233 lines
9.4 KiB
Plaintext
233 lines
9.4 KiB
Plaintext
<!-- doc/src/sgml/xplang.sgml -->
|
|
|
|
<chapter id="xplang">
|
|
<title>Procedural Languages</title>
|
|
|
|
<indexterm zone="xplang">
|
|
<primary>procedural language</primary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
<productname>PostgreSQL</productname> allows user-defined functions
|
|
to be written in other languages besides SQL and C. These other
|
|
languages are generically called <firstterm>procedural
|
|
languages</firstterm> (<acronym>PL</acronym>s). For a function
|
|
written in a procedural language, the database server has
|
|
no built-in knowledge about how to interpret the function's source
|
|
text. Instead, the task is passed to a special handler that knows
|
|
the details of the language. The handler could either do all the
|
|
work of parsing, syntax analysis, execution, etc. itself, or it
|
|
could serve as <quote>glue</quote> between
|
|
<productname>PostgreSQL</productname> and an existing implementation
|
|
of a programming language. The handler itself is a
|
|
C language function compiled into a shared object and
|
|
loaded on demand, just like any other C function.
|
|
</para>
|
|
|
|
<para>
|
|
There are currently four procedural languages available in the
|
|
standard <productname>PostgreSQL</productname> distribution:
|
|
<application>PL/pgSQL</application> (<xref linkend="plpgsql"/>),
|
|
<application>PL/Tcl</application> (<xref linkend="pltcl"/>),
|
|
<application>PL/Perl</application> (<xref linkend="plperl"/>), and
|
|
<application>PL/Python</application> (<xref linkend="plpython"/>).
|
|
There are additional procedural languages available that are not
|
|
included in the core distribution. <xref linkend="external-projects"/>
|
|
has information about finding them. In addition other languages can
|
|
be defined by users; the basics of developing a new procedural
|
|
language are covered in <xref linkend="plhandler"/>.
|
|
</para>
|
|
|
|
<sect1 id="xplang-install">
|
|
<title>Installing Procedural Languages</title>
|
|
|
|
<para>
|
|
A procedural language must be <quote>installed</quote> into each
|
|
database where it is to be used. But procedural languages installed in
|
|
the database <literal>template1</literal> are automatically available in all
|
|
subsequently created databases, since their entries in
|
|
<literal>template1</literal> will be copied by <command>CREATE DATABASE</command>.
|
|
So the database administrator can
|
|
decide which languages are available in which databases and can make
|
|
some languages available by default if desired.
|
|
</para>
|
|
|
|
<para>
|
|
For the languages supplied with the standard distribution, it is
|
|
only necessary to execute <command>CREATE EXTENSION</command>
|
|
<replaceable>language_name</replaceable> to install the language into the
|
|
current database.
|
|
The manual procedure described below is only recommended for
|
|
installing languages that have not been packaged as extensions.
|
|
</para>
|
|
|
|
<procedure>
|
|
<title>
|
|
Manual Procedural Language Installation
|
|
</title>
|
|
|
|
<para>
|
|
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 <quote>extension</quote>, so that <command>CREATE EXTENSION</command> can be
|
|
used to execute them.
|
|
</para>
|
|
|
|
<step performance="required" id="xplang-install-cr1">
|
|
<para>
|
|
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 <xref linkend="dfunc"/>. 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.
|
|
</para>
|
|
</step>
|
|
|
|
<step performance="required" id="xplang-install-cr2">
|
|
<para>
|
|
The handler must be declared with the command
|
|
<synopsis>
|
|
CREATE FUNCTION <replaceable>handler_function_name</replaceable>()
|
|
RETURNS language_handler
|
|
AS '<replaceable>path-to-shared-object</replaceable>'
|
|
LANGUAGE C;
|
|
</synopsis>
|
|
The special return type of <type>language_handler</type> tells
|
|
the database system that this function does not return one of
|
|
the defined <acronym>SQL</acronym> data types and is not directly usable
|
|
in <acronym>SQL</acronym> statements.
