functions</title>

   <para>
    The functions shown in <xref linkend="functions-controldata"/>
    print information initialized during <command>initdb</command>, such
    as the catalog version. They also show information about write-ahead
    logging and checkpoint processing. This information is cluster-wide,
    not specific to any one database. These functions provide most of the same
    information, from the same source, as the
    <xref linkend="app-pgcontroldata"/> application.
   </para>

   <table id="functions-controldata">
    <title>Control Data Functions</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_control_checkpoint</primary>
        </indexterm>
        <function>pg_control_checkpoint</function> ()
        <returnvalue>record</returnvalue>
       </para>
       <para>
        Returns information about current checkpoint state, as shown in
        <xref linkend="functions-pg-control-checkpoint"/>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_control_system</primary>
        </indexterm>
        <function>pg_control_system</function> ()
        <returnvalue>record</returnvalue>
       </para>
       <para>
        Returns information about current control file state, as shown in
        <xref linkend="functions-pg-control-system"/>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_control_init</primary>
        </indexterm>
        <function>pg_control_init</function> ()
        <returnvalue>record</returnvalue>
       </para>
       <para>
        Returns information about cluster initialization state, as shown in
        <xref linkend="functions-pg-control-init"/>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_control_recovery</primary>
        </indexterm>
        <function>pg_control_recovery</function> ()
        <returnvalue>record</returnvalue>
       </para>
       <para>
        Returns information about recovery state, as shown in
        <xref linkend="functions-pg-control-recovery"/>.
       </para></entry>
      </row>
     </tbody>
    </tgroup>
   </table>

   <table id="functions-pg-control-checkpoint">
    <title><function>pg_control_checkpoint</function> Output Columns</title>
    <tgroup cols="2">
     <thead>
      <row>
       <entry>Column Name</entry>
       <entry>Data Type</entry>
      </row>
     </thead>

     <tbody>

      <row>
       <entry><structfield>checkpoint_lsn</structfield></entry>
       <entry><type>pg_lsn</type></entry>
      </row>

      <row>
       <entry><structfield>redo_lsn</structfield></entry>
       <entry><type>pg_lsn</type></entry>
      </row>

      <row>
       <entry><structfield>redo_wal_file</structfield></entry>
       <entry><type>text</type></entry>
      </row>

      <row>
       <entry><structfield>timeline_id</structfield></entry>
       <entry><type>integer</type></entry>
      </row>

      <row>
       <entry><structfield>prev_timeline_id</structfield></entry>
       <entry><type>integer</type></entry>
      </row>

      <row>
       <entry><structfield>full_page_writes</structfield></entry>
       <entry><type>boolean</type></entry>
      </row>

      <row>
       <entry><structfield>next_xid</structfield></entry>
       <entry><type>text</type></entry>
      </row>

      <row>
       <entry><structfield>next_oid</structfield></entry>
       <entry><type>oid</type></entry>
      </row>

      <row>
       <entry><structfield>next_multixact_id</structfield></entry>
       <entry><type>xid</type></entry>
      </row>

      <row>
       <entry><structfield>next_multi_offset</structfield></entry>
       <entry><type>xid</type></entry>
      </row>

      <row>
       <entry><structfield>oldest_xid</structfield></entry>
       <entry><type>xid</type></entry>
      </row>

      <row>
       <entry><structfield>oldest_xid_dbid</structfield></entry>
       <entry><type>oid</type></entry>
      </row>

      <row>
       <entry><structfield>oldest_active_xid</structfield></entry>
       <entry><type>xid</type></entry>
      </row>

      <row>
       <entry><structfield>oldest_multi_xid</structfield></entry>
       <entry><type>xid</type></entry>
      </row>

      <row>
       <entry><structfield>oldest_multi_dbid</structfield></entry>
       <entry><type>oid</type></entry>
      </row>

      <row>
       <entry><structfield>oldest_commit_ts_xid</structfield></entry>
       <entry><type>xid</type></entry>
      </row>

      <row>
       <entry><structfield>newest_commit_ts_xid</structfield></entry>
       <entry><type>xid</type></entry>
      </row>

      <row>
       <entry><structfield>checkpoint_time</structfield></entry>
       <entry><type>timestamp with time zone</type></entry>
      </row>

     </tbody>
    </tgroup>
   </table>

   <table id="functions-pg-control-system">
    <title><function>pg_control_system</function> Output Columns</title>
    <tgroup cols="2">
     <thead>
      <row>
       <entry>Column Name</entry>
       <entry>Data Type</entry>
      </row>
     </thead>

