Event trigger procedures can be written in PL/Tcl. PostgreSQL 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 event_trigger.
The information from the trigger manager is passed to the procedure body in the following variables:
$TG_eventThe name of the event the trigger is fired for.
$TG_tagThe command tag for which the trigger is fired.
The return value of the trigger procedure is ignored.
Here's a little example event trigger procedure that simply raises a NOTICE message each time a supported command is executed:
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();