planner: "for update" should not work in a single autocommit statement (#11715)

[sre-bot]

cherry-pick #11715 to release-3.0

---

What problem does this PR solve?

mysql> show create table t;
+-------+------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                 |
+-------+------------------------------------------------------------------------------------------------------------------------------+
| t     | CREATE TABLE `t` (
  `id` int(11) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin |
+-------+------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)

mysql> select * from t where id = 9 for update;
ERROR 2013 (HY000): Lost connection to MySQL server during query

What is changed and how it works?

The bug is introduced in this PR #10972

github.com/pingcap/tidb/server.(*clientConn).Run.func1
	/media/genius/OS/project/src/github.com/pingcap/tidb/server/conn.go:600
runtime.gopanic
	/media/genius/OS/project/go/src/runtime/panic.go:522
github.com/pingcap/tidb/server.(*clientConn).writeResultset.func1
	/media/genius/OS/project/src/github.com/pingcap/tidb/server/conn.go:1268
runtime.gopanic
	/media/genius/OS/project/go/src/runtime/panic.go:522
runtime.panicmem
	/media/genius/OS/project/go/src/runtime/panic.go:82
runtime.sigpanic
	/media/genius/OS/project/go/src/runtime/signal_unix.go:390
github.com/pingcap/tidb/session.(*TxnState).LockKeys
	<autogenerated>:1
github.com/pingcap/tidb/executor.(*PointGetExecutor).lockKeyIfNeeded
	/media/genius/OS/project/src/github.com/pingcap/tidb/executor/point_get.go:152
github.com/pingcap/tidb/executor.(*PointGetExecutor).Next
	/media/genius/OS/project/src/github.com/pingcap/tidb/executor/point_get.go:132
github.com/pingcap/tidb/executor.Next
	/media/genius/OS/project/src/github.com/pingcap/tidb/executor/executor.go:200
github.com/pingcap/tidb/executor.(*recordSet).Next
	/media/genius/OS/project/src/github.com/pingcap/tidb/executor/adapter.go:113
github.com/pingcap/tidb/server.(*tidbResultSet).Next
	/media/genius/OS/project/src/github.com/pingcap/tidb/server/driver_tidb.go:365
github.com/pingcap/tidb/server.(*clientConn).writeChunks
	/media/genius/OS/project/src/github.com/pingcap/tidb/server/conn.go:1315
github.com/pingcap/tidb/server.(*clientConn).writeResultset
	/media/genius/OS/project/src/github.com/pingcap/tidb/server/conn.go:1281
github.com/pingcap/tidb/server.(*clientConn).handleQuery
	/media/genius/OS/project/src/github.com/pingcap/tidb/server/conn.go:1198
github.com/pingcap/tidb/server.(*clientConn).dispatch
	/media/genius/OS/project/src/github.com/pingcap/tidb/server/conn.go:897
github.com/pingcap/tidb/server.(*clientConn).Run
	/media/genius/OS/project/src/github.com/pingcap/tidb/server/conn.go:652
github.com/pingcap/tidb/server.(*Server).onConn
	/media/genius/OS/project/src/github.com/pingcap/tidb/server/server.go:438

The root cause of the panic is the mismatch of the life span between statement and executor.
We close the statement (or Txn in the auto-commit case) after Execute returns a RecordSet.
However, RecordSet.Next is still using the Txn, so the panic occurs.

This fix is actually a workaround: change select ... for update statement to normal select ... statement in the auto-commit case.

Check List

Tests

• Unit test

Related changes

• Need to cherry-pick to the release branch

[sre-bot]

/run-all-tests

[zz-jason]

LGTM

[winoros]

lgtm

[sre-bot]

Sorry @winoros, you don't have permission to trigger auto merge event on this branch.