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>Chapter 37. Procedural Languages</TD
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CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="XPLANG-INSTALL"
>37.1. Installing Procedural Languages</A
></H1
><P
> A procedural language must be <SPAN
CLASS="QUOTE"
>"installed"</SPAN
> into each
database where it is to be used. But procedural languages installed in
the database <TT
CLASS="LITERAL"
>template1</TT
> are automatically available in all
subsequently created databases, since their entries in
<TT
CLASS="LITERAL"
>template1</TT
> will be copied by <TT
CLASS="COMMAND"
>CREATE DATABASE</TT
>.
So the database administrator can
decide which languages are available in which databases and can make
some languages available by default if he chooses.
</P
><P
> For the languages supplied with the standard distribution, it is
only necessary to execute <TT
CLASS="COMMAND"
>CREATE LANGUAGE</TT
>
<TT
CLASS="REPLACEABLE"
><I
>language_name</I
></TT
> to install the language into the
current database. Alternatively, the program <A
HREF="app-createlang.html"
><SPAN
CLASS="APPLICATION"
>createlang</SPAN
></A
> can be used to do this from the shell
command line. For example, to install the language
<SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
> into the database
<TT
CLASS="LITERAL"
>template1</TT
>, use:
</P><PRE
CLASS="PROGRAMLISTING"
>createlang plpgsql template1</PRE
><P>
The manual procedure described below is only recommended for
installing custom languages that <TT
CLASS="COMMAND"
>CREATE LANGUAGE</TT
>
does not know about.
</P
><DIV
CLASS="PROCEDURE"
><P
><B
> Manual Procedural Language Installation
</B
></P
><P
> A procedural language is installed in a database in four steps,
which must be carried out by a database superuser. (For languages
known to <TT
CLASS="COMMAND"
>CREATE LANGUAGE</TT
>, the second and third steps
can be omitted, because they will be carried out automatically
if needed.)
</P
><OL
TYPE="1"
><LI
CLASS="STEP"
><A
NAME="XPLANG-INSTALL-CR1"
></A
><P
> 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 <A
HREF="xfunc-c.html#DFUNC"
>Section 34.9.6</A
>. 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.
</P
></LI
><LI
CLASS="STEP"
><A
NAME="XPLANG-INSTALL-CR2"
></A
><P
> The handler must be declared with the command
</P><PRE
CLASS="SYNOPSIS"
>CREATE FUNCTION <TT
CLASS="REPLACEABLE"
><I
>handler_function_name</I
></TT
>()
RETURNS language_handler
AS '<TT
CLASS="REPLACEABLE"
><I
>path-to-shared-object</I
></TT
>'
LANGUAGE C;</PRE
><P>
The special return type of <TT
CLASS="TYPE"
>language_handler</TT
> tells
the database system that this function does not return one of
the defined <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> data types and is not directly usable
in <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> statements.
</P
></LI
><LI
CLASS="STEP"
><A
NAME="XPLANG-INSTALL-CR3"
></A
><P
> Optionally, the language handler can provide a <SPAN
CLASS="QUOTE"
>"validator"</SPAN
>
function that checks a function definition for correctness without
actually executing it. The validator function is called by
<TT
CLASS="COMMAND"
>CREATE FUNCTION</TT
> if it exists. If a validator function
is provided by the handler, declare it with a command like
</P><PRE
CLASS="SYNOPSIS"
>CREATE FUNCTION <TT
CLASS="REPLACEABLE"
><I
>validator_function_name</I
></TT
>(oid)
RETURNS void
AS '<TT
CLASS="REPLACEABLE"
><I
>path-to-shared-object</I
></TT
>'
LANGUAGE C;</PRE
><P>
</P
></LI
><LI
CLASS="STEP"
><A
NAME="XPLANG-INSTALL-CR4"
></A
><P
> The PL must be declared with the command
</P><PRE
CLASS="SYNOPSIS"
>CREATE [<SPAN
CLASS="OPTIONAL"
>TRUSTED</SPAN
>] [<SPAN
CLASS="OPTIONAL"
>PROCEDURAL</SPAN
>] LANGUAGE <TT
CLASS="REPLACEABLE"
><I
>language-name</I
></TT
>
HANDLER <TT
CLASS="REPLACEABLE"
><I
>handler_function_name</I
></TT
>
[<SPAN
CLASS="OPTIONAL"
>VALIDATOR <TT
CLASS="REPLACEABLE"
><I
>validator_function_name</I
></TT
></SPAN
>] ;</PRE
><P>
The optional key word <TT
CLASS="LITERAL"
>TRUSTED</TT
> specifies that
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 <TT
CLASS="LITERAL"
>TRUSTED</TT
> flag should only be given
for languages that do not allow access to database server
internals or the file system. The languages
<SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
>,
<SPAN
CLASS="APPLICATION"
>PL/Tcl</SPAN
>, and
<SPAN
CLASS="APPLICATION"
>PL/Perl</SPAN
>
are considered trusted; the languages
<SPAN
CLASS="APPLICATION"
>PL/TclU</SPAN
>,
<SPAN
CLASS="APPLICATION"
>PL/PerlU</SPAN
>, and
<SPAN
CLASS="APPLICATION"
>PL/PythonU</SPAN
>
are designed to provide unlimited functionality and should
<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>not</I
></SPAN
> be marked trusted.
</P
></LI
></OL
></DIV
><P
> <A
HREF="xplang-install.html#XPLANG-INSTALL-EXAMPLE"
>Example 37-1</A
> shows how the manual
installation procedure would work with the language
<SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
>.
</P
><DIV
CLASS="EXAMPLE"
><A
NAME="XPLANG-INSTALL-EXAMPLE"
></A
><P
><B
>Example 37-1. Manual Installation of <SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
></B
></P
><P
> The following command tells the database server where to find the
shared object for the <SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
> language's call handler function.
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FUNCTION plpgsql_call_handler() RETURNS language_handler AS
'$libdir/plpgsql' LANGUAGE C;</PRE
><P>
</P
><P
> <SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
> has a validator function,
so we declare that too:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FUNCTION plpgsql_validator(oid) RETURNS void AS
'$libdir/plpgsql' LANGUAGE C;</PRE
><P>
</P
><P
> The command:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE TRUSTED PROCEDURAL LANGUAGE plpgsql
HANDLER plpgsql_call_handler
VALIDATOR plpgsql_validator;</PRE
><P>
then defines that the previously declared functions
should be invoked for functions and trigger procedures where the
language attribute is <TT
CLASS="LITERAL"
>plpgsql</TT
>.
</P
></DIV
><P
> In a default <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> installation,
the handler for the <SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
> language
is built and installed into the <SPAN
CLASS="QUOTE"
>"library"</SPAN
>
directory. If <SPAN
CLASS="APPLICATION"
>Tcl</SPAN
> support is configured in, the handlers
for <SPAN
CLASS="APPLICATION"
>PL/Tcl</SPAN
> and <SPAN
CLASS="APPLICATION"
>PL/TclU</SPAN
> are also built and
installed in the same location. Likewise, the <SPAN
CLASS="APPLICATION"
>PL/Perl</SPAN
> and
<SPAN
CLASS="APPLICATION"
>PL/PerlU</SPAN
> handlers are built and installed if Perl support
is configured, and the <SPAN
CLASS="APPLICATION"
>PL/PythonU</SPAN
> handler is
installed if Python support is configured.
</P
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