add unique index may cause dangle index

[wjhuang2016]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

There is no simple way to reproduce.
We need to modify the code.
Here is the test case:

func TestAddIndexMergeDeleteUniqueOnWriteOnly(t *testing.T) {
	store, dom := testkit.CreateMockStoreAndDomain(t)

	tk := testkit.NewTestKit(t, store)
	tk.MustExec("use test")
	tk.MustExec("create table t(a enum('a', 'b', 'c', 'd', 'e', 'f'), b int default 0, c int, primary key(b, a) clustered, unique key(c));")

	tk1 := testkit.NewTestKit(t, store)
	tk1.MustExec("use test")

	d := dom.DDL()
	originalCallback := d.GetHook()
	defer d.SetHook(originalCallback)
	callback := &ddl.TestDDLCallback{}
	onJobUpdatedExportedFunc := func(job *model.Job) {
		if t.Failed() {
			return
		}
		var err error
		switch job.SchemaState {
		case model.StateDeleteOnly:
		case model.StateWriteOnly:
			_, err = tk1.Exec("insert into t values ('b', 5, 4);")
			assert.NoError(t, err)
		}
	}
	callback.OnJobRunBeforeExported = onJobUpdatedExportedFunc
	d.SetHook(callback)
	tk.MustExec("alter table t add unique index idx(a);")
	tk.MustExec("admin check table t;")
}

besides:
in doReorgWorkForCreateIndex()

		case model.ReorgTypeTxnMerge:
			done, ver, err = runReorgJobAndHandleErr(w, d, t, job, tbl, indexInfo, false)
			if err != nil || !done {
				return false, ver, errors.Trace(err)
			}

			sess, _ := w.sessPool.get()
			defer w.sessPool.put(sess)
			se := newSession(sess)
			_, err = se.execute(w.ctx, "update test.t set b=7;", "")
			if err != nil {
				return false, 0, err
			}
			_, err = se.execute(w.ctx, "delete from test.t;", "")
			if err != nil {
				return false, 0, err
			}
		}
		indexInfo.BackfillState = model.BackfillStateReadyToMerge

Modify the code to execute these two queries before the index schema change to BackfillStateReadyToMerge.

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

test pass

3. What did you see instead (Required)

admin check table t;, [], error stack [admin:8223]data inconsistency in table: t, index: idx, handle: {5, 2}, index-values:"handle: {5, 2}, values: [KindMysqlEnum b KindInt64 5 KindMysqlEnum b]" != record-values:""

4. What is your TiDB version? (Required)

master

[wjhuang2016]

closed by #40672