Re: Parallelized polymorphic aggs, and aggtype vs aggoutputtype

On Fri, Jun 17, 2016 at 3:14 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> The concern I have is that you could stick it into an aggregate that isn't
> the one it's expecting to be used in, or into a slot in that aggregate
> that isn't deserialize(), and the run-time test can't detect either of
> those things.  Now maybe this is locked down sufficiently by the fact
> that we don't let non-superusers create aggregates with transtype
> INTERNAL, but that seems pretty shaky to me given the number of moving
> parts in aggregates these days and the fact that we keep adding more.

Well, I'm not averse to changing it for more security, but "there
could be a bug there in somewhere" is a bit different from "the claim
in the comment there that it's okay if we check for aggregate context
is a joke".

>>> Not to mention that CREATE
>>> FUNCTION won't allow creation of such functions, so extensions are locked
>>> out of using this feature.
>
>> Oops.
>
> I think that means we *have* to change this.

Well, we don't *have* to change things for this reason, but it's
certainly not at all desirable for user-defined aggregates to be
locked out of this functionality.  So I'm in favor of changing it.

>> I think we should break up internal into various kinds of internal
>> depending on what kind of a thing we've actually got a pointer to.
>
> Not a bad long-term project, but it's not happening in this cycle.
> I'm not very sure how we'd go about it anyway --- for examples
> like this, every new user-defined aggregate potentially wants its
> own flavor of "internal", so how do we manage that?

I think we'd want some way to easily spin up new internal-ish types.
CREATE TYPE myinternalthingy AS INTERNAL, or something like that.

-- 
Robert Haas
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