code: func (m *Meta) updateDDLJob(index int64, job *model.Job, key []byte, updateRawArgs bool) error {
  	b, err := job.Encode(updateRawArgs)
  	if err == nil {
  		err = m.txn.LSet(key, index, b)
  	}
  	return errors.Trace(err)
  }
docs: // updateDDLJob updates the DDL job with index and key.
  // updateRawArgs is used to determine whether to update the raw args when encode the job.