Bruno Wolff III wrote:
> On Sat, Oct 29, 2005 at 13:10:31 +0200,
> Martin Lesser <ml-pgsql@bettercom.de> wrote:
> > Which effects have UPDATEs on REFERENCEd TABLEs when only columns in the
> > referenced table are updated which are not part of the FOREIGN KEY
> > constraint?
>
> In 8.1 there is a check to see if the foreign key value has changed and if
> not a trigger isn't queued. In the currently released versions any update
> will fire triggers.
> The check in comment for trigger.c didn't say if this optimization applied
> to both referencing and referenced keys or just one of those.
> If you need to know more you can look at the code at:
> http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/
> for trigger.c.
It applies to both. See
src/backend/utils/adt/ri_triggers.c::RI_FKey_keyequal_upd_pk() and
RI_FKey_keyequal_upd_fk(). The first is for primary keys (pk), the
second for foreign keys (fk). These are called by
src/backend/command/triggers.c::AfterTriggerSaveEvent(). The checks
prevent the trigger from being registered at all if there is no change
in the primary/foreign key relationship.
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