Re: CTE inlining

"David G. Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> writes:
> On Tue, May 9, 2017 at 12:36 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Also, considering that this behavior has been there since 8.4,
>> I think it's sheerest chutzpah to claim that changing the docs in
>> v10 would materially reduce the backward-compatibility concerns
>> for whatever we might do in v11.

> ​No it won't, but those who are using 10 as their first version would
> probably be happy if this was covered in a bit more depth.

I think the existing doc text is perfectly clear (while David's proposed
replacement text is not).

> Even a comment
> like "Unlike most other DBMS PostgreSQL presently executes the subquery in
> the CTE​ in relative isolation. It is suggested that you document any
> intentional usage of this optimization fence as a query planning hint so
> that should the default change in the future you can update the query to
> support whatever official syntax is implemented to retain this behavior.

Well, TBH that is pre-judging what (if anything) is going to be changed
by a feature that we don't even have design consensus on, let alone a
patch for. I don't think that's an improvement or a good service to
our users; it's just promoting confusion. I think that until we do have
a design and a patch, we're better off leaving the docs reading the way
they have for the past eight years.

I'm also a bit mystified by the apparent urgency to change something,
anything, in this area when we're already past feature freeze. This
would be a fit subject for discussion several months from now when
v11 development opens, but right now it's just distracting us from
stabilizing v10.

regards, tom lane