commit ebbb52dd62ed7796cb3f0a2a33fbe6d33de3150a
Author: Simon Riggs <simon.riggs@enterprisedb.com>
Date:   Thu Mar 24 12:08:25 2022 +0000

    Test concurrent UPDATE version of read-write-unique-4.spec

diff --git a/src/test/isolation/expected/read-write-unique-5.out b/src/test/isolation/expected/read-write-unique-5.out
new file mode 100644
index 0000000000..179a17bd19
--- /dev/null
+++ b/src/test/isolation/expected/read-write-unique-5.out
@@ -0,0 +1,49 @@
+Parsed test spec with 2 sessions
+
+starting permutation: r1 r2 w1 w2 c1 c2
+step r1: SELECT COALESCE(MAX(invoice_number) + 1, 1) FROM invoice WHERE year = 2016;
+coalesce
+--------
+       3
+(1 row)
+
+step r2: SELECT COALESCE(MAX(invoice_number) + 1, 1) FROM invoice WHERE year = 2016;
+coalesce
+--------
+       3
+(1 row)
+
+step w1: UPDATE invoice SET invoice_number = 3 WHERE year = 2016;
+step w2: UPDATE invoice SET invoice_number = 3 WHERE year = 2016; <waiting ...>
+step c1: COMMIT;
+step w2: <... completed>
+ERROR:  could not serialize access due to concurrent update
+step c2: COMMIT;
+
+starting permutation: r1 w1 w2 c1 c2
+step r1: SELECT COALESCE(MAX(invoice_number) + 1, 1) FROM invoice WHERE year = 2016;
+coalesce
+--------
+       3
+(1 row)
+
+step w1: UPDATE invoice SET invoice_number = 3 WHERE year = 2016;
+step w2: UPDATE invoice SET invoice_number = 3 WHERE year = 2016; <waiting ...>
+step c1: COMMIT;
+step w2: <... completed>
+ERROR:  could not serialize access due to concurrent update
+step c2: COMMIT;
+
+starting permutation: r2 w1 w2 c1 c2
+step r2: SELECT COALESCE(MAX(invoice_number) + 1, 1) FROM invoice WHERE year = 2016;
+coalesce
+--------
+       3
+(1 row)
+
+step w1: UPDATE invoice SET invoice_number = 3 WHERE year = 2016;
+step w2: UPDATE invoice SET invoice_number = 3 WHERE year = 2016; <waiting ...>
+step c1: COMMIT;
+step w2: <... completed>
+ERROR:  could not serialize access due to concurrent update
+step c2: COMMIT;
diff --git a/src/test/isolation/isolation_schedule b/src/test/isolation/isolation_schedule
index 8e87098150..04d9e87021 100644
--- a/src/test/isolation/isolation_schedule
+++ b/src/test/isolation/isolation_schedule
@@ -5,6 +5,7 @@ test: read-write-unique
 test: read-write-unique-2
 test: read-write-unique-3
 test: read-write-unique-4
+test: read-write-unique-5
 test: simple-write-skew
 test: receipt-report
 test: temporal-range-integrity
diff --git a/src/test/isolation/specs/read-write-unique-5.spec b/src/test/isolation/specs/read-write-unique-5.spec
new file mode 100644
index 0000000000..e34e93ad98
--- /dev/null
+++ b/src/test/isolation/specs/read-write-unique-5.spec
@@ -0,0 +1,48 @@
+# Read-write-unique test.
+# Implementing a gapless sequence of ID numbers for each year.
+
+setup
+{
+  CREATE TABLE invoice (
+    year int,
+    invoice_number int,
+    PRIMARY KEY (year)
+  );
+
+  INSERT INTO invoice VALUES (2016, 2);
+}
+
+teardown
+{
+  DROP TABLE invoice;
+}
+
+session s1
+setup { BEGIN ISOLATION LEVEL SERIALIZABLE; }
+step r1 { SELECT COALESCE(MAX(invoice_number) + 1, 1) FROM invoice WHERE year = 2016; }
+step w1 { UPDATE invoice SET invoice_number = 3 WHERE year = 2016; }
+step c1 { COMMIT; }
+
+session s2
+setup { BEGIN ISOLATION LEVEL SERIALIZABLE; }
+step r2 { SELECT COALESCE(MAX(invoice_number) + 1, 1) FROM invoice WHERE year = 2016; }
+step w2 { UPDATE invoice SET invoice_number = 3 WHERE year = 2016; }
+step c2 { COMMIT; }
+
+# if they both read first then there should be an SSI conflict
+permutation r1 r2 w1 w2 c1 c2
+
+# cases where one session doesn't explicitly read before writing:
+
+# if s2 doesn't explicitly read, then trying to insert the value
+# generates a unique constraint violation after s1 commits, as if s2
+# ran after s1
+permutation r1 w1 w2 c1 c2
+
+# if s1 doesn't explicitly read, but s2 does, then s1 inserts and
+# commits first, should s2 experience an SSI failure instead of a
+# unique constraint violation?  there is no serial order of operations
+# (s1, s2) or (s2, s1) where s1 succeeds, and s2 doesn't see the row
+# in an explicit select but then fails to insert due to unique
+# constraint violation
+permutation r2 w1 w2 c1 c2