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Disable run condition optimization for some WindowFuncs

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94985c210 added code to detect when WindowFuncs were monotonic and
allowed additional quals to be "pushed down" into the subquery to be
used as WindowClause runConditions in order to short-circuit execution
in nodeWindowAgg.c.

The Node representation of runConditions wasn't well selected and
because we do qual pushdown before planning the subquery, the planning
of the subquery could perform subquery pull-up of nested subqueries.
For WindowFuncs with args, the arguments could be changed after pushing
the qual down to the subquery.

This was made more difficult by the fact that the code duplicated the
WindowFunc inside an OpExpr to include in the WindowClauses runCondition
field.  This could result in duplication of subqueries and a pull-up of
such a subquery could result in another initplan parameter being issued
for the 2nd version of the subplan.  This could result in errors such as:

ERROR:  WindowFunc not found in subplan target lists

Here in the backbranches, we don't have the flexibility to improve the
Node representation to resolve this, so instead we just disable the
runCondition optimization for ntile() unless the argument is a Const,
(v16 only) and likewise for count(expr) (both v15 and v16).  count(*) is
unaffected.  All other window functions which support this optimization
all take zero arguments and therefore are unaffected.

Bug: #18170
Reported-by: Zuming Jiang
Discussion: https://postgr.es/m/18170-f1d17bf9a0d58b24@postgresql.org
Backpatch-through 15 (master will be fixed independently)
This commit is contained in:
David Rowley 2024-05-01 16:35:37 +12:00
parent faba2f8f35
commit 7e5d20bbd1
4 changed files with 67 additions and 24 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
src/backend/utils/adt/int8.c
View File

@ -833,6 +833,21 @@ int8inc_support(PG_FUNCTION_ARGS)
SupportRequestWFuncMonotonic *req = (SupportRequestWFuncMonotonic *) rawreq;
MonotonicFunction monotonic = MONOTONICFUNC_NONE;
int frameOptions = req->window_clause->frameOptions;
WindowFunc *wfunc = req->window_func;
if (list_length(wfunc->args) == 1)
{
Node *expr = eval_const_expressions(NULL, linitial(wfunc->args));
/*
* Due to the Node representation of WindowClause runConditions in
* version prior to v17, we need to insist that the count arg is
* Const to allow safe application of the runCondition
* optimization.
*/
if (!IsA(expr, Const))
PG_RETURN_POINTER(NULL);
}
/* No ORDER BY clause then all rows are peers */
if (req->window_clause->orderClause == NIL)

1
src/backend/utils/adt/windowfuncs.c
View File

@ -14,6 +14,7 @@
#include "postgres.h"
#include "nodes/supportnodes.h"
#include "optimizer/optimizer.h"
#include "utils/builtins.h"
#include "windowapi.h"

50
src/test/regress/expected/window.out
View File

@ -3481,13 +3481,13 @@ EXPLAIN (COSTS OFF)
SELECT * FROM
(SELECT empno,
salary,
count(empno) OVER (ORDER BY salary DESC) c
count(1) OVER (ORDER BY salary DESC) c
FROM empsalary) emp
WHERE c <= 3;
QUERY PLAN
---------------------------------------------------------
QUERY PLAN
-------------------------------------------
WindowAgg
Run Condition: (count(empsalary.empno) OVER (?) <= 3)
Run Condition: (count(1) OVER (?) <= 3)
-> Sort
Sort Key: empsalary.salary DESC
-> Seq Scan on empsalary
@ -3496,7 +3496,7 @@ WHERE c <= 3;
SELECT * FROM
(SELECT empno,
salary,
count(empno) OVER (ORDER BY salary DESC) c
count(1) OVER (ORDER BY salary DESC) c
FROM empsalary) emp
WHERE c <= 3;
empno | salary | c
@ -3608,19 +3608,19 @@ WHERE rn < 3;
-> Seq Scan on empsalary
(6 rows)
-- likewise with count(empno) instead of row_number()
-- likewise with count(1) instead of row_number()
EXPLAIN (COSTS OFF)
SELECT * FROM
(SELECT empno,
depname,
salary,
count(empno) OVER (PARTITION BY depname ORDER BY salary DESC) c
count(1) OVER (PARTITION BY depname ORDER BY salary DESC) c
FROM empsalary) emp
WHERE c <= 3;
QUERY PLAN
------------------------------------------------------------
WindowAgg
Run Condition: (count(empsalary.empno) OVER (?) <= 3)
Run Condition: (count(1) OVER (?) <= 3)
-> Sort
Sort Key: empsalary.depname, empsalary.salary DESC
-> Seq Scan on empsalary
@ -3631,7 +3631,7 @@ SELECT * FROM
(SELECT empno,
depname,
salary,
count(empno) OVER (PARTITION BY depname ORDER BY salary DESC) c
count(1) OVER (PARTITION BY depname ORDER BY salary DESC) c
FROM empsalary) emp
WHERE c <= 3;
empno | depname | salary | c
@ -3653,13 +3653,13 @@ SELECT * FROM
(SELECT empno,
depname,
salary,
count(empno) OVER () c
count(1) OVER () c
FROM empsalary) emp
WHERE c = 1;
QUERY PLAN
--------------------------------------------------------
QUERY PLAN
------------------------------------------
WindowAgg
Run Condition: (count(empsalary.empno) OVER (?) = 1)
Run Condition: (count(1) OVER (?) = 1)
-> Seq Scan on empsalary
(3 rows)
@ -3667,7 +3667,7 @@ WHERE c = 1;
EXPLAIN (COSTS OFF)
SELECT * FROM
(SELECT *,
count(salary) OVER (PARTITION BY depname || '') c1, -- w1
count(1) OVER (PARTITION BY depname || '') c1, -- w1
row_number() OVER (PARTITION BY depname) rn, -- w2
count(*) OVER (PARTITION BY depname) c2, -- w2
count(*) OVER (PARTITION BY '' || depname) c3 -- w3
@ -3678,7 +3678,7 @@ SELECT * FROM
Subquery Scan on e
-> WindowAgg
Filter: ((row_number() OVER (?)) <= 1)
Run Condition: (count(empsalary.salary) OVER (?) <= 3)
Run Condition: (count(1) OVER (?) <= 3)
-> Sort
Sort Key: (((empsalary.depname)::text || ''::text))
-> WindowAgg
@ -3694,7 +3694,7 @@ SELECT * FROM
-- Ensure we correctly filter out all of the run conditions from each window
SELECT * FROM
(SELECT *,
count(salary) OVER (PARTITION BY depname || '') c1, -- w1
count(1) OVER (PARTITION BY depname || '') c1, -- w1
row_number() OVER (PARTITION BY depname) rn, -- w2
count(*) OVER (PARTITION BY depname) c2, -- w2
count(*) OVER (PARTITION BY '' || depname) c3 -- w3
@ -3765,6 +3765,24 @@ WHERE c = 1;
-> Seq Scan on empsalary
(6 rows)
-- Ensure we don't use a run condition when the WindowFunc arg contains a Var
EXPLAIN (COSTS OFF)
SELECT * FROM
(SELECT empno,
salary,
count(empno) OVER (ORDER BY empno DESC) c
FROM empsalary) emp
WHERE c = 1;
QUERY PLAN
----------------------------------------------
Subquery Scan on emp
Filter: (emp.c = 1)
-> WindowAgg
-> Sort
Sort Key: empsalary.empno DESC
-> Seq Scan on empsalary
(6 rows)
-- Ensure we don't use a run condition when the WindowFunc contains subplans
EXPLAIN (COSTS OFF)
SELECT * FROM

