mirror of
https://github.com/postgres/postgres.git
synced 2025-05-20 05:13:53 +03:00
3a9d430af5
The main problem is that DocBook SGML allows indexterm elements just
about everywhere, but DocBook XML is stricter. For example, this common
pattern
<varlistentry>
<indexterm>...</indexterm>
<term>...</term>
...
</varlistentry>
needs to be changed to something like
<varlistentry>
<term>...<indexterm>...</indexterm></term>
...
</varlistentry>
See also bb4eefe7bf518e42c73797ea37b033a5d8a8e70a.
There is currently nothing in the build system that enforces that things
stay valid, because that requires additional tools and will receive
separate consideration.
1476 lines
50 KiB
Plaintext
1476 lines
50 KiB
Plaintext
<!-- doc/src/sgml/plperl.sgml -->
|
|
|
|
<chapter id="plperl">
|
|
<title>PL/Perl - Perl Procedural Language</title>
|
|
|
|
<indexterm zone="plperl">
|
|
<primary>PL/Perl</primary>
|
|
</indexterm>
|
|
|
|
<indexterm zone="plperl">
|
|
<primary>Perl</primary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
PL/Perl is a loadable procedural language that enables you to write
|
|
<productname>PostgreSQL</productname> functions in the
|
|
<ulink url="http://www.perl.org">Perl programming language</ulink>.
|
|
</para>
|
|
|
|
<para>
|
|
The main advantage to using PL/Perl is that this allows use,
|
|
within stored functions, of the manyfold <quote>string
|
|
munging</quote> operators and functions available for Perl. Parsing
|
|
complex strings might be easier using Perl than it is with the
|
|
string functions and control structures provided in PL/pgSQL.
|
|
</para>
|
|
|
|
<para>
|
|
To install PL/Perl in a particular database, use
|
|
<literal>CREATE EXTENSION plperl</>, or from the shell command line use
|
|
<literal>createlang plperl <replaceable>dbname</></literal>.
|
|
</para>
|
|
|
|
<tip>
|
|
<para>
|
|
If a language is installed into <literal>template1</>, all subsequently
|
|
created databases will have the language installed automatically.
|
|
</para>
|
|
</tip>
|
|
|
|
<note>
|
|
<para>
|
|
Users of source packages must specially enable the build of
|
|
PL/Perl during the installation process. (Refer to <xref
|
|
linkend="installation"> for more information.) Users of
|
|
binary packages might find PL/Perl in a separate subpackage.
|
|
</para>
|
|
</note>
|
|
|
|
<sect1 id="plperl-funcs">
|
|
<title>PL/Perl Functions and Arguments</title>
|
|
|
|
<para>
|
|
To create a function in the PL/Perl language, use the standard
|
|
<xref linkend="sql-createfunction">
|
|
syntax:
|
|
|
|
<programlisting>
|
|
CREATE FUNCTION <replaceable>funcname</replaceable> (<replaceable>argument-types</replaceable>) RETURNS <replaceable>return-type</replaceable> AS $$
|
|
# PL/Perl function body
|
|
$$ LANGUAGE plperl;
|
|
</programlisting>
|
|
|
|
The body of the function is ordinary Perl code. In fact, the PL/Perl
|
|
glue code wraps it inside a Perl subroutine. A PL/Perl function is
|
|
called in a scalar context, so it can't return a list. You can return
|
|
non-scalar values (arrays, records, and sets) by returning a reference,
|
|
as discussed below.
|
|
</para>
|
|
|
|
<para>
|
|
PL/Perl also supports anonymous code blocks called with the
|
|
<xref linkend="sql-do"> statement:
|
|
|
|
<programlisting>
|
|
DO $$
|
|
# PL/Perl code
|
|
$$ LANGUAGE plperl;
|
|
</programlisting>
|
|
|
|
An anonymous code block receives no arguments, and whatever value it
|
|
might return is discarded. Otherwise it behaves just like a function.
|
|
</para>
|
|
|
|
<note>
|
|
<para>
|
|
The use of named nested subroutines is dangerous in Perl, especially if
|
|
they refer to lexical variables in the enclosing scope. Because a PL/Perl
|
|
function is wrapped in a subroutine, any named subroutine you place inside
|
|
one will be nested. In general, it is far safer to create anonymous
|
|
subroutines which you call via a coderef. For more information, see the
|
|
entries for <literal>Variable "%s" will not stay shared</literal> and
|
|
<literal>Variable "%s" is not available</literal> in the
|
|
<citerefentry><refentrytitle>perldiag</></citerefentry> man page, or
|
|
search the Internet for <quote>perl nested named subroutine</>.
|
|
</para>
|
|
</note>
|
|
|
|
<para>
|
|
The syntax of the <command>CREATE FUNCTION</command> command requires
|
|
the function body to be written as a string constant. It is usually
|
|
most convenient to use dollar quoting (see <xref
|
|
linkend="sql-syntax-dollar-quoting">) for the string constant.
|
|
If you choose to use escape string syntax <literal>E''</>,
|
|
you must double any single quote marks (<literal>'</>) and backslashes
|
|
(<literal>\</>) used in the body of the function
|
|
(see <xref linkend="sql-syntax-strings">).
|
|
</para>
|
|
|
|
<para>
|
|
Arguments and results are handled as in any other Perl subroutine:
|
|
arguments are passed in <varname>@_</varname>, and a result value
|
|
is returned with <literal>return</> or as the last expression
|
|
evaluated in the function.
|
|
</para>
|
|
|
|
<para>
|
|
For example, a function returning the greater of two integer values
|
|
could be defined as:
|
|
|
|
<programlisting>
|
|
CREATE FUNCTION perl_max (integer, integer) RETURNS integer AS $$
|
|
if ($_[0] > $_[1]) { return $_[0]; }
|
|
return $_[1];
|
|
$$ LANGUAGE plperl;
|
|
</programlisting>
|
|
</para>
|
|
|
|
<note>
|
|
<para>
|
|
Arguments will be converted from the database's encoding to UTF-8
|
|
for use inside PL/Perl, and then converted from UTF-8 back to the
|
|
database encoding upon return.
