Thanks for your reply. I read your references but still confused about the 'loops' in parallel query result.
> -> Parallel Seq Scan on c (cost=0.00..8591.67 rows=416667 width=0) (actual time=0.030..140.036 rows=333333 loops=3) In my previous example, actual row number is 333333*3=1e6(which is correct), so I think the actual time is 140.036*3ms. Do your think the loops(3) has no meaning for parallel scan node when calculate actual time?
As far as I understand it, you have to multiply the number of rows by the number of loops, but this doesn't apply to duration at least for parallel queries.