Just asking, I may be completely wrong. is this query parallel safe? can we force parallel workers, by setting low parallel_setup_cost or otherwise to make use of scatter gather and Partial HashAggregate(s)? I am just assuming more workers doing things in parallel, would require less disk spill per hash aggregate (or partial hash aggregate ?) and the scatter gather at the end.
I did some runs in my demo environment, not with the same query, some group by aggregates with around 25M rows, and it showed reasonable results, not too off. this was pg14 on ubuntu.
