hat many of these
     parameters require special source compilation flags to work at all.
    </P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="GUC-ALLOW-SYSTEM-TABLE-MODS"
></A
><TT
CLASS="VARNAME"
>allow_system_table_mods</TT
> (<TT
CLASS="TYPE"
>boolean</TT
>)</DT
><DD
><P
>        Allows modification of the structure of system tables.
        This is used by <TT
CLASS="COMMAND"
>initdb</TT
>.
        This parameter can only be set at server start.
       </P
></DD
><DT
><A
NAME="GUC-DEBUG-ASS