ddl: prevent dropping in-use resource group

ddl/ddl_api.go

@@ -7668,6 +7668,20 @@ func (d *ddl) DropResourceGroup(ctx sessionctx.Context, stmt *ast.DropResourceGr
 		return err
 	}
 
+	// check to see if some user has dependency on the group
+	exec := ctx.(sqlexec.RestrictedSQLExecutor)
+	internalCtx := kv.WithInternalSourceType(context.Background(), kv.InternalTxnDDL)
+	sql := "select user from mysql.user where lower(json_extract(user_attributes, '$.resource_group')) ='\"" + groupName.L + "\"' limit 1"
+	rows, _, err := exec.ExecRestrictedSQL(internalCtx, nil, sql)
+	if err != nil {
+		err = errors.Errorf("system table mysql.user access failed")
+		return err
+	}
+	if len(rows) != 0 {
+		err = errors.Errorf("user [%s] depends on the resource group to drop", rows[0].GetString(0))
+		return err
+	}
+
 	job := &model.Job{
 		SchemaID:   group.ID,
 		SchemaName: group.Name.L,

ddl/resource_group_test.go

@@ -160,6 +160,10 @@ func TestResourceGroupBasic(t *testing.T) {
 	tk.MustGetErrCode("create user usr_fail resource group nil_group", mysql.ErrResourceGroupNotExists)
 	tk.MustExec("create user user2")
 	tk.MustGetErrCode("alter user user2 resource group nil_group", mysql.ErrResourceGroupNotExists)
+
+	tk.MustExec("create resource group do_not_delete_rg rru_per_sec=100 wru_per_sec=200")
+	tk.MustExec("create user usr3 resource group do_not_delete_rg")
+	tk.MustContainErrMsg("drop resource group do_not_delete_rg", "user [usr3] depends on the resource group to drop")
 }
 
 func testResourceGroupNameFromIS(t *testing.T, ctx sessionctx.Context, name string) *model.ResourceGroupInfo {

errno/errname.go

@@ -1102,7 +1102,7 @@ var MySQLErrName = map[uint16]*mysql.ErrMessage{
 	ErrResourceGroupNotExists:          mysql.Message("Unknown resource group '%-.192s'", nil),
 
 	ErrColumnInChange:               mysql.Message("column %s id %d does not exist, this column may have been updated by other DDL ran in parallel", nil),
-	ErrResourceGroupSupportDisabled: mysql.Message("Resource group feature is disabled", nil),
+	ErrResourceGroupSupportDisabled: mysql.Message("Resource control feature is disabled. Run `SET GLOBAL tidb_enable_resource_control='on'` to enable the feature", nil),
 
 	// TiKV/PD errors.
 	ErrPDServerTimeout:           mysql.Message("PD server timeout: %s", nil),