code: def _read_undone_shard_from_datastore(self, shard_id=None):
      
      self._work = {}
      client = self._datastore_client
      parent_key = client.key(KIND_WORK_TYPE, self._work_type_entity_id)
      filters = [('is_completed', '=', False)]
      if shard_id is not None:
        filters.append(('shard_id', '=', shard_id))
      for entity in client.query_fetch(kind=KIND_WORK, ancestor=parent_key,
                                       filters=filters):
        work_id = entity.key.flat_path[-1]
        self.work[work_id] = dict(entity)
        if len(self._work) >= MAX_WORK_RECORDS_READ:
          break
docs: Reads undone worke pieces which are assigned to shard with given id.