Thread: ddl_command_end not firing DROP events

Hi,

I’ve created a trigger where I want to capture schema-changing events. I’m finding that DROP events are not being
triggeredwhen using “ddl_command_end". The test case below demonstrates this. I am running PostgreSQL 10.4. The trigger
isfired for the CREATE event, but not DROP TYPE or DROP TABLE. 

I came across the same question on the mailing list, but the solution was to use the “sql_drop” trigger instead.

https://www.postgresql.org/message-id/CAHE3wgjX-N%3DX9mccp4Bs-y-%3DHE%3DqayHEpXpCs1jMT%3DW0ZsYc5A%40mail.gmail.com

The documentation suggests that one should be able to use “ddl_command_end” instead of creating two triggers (i.e. one
forDROPs, another for everything else). 

Test:

CREATE FUNCTION test_event_trigger_for_drops()
        RETURNS event_trigger LANGUAGE plpgsql AS $$
DECLARE
    obj record;
BEGIN
    FOR obj IN SELECT * FROM pg_event_trigger_ddl_commands()
    LOOP
        RAISE NOTICE 'caught % event on ''%''',
                     obj.command_tag,
                     obj.object_identity;
    END LOOP;
END
$$;
CREATE EVENT TRIGGER test_event_trigger_for_drops
   ON ddl_command_end
   EXECUTE PROCEDURE test_event_trigger_for_drops();

CREATE TYPE foo AS (f1 int, f2 text);
DROP TYPE foo;
CREATE TABLE drop_test ( pk int ) WITH ( OIDS = FALSE );
DROP TABLE drop_test;

-- for ease of copy/paste to delete the above
DROP EVENT TRIGGER test_event_trigger_for_drops;
DROP FUNCTION test_event_trigger_for_drops;

Cheers,
Demitri

On 2018-Jul-08, Demitri Muna wrote:

Hi

> I’ve created a trigger where I want to capture schema-changing events.
> I’m finding that DROP events are not being triggered when using
> “ddl_command_end". The test case below demonstrates this. I am running
> PostgreSQL 10.4. The trigger is fired for the CREATE event, but not
> DROP TYPE or DROP TABLE.
> 
> I came across the same question on the mailing list, but the solution
> was to use the “sql_drop” trigger instead.
> 
> https://www.postgresql.org/message-id/CAHE3wgjX-N%3DX9mccp4Bs-y-%3DHE%3DqayHEpXpCs1jMT%3DW0ZsYc5A%40mail.gmail.com

As I recall, handling of DROP events in the ddl_command_end event is not
completely consistent. You may even find that some DROP events are not
returned by pg_event_trigger_ddl_commands.  I suggest you stick to
pg_event_trigger_dropped_objects() instead (for which you need
sql_drop).

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services