Function decodeRestoredValuesV5

pkg/tablecodec/tablecodec.go:866–903

decodeRestoredValuesV5 decodes index values whose format is introduced in TiDB 5.0. Unlike the format in TiDB 4.0, the new format is optimized for storage space: 1. If the index is a composed index, only the non-binary string column's value need to write to value, not all. 2. If a string column's co

(columns []rowcodec.ColInfo, results [][]byte, restoredVal []byte)

// 2. If a string column's collation is _bin, then we only write the number of the truncated spaces to value.
// 3. If a string column is char, not varchar, then we use the sortKey directly.
func decodeRestoredValuesV5(columns []rowcodec.ColInfo, results [][]byte, restoredVal []byte) ([][]byte, error) {
	colIDOffsets := buildColumnIDOffsets(columns)
	colInfosNeedRestore := buildRestoredColumn(columns)
	rd := rowcodec.NewByteDecoder(colInfosNeedRestore, nil, nil, nil)
	newResults, err := rd.DecodeToBytesNoHandle(colIDOffsets, restoredVal)
	if err != nil {
		return nil, errors.Trace(err)
	}
	for i := range newResults {
		noRestoreData := len(newResults[i]) == 0
		if noRestoreData {
			newResults[i] = results[i]
			continue
		}
		if collate.IsBinCollation(columns[i].Ft.GetCollate()) {
			noPaddingDatum, err := DecodeColumnValue(results[i], columns[i].Ft, nil)
			if err != nil {
				return nil, errors.Trace(err)
			}
			paddingCountDatum, err := DecodeColumnValue(newResults[i], types.NewFieldType(mysql.TypeLonglong), nil)
			if err != nil {
				return nil, errors.Trace(err)
			}
			noPaddingStr, paddingCount := noPaddingDatum.GetString(), int(paddingCountDatum.GetInt64())
			// Skip if padding count is 0.
			if paddingCount == 0 {
				newResults[i] = results[i]
				continue
			}
			newDatum := &noPaddingDatum
			newDatum.SetString(noPaddingStr+strings.Repeat(" ", paddingCount), newDatum.Collation())
			newResults[i] = newResults[i][:0]
			newResults[i] = append(newResults[i], rowcodec.BytesFlag)
			newResults[i] = codec.EncodeBytes(newResults[i], newDatum.GetBytes())
		}
	}
	return newResults, nil
}

func buildColumnIDOffsets(allCols []rowcodec.ColInfo) map[int64]int {
	colIDOffsets := make(map[int64]int, len(allCols))