one,
    copied from the scalar type.  (There's also a special case
    for <structfield>typalign</structfield>.)  Then
    the <structfield>typelem</structfield>
    and <structfield>typarray</structfield> fields of the two entries are
    set to cross-reference each other.
   </para>
  </sect2>

  <sect2 id="system-catalog-recipes">
   <title>Recipes for Editing Data Files</title>

   <para>
    Here are some suggestions about the easiest ways to perform common tasks
    when updating catalog data files.
   </para>

   <formalpara>
    <title>Add a new column with a default to a catalog:</title>
    <para>
     Add the column to the header file with
     a <literal>BKI_DEFAULT(<replaceable>value</replaceable>)</literal>
     annotation.  The data file need only be adjusted by adding the field
     in existing rows where a non-default value is needed.
    </para>
   </formalpara>

   <formalpara>
    <title>Add a default value to an existing column that doesn't have
     one:</title>
    <para>
     Add a <literal>BKI_DEFAULT</literal> annotation to the header file,
     then run <literal>make reformat-dat-files</literal> to remove
     now-redundant field entries.
    </para>
   </formalpara>

   <formalpara>
    <title>Remove a column, whether it has a default or not:</title>
    <para>
     Remove the column from the header, then run <literal>make
     reformat-dat-files</literal> to remove now-useless field entries.
    </para>
   </formalpara>

   <formalpara>
    <title>Change or remove an existing default value:</title>
    <para>
     You cannot simply change the header file, since that will cause the
     current data to be interpreted incorrectly.  First run <literal>make
     expand-dat-files</literal> to rewrite the data files with all
     default values inserted explicitly, then change or remove
     the <literal>BKI_DEFAULT</literal> annotation, then run <literal>make
     reformat-dat-files</literal> to remove superfluous fields again.
    </para>
   </formalpara>

   <formalpara>
    <title>Ad-hoc bulk editing:</title>
    <para>
     <filename>reformat_dat_file.pl</filename> can be adapted to perform
     many kinds of bulk changes.  Look for its block comments showing where
     one-off code can be inserted.  In the following example, we are going
     to consolidate two Boolean fields in <structname>pg_proc</structname>
     into a char field:

     <orderedlist>
      <listitem>
       <para>
        Add the new column, with a default,
        to <filename>pg_proc.h</filename>:
<programlisting>
+    /* see PROKIND_ categories below */
+    char        prokind BKI_DEFAULT(f);
</programlisting>
       </para>
      </listitem>

      <listitem>
       <para>
        Create a new script based on <filename>reformat_dat_file.pl</filename>
        to insert appropriate values on-the-fly:
<programlisting>
-           # At this point we have the full row in memory as a hash
-           # and can do any operations we want. As written, it only
-           # removes default values, but this script can be adapted to
-           # do one-off bulk-editing.
+           # One-off change to migrate to prokind
+           # Default has already been filled in by now, so change to other
+           # values as appropriate
+           if ($values{proisagg} eq 't')
+           {
+               $values{prokind} = 'a';
+           }
+           elsif ($values{proiswindow} eq 't')
+           {
+               $values{prokind} = 'w';
+           }
</programlisting>
       </para>
      </listitem>

      <listitem>
       <para>
        Run the new script:
<programlisting>
$ cd src/include/catalog
$ perl  rewrite_dat_with_prokind.pl  pg_proc.dat
</programlisting>
        At this point <filename>pg_proc.dat</filename> has all three
        columns, <structfield>prokind</structfield>,
        <structfield>proisagg</structfield>,
        and <structfield>proiswindow</structfield>, though they will appear
        only in rows where