From 0d25ea218666a0e76950cbb03517a014d6b3abac Mon Sep 17 00:00:00 2001 From: "Chao Li (Evan)" Date: Thu, 14 May 2026 11:59:34 +0800 Subject: [PATCH v2] Fix IGNORE NULLS nullness cache for volatile window arguments 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 Reviewed-by: Tatsuo Ishii Discussion: https://postgr.es/m/42B42506-6972-4266-8422-FB73E61D9DA7@gmail.com --- src/backend/executor/nodeWindowAgg.c | 44 +++++++++++++++---- src/test/regress/expected/window.out | 66 ++++++++++++++++++++++++++++ src/test/regress/sql/window.sql | 28 ++++++++++++ 3 files changed, 130 insertions(+), 8 deletions(-) diff --git a/src/backend/executor/nodeWindowAgg.c b/src/backend/executor/nodeWindowAgg.c index 5cc39bd9086..f1c524d00df 100644 --- a/src/backend/executor/nodeWindowAgg.c +++ b/src/backend/executor/nodeWindowAgg.c @@ -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) diff --git a/src/test/regress/expected/window.out b/src/test/regress/expected/window.out index e6aac27a2a9..de0e14a686e 100644 --- a/src/test/regress/expected/window.out +++ b/src/test/regress/expected/window.out @@ -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 diff --git a/src/test/regress/sql/window.sql b/src/test/regress/sql/window.sql index 305549b104d..17261135dc3 100644 --- a/src/test/regress/sql/window.sql +++ b/src/test/regress/sql/window.sql @@ -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; -- 2.50.1 (Apple Git-155)