|
|
</para>
|
|
</note>
|
|
|
|
<para>
|
|
If an SQL null value<indexterm><primary>null value</><secondary
|
|
sortas="PL/Perl">in PL/Perl</></indexterm> is passed to a function,
|
|
the argument value will appear as <quote>undefined</> in Perl. The
|
|
above function definition will not behave very nicely with null
|
|
inputs (in fact, it will act as though they are zeroes). We could
|
|
add <literal>STRICT</> to the function definition to make
|
|
<productname>PostgreSQL</productname> do something more reasonable:
|
|
if a null value is passed, the function will not be called at all,
|
|
but will just return a null result automatically. Alternatively,
|
|
we could check for undefined inputs in the function body. For
|
|
example, suppose that we wanted <function>perl_max</function> with
|
|
one null and one nonnull argument to return the nonnull argument,
|
|
rather than a null value:
|
|
|
|
<programlisting>
|
|
CREATE FUNCTION perl_max (integer, integer) RETURNS integer AS $$
|
|
my ($x, $y) = @_;
|
|
if (not defined $x) {
|
|
return undef if not defined $y;
|
|
return $y;
|
|
}
|
|
return $x if not defined $y;
|
|
return $x if $x > $y;
|
|
return $y;
|
|
$$ LANGUAGE plperl;
|
|
</programlisting>
|
|
As shown above, to return an SQL null value from a PL/Perl
|
|
function, return an undefined value. This can be done whether the
|
|
function is strict or not.
|
|
</para>
|
|
|
|
<para>
|
|
Anything in a function argument that is not a reference is
|
|
a string, which is in the standard <productname>PostgreSQL</productname>
|
|
external text representation for the relevant data type. In the case of
|
|
ordinary numeric or text types, Perl will just do the right thing and
|
|
the programmer will normally not have to worry about it. However, in
|
|
other cases the argument will need to be converted into a form that is
|
|
more usable in Perl. For example, the <function>decode_bytea</function>
|
|
function can be used to convert an argument of
|
|
type <type>bytea</> into unescaped binary.
|
|
</para>
|
|
|
|
<para>
|
|
Similarly, values passed back to <productname>PostgreSQL</productname>
|
|
must be in the external text representation format. For example, the
|
|
<function>encode_bytea</function> function can be used to
|
|
escape binary data for a return value of type <type>bytea</>.
|
|
</para>
|
|
|
|
<para>
|
|
Perl can return <productname>PostgreSQL</productname> arrays as
|
|
references to Perl arrays. Here is an example:
|
|
|
|
<programlisting>
|
|
CREATE OR REPLACE function returns_array()
|
|
RETURNS text[][] AS $$
|
|
return [['a"b','c,d'],['e\\f','g']];
|
|
$$ LANGUAGE plperl;
|
|
|
|
select returns_array();
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
Perl passes <productname>PostgreSQL</productname> arrays as a blessed
|
|
<type>PostgreSQL::InServer::ARRAY</type> object. This object may be treated as an array
|
|
reference or a string, allowing for backward compatibility with Perl
|
|
code written for <productname>PostgreSQL</productname> versions below 9.1 to
|
|
run. For example:
|
|
|
|
<programlisting>
|
|
CREATE OR REPLACE FUNCTION concat_array_elements(text[]) RETURNS TEXT AS $$
|
|
my $arg = shift;
|
|
my $result = "";
|
|
return undef if (!defined $arg);
|
|
|
|
# as an array reference
|
|
for (@$arg) {
|
|
$result .= $_;
|
|
}
|
|
|
|
# also works as a string
|
|
$result .= $arg;
|
|
|
|
return $result;
|
|
$$ LANGUAGE plperl;
|
|
|
|
SELECT concat_array_elements(ARRAY['PL','/','Perl']);
|
|
</programlisting>
|
|
|
|
<note>
|
|
<para>
|
|
Multidimensional arrays are represented as references to
|
|
lower-dimensional arrays of references in a way common to every Perl
|
|
programmer.
|
|
</para>
|
|
</note>
|
|
</para>
|
|
|
|
<para>
|
|
Composite-type arguments are passed to the function as references
|
|
to hashes. The keys of the hash are the attribute names of the
|
|
composite type. Here is an example:
|
|
|
|
<programlisting>
|
|
CREATE TABLE employee (
|
|
name text,
|
|
basesalary integer,
|
|
bonus integer
|
|
);
|
|
|
|
CREATE FUNCTION empcomp(employee) RETURNS integer AS $$
|
|
my ($emp) = @_;
|
|
return $emp->{basesalary} + $emp->{bonus};
|
|
$$ LANGUAGE plperl;
|
|
|
|
SELECT name, empcomp(employee.*) FROM employee;
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
A PL/Perl function can return a composite-type result using the same
|
|
approach: return a reference to a hash that has the required attributes.
|
|
For example:
|
|
|
|
<programlisting>
|
|
CREATE TYPE testrowperl AS (f1 integer, f2 text, f3 text);
|
|
|
|
CREATE OR REPLACE FUNCTION perl_row() RETURNS testrowperl AS $$
|
|
return {f2 => 'hello', f1 => 1, f3 => 'world'};
|
|
$$ LANGUAGE plperl;
|
|
|
|
SELECT * FROM perl_row();
|
|
</programlisting>
|
|
|
|
Any columns in the declared result data type that are not present in the
|
|
hash will be returned as null values.
|
|
</para>
|
|
|
|
<para>
|
|
PL/Perl functions can also return sets of either scalar or
|
|
composite types. Usually you'll want to return rows one at a
|
|
time, both to speed up startup time and to keep from queuing up
|
|
the entire result set in memory. You can do this with
|
|
<function>return_next</function> as illustrated below. Note that
|
|
after the last <function>return_next</function>, you must put
|
|
either <literal>return</literal> or (better) <literal>return
|
|
undef</literal>.
|
|
|
|
<programlisting>
|
|
CREATE OR REPLACE FUNCTION perl_set_int(int)
|
|
RETURNS SETOF INTEGER AS $$
|
|
foreach (0..$_[0]) {
|
|
return_next($_);
|
|
}
|
|
return undef;
|
|
$$ LANGUAGE plperl;
|
|
|
|
SELECT * FROM perl_set_int(5);
|
|
|
|
CREATE OR REPLACE FUNCTION perl_set()
|
|
RETURNS SETOF testrowperl AS $$
|
|
return_next({ f1 => 1, f2 => 'Hello', f3 => 'World' });
|
|
return_next({ f1 => 2, f2 => 'Hello', f3 => 'PostgreSQL' });
|
|
return_next({ f1 => 3, f2 => 'Hello', f3 => 'PL/Perl' });
|
|
return undef;
|
|
$$ LANGUAGE plperl;
|
|
</programlisting>
|
|
|
|
For small result sets, you can return a reference to an array that
|
|
contains either scalars, references to arrays, or references to
|
|
hashes for simple types, array types, and composite types,
|
|
respectively. Here are some simple examples of returning the entire
|
|
result set as an array reference:
|
|
|
|
<programlisting>
|
|
CREATE OR REPLACE FUNCTION perl_set_int(int) RETURNS SETOF INTEGER AS $$
|
|
return [0..$_[0]];
|
|
$$ LANGUAGE plperl;
|
|
|
|
SELECT * FROM perl_set_int(5);
|
|
|
|
CREATE OR REPLACE FUNCTION perl_set() RETURNS SETOF testrowperl AS $$
|
|
return [
|
|
{ f1 => 1, f2 => 'Hello', f3 => 'World' },
|
|
{ f1 => 2, f2 => 'Hello', f3 => 'PostgreSQL' },
|
|
{ f1 => 3, f2 => 'Hello', f3 => 'PL/Perl' }
|
|
];
|
|
$$ LANGUAGE plperl;
|
|
|
|
SELECT * FROM perl_set();
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
If you wish to use the <literal>strict</> pragma with your code you
|
|
have a few options. For temporary global use you can <command>SET</>
|
|
<literal>plperl.use_strict</literal> to true.
