On Sun, Aug 19, 2018 at 1:40 AM, Thomas Munro <thomas.mu...@enterprisedb.com> wrote: > A true parallel scan of an FDW would be one where each process emits > an arbitrary fraction of the tuples, but together they emit all of the > tuples. You'd almost certainly need to use some shared memory to > coordinate that. To say that you support that, I think your > GetForeignPaths() function would need to call add_partial_path(). And > unless I'm mistaken, whether or not InitializeDSMForeignScan etc are > called might be the only indication you get of whether you need to run > in parallel-aware mode. I haven't personally heard of any FDWs that > can do this yet, but I just tried hacking file_fdw to register a > partial path and it seems to work (though of course the results are > duplicated because the emitted tuples are not actually partial).
... though I just noticed that my quick test used "Single Copy" mode. I think I see why: it looks like core's create_foreignscan_path() function might need to take num_workers and set parallel_aware if > 0. So I guess this hasn't been done before and would require some more research. -- Thomas Munro http://www.enterprisedb.com
