cpu-intensive immutable function and parallel scan

Hello all

I have a cpu-intensive plpython3u function that computes a result on the value from a single column value from a simple select.This looks largely like this.

select function_name (t1.val1, 'constant1') from t1 where t1.p = '202012_1' and t1.val1 is not null;

The function is marked immutable and parallel safe.

The time spent in the function is quite substantial. The same execution plan for a query that invokes the funtion and a query that does not results in a 15-times slowdown. Explain analyze show that both queries use 5 parallel workers.

I think I could achieve some speedup by parallelizing further, distributing the cpu-work among additional workers. But, how do I achive that best?

In Oracle I would either use a parallel-hint or an alter session force parallel query parallel 8.

Regards Niels