|
|
This will affect subsequent compilations of <application>PL/Perl</>
|
|
functions, but not functions already compiled in the current session.
|
|
For permanent global use you can set <literal>plperl.use_strict</literal>
|
|
to true in the <filename>postgresql.conf</filename> file.
|
|
</para>
|
|
|
|
<para>
|
|
For permanent use in specific functions you can simply put:
|
|
<programlisting>
|
|
use strict;
|
|
</programlisting>
|
|
at the top of the function body.
|
|
</para>
|
|
|
|
<para>
|
|
The <literal>feature</> pragma is also available to <function>use</> if your Perl is version 5.10.0 or higher.
|
|
</para>
|
|
|
|
</sect1>
|
|
|
|
<sect1 id="plperl-data">
|
|
<title>Data Values in PL/Perl</title>
|
|
|
|
<para>
|
|
The argument values supplied to a PL/Perl function's code are
|
|
simply the input arguments converted to text form (just as if they
|
|
had been displayed by a <command>SELECT</command> statement).
|
|
Conversely, the <function>return</function> and <function>return_next</function>
|
|
commands will accept any string that is acceptable input format
|
|
for the function's declared return type.
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="plperl-builtins">
|
|
<title>Built-in Functions</title>
|
|
|
|
<sect2 id="plperl-database">
|
|
<title>Database Access from PL/Perl</title>
|
|
|
|
<para>
|
|
Access to the database itself from your Perl function can be done
|
|
via the following functions:
|
|
</para>
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>
|
|
<literal><function>spi_exec_query</>(<replaceable>query</replaceable> [, <replaceable>max-rows</replaceable>])</literal>
|
|
<indexterm>
|
|
<primary>spi_exec_query</primary>
|
|
<secondary>in PL/Perl</secondary>
|
|
</indexterm>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
<literal>spi_exec_query</literal> executes an SQL command and
|
|
returns the entire row set as a reference to an array of hash
|
|
references. <emphasis>You should only use this command when you know
|
|
that the result set will be relatively small.</emphasis> Here is an
|
|
example of a query (<command>SELECT</command> command) with the
|
|
optional maximum number of rows:
|
|
|
|
<programlisting>
|
|
$rv = spi_exec_query('SELECT * FROM my_table', 5);
|
|
</programlisting>
|
|
This returns up to 5 rows from the table
|
|
<literal>my_table</literal>. If <literal>my_table</literal>
|
|
has a column <literal>my_column</literal>, you can get that
|
|
value from row <literal>$i</literal> of the result like this:
|
|
<programlisting>
|
|
$foo = $rv->{rows}[$i]->{my_column};
|
|
</programlisting>
|
|
The total number of rows returned from a <command>SELECT</command>
|
|
query can be accessed like this:
|
|
<programlisting>
|
|
$nrows = $rv->{processed}
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
Here is an example using a different command type:
|
|
<programlisting>
|
|
$query = "INSERT INTO my_table VALUES (1, 'test')";
|
|
$rv = spi_exec_query($query);
|
|
</programlisting>
|
|
You can then access the command status (e.g.,
|
|
<literal>SPI_OK_INSERT</literal>) like this:
|
|
<programlisting>
|
|
$res = $rv->{status};
|
|
</programlisting>
|
|
To get the number of rows affected, do:
|
|
<programlisting>
|
|
$nrows = $rv->{processed};
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
Here is a complete example:
|
|
<programlisting>
|
|
CREATE TABLE test (
|
|
i int,
|
|
v varchar
|
|
);
|
|
|
|
INSERT INTO test (i, v) VALUES (1, 'first line');
|
|
INSERT INTO test (i, v) VALUES (2, 'second line');
|
|
INSERT INTO test (i, v) VALUES (3, 'third line');
|
|
INSERT INTO test (i, v) VALUES (4, 'immortal');
|
|
|
|
CREATE OR REPLACE FUNCTION test_munge() RETURNS SETOF test AS $$
|
|
my $rv = spi_exec_query('select i, v from test;');
|
|
my $status = $rv->{status};
|
|
my $nrows = $rv->{processed};
|
|
foreach my $rn (0 .. $nrows - 1) {
|
|
my $row = $rv->{rows}[$rn];
|
|
$row->{i} += 200 if defined($row->{i});
|
|
$row->{v} =~ tr/A-Za-z/a-zA-Z/ if (defined($row->{v}));
|
|
return_next($row);
|
|
}
|
|
return undef;
|
|
$$ LANGUAGE plperl;
|
|
|
|
SELECT * FROM test_munge();
|
|
</programlisting>
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>
|
|
<literal><function>spi_query(<replaceable>command</replaceable>)</function></literal>
|
|
<indexterm>
|
|
<primary>spi_query</primary>
|
|
<secondary>in PL/Perl</secondary>
|
|
</indexterm>
|
|
</term>
|
|
<term>
|
|
<literal><function>spi_fetchrow(<replaceable>cursor</replaceable>)</function></literal>
|
|
<indexterm>
|
|
<primary>spi_fetchrow</primary>
|
|
<secondary>in PL/Perl</secondary>
|
|
</indexterm>
|
|
</term>
|
|
<term>
|
|
<literal><function>spi_cursor_close(<replaceable>cursor</replaceable>)</function></literal>
|
|
<indexterm>
|
|
<primary>spi_cursor_close</primary>
|
|
<secondary>in PL/Perl</secondary>
|
|
</indexterm>
|
|
</term>
|
|
|
|
<listitem>
|
|
<para>
|
|
<literal>spi_query</literal> and <literal>spi_fetchrow</literal>
|
|
work together as a pair for row sets which might be large, or for cases
|
|
where you wish to return rows as they arrive.
