Re: Allow parallel DISTINCT

On Mon, Aug 16, 2021 at 10:07 PM David Rowley <dgrowleyml(at)gmail(dot)com> wrote:

> On Wed, 11 Aug 2021 at 16:51, David Rowley <dgrowleyml(at)gmail(dot)com> wrote:
> > The patch is just some plumbing work to connect all the correct paths
> > up to make it work. It's all fairly trivial.
>
> I looked at this patch again and realise that it could be done a bit
> better. For example, the previous version set the distinct_rel's FDW
> fields twice, once when making the serial paths and once when
> finalizing the partial paths.
>
> I've now added two new functions; create_final_distinct_paths and
> create_partial_distinct_paths. The responsibility of
> create_distinct_paths has changed. Instead of it creating the
> non-parallel DISTINCT paths, it calls the two new functions and also
> takes charge of calling the create_upper_paths_hook for
> UPPERREL_DISTINCT plus the FDW GetForeignUpperPaths() call. I think
> this is nicer as I'd previously added a new parameter to
> create_distinct_paths() so I could tell it not to call the hook as I
> didn't want to call that twice on the same relation as it would no
> doubt result in some plugin just creating the same paths again.
>
> I've also changed my mind about the previous choice I'd made not to
> call GetForeignUpperPaths for the UPPERREL_PARTIAL_DISTINCT. I now
> think that's ok.
>
> I think this is a fairly trivial patch that just does a bit of wiring
> up of paths. Unless anyone has anything to say about it in the next
> few days, I'll be looking at it again with intensions to push it.
>
> David
>
>
> Hi, David:
Can you attach updated patch so that we know more detail about the two new
functions; create_final_distinct_paths and
create_partial_distinct_paths ?

Thanks