A procedural language must be "installed" into each
database where it is to be used. But procedural languages installed in
the template1 database are automatically available in all
subsequently created databases. So the database administrator can
decide which languages are available in which databases, and can make
some languages available by default if he chooses.
For the languages supplied with the standard distribution, the
shell script createlang may be used instead
of carrying out the details by hand. For example, to install PL/pgSQL
into the template1 database, use
createlang plpgsql template1
The manual procedure described below is only recommended for
installing custom languages that createlang
does not know about.
Manual Procedural Language Installation
A procedural language is installed in the database in three
steps, which must be carried out by a database superuser.
The shared object for the language handler must be compiled and
installed into an appropriate library directory. This works in the same
way as building and installing modules with regular user-defined C
functions does; see Section 9.5.8.
The handler must be declared with the command
CREATE FUNCTION handler_function_name ()
RETURNS LANGUAGE_HANDLER AS
'path-to-shared-object' LANGUAGE C;
The special return type of LANGUAGE_HANDLER tells
the database that this function does not return one of
the defined SQL data types and is not directly usable
in SQL statements.
The PL must be declared with the command
CREATE [TRUSTED] [PROCEDURAL] LANGUAGE language-name
HANDLER handler_function_name;
The optional key word TRUSTED tells whether
ordinary database users that have no superuser privileges should
be allowed to use this language to create functions and trigger
procedures. Since PL functions are executed inside the database
server, the TRUSTED flag should only be given
for languages that do not allow access to database server
internals or the file system. The languages
PL/pgSQL,
PL/Tcl,
PL/Perl, and
PL/Python are known to be trusted;
the languages PL/TclU and
PL/PerlU are designed to provide
unlimited functionality should not be
marked trusted.
In a default PostgreSQL installation,
the handler for the PL/pgSQL language
is built and installed into the "library"
directory. If Tcl/Tk support is configured in, the handlers for
PL/Tcl and PL/TclU are also built and installed in the same
location. Likewise, the PL/Perl and PL/PerlU handlers are built
and installed if Perl support is configured, and PL/Python is
installed if Python support is configured. The
createlang script automates step 2 and step 3 described above.
Example 18-1. Manual Installation of PL/pgSQL
The following command tells the database server where to find the
shared object for the PL/pgSQL language's call handler function.
CREATE FUNCTION plpgsql_call_handler () RETURNS LANGUAGE_HANDLER AS
'$libdir/plpgsql' LANGUAGE C;
The command
CREATE TRUSTED PROCEDURAL LANGUAGE plpgsql
HANDLER plpgsql_call_handler;
then defines that the previously declared call handler function
should be invoked for functions and trigger procedures where the
language attribute is plpgsql.
