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Manual Procedural Language Installation

A procedural language is installed in a database in five steps, which must be carried out by a database superuser. In most cases the required SQL commands should be packaged as the installation script of an“extension”, so thatCREATE EXTENSION can be used to execute them.

1. 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; seeSection 36.10.5. Often, the language handler will depend on an external library that provides the actual programming language engine; if so, that must be installed as well.

2. The handler must be declared with the command

   CREATE FUNCTIONhandler_function_name()    RETURNS language_handler    AS 'path-to-shared-object'    LANGUAGE C;

   The special return type oflanguage_handler tells the database system that this function does not return one of the definedSQL data types and is not directly usable inSQL statements.

3. Optionally, the language handler can provide an“inline” handler function that executes anonymous code blocks (DO commands) written in this language. If an inline handler function is provided by the language, declare it with a command like

   CREATE FUNCTIONinline_function_name(internal)    RETURNS void    AS 'path-to-shared-object'    LANGUAGE C;

4. Optionally, the language handler can provide a“validator” function that checks a function definition for correctness without actually executing it. The validator function is called byCREATE FUNCTION if it exists. If a validator function is provided by the language, declare it with a command like

   CREATE FUNCTIONvalidator_function_name(oid)    RETURNS void    AS 'path-to-shared-object'    LANGUAGE C STRICT;

5. Finally, the PL must be declared with the command

   CREATE [TRUSTED] LANGUAGElanguage_name    HANDLERhandler_function_name    [INLINEinline_function_name]    [VALIDATORvalidator_function_name] ;

   The optional key wordTRUSTED specifies that the language does not grant access to data that the user would not otherwise have. Trusted languages are designed for ordinary database users (those without superuser privilege) and allows them to safely create functions and procedures. Since PL functions are executed inside the database server, theTRUSTED flag should only be given for languages that do not allow access to database server internals or the file system. The languagesPL/pgSQL,PL/Tcl, andPL/Perl are considered trusted; the languagesPL/TclU,PL/PerlU, andPL/PythonU are designed to provide unlimited functionality and shouldnot be marked trusted.

Example 40.1. Manual Installation ofPL/Perl

CREATE FUNCTION plperl_call_handler() RETURNS language_handler AS    '$libdir/plperl' LANGUAGE C;

CREATE FUNCTION plperl_inline_handler(internal) RETURNS void AS    '$libdir/plperl' LANGUAGE C STRICT;CREATE FUNCTION plperl_validator(oid) RETURNS void AS    '$libdir/plperl' LANGUAGE C STRICT;

CREATE TRUSTED LANGUAGE plperl    HANDLER plperl_call_handler    INLINE plperl_inline_handler    VALIDATOR plperl_validator;