Unistore TiDB cannot handle foreign key in transaction

[YangKeao]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Prepare:

create table parent (id int primary key);
create table child(id int primary key, ref int, foreign key (ref) references parent(id));

insert into parent values (1);

Execute:

Transaction 1	Transaction 2
BEGIN;	BEGIN;
INSERT INTO child VALUES (1, 1);
	UPDATE parent SET id = 2 WHERE id = 1
COMMIT;
	COMMIT;

2. What did you expect to see? (Required)

UPDATE in transaction 2 failed.

3. What did you see instead (Required)

UPDATE in transaction 2 success.

4. What is your TiDB version? (Required)

master fa723c, with unistore.

This issue cannot be reproduced in TiKV store.

[YangKeao]

A test case:

func TestLockKeysInInsertIgnore(t *testing.T) {
	store := testkit.CreateMockStore(t)
	tk := testkit.NewTestKit(t, store)
	tk.MustExec("use test")
	tk.MustExec("create table t1 (id int primary key);")
	tk.MustExec("create table t2 (id int primary key, foreign key fk (id) references t1(id));")
	tk.MustExec("insert into t1 values (1)")
	tk.MustExec("BEGIN")
	tk.MustExec("INSERT INTO t2 VALUES (1)")
	var wg sync.WaitGroup
	var tk2CommitTime time.Time
	tk2StartTime := time.Now()
	wg.Add(1)
	go func() {
		defer wg.Done()
		tk2 := testkit.NewTestKit(t, store)
		tk2.MustExec("use test")
		tk2.MustExec("BEGIN")
		require.NotNil(t, tk2.ExecToErr("UPDATE t1 SET id = 2 WHERE id = 1"))
		tk2.MustExec("COMMIT")
		tk2CommitTime = time.Now()
	}()
	sleepDuration := 500 * time.Millisecond
	time.Sleep(sleepDuration)
	tk.MustExec("COMMIT")
	wg.Wait()
	require.Greater(t, tk2CommitTime.Sub(tk2StartTime), sleepDuration)
	tk.MustQuery("SELECT * FROM t1").Check(testkit.Rows("1"))
	tk.MustQuery("SELECT * FROM t2").Check(testkit.Rows("1"))
}

@you06 Told me it's a bug of unistore fair lock mechanism. This test will pass if we disable the tidb_pessimistic_txn_fair_locking for testkit2.