code: public function setTransactionIsolationLevel($level)
      {
          // translate SQL92 levels to CUBRID levels:
          switch ($level) {
              case Transaction::SERIALIZABLE:
                  $level = '6'; // SERIALIZABLE
                  break;
              case Transaction::REPEATABLE_READ:
                  $level = '5'; // REPEATABLE READ CLASS with REPEATABLE READ INSTANCES
                  break;
              case Transaction::READ_COMMITTED:
                  $level = '4'; // REPEATABLE READ CLASS with READ COMMITTED INSTANCES
                  break;
              case Transaction::READ_UNCOMMITTED:
                  $level = '3'; // REPEATABLE READ CLASS with READ UNCOMMITTED INSTANCES
                  break;
          }
          parent::setTransactionIsolationLevel($level);
      }
docs: {@inheritdoc}
  @see http://www.cubrid.org/manual/91/en/sql/transaction.html#database-concurrency