PL/Tcl has support for autoloading Tcl code when used.
It recognizes a special table, pltcl_modules, which
is presumed to contain modules of Tcl code. If this table
exists, the module unknown is fetched from the table
and loaded into the Tcl interpreter immediately before the first
execution of a PL/Tcl function in a database session. (This
happens separately for each Tcl interpreter, if more than one is
used in a session; see Section 40.4.)
While the unknown module could actually contain any
initialization script you need, it normally defines a Tcl
unknown procedure that is invoked whenever Tcl does
not recognize an invoked procedure name. PL/Tcl's standard version
of this procedure tries to find a module in pltcl_modules
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 pltcl_modfuncs provides an index of
which functions are defined by which modules, so that the lookup
is reasonably quick.
The PostgreSQL distribution includes
support scripts to maintain these tables:
pltcl_loadmod, pltcl_listmod,
pltcl_delmod, as well as source for the standard
unknown module in share/unknown.pltcl. This module
must be loaded
into each database initially to support the autoloading mechanism.
The tables pltcl_modules and pltcl_modfuncs
must be readable by all, but it is wise to make them owned and
writable only by the database administrator. As a security
precaution, PL/Tcl will ignore pltcl_modules (and thus,
not attempt to load the unknown module) unless it is
owned by a superuser. But update privileges on this table can be
granted to other users, if you trust them sufficiently.