<term><literal>$_TD-&gt;{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-&gt;{argc}</literal></term>
     <listitem>
      <para>
       Number of arguments of the trigger function
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><literal>@{$_TD-&gt;{args}}</literal></term>
     <listitem>
      <para>
       Arguments of the trigger function.  Does not exist if <literal>$_TD-&gt;{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 $$
    if (($_TD-&gt;{new}{i} &gt;= 100) || ($_TD-&gt;{new}{i} &lt;= 0)) {
        return "SKIP";    # skip INSERT/UPDATE command
    } elsif ($_TD-&gt;{new}{v} ne "immortal") {
        $_TD-&gt;{new}{v} .= "(modified by trigger)";
        return "MODIFY";  # modify row and execute INSERT/UPDATE command
    } else {
        return;           # execute INSERT/UPDATE command
    }
$$ LANGUAGE plperl;

CREATE TRIGGER test_valid_id_trig
    BEFORE INSERT OR UPDATE ON test
    FOR EACH ROW EXECUTE FUNCTION 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</varname> 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-&gt;{event}</literal></term>
     <listitem>
      <para>
       The name of the event the trigger is fired for.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><literal>$_TD-&gt;{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 function 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 FUNCTION 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</application>.
  </para>

  <variablelist>

     <varlistentry id="guc-plperl-on-init" xreflabel="plperl.on_init">
      <term>
       <varname>plperl.on_init</varname> (<type>string</type>)