I was curious when create_gather_path() sets single_copy, but could not find
any place in the tree where a path with num_workers==0 is added to
partial_pathlist. This patch removes the field.
--
Antonin Houska
Web: https://www.cybertec-postgresql.com
>From 3f434cfb8b7eb70049650d1f324fe8cbaf1267cb Mon Sep 17 00:00:00 2001
From: Antonin Houska <a...@cybertec.at>
Date: Thu, 12 Dec 2024 10:22:40 +0100
Subject: [PATCH] Remove the single_copy field from GatherPath.
While single_copy is useful in the Gather plan, it's set regardless the value
in GatherPath: standard_planner() sets the flag on a new instance of Gather,
for which there is no corresponding GatherPath. Furthermore, the field is
never set in GatherPath anyway because parial paths always have
parallel_workers > 0.
---
src/backend/optimizer/plan/createplan.c | 6 ++----
src/backend/optimizer/util/pathnode.c | 9 +--------
src/include/nodes/pathnodes.h | 4 +---
3 files changed, 4 insertions(+), 15 deletions(-)
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 178c572b02..dfceb3e615 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -300,7 +300,7 @@ static Unique *make_unique_from_sortclauses(Plan *lefttree, List *distinctList);
static Unique *make_unique_from_pathkeys(Plan *lefttree,
List *pathkeys, int numCols);
static Gather *make_gather(List *qptlist, List *qpqual,
- int nworkers, int rescan_param, bool single_copy, Plan *subplan);
+ int nworkers, int rescan_param, Plan *subplan);
static SetOp *make_setop(SetOpCmd cmd, SetOpStrategy strategy, Plan *lefttree,
List *distinctList, AttrNumber flagColIdx, int firstFlag,
long numGroups);
@@ -1940,7 +1940,6 @@ create_gather_plan(PlannerInfo *root, GatherPath *best_path)
NIL,
best_path->num_workers,
assign_special_exec_param(root),
- best_path->single_copy,
subplan);
copy_generic_path_info(&gather_plan->plan, &best_path->path);
@@ -6930,7 +6929,6 @@ make_gather(List *qptlist,
List *qpqual,
int nworkers,
int rescan_param,
- bool single_copy,
Plan *subplan)
{
Gather *node = makeNode(Gather);
@@ -6942,7 +6940,7 @@ make_gather(List *qptlist,
plan->righttree = NULL;
node->num_workers = nworkers;
node->rescan_param = rescan_param;
- node->single_copy = single_copy;
+ node->single_copy = false;
node->invisible = false;
node->initParam = NULL;
diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
index fc97bf6ee2..f03240c77a 100644
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -2059,15 +2059,8 @@ create_gather_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath,
pathnode->path.pathkeys = NIL; /* Gather has unordered result */
pathnode->subpath = subpath;
+ Assert(subpath->parallel_workers > 0);
pathnode->num_workers = subpath->parallel_workers;
- pathnode->single_copy = false;
-
- if (pathnode->num_workers == 0)
- {
- pathnode->path.pathkeys = subpath->pathkeys;
- pathnode->num_workers = 1;
- pathnode->single_copy = true;
- }
cost_gather(pathnode, root, rel, pathnode->path.param_info, rows);
diff --git a/src/include/nodes/pathnodes.h b/src/include/nodes/pathnodes.h
index 0759e00e96..0c7df1e6fa 100644
--- a/src/include/nodes/pathnodes.h
+++ b/src/include/nodes/pathnodes.h
@@ -2045,14 +2045,12 @@ typedef struct UniquePath
/*
* GatherPath runs several copies of a plan in parallel and collects the
- * results. The parallel leader may also execute the plan, unless the
- * single_copy flag is set.
+ * results.
*/
typedef struct GatherPath
{
Path path;
Path *subpath; /* path for each worker */
- bool single_copy; /* don't execute path more than once */
int num_workers; /* number of workers sought to help */
} GatherPath;
--
2.45.2
