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Fix IGNORE NULLS nullness cache for volatile window arguments.

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The IGNORE NULLS implementation caches whether a window function argument
evaluated to NULL or NOT NULL for a given partition row.  That is safe for
ordinary expressions, but not for volatile expressions, where evaluating the
same argument on the same row can produce a different NULL/NOT NULL result
later.

This could produce wrong results in two ways.  A row previously cached as
NULL could be skipped even though a later evaluation would return NOT NULL.
Conversely, a row cached as NOT NULL could be chosen as the target row, then
re-evaluated to fetch the actual value and return NULL.

Make the nullness cache conditional per argument.  Do not use it for
arguments containing volatile functions or subplans, following the same
conservative approach used for moving window aggregates.  Also avoid
re-evaluating non-cacheable partition arguments after the scan has already
found the target row.

Add regression tests covering volatile arguments and subplan arguments with
IGNORE NULLS.

Author: Chao Li <lic@highgo.com>
Reviewed-by: Tatsuo Ishii <ishii@postgresql.org>
Discussion: https://postgr.es/m/42B42506-6972-4266-8422-FB73E61D9DA7@gmail.com
This commit is contained in:
Tatsuo Ishii 2026-05-18 12:09:37 +09:00
parent e7b416b2fa
commit 26269fe3c8
3 changed files with 130 additions and 8 deletions
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44
src/backend/executor/nodeWindowAgg.c
View file

@ -76,6 +76,7 @@ typedef struct WindowObjectData
int64 *num_notnull_info; /* track size (number of tuples in
* partition) of the notnull_info array
* for each func args */
bool *notnull_info_cacheable; /* can we cache notnull_info? */
/*
* Null treatment options. One of: NO_NULLTREATMENT, PARSER_IGNORE_NULLS,
@ -3518,8 +3519,23 @@ init_notnull_info(WindowObject winobj, WindowStatePerFunc perfuncstate)
if (winobj->ignore_nulls == PARSER_IGNORE_NULLS)
{
int argno = 0;
ListCell *lc;
winobj->notnull_info = palloc0_array(uint8 *, numargs);
winobj->num_notnull_info = palloc0_array(int64, numargs);
winobj->notnull_info_cacheable = palloc_array(bool, numargs);
foreach(lc, perfuncstate->wfunc->args)
{
Node *arg = (Node *) lfirst(lc);
winobj->notnull_info_cacheable[argno] =
!contain_volatile_functions(arg) &&
!contain_subplans(arg);
argno++;
}
}
}
@ -3580,6 +3596,9 @@ get_notnull_info(WindowObject winobj, int64 pos, int argno)
uint8 mb;
int64 bpos;
if (!winobj->notnull_info_cacheable[argno])
return NN_UNKNOWN;
grow_notnull_info(winobj, pos, argno);
bpos = NN_POS_TO_BYTES(pos);
mbp = winobj->notnull_info[argno];
@ -3603,6 +3622,9 @@ put_notnull_info(WindowObject winobj, int64 pos, int argno, bool isnull)
uint8 val = isnull ? NN_NULL : NN_NOTNULL;
int shift;
if (!winobj->notnull_info_cacheable[argno])
return;
grow_notnull_info(winobj, pos, argno);
bpos = NN_POS_TO_BYTES(pos);
mbp = winobj->notnull_info[argno];
@ -3812,6 +3834,7 @@ WinGetFuncArgInPartition(WindowObject winobj, int argno,
int notnull_relpos;
int forward;
bool myisout;
bool got_datum;
Assert(WindowObjectIsValid(winobj));
winstate = winobj->winstate;
@ -3860,6 +3883,7 @@ WinGetFuncArgInPartition(WindowObject winobj, int argno,
notnull_relpos = abs(relpos);
forward = relpos > 0 ? 1 : -1;
myisout = false;
got_datum = false;
datum = 0;
/*
@ -3905,25 +3929,29 @@ WinGetFuncArgInPartition(WindowObject winobj, int argno,
{
/*
* NOT NULL info does not exist yet. Get tuple and evaluate func
* arg in partition. We ignore the return value from
* gettuple_eval_partition because we are just interested in
* whether we are inside or outside of partition, NULL or NOT
* NULL.
* arg in partition. Keep the return value in case this row is the
* target; re-evaluating a volatile argument could give a
* different nullness status.
*/
(void) gettuple_eval_partition(winobj, argno,
abs_pos, isnull, &myisout);
datum = gettuple_eval_partition(winobj, argno,
abs_pos, isnull, &myisout);
if (myisout) /* out of partition? */
break;
if (!*isnull)
{
notnull_offset++;
if (notnull_offset >= notnull_relpos)
got_datum = true;
}
/* record the row status */
put_notnull_info(winobj, abs_pos, argno, *isnull);
}
} while (notnull_offset < notnull_relpos);
/* get tuple and evaluate func arg in partition */
datum = gettuple_eval_partition(winobj, argno,
abs_pos, isnull, &myisout);
if (!got_datum)
datum = gettuple_eval_partition(winobj, argno,
abs_pos, isnull, &myisout);
if (!myisout && set_mark)
WinSetMarkPosition(winobj, mark_pos);
if (isout)

