diff options
Diffstat (limited to 'src/backend/optimizer/plan/planner.c')
| -rw-r--r-- | src/backend/optimizer/plan/planner.c | 39 |
1 files changed, 21 insertions, 18 deletions
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c index dad35e56f58..094c7082b14 100644 --- a/src/backend/optimizer/plan/planner.c +++ b/src/backend/optimizer/plan/planner.c @@ -1788,36 +1788,39 @@ grouping_planner(PlannerInfo *root, bool inheritance_update, Path *subpath = (Path *) lfirst(lc); Path *newpath; + /* Shouldn't have any parameterized paths anymore */ + Assert(subpath->param_info == NULL); + /* * We can't use apply_projection_to_path() here, because there * could already be pointers to these paths, and therefore we - * cannot modify them in place. Instead, we must use - * create_projection_path(). The good news is this won't - * actually insert a Result node into the final plan unless - * it's needed, but the bad news is that it will charge for - * the node whether it's needed or not. Therefore, if the - * target list is already what we need it to be, just leave - * this partial path alone. + * dare not modify them in place. Instead, we must use + * create_projection_path() unconditionally. */ - if (equal(scanjoin_target->exprs, subpath->pathtarget->exprs)) - continue; - - Assert(subpath->param_info == NULL); newpath = (Path *) create_projection_path(root, current_rel, subpath, scanjoin_target); - if (is_projection_capable_path(subpath)) + + /* + * Although create_projection_path() inserts a ProjectionPath + * unconditionally, create_projection_plan() will only insert + * a Result node if the subpath is not projection-capable, so + * we should discount the cost of that node if it will not + * actually get inserted. (This is pretty grotty but we can + * improve it later if it seems important.) + */ + if (equal(scanjoin_target->exprs, subpath->pathtarget->exprs)) { - /* - * Since the target lists differ, a projection path is - * essential, but it will disappear at plan creation time - * because the subpath is projection-capable. So avoid - * charging anything for the disappearing node. - */ + /* at most we need a relabeling of the subpath */ newpath->startup_cost = subpath->startup_cost; newpath->total_cost = subpath->total_cost; } + else if (is_projection_capable_path(subpath)) + { + /* need to project, but we don't need a Result */ + newpath->total_cost -= cpu_tuple_cost * subpath->rows; + } lfirst(lc) = newpath; } |