ddl: fix enable metadata lock (#41913)

close #41796
pingcap · Mar 8, 2023 · ed04e26 · ed04e26
1 parent e1cc3ac
commit ed04e26
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Showing 2 changed files with 25 additions and 21 deletions.
diff --git a/ddl/ddl.go b/ddl/ddl.go
@@ -1239,33 +1239,16 @@ func (d *ddl) startCleanDeadTableLock() {
 	}
 }
 
-// SwitchMDL enables MDL or disable DDL.
+// SwitchMDL enables MDL or disable MDL.
 func (d *ddl) SwitchMDL(enable bool) error {
-	ctx, cancel := context.WithTimeout(context.Background(), time.Second*30)
-	defer cancel()
-
-	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
-	}
-
 	isEnableBefore := variable.EnableMDL.Load()
 	if isEnableBefore == enable {
 		return nil
 	}
 
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second*30)
+	defer cancel()
+
 	// Check if there is any DDL running.
 	// This check can not cover every corner cases, so users need to guarantee that there is no DDL running by themselves.
 	sess, err := d.sessPool.get()

diff --git a/ddl/metadatalocktest/mdl_test.go b/ddl/metadatalocktest/mdl_test.go
@@ -904,6 +904,27 @@ func TestMDLEnable2Disable(t *testing.T) {
 	tk.MustExec("admin check table t")
 }
 
+func TestSwitchMDL(t *testing.T) {
+	store, dom := testkit.CreateMockStoreAndDomain(t)
+	sv := server.CreateMockServer(t, store)
+
+	sv.SetDomain(dom)
+	dom.InfoSyncer().SetSessionManager(sv)
+	defer sv.Close()
+
+	conn := server.CreateMockConn(t, sv)
+	tk := testkit.NewTestKitWithSession(t, store, conn.Context().Session)
+
+	tk.MustExec("set global tidb_enable_metadata_lock=0")
+	tk.MustQuery("show global variables like 'tidb_enable_metadata_lock'").Check(testkit.Rows("tidb_enable_metadata_lock OFF"))
+
+	tk.MustExec("set global tidb_enable_metadata_lock=1")
+	tk.MustQuery("show global variables like 'tidb_enable_metadata_lock'").Check(testkit.Rows("tidb_enable_metadata_lock ON"))
+
+	tk.MustExec("set global tidb_enable_metadata_lock=0")
+	tk.MustQuery("show global variables like 'tidb_enable_metadata_lock'").Check(testkit.Rows("tidb_enable_metadata_lock OFF"))
+}
+
 func TestMDLViewItself(t *testing.T) {
 	store, dom := testkit.CreateMockStoreAndDomain(t)
 	sv := server.CreateMockServer(t, store)