Can't open metadata lock

[jiyfhust]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

mysql> show global variables like "%tidb_enable_metadata_lock%";
+---------------------------+-------+
| Variable_name             | Value |
+---------------------------+-------+
| tidb_enable_metadata_lock | ON    |
+---------------------------+-------+
1 row in set (0.00 sec)

mysql> set global tidb_enable_metadata_lock=0;
Query OK, 0 rows affected (0.15 sec)

mysql> show global variables like "%tidb_enable_metadata_lock%";
+---------------------------+-------+
| Variable_name             | Value |
+---------------------------+-------+
| tidb_enable_metadata_lock | OFF   |
+---------------------------+-------+
1 row in set (0.00 sec)

mysql> set global tidb_enable_metadata_lock=1;
Query OK, 0 rows affected (0.02 sec)

mysql> show global variables like "%tidb_enable_metadata_lock%";
+---------------------------+-------+
| Variable_name             | Value |
+---------------------------+-------+
| tidb_enable_metadata_lock | OFF   |
+---------------------------+-------+
1 row in set (0.00 sec)

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

mysql> set global tidb_enable_metadata_lock=1;
Query OK, 0 rows affected (0.02 sec)


mysql> show global variables like "%tidb_enable_metadata_lock%";
+---------------------------+-------+
| Variable_name             | Value |
+---------------------------+-------+
| tidb_enable_metadata_lock | ON    |
+---------------------------+-------+
1 row in set (0.00 sec)

3. What did you see instead (Required)

Is it the reason for the problem?

tidb/ddl/ddl.go

Line 1247 in 96e345d

if enable {

	if enable {
		sql := fmt.Sprintf("UPDATE HIGH_PRIORITY %[1]s.%[2]s SET VARIABLE_VALUE = %[4]d WHERE VARIABLE_NAME = '%[3]s'",
			mysql.SystemDB, mysql.GlobalVariablesTable, variable.TiDBEnableMDL, 0)
		sess, err := d.sessPool.get()
		if err != nil {
			logutil.BgLogger().Warn("[ddl] get session failed", zap.Error(err))
			return nil
		}
		defer d.sessPool.put(sess)
		se := newSession(sess)
		_, err = se.execute(ctx, sql, "disableMDL")
		if err != nil {
			logutil.BgLogger().Warn("[ddl] disable MDL failed", zap.Error(err))
		}
		return nil
	}

4. What is your TiDB version? (Required)

mysql> SELECT tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v6.6.0
Edition: Community
Git Commit Hash: f4ca0821fb96a2bdd37d2fb97eb26c07fc58d4e4
Git Branch: heads/refs/tags/v6.6.0
UTC Build Time: 2023-02-17 14:49:02
GoVersion: go1.19.5
Race Enabled: false
TiKV Min Version: 6.2.0-alpha
Check Table Before Drop: false
Store: tikv
1 row in set (0.00 sec)

[wjhuang2016]

Thanks for reporting this bug, it was introduced by PR

[jiyfhust]

@wjhuang2016 It seems remove the code can fix it?
Need i make a pull request for it?