     <tbody>

      <row>
       <entry><structfield>pg_control_version</structfield></entry>
       <entry><type>integer</type></entry>
      </row>

      <row>
       <entry><structfield>catalog_version_no</structfield></entry>
       <entry><type>integer</type></entry>
      </row>

      <row>
       <entry><structfield>system_identifier</structfield></entry>
       <entry><type>bigint</type></entry>
      </row>

      <row>
       <entry><structfield>pg_control_last_modified</structfield></entry>
       <entry><type>timestamp with time zone</type></entry>
      </row>

     </tbody>
    </tgroup>
   </table>

   <table id="functions-pg-control-init">
    <title><function>pg_control_init</function> Output Columns</title>
    <tgroup cols="2">
     <thead>
      <row>
       <entry>Column Name</entry>
       <entry>Data Type</entry>
      </row>
     </thead>

     <tbody>

      <row>
       <entry><structfield>max_data_alignment</structfield></entry>
       <entry><type>integer</type></entry>
      </row>

      <row>
       <entry><structfield>database_block_size</structfield></entry>
       <entry><type>integer</type></entry>
      </row>

      <row>
       <entry><structfield>blocks_per_segment</structfield></entry>
       <entry><type>integer</type></entry>
      </row>

      <row>
       <entry><structfield>wal_block_size</structfield></entry>
       <entry><type>integer</type></entry>
      </row>

      <row>
       <entry><structfield>bytes_per_wal_segment</structfield></entry>
       <entry><type>integer</type></entry>
      </row>

      <row>
       <entry><structfield>max_identifier_length</structfield></entry>
       <entry><type>integer</type></entry>
      </row>

      <row>
       <entry><structfield>max_index_columns</structfield></entry>
       <entry><type>integer</type></entry>
      </row>

      <row>
       <entry><structfield>max_toast_chunk_size</structfield></entry>
       <entry><type>integer</type></entry>
      </row>

      <row>
       <entry><structfield>large_object_chunk_size</structfield></entry>
       <entry><type>integer</type></entry>
      </row>

      <row>
       <entry><structfield>float8_pass_by_value</structfield></entry>
       <entry><type>boolean</type></entry>
      </row>

      <row>
       <entry><structfield>data_page_checksum_version</structfield></entry>
       <entry><type>integer</type></entry>
      </row>

      <row>
       <entry><structfield>default_char_signedness</structfield></entry>
       <entry><type>boolean</type></entry>
      </row>

     </tbody>
    </tgroup>
   </table>

   <table id="functions-pg-control-recovery">
    <title><function>pg_control_recovery</function> Output Columns</title>
    <tgroup cols="2">
     <thead>
      <row>
       <entry>Column Name</entry>
       <entry>Data Type</entry>
      </row>
     </thead>

     <tbody>

      <row>
       <entry><structfield>min_recovery_end_lsn</structfield></entry>
       <entry><type>pg_lsn</type></entry>
      </row>

      <row>
       <entry><structfield>min_recovery_end_timeline</structfield></entry>
       <entry><type>integer</type></entry>
      </row>

      <row>
       <entry><structfield>backup_start_lsn</structfield></entry>
       <entry><type>pg_lsn</type></entry>
      </row>

      <row>
       <entry><structfield>backup_end_lsn</structfield></entry>
       <entry><type>pg_lsn</type></entry>
      </row>

      <row>
       <entry><structfield>end_of_backup_record_required</structfield></entry>
       <entry><type>boolean</type></entry>
      </row>

     </tbody>
    </tgroup>
   </table>

  </sect2>

  <sect2 id="functions-info-version">
   <title>Version Information Functions</title>

   <para>
    The functions shown in <xref linkend="functions-version"/>
    print version information.
   </para>

   <table id="functions-version">
    <title>Version Information Functions</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>version</primary>
        </indexterm>
        <function>version</function> ()
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Returns a string describing the <productname>PostgreSQL</productname>
        server's version.  You can also get this information from
        <xref linkend="guc-server-version"/>, or for a machine-readable
        version use <xref linkend="guc-server-version-num"/>.  Software
        developers should use <varname>server_version_num</varname> (available
        since 8.2) or <xref linkend="libpq-PQserverVersion"/> instead of
        parsing the text version.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>unicode_version</primary>
        </indexterm>
        <function>unicode_version</function> ()
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Returns a string representing the version of Unicode used by
        <productname>PostgreSQL</productname>.
       </para></entry>
      </row>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>icu_unicode_version</primary>
        </indexterm>
        <function>icu_unicode_version</function> ()
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Returns a string representing the version of Unicode used by ICU, if
        the server was built with ICU support; otherwise returns
        <literal>NULL</literal> </para></entry>
      </row>
     </tbody>
    </tgroup>
   </table>

