On Wed, Apr 20, 2022 at 10:01 AM bu...@sohu.com <bu...@sohu.com> wrote: > for now fuction cost_subqueryscan always using *total* rows even parallel > path. like this: > > Gather (rows=30000) > Workers Planned: 2 > -> Subquery Scan (rows=30000) -- *total* rows, should be equal subpath > -> Parallel Seq Scan (rows=10000)
OK, that's bad. > Maybe the codes: > > /* Mark the path with the correct row estimate */ > if (param_info) > path->path.rows = param_info->ppi_rows; > else > path->path.rows = baserel->rows; > > should change to: > > /* Mark the path with the correct row estimate */ > if (path->path.parallel_workers > 0) > path->path.rows = path->subpath->rows; > else if (param_info) > path->path.rows = param_info->ppi_rows; > else > path->path.rows = baserel->rows; Suppose parallelism is not in use and that param_info is NULL. Then, is path->subpath->rows guaranteed to be equal to baserel->rows? If yes, then we don't need to a three-part if statement as you propose here and can just change the "else" clause to say path->path.rows = path->subpath->rows. If no, then your change gives the wrong answer. -- Robert Haas EDB: http://www.enterprisedb.com