|
|
</para>
|
|
</step>
|
|
|
|
<step performance="optional" id="xplang-install-cr3">
|
|
<para>
|
|
Optionally, the language handler can provide an <quote>inline</quote>
|
|
handler function that executes anonymous code blocks
|
|
(<xref linkend="sql-do"/> commands)
|
|
written in this language. If an inline handler function
|
|
is provided by the language, declare it with a command like
|
|
<synopsis>
|
|
CREATE FUNCTION <replaceable>inline_function_name</replaceable>(internal)
|
|
RETURNS void
|
|
AS '<replaceable>path-to-shared-object</replaceable>'
|
|
LANGUAGE C;
|
|
</synopsis>
|
|
</para>
|
|
</step>
|
|
|
|
<step performance="optional" id="xplang-install-cr4">
|
|
<para>
|
|
Optionally, the language handler can provide a <quote>validator</quote>
|
|
function that checks a function definition for correctness without
|
|
actually executing it. The validator function is called by
|
|
<command>CREATE FUNCTION</command> if it exists. If a validator function
|
|
is provided by the language, declare it with a command like
|
|
<synopsis>
|
|
CREATE FUNCTION <replaceable>validator_function_name</replaceable>(oid)
|
|
RETURNS void
|
|
AS '<replaceable>path-to-shared-object</replaceable>'
|
|
LANGUAGE C STRICT;
|
|
</synopsis>
|
|
</para>
|
|
</step>
|
|
|
|
<step performance="required" id="xplang-install-cr5">
|
|
<para>
|
|
Finally, the PL must be declared with the command
|
|
<synopsis>
|
|
CREATE <optional>TRUSTED</optional> LANGUAGE <replaceable>language_name</replaceable>
|
|
HANDLER <replaceable>handler_function_name</replaceable>
|
|
<optional>INLINE <replaceable>inline_function_name</replaceable></optional>
|
|
<optional>VALIDATOR <replaceable>validator_function_name</replaceable></optional> ;
|
|
</synopsis>
|
|
The optional key word <literal>TRUSTED</literal> 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, the <literal>TRUSTED</literal> flag should only be given
|
|
for languages that do not allow access to database server
|
|
internals or the file system. The languages
|
|
<application>PL/pgSQL</application>,
|
|
<application>PL/Tcl</application>, and
|
|
<application>PL/Perl</application>
|
|
are considered trusted; the languages
|
|
<application>PL/TclU</application>,
|
|
<application>PL/PerlU</application>, and
|
|
<application>PL/PythonU</application>
|
|
are designed to provide unlimited functionality and should
|
|
<emphasis>not</emphasis> be marked trusted.
|
|
</para>
|
|
</step>
|
|
</procedure>
|
|
|
|
<para>
|
|
<xref linkend="xplang-install-example"/> shows how the manual
|
|
installation procedure would work with the language
|
|
<application>PL/Perl</application>.
|
|
</para>
|
|
|
|
<example id="xplang-install-example">
|
|
<title>Manual Installation of <application>PL/Perl</application></title>
|
|
|
|
<para>
|
|
The following command tells the database server where to find the
|
|
shared object for the <application>PL/Perl</application> language's call
|
|
handler function:
|
|
|
|
<programlisting>
|
|
CREATE FUNCTION plperl_call_handler() RETURNS language_handler AS
|
|
'$libdir/plperl' LANGUAGE C;
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
<application>PL/Perl</application> has an inline handler function
|
|
and a validator function, so we declare those too:
|
|
|
|
<programlisting>
|
|
CREATE FUNCTION plperl_inline_handler(internal) RETURNS void AS
|
|
'$libdir/plperl' LANGUAGE C STRICT;
|
|
|
|
CREATE FUNCTION plperl_validator(oid) RETURNS void AS
|
|
'$libdir/plperl' LANGUAGE C STRICT;
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
The command:
|
|
<programlisting>
|
|
CREATE TRUSTED LANGUAGE plperl
|
|
HANDLER plperl_call_handler
|
|
INLINE plperl_inline_handler
|
|
VALIDATOR plperl_validator;
|
|
</programlisting>
|
|
then defines that the previously declared functions
|
|
should be invoked for functions and procedures where the
|
|
language attribute is <literal>plperl</literal>.
|
|
</para>
|
|
</example>
|
|
|
|
<para>
|
|
In a default <productname>PostgreSQL</productname> installation,
|
|
the handler for the <application>PL/pgSQL</application> language
|
|
is built and installed into the <quote>library</quote>
|
|
directory; furthermore, the <application>PL/pgSQL</application> language
|
|
itself is installed in all databases.
|
|
If <application>Tcl</application> support is configured in, the handlers for
|
|
<application>PL/Tcl</application> and <application>PL/TclU</application> are built and installed
|
|
in the library directory, but the language itself is not installed in any
|
|
database by default.
|
|
Likewise, the <application>PL/Perl</application> and <application>PL/PerlU</application>
|
|
handlers are built and installed if Perl support is configured, and the
|
|
<application>PL/PythonU</application> handler is installed if Python support is
|
|
configured, but these languages are not installed by default.
|
|
</para>
|
|
|
|
</sect1>
|
|
|
|
</chapter>
|