code: func GetTableIndexKeyRange(tableID, indexID int64) (startKey, endKey []byte) {
  	startKey = EncodeIndexSeekKey(tableID, indexID, nil)
  	endKey = EncodeIndexSeekKey(tableID, indexID, []byte{255})
  	return
  }
docs: // GetTableIndexKeyRange returns table index's key range with tableID and indexID.