66
src/test/regress/expected/window.out
View file

@ -5964,6 +5964,72 @@ WINDOW w AS (ORDER BY x ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING);
5 | 4
(5 rows)
-- volatile arguments cannot use the IGNORE NULLS nullness cache
CREATE TEMPORARY SEQUENCE null_treatment_seq;
CREATE FUNCTION pg_temp.volatile_null(i int) RETURNS int
LANGUAGE sql VOLATILE AS
$$
SELECT CASE WHEN nextval('null_treatment_seq') % 2 = 0 THEN i ELSE NULL END;
$$;
SELECT x,
first_value(pg_temp.volatile_null(x)) IGNORE NULLS
OVER (ORDER BY x ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)
FROM generate_series(1,5) g(x);
x | first_value
---+-------------
1 |
2 | 1
3 | 2
4 | 2
5 | 2
(5 rows)
SELECT last_value FROM null_treatment_seq;
last_value
------------
8
(1 row)
ALTER SEQUENCE null_treatment_seq RESTART WITH 1;
SELECT x,
lead(pg_temp.volatile_null(x), 1) IGNORE NULLS OVER (ORDER BY x)
FROM generate_series(1,5) g(x);
x | lead
---+------
1 | 3
2 | 4
3 | 5
4 |
5 |
(5 rows)
SELECT last_value FROM null_treatment_seq;
last_value
------------
7
(1 row)
ALTER SEQUENCE null_treatment_seq RESTART WITH 1;
SELECT x,
first_value((SELECT CASE WHEN nextval('null_treatment_seq') % 2 = 0
THEN x ELSE NULL END)) IGNORE NULLS
OVER (ORDER BY x ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)
FROM generate_series(1,5) g(x);
x | first_value
---+-------------
1 |
2 | 1
3 | 2
4 | 2
5 | 2
(5 rows)
SELECT last_value FROM null_treatment_seq;
last_value
------------
8
(1 row)
--cleanup
DROP TABLE planets CASCADE;
NOTICE: drop cascades to view planets_view

28
src/test/regress/sql/window.sql
View file

@ -2157,5 +2157,33 @@ SELECT x,
FROM generate_series(1,5) g(x)
WINDOW w AS (ORDER BY x ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING);
-- volatile arguments cannot use the IGNORE NULLS nullness cache
CREATE TEMPORARY SEQUENCE null_treatment_seq;
CREATE FUNCTION pg_temp.volatile_null(i int) RETURNS int
LANGUAGE sql VOLATILE AS
$$
SELECT CASE WHEN nextval('null_treatment_seq') % 2 = 0 THEN i ELSE NULL END;
$$;
SELECT x,
first_value(pg_temp.volatile_null(x)) IGNORE NULLS
OVER (ORDER BY x ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)
FROM generate_series(1,5) g(x);
SELECT last_value FROM null_treatment_seq;
ALTER SEQUENCE null_treatment_seq RESTART WITH 1;
SELECT x,
lead(pg_temp.volatile_null(x), 1) IGNORE NULLS OVER (ORDER BY x)
FROM generate_series(1,5) g(x);
SELECT last_value FROM null_treatment_seq;
ALTER SEQUENCE null_treatment_seq RESTART WITH 1;
SELECT x,
first_value((SELECT CASE WHEN nextval('null_treatment_seq') % 2 = 0
THEN x ELSE NULL END)) IGNORE NULLS
OVER (ORDER BY x ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)
FROM generate_series(1,5) g(x);
SELECT last_value FROM null_treatment_seq;
--cleanup
DROP TABLE planets CASCADE;