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Commit8b2e9fd

Browse files
author
Richard Guo
committed
Remove redundant code in create_gather_merge_path
In create_gather_merge_path, we should always guarantee that thesubpath is adequately ordered, and we do not add a Sort node increateplan.c for a Gather Merge node. Therefore, the 'else' branch increate_gather_merge_path, which computes the cost for a Sort node, isredundant.This patch removes the redundant code and emits an error if thesubpath is not sufficiently ordered. Meanwhile, this patch changesthe check for the subpath's pathkeys in create_gather_merge_plan to anAssert.Author: Richard GuoDiscussion:https://postgr.es/m/CAMbWs48u=0bWf3epVtULjJ-=M9Hbkz+ieZQAOS=BfbXZFqbDCg@mail.gmail.com
1 parent581df21 commit8b2e9fd

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2 files changed

+14
-30
lines changed

2 files changed

+14
-30
lines changed

‎src/backend/optimizer/plan/createplan.c

Lines changed: 2 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -1987,16 +1987,11 @@ create_gather_merge_plan(PlannerInfo *root, GatherMergePath *best_path)
19871987
&gm_plan->collations,
19881988
&gm_plan->nullsFirst);
19891989

1990-
19911990
/*
19921991
* All gather merge paths should have already guaranteed the necessary
1993-
* sort order either by adding an explicit sort node or by using presorted
1994-
* input. We can't simply add a sort here on additional pathkeys, because
1995-
* we can't guarantee the sort would be safe. For example, expressions may
1996-
* be volatile or otherwise parallel unsafe.
1992+
* sort order. See create_gather_merge_path.
19971993
*/
1998-
if (!pathkeys_contained_in(pathkeys,best_path->subpath->pathkeys))
1999-
elog(ERROR,"gather merge input not sufficiently sorted");
1994+
Assert(pathkeys_contained_in(pathkeys,best_path->subpath->pathkeys));
20001995

20011996
/* Now insert the subplan under GatherMerge. */
20021997
gm_plan->plan.lefttree=subplan;

‎src/backend/optimizer/util/pathnode.c

Lines changed: 12 additions & 23 deletions
Original file line numberDiff line numberDiff line change
@@ -1889,6 +1889,16 @@ create_gather_merge_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath,
18891889
Assert(subpath->parallel_safe);
18901890
Assert(pathkeys);
18911891

1892+
/*
1893+
* The subpath should guarantee that it is adequately ordered either by
1894+
* adding an explicit sort node or by using presorted input. We cannot
1895+
* add an explicit Sort node for the subpath in createplan.c on additional
1896+
* pathkeys, because we can't guarantee the sort would be safe. For
1897+
* example, expressions may be volatile or otherwise parallel unsafe.
1898+
*/
1899+
if (!pathkeys_contained_in(pathkeys,subpath->pathkeys))
1900+
elog(ERROR,"gather merge input not sufficiently sorted");
1901+
18921902
pathnode->path.pathtype=T_GatherMerge;
18931903
pathnode->path.parent=rel;
18941904
pathnode->path.param_info=get_baserel_parampathinfo(root,rel,
@@ -1900,29 +1910,8 @@ create_gather_merge_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath,
19001910
pathnode->path.pathkeys=pathkeys;
19011911
pathnode->path.pathtarget=target ?target :rel->reltarget;
19021912

1903-
if (pathkeys_contained_in(pathkeys,subpath->pathkeys))
1904-
{
1905-
/* Subpath is adequately ordered, we won't need to sort it */
1906-
input_startup_cost+=subpath->startup_cost;
1907-
input_total_cost+=subpath->total_cost;
1908-
}
1909-
else
1910-
{
1911-
/* We'll need to insert a Sort node, so include cost for that */
1912-
Pathsort_path;/* dummy for result of cost_sort */
1913-
1914-
cost_sort(&sort_path,
1915-
root,
1916-
pathkeys,
1917-
subpath->total_cost,
1918-
subpath->rows,
1919-
subpath->pathtarget->width,
1920-
0.0,
1921-
work_mem,
1922-
-1);
1923-
input_startup_cost+=sort_path.startup_cost;
1924-
input_total_cost+=sort_path.total_cost;
1925-
}
1913+
input_startup_cost+=subpath->startup_cost;
1914+
input_total_cost+=subpath->total_cost;
19261915

19271916
cost_gather_merge(pathnode,root,rel,pathnode->path.param_info,
19281917
input_startup_cost,input_total_cost,rows);

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