Re: Parallel grouping sets

Hi Amit,

Thanks for reviewing these two patches.

On Sat, Jan 25, 2020 at 6:31 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:

>
> This is what I also understood after reading this thread. So, my
> question is why not just review v3 and commit something on those lines
> even though it would take a bit more time. It is possible that if we
> decide to go with v5, we can make it happen earlier, but later when we
> try to get v3, the code committed as part of v5 might not be of any
> use or if it is useful, then in which cases?
>

Yes, approach #2 (v3) would be generally better than approach #1 (v5) in
performance. I started with approach #1 because it is much easier.

If we decide to go with approach #2, I think we can now concentrate on
v3 patch.

For v3 patch, we have some other idea, which is to perform a normal
grouping sets aggregation in the final phase, with 'GroupingSetId'
included in the group keys (as described in the previous email). With
this idea, we can avoid a lot of hacky codes in current v3 patch.

Thanks
Richard