25
src/test/regress/sql/window.sql
View File

@ -1068,14 +1068,14 @@ EXPLAIN (COSTS OFF)
SELECT * FROM
(SELECT empno,
salary,
count(empno) OVER (ORDER BY salary DESC) c
count(1) OVER (ORDER BY salary DESC) c
FROM empsalary) emp
WHERE c <= 3;
SELECT * FROM
(SELECT empno,
salary,
count(empno) OVER (ORDER BY salary DESC) c
count(1) OVER (ORDER BY salary DESC) c
FROM empsalary) emp
WHERE c <= 3;
@ -1131,13 +1131,13 @@ SELECT empno, depname FROM
FROM empsalary) emp
WHERE rn < 3;
-- likewise with count(empno) instead of row_number()
-- likewise with count(1) instead of row_number()
EXPLAIN (COSTS OFF)
SELECT * FROM
(SELECT empno,
depname,
salary,
count(empno) OVER (PARTITION BY depname ORDER BY salary DESC) c
count(1) OVER (PARTITION BY depname ORDER BY salary DESC) c
FROM empsalary) emp
WHERE c <= 3;
@ -1146,7 +1146,7 @@ SELECT * FROM
(SELECT empno,
depname,
salary,
count(empno) OVER (PARTITION BY depname ORDER BY salary DESC) c
count(1) OVER (PARTITION BY depname ORDER BY salary DESC) c
FROM empsalary) emp
WHERE c <= 3;
@ -1157,7 +1157,7 @@ SELECT * FROM
(SELECT empno,
depname,
salary,
count(empno) OVER () c
count(1) OVER () c
FROM empsalary) emp
WHERE c = 1;
@ -1165,7 +1165,7 @@ WHERE c = 1;
EXPLAIN (COSTS OFF)
SELECT * FROM
(SELECT *,
count(salary) OVER (PARTITION BY depname || '') c1, -- w1
count(1) OVER (PARTITION BY depname || '') c1, -- w1
row_number() OVER (PARTITION BY depname) rn, -- w2
count(*) OVER (PARTITION BY depname) c2, -- w2
count(*) OVER (PARTITION BY '' || depname) c3 -- w3
@ -1175,7 +1175,7 @@ SELECT * FROM
-- Ensure we correctly filter out all of the run conditions from each window
SELECT * FROM
(SELECT *,
count(salary) OVER (PARTITION BY depname || '') c1, -- w1
count(1) OVER (PARTITION BY depname || '') c1, -- w1
row_number() OVER (PARTITION BY depname) rn, -- w2
count(*) OVER (PARTITION BY depname) c2, -- w2
count(*) OVER (PARTITION BY '' || depname) c3 -- w3
@ -1215,6 +1215,15 @@ SELECT * FROM
FROM empsalary) emp
WHERE c = 1;
-- Ensure we don't use a run condition when the WindowFunc arg contains a Var
EXPLAIN (COSTS OFF)
SELECT * FROM
(SELECT empno,
salary,
count(empno) OVER (ORDER BY empno DESC) c
FROM empsalary) emp
WHERE c = 1;
-- Ensure we don't use a run condition when the WindowFunc contains subplans
EXPLAIN (COSTS OFF)
SELECT * FROM