  </sect2>

  <sect2 id="functions-info-wal-summary">
   <title>WAL Summarization Information Functions</title>

   <para>
    The functions shown in <xref linkend="functions-wal-summary"/>
    print information about the status of WAL summarization.
    See <xref linkend="guc-summarize-wal" />.
   </para>

   <table id="functions-wal-summary">
    <title>WAL Summarization Information Functions</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_available_wal_summaries</primary>
        </indexterm>
        <function>pg_available_wal_summaries</function> ()
        <returnvalue>setof record</returnvalue>
        ( <parameter>tli</parameter> <type>bigint</type>,
        <parameter>start_lsn</parameter> <type>pg_lsn</type>,
        <parameter>end_lsn</parameter> <type>pg_lsn</type> )
       </para>
       <para>
        Returns information about the WAL summary files present in the
        data directory, under <literal>pg_wal/summaries</literal>.
        One row will be returned per WAL summary file. Each file summarizes
        WAL on the indicated TLI within the indicated LSN range. This function
        might be useful to determine whether enough WAL summaries are present
        on the server to take an incremental backup based on some prior
        backup whose start LSN is known.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_wal_summary_contents</primary>
        </indexterm>
        <function>pg_wal_summary_contents</function> ( <parameter>tli</parameter> <type>bigint</type>, <parameter>start_lsn</parameter> <type>pg_lsn</type>, <parameter>end_lsn</parameter> <type>pg_lsn</type> )
        <returnvalue>setof record</returnvalue>
        ( <parameter>relfilenode</parameter> <type>oid</type>,
        <parameter>reltablespace</parameter> <type>oid</type>,
        <parameter>reldatabase</parameter> <type>oid</type>,
        <parameter>relforknumber</parameter> <type>smallint</type>,
        <parameter>relblocknumber</parameter> <type>bigint</type>,
        <parameter>is_limit_block</parameter> <type>boolean</type> )
       </para>
       <para>
        Returns one information about the contents of a single WAL summary file
        identified by TLI and starting and ending LSNs. Each row with
        <literal>is_limit_block</literal> false indicates that the block
        identified by the remaining output columns was modified by at least
        one WAL record within the range of records summarized by this file.
        Each row with <literal>is_limit_block</literal> true indicates either
        that (a) the relation fork was truncated to the length given by
        <literal>relblocknumber</literal> within the relevant range of WAL
        records or (b) that the relation fork was created or dropped within
        the relevant range of WAL records; in such cases,
        <literal>relblocknumber</literal> will be zero.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_get_wal_summarizer_state</primary>
        </indexterm>
        <function>pg_get_wal_summarizer_state</function> ()
        <returnvalue>record</returnvalue>
        ( <parameter>summarized_tli</parameter> <type>bigint</type>,
        <parameter>summarized_lsn</parameter> <type>pg_lsn</type>,
        <parameter>pending_lsn</parameter> <type>pg_lsn</type>,
        <parameter>summarizer_pid</parameter> <type>int</type> )
       </para>
       <para>
        Returns information about the progress of the WAL summarizer. If the
        WAL summarizer has never run since the instance was started, then
        <literal>summarized_tli</literal> and <literal>summarized_lsn</literal>
        will be <literal>0</literal> and <literal>0/00000000</literal> respectively;
        otherwise, they will be the TLI and ending LSN of the last WAL summary
        file written to disk. If the WAL summarizer is currently running,
        <literal>pending_lsn</literal> will be the ending LSN of the last
        record that it has consumed, which must always be greater than or
        equal to <literal>summarized_lsn</literal>; if the WAL summarizer is
        not running, it will be equal to <literal>summarized_lsn</literal>.
        <literal>summarizer_pid</literal> is the PID of the WAL summarizer
        process, if it is running, and otherwise NULL.
       </para>
       <para>
        As a special exception, the WAL summarizer will refuse to generate
        WAL summary files if run on WAL generated under
        <literal>wal_level=minimal</literal>, since such summaries would be
        unsafe to use as the basis for an incremental backup. In this case,
        the fields above will continue to advance as if summaries were being
        generated, but nothing will be written to disk. Once the summarizer
        reaches WAL generated while <literal>wal_level</literal> was set
        to <literal>replica</literal> or higher, it will resume writing
        summaries to disk.
       </para></entry>
      </row>
     </tbody>
    </tgroup>
   </table>

  </sect2>

  </sect1>
