code: func LoadGlobalVars(ctx sessionctx.Context, varNames []string) error {
  	if sctx, ok := ctx.(sqlexec.RestrictedSQLExecutor); ok {
  		nameList := ""
  		for i, name := range varNames {
  			if i > 0 {
  				nameList += ", "
  			}
  			nameList += fmt.Sprintf("'%s'", name)
  		}
  		sql := fmt.Sprintf(loadGlobalVarsSQL, nameList)
  		rows, _, err := sctx.ExecRestrictedSQL(ctx, sql)
  		if err != nil {
  			return errors.Trace(err)
  		}
  		for _, row := range rows {
  			varName := row.GetString(0)
  			varValue := row.GetString(1)
  			variable.SetLocalSystemVar(varName, varValue)
  		}
  	}
  	return nil
  }
docs: // LoadGlobalVars loads global variable from mysql.global_variables.