Re: Add comments about fire_triggers argument in ri_triggers.c - Mailing list pgsql-hackers

On Mon, 30 Mar 2026 10:16:02 +0900
Amit Langote <amitlangote09@gmail.com> wrote:

> On Fri, Mar 27, 2026 at 2:36 PM Amit Langote <amitlangote09@gmail.com> wrote:
> > On Fri, Mar 27, 2026 at 12:01 PM Yugo Nagata <nagata@sraoss.co.jp> wrote:
> > > On Fri, 27 Mar 2026 09:39:17 +0900
> > > Amit Langote <amitlangote09@gmail.com> wrote:
> > >
> > > > On Fri, Mar 27, 2026 at 12:56 AM Yugo Nagata <nagata@sraoss.co.jp> wrote:
> > > > >
> > > > > Hi,
> > > > >
> > > > > Thank you all for the review and comments.
> > > > >
> > > > > > Yes Amit, I agree that SPI_execute_snapshot() comments do provide some
> > > > > > context on AFTER triggers, but I still feel the newly added comment
> > > > > > in ri_PerformCheck() gives additional context on why the fire_triggers is
> > > > > > set to false.
> > > > >
> > > > > Yes, that is what I intended. The existing comments on
> > > > > SPI_execute_snapshot() explain how the fire_triggers parameter works,
> > > > > but I would like to add a comment explaining why the AFTER trigger for
> > > > > RI needs to set it to false.
> > > > >
> > > > > If the explanation of the effect of fire_triggers seems redundant, I am
> > > > > fine with the following shorter version:
> > > > >
> > > > > +        * Set fire_triggers to false to ensure that check triggers fire after all
> > > > > +        * RI updates on the same row are complete.
> > > >
> > > > Thanks for the updated patch.  Yes, adding the comment might be good,
> > > > but I'd suggest a small tweak:
> > > >
> > > > +        * Set fire_triggers to false to ensure that AFTER triggers
> > > > are queued in
> > > > +        * the outer query's after-trigger context and fire after all
> > > > RI updates on
> > > > +        * the same row are complete, rather than immediately.
> > > >
> > > > Two changes:
> > > >
> > > > * "check triggers" -> "AFTER triggers", since fire_triggers=false
> > > > affects any AFTER triggers queued during the SPI execution, not just
> > > > RI check triggers.
> > > >
> > > > * mention of the outer query's after-trigger context to explain the
> > > > mechanism by which the deferral works.
> > > >
> > > > Does that additional context help?
> > >
> > > Thank you for the suggestion.
> > > That looks good to me. It is clearer than the previous version.
> >
> > Ok, will push the attached.
> 
> Pushed.

Thank you!
 
> I verified locally with a test case involving a CASCADE DELETE on two
> parent rows that the comment is indeed accurate:
> 
> CREATE TABLE parent (id int PRIMARY KEY);
> CREATE TABLE child (id int REFERENCES parent ON DELETE CASCADE);
> CREATE TABLE log (seq serial, msg text);
> 
> CREATE OR REPLACE FUNCTION child_after_del() RETURNS trigger AS $$
> BEGIN
>   INSERT INTO log(msg) VALUES ('child deleted: ' || OLD.id);
>   RETURN NULL;
> END;
> $$ LANGUAGE plpgsql;
> 
> CREATE TRIGGER "A_child_after_del_trig"
> AFTER DELETE ON child
> FOR EACH ROW EXECUTE FUNCTION child_after_del();
> CREATE OR REPLACE FUNCTION parent_after_del() RETURNS trigger AS $$
> BEGIN
>   INSERT INTO log(msg) VALUES ('parent deleted: ' || OLD.id);
>   RETURN NULL;
> END;
> $$ LANGUAGE plpgsql;
> 
> CREATE TRIGGER "A_parent_after_del_trig"
> AFTER DELETE ON parent
> FOR EACH ROW EXECUTE FUNCTION parent_after_del();
> 
> INSERT INTO parent VALUES (1), (2);
> INSERT INTO child VALUES (1), (2);
> DELETE FROM parent;
> 
> SELECT msg FROM log ORDER BY seq;
>         msg
> -------------------
>  parent deleted: 1
>  parent deleted: 2
>  child deleted: 1
>  child deleted: 2
> (4 rows)
> 
Thank you for the verification.
This behavior seems consistent with the comment.

Regards,
Yugo Nagata


-- 
Yugo Nagata <nagata@sraoss.co.jp>