void (*ReScanCustomScan) (CustomScanState *node);
</programlisting>
    Rewind the current scan to the beginning and prepare to rescan the
    relation.
   </para>

   <para>
<programlisting>
void (*MarkPosCustomScan) (CustomScanState *node);
</programlisting>
    Save the current scan position so that it can subsequently be restored
    by the <function>RestrPosCustomScan</function> callback.  This callback is
    optional, and need only be supplied if the
    <literal>CUSTOMPATH_SUPPORT_MARK_RESTORE</literal> flag is set.
   </para>

   <para>
<programlisting>
void (*RestrPosCustomScan) (CustomScanState *node);
</programlisting>
    Restore the previous scan position as saved by the
    <function>MarkPosCustomScan</function> callback.  This callback is optional,
    and need only be supplied if the
    <literal>CUSTOMPATH_SUPPORT_MARK_RESTORE</literal> flag is set.
   </para>

   <para>
<programlisting>
Size (*EstimateDSMCustomScan) (CustomScanState *node,
                               ParallelContext *pcxt);
</programlisting>
    Estimate the amount of dynamic shared memory that will be required
    for parallel operation.  This may be higher than the amount that will
    actually be used, but it must not be lower.  The return value is in bytes.
    This callback is optional, and need only be supplied if this custom
    scan provider supports parallel execution.
   </para>

   <para>
<programlisting>
void (*InitializeDSMCustomScan) (CustomScanState *node,
                                 ParallelContext *pcxt,
                                 void *coordinate);
</programlisting>
    Initialize the dynamic shared memory that will be required for parallel
    operation.  <literal>coordinate</literal> points to a shared memory area of
    size equal to the return value of <function>EstimateDSMCustomScan</function>.
    This callback is optional, and need only be supplied if this custom
    scan provider supports parallel execution.
   </para>

   <para>
<programlisting>
void (*ReInitializeDSMCustomScan) (CustomScanState *node,
                                   ParallelContext *pcxt,
                                   void *coordinate);
</programlisting>
    Re-initialize