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PL/Tcl: Add event trigger support

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From: Dimitri Fontaine <dimitri@2ndQuadrant.fr>
This commit is contained in:
Peter Eisentraut
2013-11-23 21:32:00 -05:00
parent 45e02e3232
commit a5036ca998
4 changed files with 188 additions and 23 deletions
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59
doc/src/sgml/pltcl.sgml
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@ -711,6 +711,65 @@ CREATE TRIGGER trig_mytab_modcount BEFORE INSERT OR UPDATE ON mytab
</para>
</sect1>
<sect1 id="pltcl-event-trigger">
<title>Event Trigger Procedures in PL/Tcl</title>
<indexterm>
<primary>event trigger</primary>
<secondary>in PL/Tcl</secondary>
</indexterm>
<para>
Event trigger procedures can be written in PL/Tcl.
<productname>PostgreSQL</productname> requires that a procedure that is
to be called as an event trigger must be declared as a function with no
arguments and a return type of <literal>event_trigger</>.
</para>
<para>
The information from the trigger manager is passed to the procedure body
in the following variables:
<variablelist>
<varlistentry>
<term><varname>$TG_event</varname></term>
<listitem>
<para>
The name of the event the trigger is fired for.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>$TG_tag</varname></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's a little example event trigger procedure that simply raises
a <literal>NOTICE</literal> message each time a supported command is
executed:
<programlisting>
CREATE OR REPLACE FUNCTION tclsnitch() RETURNS event_trigger AS $$
elog NOTICE "tclsnitch: $TG_event $TG_tag"
$$ LANGUAGE pltcl;
CREATE EVENT TRIGGER tcl_a_snitch ON ddl_command_start EXECUTE PROCEDURE tclsnitch();
</programlisting>
</para>
</sect1>
<sect1 id="pltcl-unknown">
<title>Modules and the <function>unknown</> Command</title>
<para>