cherry pick pingcap#33653 to release-5.4

Signed-off-by: ti-srebot <ti-srebot@pingcap.com>

executor/builder.go

@@ -112,6 +112,7 @@ func newExecutorBuilder(ctx sessionctx.Context, is infoschema.InfoSchema, ti *Te
 		ctx:              ctx,
 		is:               is,
 		Ti:               ti,
+		snapshotTSCached: isStaleness,
 		snapshotTS:       snapshotTS,
 		isStaleness:      isStaleness,
 		readReplicaScope: replicaReadScope,

executor/stale_txn_test.go

@@ -1245,3 +1245,21 @@ func (s *testStaleTxnSerialSuite) TestStaleReadNoExtraTSORequest(c *C) {
 	tk.MustQuery("select * from t")
 	failpoint.Disable("github.com/pingcap/tidb/session/assertTSONotRequest")
 }
+
+func TestIssue30872(t *testing.T) {
+	store, _, clean := testkit.CreateMockStoreAndDomain(t)
+	defer clean()
+
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("set tidb_txn_mode='pessimistic'")
+	tk.MustExec("set tx_isolation = 'READ-COMMITTED'")
+	tk.MustExec("create table t1 (id int primary key, v int)")
+	tk.MustExec("insert into t1 values(1, 10)")
+	time.Sleep(time.Millisecond * 100)
+	tk.MustExec("set @a=now(6)")
+	time.Sleep(time.Millisecond * 100)
+	tk.MustExec("update t1 set v=100 where id=1")
+	tk.MustExec("set autocommit=0")
+	tk.MustQuery("select * from t1 as of timestamp @a").Check(testkit.Rows("1 10"))
+}