Re: [v9.5] Custom Plan API

* Robert Haas (robertmhaas@gmail.com) wrote:
> Well, I consider that somewhat good news, because I think it would be
> rather nice if we could get by with solving one problem at a time, and
> if the executor part is close to being well-solved, excellent.

Sadly, I'm afraid the news really isn't all that good in the end..

> My ignorance is probably showing here, but I guess I don't understand
> why it's so hard to deal with the planner side of things.  My
> perhaps-naive impression is that a Seq Scan node, or even an Index
> Scan node, is not all that complicated.  If we just want to inject
> some more things that behave a lot like those into various baserels, I
> guess I don't understand why that's especially hard.

That's not what is being asked for here though...

> Now I do understand that part of what KaiGai wants to do here is
> inject custom scan paths as additional paths for *joinrels*.  And I
> can see why that would be somewhat more complicated.  But I also don't
> see why that's got to be part of the initial commit.

I'd say it's more than "part" of what the goal is here- it's more or
less what everything boils down to.  Oh, plus being able to replace
aggregates with a GPU-based operation instead, but that's no trivially
done thing either really (if it is, let's get it done for FDWs
already...).
Thanks,
    Stephen