From 85ccd09759b06a383c89b985b45827e0c631186e Mon Sep 17 00:00:00 2001
From: Peter Geoghegan <pg@bowt.ie>
Date: Sat, 1 Aug 2026 18:30:22 -0400
Subject: [PATCH] Add isolation test for SET NOT NULL with an older snapshot

---
 .../expected/alter-table-set-not-null.out     | 18 ++++++++++++
 src/test/isolation/isolation_schedule         |  1 +
 .../specs/alter-table-set-not-null.spec       | 29 +++++++++++++++++++
 3 files changed, 48 insertions(+)
 create mode 100644 src/test/isolation/expected/alter-table-set-not-null.out
 create mode 100644 src/test/isolation/specs/alter-table-set-not-null.spec

diff --git a/src/test/isolation/expected/alter-table-set-not-null.out b/src/test/isolation/expected/alter-table-set-not-null.out
new file mode 100644
index 000000000..592b849e9
--- /dev/null
+++ b/src/test/isolation/expected/alter-table-set-not-null.out
@@ -0,0 +1,18 @@
+Parsed test spec with 2 sessions
+
+starting permutation: s1snap s2del s2nn s1read s1c
+step s1snap: SELECT 1 AS snapshot_taken;
+snapshot_taken
+--------------
+             1
+(1 row)
+
+step s2del: DELETE FROM nn WHERE a IS NULL;
+step s2nn: ALTER TABLE nn ALTER COLUMN a SET NOT NULL;
+step s1read: SELECT a, b, c FROM nn;
+a| b| c
+-+--+--
+ |42|43
+(1 row)
+
+step s1c: COMMIT;
diff --git a/src/test/isolation/isolation_schedule b/src/test/isolation/isolation_schedule
index df8ce44ed..949cae989 100644
--- a/src/test/isolation/isolation_schedule
+++ b/src/test/isolation/isolation_schedule
@@ -95,6 +95,7 @@ test: alter-table-1
 test: alter-table-2
 test: alter-table-3
 test: alter-table-4
+test: alter-table-set-not-null
 test: create-trigger
 test: sequence-ddl
 test: async-notify
diff --git a/src/test/isolation/specs/alter-table-set-not-null.spec b/src/test/isolation/specs/alter-table-set-not-null.spec
new file mode 100644
index 000000000..37f3dc03e
--- /dev/null
+++ b/src/test/isolation/specs/alter-table-set-not-null.spec
@@ -0,0 +1,29 @@
+# ALTER TABLE - SET NOT NULL with an older snapshot
+#
+# SET NOT NULL validates the column by scanning only the rows visible to its
+# own snapshot, and does not rewrite the table.  A transaction holding an
+# older snapshot can therefore still see a row whose column is null, and must
+# continue to read that row correctly.
+
+setup
+{
+ CREATE TABLE nn (a int, b int, c int);
+ INSERT INTO nn VALUES (NULL, 42, 43);
+}
+
+teardown
+{
+ DROP TABLE nn;
+}
+
+session s1
+setup		{ BEGIN ISOLATION LEVEL REPEATABLE READ; }
+step s1snap	{ SELECT 1 AS snapshot_taken; }
+step s1read	{ SELECT a, b, c FROM nn; }
+step s1c	{ COMMIT; }
+
+session s2
+step s2del	{ DELETE FROM nn WHERE a IS NULL; }
+step s2nn	{ ALTER TABLE nn ALTER COLUMN a SET NOT NULL; }
+
+permutation s1snap s2del s2nn s1read s1c
-- 
2.53.0