|
|
<literal>spi_fetchrow</literal> works <emphasis>only</emphasis> with
|
|
<literal>spi_query</literal>. The following example illustrates how
|
|
you use them together:
|
|
|
|
<programlisting>
|
|
CREATE TYPE foo_type AS (the_num INTEGER, the_text TEXT);
|
|
|
|
CREATE OR REPLACE FUNCTION lotsa_md5 (INTEGER) RETURNS SETOF foo_type AS $$
|
|
use Digest::MD5 qw(md5_hex);
|
|
my $file = '/usr/share/dict/words';
|
|
my $t = localtime;
|
|
elog(NOTICE, "opening file $file at $t" );
|
|
open my $fh, '<', $file # ooh, it's a file access!
|
|
or elog(ERROR, "cannot open $file for reading: $!");
|
|
my @words = <$fh>;
|
|
close $fh;
|
|
$t = localtime;
|
|
elog(NOTICE, "closed file $file at $t");
|
|
chomp(@words);
|
|
my $row;
|
|
my $sth = spi_query("SELECT * FROM generate_series(1,$_[0]) AS b(a)");
|
|
while (defined ($row = spi_fetchrow($sth))) {
|
|
return_next({
|
|
the_num => $row->{a},
|
|
the_text => md5_hex($words[rand @words])
|
|
});
|
|
}
|
|
return;
|
|
$$ LANGUAGE plperlu;
|
|
|
|
SELECT * from lotsa_md5(500);
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
Normally, <function>spi_fetchrow</> should be repeated until it
|
|
returns <literal>undef</literal>, indicating that there are no more
|
|
rows to read. The cursor returned by <literal>spi_query</literal>
|
|
is automatically freed when
|
|
<function>spi_fetchrow</> returns <literal>undef</literal>.
|
|
If you do not wish to read all the rows, instead call
|
|
<function>spi_cursor_close</> to free the cursor.
|
|
Failure to do so will result in memory leaks.
|
|
</para>
|
|
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>
|
|
<literal><function>spi_prepare(<replaceable>command</replaceable>, <replaceable>argument types</replaceable>)</function></literal>
|
|
<indexterm>
|
|
<primary>spi_prepare</primary>
|
|
<secondary>in PL/Perl</secondary>
|
|
</indexterm>
|
|
</term>
|
|
<term>
|
|
<literal><function>spi_query_prepared(<replaceable>plan</replaceable>, <replaceable>arguments</replaceable>)</function></literal>
|
|
<indexterm>
|
|
<primary>spi_query_prepared</primary>
|
|
<secondary>in PL/Perl</secondary>
|
|
</indexterm>
|
|
</term>
|
|
<term>
|
|
<literal><function>spi_exec_prepared(<replaceable>plan</replaceable> [, <replaceable>attributes</replaceable>], <replaceable>arguments</replaceable>)</function></literal>
|
|
<indexterm>
|
|
<primary>spi_exec_prepared</primary>
|
|
<secondary>in PL/Perl</secondary>
|
|
</indexterm>
|
|
</term>
|
|
<term>
|
|
<literal><function>spi_freeplan(<replaceable>plan</replaceable>)</function></literal>
|
|
<indexterm>
|
|
<primary>spi_freeplan</primary>
|
|
<secondary>in PL/Perl</secondary>
|
|
</indexterm>
|
|
</term>
|
|
|
|
<listitem>
|
|
<para>
|
|
<literal>spi_prepare</literal>, <literal>spi_query_prepared</literal>, <literal>spi_exec_prepared</literal>,
|
|
and <literal>spi_freeplan</literal> implement the same functionality but for prepared queries.
|
|
<literal>spi_prepare</literal> accepts a query string with numbered argument placeholders ($1, $2, etc)
|
|
and a string list of argument types:
|
|
<programlisting>
|
|
$plan = spi_prepare('SELECT * FROM test WHERE id > $1 AND name = $2',
|
|
'INTEGER', 'TEXT');
|
|
</programlisting>
|
|
Once a query plan is prepared by a call to <literal>spi_prepare</literal>, the plan can be used instead
|
|
of the string query, either in <literal>spi_exec_prepared</literal>, where the result is the same as returned
|
|
by <literal>spi_exec_query</literal>, or in <literal>spi_query_prepared</literal> which returns a cursor
|
|
exactly as <literal>spi_query</literal> does, which can be later passed to <literal>spi_fetchrow</literal>.
|
|
The optional second parameter to <literal>spi_exec_prepared</literal> is a hash reference of attributes;
|
|
the only attribute currently supported is <literal>limit</literal>, which sets the maximum number of rows returned by a query.
|
|
</para>
|
|
|
|
<para>
|
|
The advantage of prepared queries is that is it possible to use one prepared plan for more
|
|
than one query execution. After the plan is not needed anymore, it can be freed with
|
|
<literal>spi_freeplan</literal>:
|
|
<programlisting>
|
|
CREATE OR REPLACE FUNCTION init() RETURNS VOID AS $$
|
|
$_SHARED{my_plan} = spi_prepare('SELECT (now() + $1)::date AS now',
|
|
'INTERVAL');
|
|
$$ LANGUAGE plperl;
|
|
|
|
CREATE OR REPLACE FUNCTION add_time( INTERVAL ) RETURNS TEXT AS $$
|
|
return spi_exec_prepared(
|
|
$_SHARED{my_plan},
|
|
$_[0]
|
|
)->{rows}->[0]->{now};
|
|
$$ LANGUAGE plperl;
|
|
|
|
CREATE OR REPLACE FUNCTION done() RETURNS VOID AS $$
|
|
spi_freeplan( $_SHARED{my_plan});
|
|
undef $_SHARED{my_plan};
|
|
$$ LANGUAGE plperl;
|
|
|
|
SELECT init();
|
|
SELECT add_time('1 day'), add_time('2 days'), add_time('3 days');
|
|
SELECT done();
|
|
|
|
add_time | add_time | add_time
|
|
------------+------------+------------
|
|
2005-12-10 | 2005-12-11 | 2005-12-12
|
|
</programlisting>
|
|
Note that the parameter subscript in <literal>spi_prepare</literal> is defined via
|
|
$1, $2, $3, etc, so avoid declaring query strings in double quotes that might easily
|
|
lead to hard-to-catch bugs.
