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Remove PL/Tcl's "module" facility.

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PL/Tcl has long had a facility whereby Tcl code could be autoloaded from
a database table named "pltcl_modules".  However, nobody is using it, as
evidenced by the recent discovery that it's never been fixed to work with
standard_conforming_strings turned on.  Moreover, it's rather shaky from
a security standpoint, and the table design is very old and crufty (partly
because it dates from before we had TOAST).  A final problem is that
because the table-population scripts depend on the Tcl client library
Pgtcl, which we removed from the core distribution in 2004, it's
impossible to create a self-contained regression test for the feature.
Rather than try to surmount these problems, let's just remove it.

A follow-on patch will provide a way to execute user-defined
initialization code, similar to features that exist in plperl and plv8.
With that, it will be possible to implement this feature or similar ones
entirely in userspace, which is where it belongs.

Discussion: https://postgr.es/m/22067.1488046447@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2017-02-27 11:20:22 -05:00
parent 2ed193c904
commit 817f2a5863
10 changed files with 0 additions and 1029 deletions
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45
doc/src/sgml/pltcl.sgml
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@ -902,51 +902,6 @@ if {[catch { spi_exec $sql_command }]} {
</para>
</sect1>
<sect1 id="pltcl-unknown">
<title>Modules and the <function>unknown</> Command</title>
<para>
PL/Tcl has support for autoloading Tcl code when used.
It recognizes a special table, <literal>pltcl_modules</>, which
is presumed to contain modules of Tcl code. If this table
exists, the module <literal>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 <xref linkend="pltcl-global">.)
</para>
<para>
While the <literal>unknown</> module could actually contain any
initialization script you need, it normally defines a Tcl
<function>unknown</> procedure that is invoked whenever Tcl does
not recognize an invoked procedure name. <application>PL/Tcl</>'s standard version
of this procedure tries to find a module in <literal>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 <literal>pltcl_modfuncs</> provides an index of
which functions are defined by which modules, so that the lookup
is reasonably quick.
</para>
<para>
The <productname>PostgreSQL</productname> distribution includes
support scripts to maintain these tables:
<command>pltcl_loadmod</>, <command>pltcl_listmod</>,
<command>pltcl_delmod</>, as well as source for the standard
<literal>unknown</> module in <filename>share/unknown.pltcl</>. This module
must be loaded
into each database initially to support the autoloading mechanism.
</para>
<para>
The tables <literal>pltcl_modules</> and <literal>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 <literal>pltcl_modules</> (and thus,
not attempt to load the <literal>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.
</para>
</sect1>
<sect1 id="pltcl-procnames">
<title>Tcl Procedure Names</title>