BUG #14815: event trigger in extension

gomer94@yandex.ru writes:

I want to create extension with sql like:

CREATE OR REPLACE FUNCTION keep_any_ddl_command() RETURNS event_trigger
LANGUAGE plpgsql
AS $$
BEGIN
SELECT classid, objid, objsubid FROM
pg_event_trigger_ddl_commands();

-- some insert code;
END;
$$;

CREATE TABLE ddl_events();

CREATE EVENT TRIGGER keep_all_ddl ON ddl_command_end
EXECUTE PROCEDURE keep_any_ddl_command();

I think the reason this fails is that on the way out of the CREATE
EXTENSION command, the event trigger code sees that an event trigger
exists, so it tries to call it. But because no event trigger existed
when we started the CREATE EXTENSION command, the necessary
infrastructure hasn't been set up --- in particular,
EventTriggerBeginCompleteQuery did nothing at the time.

This seems like it would be an equal hazard for any situation where
CREATE EVENT TRIGGER is executed not at top level. Don't see an
easy fix right offhand.

regards, tom lane

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On Sun, Sep 17, 2017 at 4:52 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:

I think the reason this fails is that on the way out of the CREATE
EXTENSION command, the event trigger code sees that an event trigger
exists, so it tries to call it. But because no event trigger existed
when we started the CREATE EXTENSION command, the necessary
infrastructure hasn't been set up --- in particular,
EventTriggerBeginCompleteQuery did nothing at the time.

That's rather tricky, the failure happens when doing the CREATE EVENT
TRIGGER command within the CREATE EXTENSION command which is done
within ProcessUtilitySlow. I am wondering if a somewhat-elegant way to
solve such problems would be to introduce a function able to
temporarily disable and enable event triggers to happen in the context
of an extension creation, in a design similar to
pg_extension_config_dump.
--
Michael

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