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>39.7. Modules and the <CODE
CLASS="FUNCTION"
>unknown</CODE
> command</A
></H1
><P
>        PL/Tcl has support for autoloading Tcl code when used.
        It recognizes a special table, <TT
CLASS="LITERAL"
>pltcl_modules</TT
>, which
        is presumed to contain modules of Tcl code.  If this table
        exists, the module <TT
CLASS="LITERAL"
>unknown</TT
> is fetched from the table
        and loaded into the Tcl interpreter immediately after creating
        the interpreter.
       </P
><P
>        While the <TT
CLASS="LITERAL"
>unknown</TT
> module could actually contain any
        initialization script you need, it normally defines a Tcl
        <CODE
CLASS="FUNCTION"
>unknown</CODE
> procedure that is invoked whenever Tcl does
        not recognize an invoked procedure name.  <SPAN
CLASS="APPLICATION"
>PL/Tcl</SPAN
>'s standard version
        of this procedure tries to find a module in <TT
CLASS="LITERAL"
>pltcl_modules</TT
>
        that will define the required procedure.  If one is found, it is
        loaded into the interpreter, and then execution is allowed to
        proceed with the originally attempted procedure call.  A
        secondary table <TT
CLASS="LITERAL"
>pltcl_modfuncs</TT
> provides an index of
        which functions are defined by which modules, so that the lookup
        is reasonably quick.
       </P
><P
>        The <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> distribution includes
        support scripts to maintain these tables:
        <TT
CLASS="COMMAND"
>pltcl_loadmod</TT
>, <TT
CLASS="COMMAND"
>pltcl_listmod</TT
>,
        <TT
CLASS="COMMAND"
>pltcl_delmod</TT
>, as well as source for the standard
        <TT
CLASS="LITERAL"
>unknown</TT
> module in <TT
CLASS="FILENAME"
>share/unknown.pltcl</TT
>.  This module
        must be loaded
        into each database initially to support the autoloading mechanism.
       </P
><P
>        The tables <TT
CLASS="LITERAL"
>pltcl_modules</TT
> and <TT
CLASS="LITERAL"
>pltcl_modfuncs</TT
>
        must be readable by all, but it is wise to make them owned and
        writable only by the database administrator.
       </P
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