|
|
</para>
|
|
|
|
<para>
|
|
Another example illustrates usage of an optional parameter in <literal>spi_exec_prepared</literal>:
|
|
<programlisting>
|
|
CREATE TABLE hosts AS SELECT id, ('192.168.1.'||id)::inet AS address
|
|
FROM generate_series(1,3) AS id;
|
|
|
|
CREATE OR REPLACE FUNCTION init_hosts_query() RETURNS VOID AS $$
|
|
$_SHARED{plan} = spi_prepare('SELECT * FROM hosts
|
|
WHERE address << $1', 'inet');
|
|
$$ LANGUAGE plperl;
|
|
|
|
CREATE OR REPLACE FUNCTION query_hosts(inet) RETURNS SETOF hosts AS $$
|
|
return spi_exec_prepared(
|
|
$_SHARED{plan},
|
|
{limit => 2},
|
|
$_[0]
|
|
)->{rows};
|
|
$$ LANGUAGE plperl;
|
|
|
|
CREATE OR REPLACE FUNCTION release_hosts_query() RETURNS VOID AS $$
|
|
spi_freeplan($_SHARED{plan});
|
|
undef $_SHARED{plan};
|
|
$$ LANGUAGE plperl;
|
|
|
|
SELECT init_hosts_query();
|
|
SELECT query_hosts('192.168.1.0/30');
|
|
SELECT release_hosts_query();
|
|
|
|
query_hosts
|
|
-----------------
|
|
(1,192.168.1.1)
|
|
(2,192.168.1.2)
|
|
(2 rows)
|
|
</programlisting>
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</sect2>
|
|
|
|
<sect2 id="plperl-utility-functions">
|
|
<title>Utility Functions in PL/Perl</title>
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>
|
|
<literal><function>elog(<replaceable>level</replaceable>, <replaceable>msg</replaceable>)</function></literal>
|
|
<indexterm>
|
|
<primary>elog</primary>
|
|
<secondary>in PL/Perl</secondary>
|
|
</indexterm>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
Emit a log or error message. Possible levels are
|
|
<literal>DEBUG</>, <literal>LOG</>, <literal>INFO</>,
|
|
<literal>NOTICE</>, <literal>WARNING</>, and <literal>ERROR</>.
|
|
<literal>ERROR</>
|
|
raises an error condition; if this is not trapped by the surrounding
|
|
Perl code, the error propagates out to the calling query, causing
|
|
the current transaction or subtransaction to be aborted. This
|
|
is effectively the same as the Perl <literal>die</> command.
|
|
The other levels only generate messages of different
|
|
priority levels.
|
|
Whether messages of a particular priority are reported to the client,
|
|
written to the server log, or both is controlled by the
|
|
<xref linkend="guc-log-min-messages"> and
|
|
<xref linkend="guc-client-min-messages"> configuration
|
|
variables. See <xref linkend="runtime-config"> for more
|
|
information.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>
|
|
<literal><function>quote_literal(<replaceable>string</replaceable>)</function></literal>
|
|
<indexterm>
|
|
<primary>quote_literal</primary>
|
|
<secondary>in PL/Perl</secondary>
|
|
</indexterm>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
Return the given string suitably quoted to be used as a string literal in an SQL
|
|
statement string. Embedded single-quotes and backslashes are properly doubled.
|
|
Note that <function>quote_literal</> returns undef on undef input; if the argument
|
|
might be undef, <function>quote_nullable</> is often more suitable.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>
|
|
<literal><function>quote_nullable(<replaceable>string</replaceable>)</function></literal>
|
|
<indexterm>
|
|
<primary>quote_nullable</primary>
|
|
<secondary>in PL/Perl</secondary>
|
|
</indexterm>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
Return the given string suitably quoted to be used as a string literal in an SQL
|
|
statement string; or, if the argument is undef, return the unquoted string "NULL".
|
|
Embedded single-quotes and backslashes are properly doubled.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>
|
|
<literal><function>quote_ident(<replaceable>string</replaceable>)</function></literal>
|
|
<indexterm>
|
|
<primary>quote_ident</primary>
|
|
<secondary>in PL/Perl</secondary>
|
|
</indexterm>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
Return the given string suitably quoted to be used as an identifier in
|
|
an SQL statement string. Quotes are added only if necessary (i.e., if
|
|
the string contains non-identifier characters or would be case-folded).
|
|
Embedded quotes are properly doubled.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>
|
|
<literal><function>decode_bytea(<replaceable>string</replaceable>)</function></literal>
|
|
<indexterm>
|
|
<primary>decode_bytea</primary>
|
|
<secondary>in PL/Perl</secondary>
|
|
</indexterm>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
Return the unescaped binary data represented by the contents of the given string,
|
|
which should be <type>bytea</type> encoded.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>
|
|
<literal><function>encode_bytea(<replaceable>string</replaceable>)</function></literal>
|
|
<indexterm>
|
|
<primary>encode_bytea</primary>
|
|
<secondary>in PL/Perl</secondary>
|
|
</indexterm>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
Return the <type>bytea</type> encoded form of the binary data contents of the given string.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>
|
|
<literal><function>encode_array_literal(<replaceable>array</replaceable>)</function></literal>
|
|
<indexterm>
|
|
<primary>encode_array_literal</primary>
|
|
<secondary>in PL/Perl</secondary>
|
|
</indexterm>
|
|
</term>
|
|
<term>
|
|
<literal><function>encode_array_literal(<replaceable>array</replaceable>, <replaceable>delimiter</replaceable>)</function></literal>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
Returns the contents of the referenced array as a string in array literal format
|
|
(see <xref linkend="arrays-input">).
|
|
Returns the argument value unaltered if it's not a reference to an array.
|
|
The delimiter used between elements of the array literal defaults to "<literal>, </literal>"
|
|
if a delimiter is not specified or is undef.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>
|
|
<literal><function>encode_typed_literal(<replaceable>value</replaceable>, <replaceable>typename</replaceable>)</function></literal>
|
|
<indexterm>
|
|
<primary>encode_typed_literal</primary>
|
|
<secondary>in PL/Perl</secondary>
|
|
</indexterm>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
Converts a Perl variable to the value of the data type passed as a
|
|
second argument and returns a string representation of this value.
|
|
Correctly handles nested arrays and values of composite types.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>
|
|
<literal><function>encode_array_constructor(<replaceable>array</replaceable>)</function></literal>
|
|
<indexterm>
|
|
<primary>encode_array_constructor</primary>
|
|
<secondary>in PL/Perl</secondary>
|
|
</indexterm>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
Returns the contents of the referenced array as a string in array constructor format
|
|
(see <xref linkend="sql-syntax-array-constructors">).
|
|
Individual values are quoted using <function>quote_nullable</function>.
|
|
Returns the argument value, quoted using <function>quote_nullable</function>,
|
|
if it's not a reference to an array.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>
|
|
<literal><function>looks_like_number(<replaceable>string</replaceable>)</function></literal>
|
|
<indexterm>
|
|
<primary>looks_like_number</primary>
|
|
<secondary>in PL/Perl</secondary>
|
|
</indexterm>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
Returns a true value if the content of the given string looks like a
|
|
number, according to Perl, returns false otherwise.
