Re: WIP: Upper planner pathification

Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> writes:
> On Mon, Mar 7, 2016 at 9:13 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> AFAICS, those are about generating partial paths, which is a completely
>> different thing from whether a regular path is parallel-safe or not.

> Okay, but the main point I wanted to convey is that I think setting
> parallel_degree = 0 in mergejoin path is not necessarily a copy-paste
> error.

Perhaps it was intentional when written, but if Robert's advice is correct
that the new upper-planner path nodes should copy up parallel_degree from
their children, then it cannot be the case that parallel_degree>0 in a
node above the scan level implies that that node type has any special
behavior for parallelism.

I continue to bemoan the lack of documentation about what these fields
mean. As far as I can find, the sum total of the documentation about
this field is

int parallel_degree; /* desired parallel degree; 0 = not parallel */

Last I checked, "degree" meant 1/360'th part of a circle, or some
fraction of the distance between water's freezing and boiling points,
or possibly an award for academic achievement. So I'm not really
going to hold still for any claim that this is self-explanatory.

regards, tom lane