Add subxid-overflow "isolation" test

This test covers a few lines of subxid-overflow-handling code in various
part of the backend, which are otherwise uncovered.

Author: Simon Riggs <simon.riggs@enterprisedb.com>
Reviewed-by: Dilip Kumar <dilipbalaut@gmail.com>
Discussion: https://postgr.es/m/CANbhV-H8ov5+nCMBYQFKhO+UZJjrFgY_ORiMWr3RhS4+x44PzA@mail.gmail.com

src/include/storage/proc.h

@@ -32,6 +32,8 @@
  * If none of the caches have overflowed, we can assume that an XID that's not
  * listed anywhere in the PGPROC array is not a running transaction.  Else we
  * have to look at pg_subtrans.
+ *
+ * See src/test/isolation/specs/subxid-overflow.spec if you change this.
  */
 #define PGPROC_MAX_CACHED_SUBXIDS 64	/* XXX guessed-at value */
 

src/test/isolation/expected/subxid-overflow.out

@@ -0,0 +1,82 @@
+Parsed test spec with 3 sessions
+
+starting permutation: ins subxov xmax s2sel s1c
+step ins: TRUNCATE subxids; INSERT INTO subxids VALUES (0, 0);
+step subxov: BEGIN; SELECT gen_subxids(100);
+gen_subxids
+-----------
+           
+(1 row)
+
+step xmax: BEGIN; INSERT INTO subxids VALUES (99, 0); COMMIT;
+step s2sel: SELECT val FROM subxids WHERE subx = 0;
+val
+---
+  0
+(1 row)
+
+step s1c: COMMIT;
+
+starting permutation: ins subxov sub3 xmax s2brr s2s3 s3c s2s3 s2c s1c
+step ins: TRUNCATE subxids; INSERT INTO subxids VALUES (0, 0);
+step subxov: BEGIN; SELECT gen_subxids(100);
+gen_subxids
+-----------
+           
+(1 row)
+
+step sub3: BEGIN; SAVEPOINT s; INSERT INTO subxids VALUES (1, 0);
+step xmax: BEGIN; INSERT INTO subxids VALUES (99, 0); COMMIT;
+step s2brr: BEGIN ISOLATION LEVEL REPEATABLE READ;
+step s2s3: SELECT val FROM subxids WHERE subx = 1;
+val
+---
+(0 rows)
+
+step s3c: COMMIT;
+step s2s3: SELECT val FROM subxids WHERE subx = 1;
+val
+---
+(0 rows)
+
+step s2c: COMMIT;
+step s1c: COMMIT;
+
+starting permutation: ins subxov sub3 xmax s2brc s2s3 s3c s2s3 s2c s1c
+step ins: TRUNCATE subxids; INSERT INTO subxids VALUES (0, 0);
+step subxov: BEGIN; SELECT gen_subxids(100);
+gen_subxids
+-----------
+           
+(1 row)
+
+step sub3: BEGIN; SAVEPOINT s; INSERT INTO subxids VALUES (1, 0);
+step xmax: BEGIN; INSERT INTO subxids VALUES (99, 0); COMMIT;
+step s2brc: BEGIN ISOLATION LEVEL READ COMMITTED;
+step s2s3: SELECT val FROM subxids WHERE subx = 1;
+val
+---
+(0 rows)
+
+step s3c: COMMIT;
+step s2s3: SELECT val FROM subxids WHERE subx = 1;
+val
+---
+  0
+(1 row)
+
+step s2c: COMMIT;
+step s1c: COMMIT;
+
+starting permutation: ins subxov xmax s2upd s1c
+step ins: TRUNCATE subxids; INSERT INTO subxids VALUES (0, 0);
+step subxov: BEGIN; SELECT gen_subxids(100);
+gen_subxids
+-----------
+           
+(1 row)
+
+step xmax: BEGIN; INSERT INTO subxids VALUES (99, 0); COMMIT;
+step s2upd: UPDATE subxids SET val = 1 WHERE subx = 0; <waiting ...>
+step s1c: COMMIT;
+step s2upd: <... completed>

src/test/isolation/isolation_schedule

@@ -34,6 +34,7 @@ test: fk-deadlock2
 test: fk-partitioned-1
 test: fk-partitioned-2
 test: fk-snapshot
+test: subxid-overflow
 test: eval-plan-qual
 test: eval-plan-qual-trigger
 test: lock-update-delete

src/test/isolation/specs/subxid-overflow.spec

@@ -0,0 +1,79 @@
+# 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, val integer);
+
+CREATE OR REPLACE FUNCTION gen_subxids (n integer)
+ RETURNS VOID
+ LANGUAGE plpgsql
+AS $$
+BEGIN
+  IF n <= 0 THEN
+	UPDATE subxids SET val = 1 WHERE subx = 0;
+    RETURN;
+  ELSE
+    PERFORM gen_subxids(n - 1);
+    RETURN;
+  END IF;
+EXCEPTION /* generates a subxid */
+  WHEN raise_exception THEN NULL;
+END;
+$$;
+}
+
+teardown
+{
+ DROP TABLE subxids;
+ DROP FUNCTION gen_subxids(integer);
+}
+
+session s1
+# setup step for each test
+step ins	{ TRUNCATE subxids; INSERT INTO subxids VALUES (0, 0); }
+# long running transaction with overflowed subxids
+step subxov	{ BEGIN; SELECT gen_subxids(100); }
+# commit should always come last to make this long running
+step s1c	{ COMMIT; }
+
+session s2
+# move xmax forwards
+step xmax	{ BEGIN; INSERT INTO subxids VALUES (99, 0); COMMIT;}
+
+# step for test1
+step s2sel	{ SELECT val FROM subxids WHERE subx = 0; }
+
+# steps for test2
+step s2brr { BEGIN ISOLATION LEVEL REPEATABLE READ; }
+step s2brc { BEGIN ISOLATION LEVEL READ COMMITTED; }
+# look for data written by sub3
+step s2s3	{ SELECT val FROM subxids WHERE subx = 1; }
+step s2c	{ COMMIT; }
+
+# step for test3
+step s2upd	{ UPDATE subxids SET val = 1 WHERE subx = 0; }
+
+session s3
+# transaction with subxids that can commit before s1c
+step sub3	{ BEGIN; SAVEPOINT s; INSERT INTO subxids VALUES (1, 0); }
+step s3c	{ COMMIT; }
+
+# test1
+# s2sel will see subxid as still running
+# designed to test XidInMVCCSnapshot() when overflows, xid is found
+permutation ins subxov xmax s2sel s1c
+
+# test2
+# designed to test XidInMVCCSnapshot() when overflows, xid is not found
+# both SELECTs invisible
+permutation ins subxov sub3 xmax s2brr s2s3 s3c s2s3 s2c s1c
+# 2nd SELECT visible after commit
+permutation ins subxov sub3 xmax s2brc s2s3 s3c s2s3 s2c s1c
+
+# test3
+# designed to test XactLockTableWait() for overflows
+permutation ins subxov xmax s2upd s1c