Fabric MVCC 简介

// validateKVRead performs mvcc check for a key read during transaction simulation.
// i.e., it checks whether a key/version combination is already updated in the statedb (by an already committed block)
// or in the updates (by a preceding valid transaction in the current block)
func (v *validator) validateKVRead(ns string, kvRead *kvrwset.KVRead, updates *privacyenabledstate.PubUpdateBatch) (bool, error) {
    readVersion := rwsetutil.NewVersion(kvRead.Version)
	if updates.Exists(ns, kvRead.Key) {
		logger.Warnw("Transaction invalidation due to version mismatch, key in readset has been updated in a prior transaction in this block",
			"namespace", ns, "key", kvRead.Key, "readVersion", readVersion)
		return false, nil
	}
	committedVersion, err := v.db.GetVersion(ns, kvRead.Key)
	if err != nil {
		return false, err
	}

	logger.Debugw("Comparing readset version to committed version",
		"namespace", ns, "key", kvRead.Key, "readVersion", readVersion, "committedVersion", committedVersion)

	if !version.AreSame(committedVersion, readVersion) {
		logger.Warnw("Transaction invalidation due to version mismatch, readset version does not match committed version",
			"namespace", ns, "key", kvRead.Key, "readVersion", readVersion, "committedVersion", committedVersion)
		return false, nil
	}
	return true, nil
}

// Height represents the height of a transaction in blockchain
type Height struct {
	BlockNum uint64
	TxNum    uint64
}

// NewHeight constructs a new instance of Height
func NewHeight(blockNum, txNum uint64) *Height {
	return &Height{blockNum, txNum}
}

// NewHeightFromBytes constructs a new instance of Height from serialized bytes
func NewHeightFromBytes(b []byte) (*Height, int, error) {
	blockNum, n1, err := util.DecodeOrderPreservingVarUint64(b)
	if err != nil {
		return nil, -1, err
	}
	txNum, n2, err := util.DecodeOrderPreservingVarUint64(b[n1:])
	if err != nil {
		return nil, -1, err
	}
	return NewHeight(blockNum, txNum), n1 + n2, nil
}

// ToBytes serializes the Height
func (h *Height) ToBytes() []byte {
	blockNumBytes := util.EncodeOrderPreservingVarUint64(h.BlockNum)
	txNumBytes := util.EncodeOrderPreservingVarUint64(h.TxNum)
	return append(blockNumBytes, txNumBytes...)
}

// Compare returns -1, zero, or +1 based on whether this height is
// less than, equals to, or greater than the specified height respectively.
func (h *Height) Compare(h1 *Height) int {
	switch {
	case h.BlockNum < h1.BlockNum:
		return -1
	case h.BlockNum > h1.BlockNum:
		return 1
	case h.TxNum < h1.TxNum:
		return -1
	case h.TxNum > h1.TxNum:
		return 1
	default:
		return 0
	}
}

// String returns string for printing
func (h *Height) String() string {
	if h == nil {
		return "<nil>"
	}
	return fmt.Sprintf("{BlockNum: %d, TxNum: %d}", h.BlockNum, h.TxNum)
}

// AreSame returns true if both the heights are either nil or equal
func AreSame(h1 *Height, h2 *Height) bool {
	if h1 == nil {
		return h2 == nil
	}
	if h2 == nil {
		return false
	}
	return h1.Compare(h2) == 0
}