generate_partition_wise_join_paths prints debug info, if
OPTIMIZER_DEBUG, using debug_print_rel at the end of each iteration for
collecting non-dummy child-joins, but I noticed that we pass to that
function the parent's RelOptInfo, not such a child-join's RelOptInfo. I
don't think it's intentional, so here is a patch for fixing that.
Best regards,
Etsuro Fujita