code: func (us *UnionScanExec) rowWithColsInTxn(t table.Table, h int64, cols []*table.Column) ([]types.Datum, error) {
  	key := t.RecordKey(h)
  	txn, err := us.ctx.Txn(true)
  	if err != nil {
  		return nil, err
  	}
  	value, err := txn.GetMemBuffer().Get(key)
  	if err != nil {
  		return nil, err
  	}
  	v, _, err := tables.DecodeRawRowData(us.ctx, t.Meta(), h, cols, value)
  	if err != nil {
  		return nil, err
  	}
  	return v, nil
  }
docs: // rowWithColsInTxn gets the row from the transaction buffer.