|
|
Returns undef if the argument is undef. Leading and trailing space is
|
|
ignored. <literal>Inf</> and <literal>Infinity</> are regarded as numbers.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>
|
|
<literal><function>is_array_ref(<replaceable>argument</replaceable>)</function></literal>
|
|
<indexterm>
|
|
<primary>is_array_ref</primary>
|
|
<secondary>in PL/Perl</secondary>
|
|
</indexterm>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
Returns a true value if the given argument may be treated as an
|
|
array reference, that is, if ref of the argument is <literal>ARRAY</> or
|
|
<literal>PostgreSQL::InServer::ARRAY</>. Returns false otherwise.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
</variablelist>
|
|
</sect2>
|
|
</sect1>
|
|
|
|
<sect1 id="plperl-global">
|
|
<title>Global Values in PL/Perl</title>
|
|
|
|
<para>
|
|
You can use the global hash <varname>%_SHARED</varname> to store
|
|
data, including code references, between function calls for the
|
|
lifetime of the current session.
|
|
</para>
|
|
|
|
<para>
|
|
Here is a simple example for shared data:
|
|
<programlisting>
|
|
CREATE OR REPLACE FUNCTION set_var(name text, val text) RETURNS text AS $$
|
|
if ($_SHARED{$_[0]} = $_[1]) {
|
|
return 'ok';
|
|
} else {
|
|
return "cannot set shared variable $_[0] to $_[1]";
|
|
}
|
|
$$ LANGUAGE plperl;
|
|
|
|
CREATE OR REPLACE FUNCTION get_var(name text) RETURNS text AS $$
|
|
return $_SHARED{$_[0]};
|
|
$$ LANGUAGE plperl;
|
|
|
|
SELECT set_var('sample', 'Hello, PL/Perl! How''s tricks?');
|
|
SELECT get_var('sample');
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
Here is a slightly more complicated example using a code reference:
|
|
|
|
<programlisting>
|
|
CREATE OR REPLACE FUNCTION myfuncs() RETURNS void AS $$
|
|
$_SHARED{myquote} = sub {
|
|
my $arg = shift;
|
|
$arg =~ s/(['\\])/\\$1/g;
|
|
return "'$arg'";
|
|
};
|
|
$$ LANGUAGE plperl;
|
|
|
|
SELECT myfuncs(); /* initializes the function */
|
|
|
|
/* Set up a function that uses the quote function */
|
|
|
|
CREATE OR REPLACE FUNCTION use_quote(TEXT) RETURNS text AS $$
|
|
my $text_to_quote = shift;
|
|
my $qfunc = $_SHARED{myquote};
|
|
return &$qfunc($text_to_quote);
|
|
$$ LANGUAGE plperl;
|
|
</programlisting>
|
|
|
|
(You could have replaced the above with the one-liner
|
|
<literal>return $_SHARED{myquote}->($_[0]);</literal>
|
|
at the expense of readability.)
|
|
</para>
|
|
|
|
<para>
|
|
For security reasons, PL/Perl executes functions called by any one SQL role
|
|
in a separate Perl interpreter for that role. This prevents accidental or
|
|
malicious interference by one user with the behavior of another user's
|
|
PL/Perl functions. Each such interpreter has its own value of the
|
|
<varname>%_SHARED</varname> variable and other global state. Thus, two
|
|
PL/Perl functions will share the same value of <varname>%_SHARED</varname>
|
|
if and only if they are executed by the same SQL role. In an application
|
|
wherein a single session executes code under multiple SQL roles (via
|
|
<literal>SECURITY DEFINER</> functions, use of <command>SET ROLE</>, etc)
|
|
you may need to take explicit steps to ensure that PL/Perl functions can
|
|
share data via <varname>%_SHARED</varname>. To do that, make sure that
|
|
functions that should communicate are owned by the same user, and mark
|
|
them <literal>SECURITY DEFINER</>. You must of course take care that
|
|
such functions can't be used to do anything unintended.
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="plperl-trusted">
|
|
<title>Trusted and Untrusted PL/Perl</title>
|
|
|
|
<indexterm zone="plperl-trusted">
|
|
<primary>trusted</primary>
|
|
<secondary>PL/Perl</secondary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
Normally, PL/Perl is installed as a <quote>trusted</> programming
|
|
language named <literal>plperl</>. In this setup, certain Perl
|
|
operations are disabled to preserve security. In general, the
|
|
operations that are restricted are those that interact with the
|
|
environment. This includes file handle operations,
|
|
<literal>require</literal>, and <literal>use</literal> (for
|
|
external modules). There is no way to access internals of the
|
|
database server process or to gain OS-level access with the
|
|
permissions of the server process,
|
|
as a C function can do. Thus, any unprivileged database user can
|
|
be permitted to use this language.
|
|
</para>
|
|
|
|
<para>
|
|
Here is an example of a function that will not work because file
|
|
system operations are not allowed for security reasons:
|
|
<programlisting>
|
|
CREATE FUNCTION badfunc() RETURNS integer AS $$
|
|
my $tmpfile = "/tmp/badfile";
|
|
open my $fh, '>', $tmpfile
|
|
or elog(ERROR, qq{could not open the file "$tmpfile": $!});
|
|
print $fh "Testing writing to a file\n";
|
|
close $fh or elog(ERROR, qq{could not close the file "$tmpfile": $!});
|
|
return 1;
|
|
$$ LANGUAGE plperl;
|
|
</programlisting>
|
|
The creation of this function will fail as its use of a forbidden
|
|
operation will be caught by the validator.
|
|
</para>
|
|
|
|
<para>
|
|
Sometimes it is desirable to write Perl functions that are not
|
|
restricted. For example, one might want a Perl function that sends
|
|
mail. To handle these cases, PL/Perl can also be installed as an
|
|
<quote>untrusted</> language (usually called
|
|
<application>PL/PerlU</application><indexterm><primary>PL/PerlU</></indexterm>).
|
|
In this case the full Perl language is available. When installing the
|
|
language, the language name <literal>plperlu</literal> will select
|
|
the untrusted PL/Perl variant.
|
|
</para>
|
|
|
|
<para>
|
|
The writer of a <application>PL/PerlU</> function must take care that the function
|
|
cannot be used to do anything unwanted, since it will be able to do
|
|
anything that could be done by a user logged in as the database
|
|
administrator. Note that the database system allows only database
|
|
superusers to create functions in untrusted languages.
|
|
</para>
|
|
|
|
<para>
|
|
If the above function was created by a superuser using the language
|
|
<literal>plperlu</>, execution would succeed.
