in the <literal>areq</literal>.
    </para>

    <para>
<programlisting>
void
ForeignAsyncConfigureWait(AsyncRequest *areq);
</programlisting>
     Configure a file descriptor event for which the
     <structname>ForeignScan</structname> node wishes to wait.
     This function will only be called when the
     <structname>ForeignScan</structname> node has the
     <literal>areq-&gt;callback_pending</literal> flag set, and should add
     the event to the <structfield>as_eventset</structfield> of the parent
     <structname>Append</structname> node described by the
     <literal>areq</literal>.  See the comments for
     <function>ExecAsyncConfigureWait</function> in
     <filename>src/backend/executor/execAsync.c</filename> for additional
     information.  When the file descriptor event occurs,
     <function>ForeignAsyncNotify</function> will be called.
    </para>

    <para>
<programlisting>
void
ForeignAsyncNotify(AsyncRequest *areq);
</programlisting>
     Process a relevant event that has occurred, then produce one tuple
     asynchronously from the <structname>ForeignScan</structname> node.
     This function should set the output parameters in the
     <literal>areq</literal> in the same way as
     <function>ForeignAsyncRequest</function>.
    </para>
   </sect2>

   <sect2 id="fdw-callbacks-reparameterize-paths">
    <title>FDW Routines for Reparameterization of Paths</title>

    <para>
<programlisting>
List *
ReparameterizeForeignPathByChild(PlannerInfo *root, List *fdw_private,
                                 RelOptInfo *child_rel);
</programlisting>
    This function is called while converting a path parameterized by the
    top-most parent of the given child relation <literal>child_rel</literal> to be
    parameterized by the child relation. The function is used to reparameterize
    any paths or translate any expression nodes saved in the given
    <literal>fdw_private</literal> member of a <structname>ForeignPath</structname>. The
    callback may use <literal>reparameterize_path_by_child</literal>,
    <literal>adjust_appendrel_attrs</literal> or
    <literal>adjust_appendrel_attrs_multilevel</literal> as required.
    </para>
   </sect2>

   </sect1>

   <sect1 id="fdw-helpers">
    <title>Foreign Data Wrapper Helper Functions</title>

    <para>
     Several helper functions are exported from the core server so that
     authors of foreign data wrappers can get easy access to attributes of
     FDW-related objects, such as FDW options.
     To use any of these functions, you need to include the header file
     <filename>foreign/foreign.h</filename> in your source file.
     That header also defines the struct types that are returned by
     these functions.
    </para>

    <para>
<programlisting>
ForeignDataWrapper *
GetForeignDataWrapperExtended(Oid fdwid, bits16 flags);
</programlisting>

     This function returns a <structname>ForeignDataWrapper</structname>
     object for the foreign-data wrapper with the given OID.  A
     <structname>ForeignDataWrapper</structname> object contains properties
     of the FDW (see <filename>foreign/foreign.h</filename> for details).
     <structfield>flags</structfield> is a bitwise-or'd bit mask indicating
     an extra set of options.  It can take the value
     <literal>FDW_MISSING_OK</literal>, in which case a <literal>NULL</literal>
     result is returned to the caller instead of an error for an undefined
     object.
    </para>

    <para>
<programlisting>
ForeignDataWrapper *
GetForeignDataWrapper(Oid fdwid);
</programlisting>

     This function returns a <structname>ForeignDataWrapper</structname>
     object for the foreign-data wrapper with the given OID.  A
     <structname>ForeignDataWrapper</structname> object contains properties
     of the FDW (see <filename>foreign/foreign.h</filename> for details).
    </para>

    <para>
<programlisting>
ForeignServer *
GetForeignServerExtended(Oid serverid, bits16 flags);
</programlisting>

     This function