diff options
Diffstat (limited to 'src/backend/optimizer/util/pathnode.c')
| -rw-r--r-- | src/backend/optimizer/util/pathnode.c | 42 |
1 files changed, 35 insertions, 7 deletions
diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c index 169e51e7921..56de8fc370a 100644 --- a/src/backend/optimizer/util/pathnode.c +++ b/src/backend/optimizer/util/pathnode.c @@ -1242,7 +1242,6 @@ create_append_path(PlannerInfo *root, pathnode->path.parallel_aware = parallel_aware; pathnode->path.parallel_safe = rel->consider_parallel; pathnode->path.parallel_workers = parallel_workers; - pathnode->path.pathkeys = NIL; /* result is always considered unsorted */ pathnode->partitioned_rels = list_copy(partitioned_rels); /* @@ -1276,7 +1275,26 @@ create_append_path(PlannerInfo *root, Assert(!parallel_aware || pathnode->path.parallel_safe); - cost_append(pathnode); + /* + * If there's exactly one child path, the Append is a no-op and will be + * discarded later (in setrefs.c); therefore, we can inherit the child's + * size, cost, and pathkeys if any. Otherwise, it's unsorted, and we must + * do the normal costsize calculation. + */ + if (list_length(pathnode->subpaths) == 1) + { + Path *child = (Path *) linitial(pathnode->subpaths); + + pathnode->path.rows = child->rows; + pathnode->path.startup_cost = child->startup_cost; + pathnode->path.total_cost = child->total_cost; + pathnode->path.pathkeys = child->pathkeys; + } + else + { + pathnode->path.pathkeys = NIL; /* unsorted if more than 1 subpath */ + cost_append(pathnode); + } /* If the caller provided a row estimate, override the computed value. */ if (rows >= 0) @@ -1408,11 +1426,21 @@ create_merge_append_path(PlannerInfo *root, Assert(bms_equal(PATH_REQ_OUTER(subpath), required_outer)); } - /* Now we can compute total costs of the MergeAppend */ - cost_merge_append(&pathnode->path, root, - pathkeys, list_length(subpaths), - input_startup_cost, input_total_cost, - pathnode->path.rows); + /* + * Now we can compute total costs of the MergeAppend. If there's exactly + * one child path, the MergeAppend is a no-op and will be discarded later + * (in setrefs.c); otherwise we do the normal cost calculation. + */ + if (list_length(subpaths) == 1) + { + pathnode->path.startup_cost = input_startup_cost; + pathnode->path.total_cost = input_total_cost; + } + else + cost_merge_append(&pathnode->path, root, + pathkeys, list_length(subpaths), + input_startup_cost, input_total_cost, + pathnode->path.rows); return pathnode; } |