|
|
</para>
|
|
|
|
<para>
|
|
In the same way, anonymous code blocks written in Perl can use
|
|
restricted operations if the language is specified as
|
|
<literal>plperlu</> rather than <literal>plperl</>, but the caller
|
|
must be a superuser.
|
|
</para>
|
|
|
|
<note>
|
|
<para>
|
|
While <application>PL/Perl</> functions run in a separate Perl
|
|
interpreter for each SQL role, all <application>PL/PerlU</> functions
|
|
executed in a given session run in a single Perl interpreter (which is
|
|
not any of the ones used for <application>PL/Perl</> functions).
|
|
This allows <application>PL/PerlU</> functions to share data freely,
|
|
but no communication can occur between <application>PL/Perl</> and
|
|
<application>PL/PerlU</> functions.
|
|
</para>
|
|
</note>
|
|
|
|
<note>
|
|
<para>
|
|
Perl cannot support multiple interpreters within one process unless
|
|
it was built with the appropriate flags, namely either
|
|
<literal>usemultiplicity</> or <literal>useithreads</>.
|
|
(<literal>usemultiplicity</> is preferred unless you actually need
|
|
to use threads. For more details, see the
|
|
<citerefentry><refentrytitle>perlembed</></citerefentry> man page.)
|
|
If <application>PL/Perl</> is used with a copy of Perl that was not built
|
|
this way, then it is only possible to have one Perl interpreter per
|
|
session, and so any one session can only execute either
|
|
<application>PL/PerlU</> functions, or <application>PL/Perl</> functions
|
|
that are all called by the same SQL role.
|
|
</para>
|
|
</note>
|
|
|
|
</sect1>
|
|
|
|
<sect1 id="plperl-triggers">
|
|
<title>PL/Perl Triggers</title>
|
|
|
|
<para>
|
|
PL/Perl can be used to write trigger functions. In a trigger function,
|
|
the hash reference <varname>$_TD</varname> contains information about the
|
|
current trigger event. <varname>$_TD</> is a global variable,
|
|
which gets a separate local value for each invocation of the trigger.
|
|
The fields of the <varname>$_TD</varname> hash reference are:
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><literal>$_TD->{new}{foo}</literal></term>
|
|
<listitem>
|
|
<para>
|
|
<literal>NEW</literal> value of column <literal>foo</literal>
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>$_TD->{old}{foo}</literal></term>
|
|
<listitem>
|
|
<para>
|
|
<literal>OLD</literal> value of column <literal>foo</literal>
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>$_TD->{name}</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Name of the trigger being called
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>$_TD->{event}</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Trigger event: <literal>INSERT</>, <literal>UPDATE</>,
|
|
<literal>DELETE</>, <literal>TRUNCATE</>, or <literal>UNKNOWN</>
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>$_TD->{when}</literal></term>
|
|
<listitem>
|
|
<para>
|
|
When the trigger was called: <literal>BEFORE</literal>,
|
|
<literal>AFTER</literal>, <literal>INSTEAD OF</literal>, or
|
|
<literal>UNKNOWN</literal>
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>$_TD->{level}</literal></term>
|
|
<listitem>
|
|
<para>
|
|
The trigger level: <literal>ROW</literal>, <literal>STATEMENT</literal>, or <literal>UNKNOWN</literal>
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>$_TD->{relid}</literal></term>
|
|
<listitem>
|
|
<para>
|
|
OID of the table on which the trigger fired
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>$_TD->{table_name}</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Name of the table on which the trigger fired
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>$_TD->{relname}</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Name of the table on which the trigger fired. This has been deprecated,
|
|
and could be removed in a future release.
|
|
Please use $_TD->{table_name} instead.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>$_TD->{table_schema}</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Name of the schema in which the table on which the trigger fired, is
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>$_TD->{argc}</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Number of arguments of the trigger function
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>@{$_TD->{args}}</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Arguments of the trigger function. Does not exist if <literal>$_TD->{argc}</literal> is 0.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
</variablelist>
|
|
</para>
|
|
|
|
<para>
|
|
Row-level triggers can return one of the following:
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><literal>return;</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Execute the operation
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>"SKIP"</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Don't execute the operation
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>"MODIFY"</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Indicates that the <literal>NEW</literal> row was modified by
|
|
the trigger function
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</para>
|
|
|
|
<para>
|
|
Here is an example of a trigger function, illustrating some of the
|
|
above:
|
|
<programlisting>
|
|
CREATE TABLE test (
|
|
i int,
|
|
v varchar
|
|
);
|
|
|
|
CREATE OR REPLACE FUNCTION valid_id() RETURNS trigger AS $$
|
|
if (($_TD->{new}{i} >= 100) || ($_TD->{new}{i} <= 0)) {
|
|
return "SKIP"; # skip INSERT/UPDATE command
|
|
} elsif ($_TD->{new}{v} ne "immortal") {
|
|
$_TD->{new}{v} .= "(modified by trigger)";
|
|
return "MODIFY"; # modify row and execute INSERT/UPDATE command
|
|
} else {
|
|
return; # execute INSERT/UPDATE command
|
|
}
|
|
$$ LANGUAGE plperl;
|
|
|
|
CREATE TRIGGER test_valid_id_trig
|
|
BEFORE INSERT OR UPDATE ON test
|
|
FOR EACH ROW EXECUTE PROCEDURE valid_id();
|
|
</programlisting>
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="plperl-event-triggers">
|
|
<title>PL/Perl Event Triggers</title>
|
|
|
|
<para>
|
|
PL/Perl can be used to write event trigger functions. In an event trigger
|
|
function, the hash reference <varname>$_TD</varname> contains information
|
|
about the current trigger event. <varname>$_TD</> is a global variable,
|
|
which gets a separate local value for each invocation of the trigger. The
|
|
fields of the <varname>$_TD</varname> hash reference are:
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><literal>$_TD->{event}</literal></term>
|
|
<listitem>
|
|
<para>
|
|
The name of the event the trigger is fired for.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>$_TD->{tag}</literal></term>
|
|
<listitem>
|
|
<para>
|
|
The command tag for which the trigger is fired.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</para>
|
|
|
|
<para>
|
|
The return value of the trigger procedure is ignored.
|
|
</para>
|
|
|
|
<para>
|
|
Here is an example of an event trigger function, illustrating some of the
|
|
above:
|
|
<programlisting>
|
|
CREATE OR REPLACE FUNCTION perlsnitch() RETURNS event_trigger AS $$
|
|
elog(NOTICE, "perlsnitch: " . $_TD->{event} . " " . $_TD->{tag} . " ");
|
|
$$ LANGUAGE plperl;
|
|
|
|
CREATE EVENT TRIGGER perl_a_snitch
|
|
ON ddl_command_start
|
|
EXECUTE PROCEDURE perlsnitch();
|
|
</programlisting>
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="plperl-under-the-hood">
|
|
<title>PL/Perl Under the Hood</title>
|
|
|
|
<sect2 id="plperl-config">
|
|
<title>Configuration</title>
|
|
|
|
<para>
|
|
This section lists configuration parameters that affect <application>PL/Perl</>.
