commit cdda7d36c59e20583f69130d2d05f20f6879d12f
Author: Simon Riggs <simon.riggs@enterprisedb.com>
Date:   Mon Aug 8 12:15:01 2022 +0100

    New iso tests for subxid-overflow

diff --git a/src/test/isolation/expected/subxid-overflow.out b/src/test/isolation/expected/subxid-overflow.out
new file mode 100644
index 0000000000..f6c96f9a34
--- /dev/null
+++ b/src/test/isolation/expected/subxid-overflow.out
@@ -0,0 +1,17 @@
+Parsed test spec with 2 sessions
+
+starting permutation: subxid xmax s2sel s1c
+step subxid: BEGIN; SELECT gen_subxids(100);
+gen_subxids
+-----------
+           
+(1 row)
+
+step xmax: BEGIN; INSERT INTO subxids VALUES (1); COMMIT;
+step s2sel: SELECT count(*) FROM subxids WHERE subx = 0;
+count
+-----
+    0
+(1 row)
+
+step s1c: COMMIT;
diff --git a/src/test/isolation/isolation_schedule b/src/test/isolation/isolation_schedule
index 529a4cbd4d..7e10cfe022 100644
--- a/src/test/isolation/isolation_schedule
+++ b/src/test/isolation/isolation_schedule
@@ -1,3 +1,4 @@
+test: subxid-overflow
 test: read-only-anomaly
 test: read-only-anomaly-2
 test: read-only-anomaly-3
diff --git a/src/test/isolation/specs/subxid-overflow.spec b/src/test/isolation/specs/subxid-overflow.spec
new file mode 100644
index 0000000000..fda9f449f1
--- /dev/null
+++ b/src/test/isolation/specs/subxid-overflow.spec
@@ -0,0 +1,46 @@
+# Subtransaction overflow
+#
+# This test is designed to cover some code paths which only occur when
+# one transaction has overflowed the subtransaction cache.
+
+setup
+{
+DROP TABLE IF EXISTS subxids;
+CREATE TABLE subxids (subx integer);
+
+CREATE OR REPLACE FUNCTION gen_subxids (n integer)
+ RETURNS VOID
+ LANGUAGE plpgsql
+AS $$
+BEGIN
+  IF n <= 0 THEN
+    INSERT INTO subxids VALUES (0);
+    RETURN;
+  ELSE
+    PERFORM gen_subxids(n - 1);
+    RETURN;
+  END IF;
+EXCEPTION /* generates a subxid */
+  WHEN raise_exception THEN NULL;
+END;
+$$;
+}
+
+teardown
+{
+ DROP TABLE subxids;
+ DROP FUNCTION gen_subxids(integer);
+}
+
+session s1
+step subxid	{ BEGIN; SELECT gen_subxids(100); }
+step s1c	{ COMMIT; }
+
+session s2
+# move xmax forwards
+step xmax	{ BEGIN; INSERT INTO subxids VALUES (1); COMMIT;}
+# will see step subxid as still running
+step s2sel	{ SELECT count(*) FROM subxids WHERE subx = 0; }
+
+# s2sel will see subxid as still running
+permutation subxid xmax s2sel s1c