code: func (m *Meta) ListDatabases() ([]*model.DBInfo, error) {
  	res, err := m.txn.HGetAll(mDBs)
  	if err != nil {
  		return nil, errors.Trace(err)
  	}
  
  	dbs := make([]*model.DBInfo, 0, len(res))
  	for _, r := range res {
  		dbInfo := &model.DBInfo{}
  		err = json.Unmarshal(r.Value, dbInfo)
  		if err != nil {
  			return nil, errors.Trace(err)
  		}
  		dbs = append(dbs, dbInfo)
  	}
  	return dbs, nil
  }
docs: // ListDatabases shows all databases.