|
|
</para>
|
|
|
|
<variablelist>
|
|
|
|
<varlistentry id="guc-plperl-on-init" xreflabel="plperl.on_init">
|
|
<term>
|
|
<varname>plperl.on_init</varname> (<type>string</type>)
|
|
<indexterm>
|
|
<primary><varname>plperl.on_init</> configuration parameter</primary>
|
|
</indexterm>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
Specifies Perl code to be executed when a Perl interpreter is first
|
|
initialized, before it is specialized for use by <literal>plperl</> or
|
|
<literal>plperlu</>.
|
|
The SPI functions are not available when this code is executed.
|
|
If the code fails with an error it will abort the initialization of
|
|
the interpreter and propagate out to the calling query, causing the
|
|
current transaction or subtransaction to be aborted.
|
|
</para>
|
|
<para>
|
|
The Perl code is limited to a single string. Longer code can be placed
|
|
into a module and loaded by the <literal>on_init</> string.
|
|
Examples:
|
|
<programlisting>
|
|
plperl.on_init = 'require "plperlinit.pl"'
|
|
plperl.on_init = 'use lib "/my/app"; use MyApp::PgInit;'
|
|
</programlisting>
|
|
</para>
|
|
<para>
|
|
Any modules loaded by <literal>plperl.on_init</>, either directly or
|
|
indirectly, will be available for use by <literal>plperl</>. This may
|
|
create a security risk. To see what modules have been loaded you can use:
|
|
<programlisting>
|
|
DO 'elog(WARNING, join ", ", sort keys %INC)' LANGUAGE plperl;
|
|
</programlisting>
|
|
</para>
|
|
<para>
|
|
Initialization will happen in the postmaster if the plperl library is
|
|
included in <xref linkend="guc-shared-preload-libraries">, in which
|
|
case extra consideration should be given to the risk of destabilizing
|
|
the postmaster. The principal reason for making use of this feature
|
|
is that Perl modules loaded by <literal>plperl.on_init</> need be
|
|
loaded only at postmaster start, and will be instantly available
|
|
without loading overhead in individual database sessions. However,
|
|
keep in mind that the overhead is avoided only for the first Perl
|
|
interpreter used by a database session — either PL/PerlU, or
|
|
PL/Perl for the first SQL role that calls a PL/Perl function. Any
|
|
additional Perl interpreters created in a database session will have
|
|
to execute <literal>plperl.on_init</> afresh. Also, on Windows there
|
|
will be no savings whatsoever from preloading, since the Perl
|
|
interpreter created in the postmaster process does not propagate to
|
|
child processes.
|
|
</para>
|
|
<para>
|
|
This parameter can only be set in the <filename>postgresql.conf</filename> file or on the server command line.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry id="guc-plperl-on-plperl-init" xreflabel="plperl.on_plperl_init">
|
|
<term>
|
|
<varname>plperl.on_plperl_init</varname> (<type>string</type>)
|
|
<indexterm>
|
|
<primary><varname>plperl.on_plperl_init</> configuration parameter</primary>
|
|
</indexterm>
|
|
</term>
|
|
<term>
|
|
<varname>plperl.on_plperlu_init</varname> (<type>string</type>)
|
|
<indexterm>
|
|
<primary><varname>plperl.on_plperlu_init</> configuration parameter</primary>
|
|
</indexterm>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
These parameters specify Perl code to be executed when a Perl
|
|
interpreter is specialized for <literal>plperl</> or
|
|
<literal>plperlu</> respectively. This will happen when a PL/Perl or
|
|
PL/PerlU function is first executed in a database session, or when
|
|
an additional interpreter has to be created because the other language
|
|
is called or a PL/Perl function is called by a new SQL role. This
|
|
follows any initialization done by <literal>plperl.on_init</>.
|
|
The SPI functions are not available when this code is executed.
|
|
The Perl code in <literal>plperl.on_plperl_init</> is executed after
|
|
<quote>locking down</> the interpreter, and thus it can only perform
|
|
trusted operations.
|
|
</para>
|
|
<para>
|
|
If the code fails with an error it will abort the initialization and
|
|
propagate out to the calling query, causing the current transaction or
|
|
subtransaction to be aborted. Any actions already done within Perl
|
|
won't be undone; however, that interpreter won't be used again.
|
|
If the language is used again the initialization will be attempted
|
|
again within a fresh Perl interpreter.
|
|
</para>
|
|
<para>
|
|
Only superusers can change these settings. Although these settings
|
|
can be changed within a session, such changes will not affect Perl
|
|
interpreters that have already been used to execute functions.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry id="guc-plperl-use-strict" xreflabel="plperl.use_strict">
|
|
<term>
|
|
<varname>plperl.use_strict</varname> (<type>boolean</type>)
|
|
<indexterm>
|
|
<primary><varname>plperl.use_strict</> configuration parameter</primary>
|
|
</indexterm>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
When set true subsequent compilations of PL/Perl functions will have
|
|
the <literal>strict</> pragma enabled. This parameter does not affect
|
|
functions already compiled in the current session.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
</variablelist>
|
|
</sect2>
|
|
|
|
<sect2 id="plperl-missing">
|
|
<title>Limitations and Missing Features</title>
|
|
|
|
<para>
|
|
The following features are currently missing from PL/Perl, but they
|
|
would make welcome contributions.
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
PL/Perl functions cannot call each other directly.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
SPI is not yet fully implemented.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
If you are fetching very large data sets using
|
|
<literal>spi_exec_query</literal>, you should be aware that
|
|
these will all go into memory. You can avoid this by using
|
|
<literal>spi_query</literal>/<literal>spi_fetchrow</literal> as
|
|
illustrated earlier.
|
|
</para>
|
|
<para>
|
|
A similar problem occurs if a set-returning function passes a
|
|
large set of rows back to PostgreSQL via <literal>return</literal>. You
|
|
can avoid this problem too by instead using
|
|
<literal>return_next</literal> for each row returned, as shown
|
|
previously.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
When a session ends normally, not due to a fatal error, any
|
|
<literal>END</> blocks that have been defined are executed.
|
|
Currently no other actions are performed. Specifically,
|
|
file handles are not automatically flushed and objects are
|
|
not automatically destroyed.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
</sect2>
|
|
|
|
</sect1>
|
|
|
|
</chapter>
|