Re: Allow INSTEAD OF DELETE triggers to modify the tuple for RETURNING

On Fri, Jul 1, 2016 at 2:12 AM, I wrote:

> Currently the tuple returned by INSTEAD OF triggers on DELETEs is only
> used to determine whether to pretend that the DELETE happened or not, which
> is often not helpful enough; for example, the actual tuple might have been
> concurrently UPDATEd by another transaction and one or more of the columns
> now hold values different from those in the planSlot tuple. Attached is an
> example case which is impossible to properly implement under the current
> behavior. For what it's worth, the current behavior seems to be an
> accident; before INSTEAD OF triggers either the tuple was already locked
> (in case of BEFORE triggers) or the actual pre-DELETE version of the tuple
> was fetched from the heap.
>
> So I'm suggesting to change this behavior and allow INSTEAD OF DELETE
> triggers to modify the OLD tuple and use that for RETURNING instead of
> returning the tuple in planSlot. Attached is a WIP patch implementing that.
>
> Is there any reason why we wouldn't want to change the current behavior?

Since nobody seems to have came up with a reason, here's a patch for that
with test cases and some documentation changes. I'll also be adding this
to the open commit fest, as is customary.

.m