On Wed, 11 Aug 2021 at 16:51, David Rowley <dgrowleyml@gmail.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
