Hi,
The get_parameterized_baserel_size function does not differentiate for PARTITIONED_REL and always appends the rel's own restriction clauses. However, for PARTITIONED_REL, rel->tuples is computed in set_append_rel_size which comes from the sum of lived childrel->rows. It is important to note that childrel->rows is the estimated number of result tuples, meaning it already includes the effect of the rel's own restriction clauses.
Therefore, get_parameterized_baserel_size should not append the rel's own restriction clauses again for PARTITIONED_REL. It seems there might be a mistake here. Although I have not found any SQL that causes issues, this looks like a potential problem. The correct code should handle this situation appropriately like this.
--- a/src/backend/optimizer/path/costsize.c +++ b/src/backend/optimizer/path/costsize.c @@ -5365,7 +5365,10 @@ get_parameterized_baserel_size(PlannerInfo *root, RelOptInfo *rel, * restriction clauses. Note that we force the clauses to be treated as * non-join clauses during selectivity estimation. */ - allclauses = list_concat_copy(param_clauses, rel->baserestrictinfo); + if (rel->reloptkind == RELOPT_BASEREL && IS_PARTITIONED_REL(rel)) + allclauses = list_copy(param_clauses); + else + allclauses = list_concat_copy(param_clauses, rel->baserestrictinfo); nrows = rel->tuples * clauselist_selectivity(root, allclauses,
