From 6e6668b04bc4e47df4e6e7ea8154e5abd28a209b Mon Sep 17 00:00:00 2001
From: shihao zhong <zhong950419@gmail.com>
Date: Tue, 27 Oct 2026 21:32:59 -0400
Subject: [PATCH 2/3] Add an isolation test for not-null constraints seen by
 older snapshots.

---
 .../expected/notnull-old-snapshot.out         | 85 +++++++++++++++++++
 src/test/isolation/isolation_schedule         |  1 +
 .../isolation/specs/notnull-old-snapshot.spec | 34 ++++++++
 3 files changed, 120 insertions(+)
 create mode 100644 src/test/isolation/expected/notnull-old-snapshot.out
 create mode 100644 src/test/isolation/specs/notnull-old-snapshot.spec

diff --git a/src/test/isolation/expected/notnull-old-snapshot.out b/src/test/isolation/expected/notnull-old-snapshot.out
new file mode 100644
index 00000000000..4c766cd710e
--- /dev/null
+++ b/src/test/isolation/expected/notnull-old-snapshot.out
@@ -0,0 +1,85 @@
+Parsed test spec with 2 sessions
+
+starting permutation: s1_begin s2_validate s1_isnull s1_counta s1_cols s1_coalesce s1_commit
+step s1_begin: BEGIN ISOLATION LEVEL REPEATABLE READ; SELECT count(*) FROM nn_snap WHERE a IS NULL;
+count
+-----
+    5
+(1 row)
+
+step s2_validate: UPDATE nn_snap SET a = 0 WHERE a IS NULL; ALTER TABLE nn_snap VALIDATE CONSTRAINT nn_snap_a_nn;
+step s1_isnull: SELECT count(*) FROM nn_snap WHERE a IS NULL;
+count
+-----
+    5
+(1 row)
+
+step s1_counta: SELECT count(a), count(*) FROM nn_snap;
+count|count
+-----+-----
+    5|   10
+(1 row)
+
+step s1_cols: SELECT id, a, b FROM nn_snap WHERE id <= 5;
+id|a|  b
+--+-+---
+ 1| |101
+ 2| |102
+ 3| |103
+ 4| |104
+ 5| |105
+(5 rows)
+
+step s1_coalesce: SELECT id, coalesce(a, -1) FROM nn_snap WHERE id <= 5;
+id|coalesce
+--+--------
+ 1|      -1
+ 2|      -1
+ 3|      -1
+ 4|      -1
+ 5|      -1
+(5 rows)
+
+step s1_commit: COMMIT;
+
+starting permutation: s1_snap s2_setnotnull s1_isnull s1_counta s1_cols s1_coalesce s1_commit
+step s1_snap: BEGIN ISOLATION LEVEL REPEATABLE READ; SELECT 1;
+?column?
+--------
+       1
+(1 row)
+
+step s2_setnotnull: ALTER TABLE nn_snap DROP CONSTRAINT nn_snap_a_nn; UPDATE nn_snap SET a = 0 WHERE a IS NULL; ALTER TABLE nn_snap ALTER a SET NOT NULL;
+step s1_isnull: SELECT count(*) FROM nn_snap WHERE a IS NULL;
+count
+-----
+    5
+(1 row)
+
+step s1_counta: SELECT count(a), count(*) FROM nn_snap;
+count|count
+-----+-----
+    5|   10
+(1 row)
+
+step s1_cols: SELECT id, a, b FROM nn_snap WHERE id <= 5;
+id|a|  b
+--+-+---
+ 1| |101
+ 2| |102
+ 3| |103
+ 4| |104
+ 5| |105
+(5 rows)
+
+step s1_coalesce: SELECT id, coalesce(a, -1) FROM nn_snap WHERE id <= 5;
+id|coalesce
+--+--------
+ 1|      -1
+ 2|      -1
+ 3|      -1
+ 4|      -1
+ 5|      -1
+(5 rows)
+
+step s1_commit: COMMIT;
diff --git a/src/test/isolation/isolation_schedule b/src/test/isolation/isolation_schedule
index bf9a2037c70..074d0183802 100644
--- a/src/test/isolation/isolation_schedule
+++ b/src/test/isolation/isolation_schedule
@@ -99,6 +99,7 @@ test: alter-table-1
 test: alter-table-2
 test: alter-table-3
 test: alter-table-4
+test: notnull-old-snapshot
 test: create-trigger
 test: sequence-ddl
 test: async-notify
diff --git a/src/test/isolation/specs/notnull-old-snapshot.spec b/src/test/isolation/specs/notnull-old-snapshot.spec
new file mode 100644
index 00000000000..09c311ed113
--- /dev/null
+++ b/src/test/isolation/specs/notnull-old-snapshot.spec
@@ -0,0 +1,34 @@
+# A snapshot older than a not-null constraint can still see tuples with
+# nulls in the constrained column.  Neither the planner nor the tuple
+# deforming fast path may rely on the constraint for such a snapshot.
+
+setup
+{
+  CREATE TABLE nn_snap (id int PRIMARY KEY, a int, b int, c text);
+  INSERT INTO nn_snap SELECT g, CASE WHEN g <= 5 THEN NULL ELSE g * 10 END,
+    g + 100, 'c' || g FROM generate_series(1, 10) g;
+  ALTER TABLE nn_snap ADD CONSTRAINT nn_snap_a_nn NOT NULL a NOT VALID;
+}
+
+teardown
+{
+  DROP TABLE nn_snap;
+}
+
+session s1
+step s1_begin		{ BEGIN ISOLATION LEVEL REPEATABLE READ; SELECT count(*) FROM nn_snap WHERE a IS NULL; }
+step s1_snap		{ BEGIN ISOLATION LEVEL REPEATABLE READ; SELECT 1; }
+step s1_isnull		{ SELECT count(*) FROM nn_snap WHERE a IS NULL; }
+step s1_counta		{ SELECT count(a), count(*) FROM nn_snap; }
+step s1_cols		{ SELECT id, a, b FROM nn_snap WHERE id <= 5; }
+step s1_coalesce	{ SELECT id, coalesce(a, -1) FROM nn_snap WHERE id <= 5; }
+step s1_commit		{ COMMIT; }
+
+session s2
+step s2_validate	{ UPDATE nn_snap SET a = 0 WHERE a IS NULL; ALTER TABLE nn_snap VALIDATE CONSTRAINT nn_snap_a_nn; }
+step s2_setnotnull	{ ALTER TABLE nn_snap DROP CONSTRAINT nn_snap_a_nn; UPDATE nn_snap SET a = 0 WHERE a IS NULL; ALTER TABLE nn_snap ALTER a SET NOT NULL; }
+
+# constraint validated after s1 took its snapshot and read the table
+permutation s1_begin s2_validate s1_isnull s1_counta s1_cols s1_coalesce s1_commit
+# constraint created after s1 took its snapshot
+permutation s1_snap s2_setnotnull s1_isnull s1_counta s1_cols s1_coalesce s1_commit
-- 
2.37.1 (Apple Git-137.1)