On Fri, Dec 2, 2022 at 9:13 PM Tom Lane <t...@sss.pgh.pa.us> wrote: > > Ashutosh Bapat <ashutosh.bapat....@gmail.com> writes: > > On Fri, Dec 2, 2022 at 8:25 AM Tom Lane <t...@sss.pgh.pa.us> wrote: > >> Unfortunately, I don't have an example that produces such a > >> failure against HEAD. It seems certain to me that such cases > >> exist, though, so I'd like to apply and back-patch the attached. > > > From this comment, that I wrote back when I implemented that function, > > I wonder if we thought MaterialPath wouldn't appear on the inner side > > of nestloop join. But that can't be the case. Or probably we didn't > > find MaterialPath being there from our tests. > > * This function is currently only applied to the inner side of a > > nestloop > > * join that is being partitioned by the partitionwise-join code. > > Hence, > > * we need only support path types that plausibly arise in that context. > > But I think it's good to have MaterialPath there. > > So thinking about this a bit: the reason it is okay if reparameterize_path > fails is that it's not fatal. We just go on our way without making > a parameterized path for that appendrel. However, if > reparameterize_path_by_child fails for every available child path, > we end up with "could not devise a query plan", because the > partitionwise-join code is brittle and won't tolerate failure > to build a parent-join path. Seems like we should be willing to > fall back to a non-partitionwise join in that case. > > regards, tom lane
partition-wise join should be willing to fallback to non-partitionwise join in such a case. After spending a few minutes with the code, I think generate_partitionwise_join_paths() should not call set_cheapest() is the pathlist of the child is NULL and should just wind up and avoid adding any path. -- Best Wishes, Ashutosh Bapat
