On Thu, May 16, 2019 at 3:22 PM Thomas Munro <thomas.mu...@gmail.com> wrote:
> Admittedly I don't have a patch, just a bunch of handwaving. One > reason I haven't attempted to write it is because although I know how > to do the non-parallel version using a BufFile full of match bits in > sync with the tuples for outer joins, I haven't figured out how to do > it for parallel-aware hash join, because then each loop over the outer > batch could see different tuples in each participant. You could use > the match bit in HashJoinTuple header, but then you'd have to write > all the tuples out again, which is more IO than I want to do. I'll > probably start another thread about that. > > Going back to the idea of using the match bit in the HashJoinTuple header and writing out all of the outer side for every chunk of the inner side, I was wondering if there was something we could do that was kind of like mmap'ing the outer side file to give the workers in parallel hashjoin the ability to update a match bit in the tuple in place and avoid writing the whole outer side out each time. -- Melanie Plageman
