code: func (m *Meta) GetAllHistoryDDLJobs() ([]*model.Job, error) {
  	pairs, err := m.txn.HGetAll(mDDLJobHistoryKey)
  	if err != nil {
  		return nil, errors.Trace(err)
  	}
  	jobs := make([]*model.Job, 0, len(pairs))
  	for _, pair := range pairs {
  		job := &model.Job{}
  		err = job.Decode(pair.Value)
  		if err != nil {
  			return nil, errors.Trace(err)
  		}
  		jobs = append(jobs, job)
  	}
  	sorter := &jobsSorter{jobs: jobs}
  	sort.Sort(sorter)
  	return jobs, nil
  }
docs: // GetAllHistoryDDLJobs gets all history DDL jobs.