Re: delta relations in AFTER triggers

On Sat, Jul 5, 2014 at 5:38 PM, Kevin Grittner <kgrittn(at)ymail(dot)com> wrote:
> it seems to me that we need the full tuple to support triggers on
> FDWs, so the TID approach would be an optimization for a subset of
> the cases, and would probably be more appropriate, if we do it at
> all, in a follow-on patch
> If you disagree with that assessment, now would be a good
> time to explain your reasoning.

Maybe I just have a limited imagination because I've never found a use
for FDWs personally. But recording changes from a trigger on a FDW
table doesn't seem that useful, since you can only capture changes
done by the local node. I expect that in many situations there are
multiple writers accessing the same underlying remote table. Certainly
it's can't guarantee the consistency of materialized views.

> I took a look at whether I could avoid making OLD and NEW
> non-reserved keywords, but I didn't see how to do that without
> making FOR at least partially reserved. If someone sees a way to
> do this without creating three new unreserved keywords
> (REFERENCING, OLD, and NEW) I'm all ears.

Sorry, I know I am very late to make this point, so feel free to ignore this.

I'm not a fan of the SQL standard syntax for this feature. One nice
thing about PostgreSQL's triggers is that you can declare the trigger
function once and re-use it on many tables. It would make more sense
if the same function declaration could say what variable/relation
names it wants to use. They're more like function argument names, not
some metadata about a table-function relationship.

Putting these in the CREATE TRIGGER command means you have to repeat
them for each table you want to apply the trigger to. It introduces
the possibility of making more mistakes without any gain in
flexibility.

But then again, I understand that there's value in supporting standard syntax.

Regards,
Marti