// loadLastIndex retrieves the last index from storage.
func (r *Replica) loadLastIndex() (uint64, error) {
	lastIndex := uint64(0)
	v, _, err := engine.MVCCGet(r.rm.Engine(),
		keys.RaftLastIndexKey(r.Desc().RangeID),
		roachpb.ZeroTimestamp, true /* consistent */, nil)
	if err != nil {
		return 0, err
	}
	if v != nil {
		var err error
		_, lastIndex, err = encoding.DecodeUint64(v.GetRawBytes())
		if err != nil {
			return 0, err
		}
	} else {
		// The log is empty, which means we are either starting from scratch
		// or the entire log has been truncated away. raftTruncatedState
		// handles both cases.
		lastEnt, err := r.raftTruncatedState()
		if err != nil {
			return 0, err
		}
		lastIndex = lastEnt.Index
	}
	return lastIndex, nil
}

func (rc *ResponseCache) decodeResponseCacheKey(encKey proto.EncodedKey) (proto.ClientCmdID, error) {
	ret := proto.ClientCmdID{}
	key, _, isValue := engine.MVCCDecodeKey(encKey)
	if isValue {
		return ret, util.Errorf("key %s is not a raw MVCC value", encKey)
	}
	if !bytes.HasPrefix(key, keys.LocalRangeIDPrefix) {
		return ret, util.Errorf("key %s does not have %s prefix", key, keys.LocalRangeIDPrefix)
	}
	// Cut the prefix and the Raft ID.
	b := key[len(keys.LocalRangeIDPrefix):]
	b, _ = encoding.DecodeUvarint(b)
	if !bytes.HasPrefix(b, keys.LocalResponseCacheSuffix) {
		return ret, util.Errorf("key %s does not contain the response cache suffix %s",
			key, keys.LocalResponseCacheSuffix)
	}
	// Cut the response cache suffix.
	b = b[len(keys.LocalResponseCacheSuffix):]
	// Now, decode the command ID.
	b, wt := encoding.DecodeUvarint(b)
	b, rd := encoding.DecodeUint64(b)
	if len(b) > 0 {
		return ret, util.Errorf("key %s has leftover bytes after decode: %s; indicates corrupt key",
			encKey, b)
	}
	ret.WallTime = int64(wt)
	ret.Random = int64(rd)
	return ret, nil
}

// GetInteger decodes an int64 value from the bytes field of the receiver. If
// the bytes field is not 0 or 8 bytes in length an error will be returned.
func (v *Value) GetInteger() (int64, error) {
	if v == nil || len(v.Bytes) == 0 {
		return 0, nil
	}
	if len(v.Bytes) != 8 {
		return 0, fmt.Errorf("uint64 value should be exactly 8 bytes: %d", len(v.Bytes))
	}
	_, u := encoding.DecodeUint64(v.Bytes)
	return int64(u), nil
}

func raftLogKeyPrint(key roachpb.Key) string {
	var logIndex uint64
	var err error
	key, logIndex, err = encoding.DecodeUint64(key)
	if err != nil {
		return fmt.Sprintf("/err<%v:%q>", err, []byte(key))
	}

	return fmt.Sprintf("/logIndex:%d", logIndex)
}

// GetInt decodes an int64 value from the bytes field of the receiver. If the
// bytes field is not 8 bytes in length or the tag is not INT an error will be
// returned.
func (v *Value) GetInt() (int64, error) {
	if tag := v.GetTag(); tag != ValueType_INT {
		return 0, fmt.Errorf("value type is not INT: %s", tag)
	}
	if len(v.Bytes) != 8 {
		return 0, fmt.Errorf("uint64 value should be exactly 8 bytes: %d", len(v.Bytes))
	}
	_, u := encoding.DecodeUint64(v.Bytes)
	return int64(u), nil
}

// GetFloat decodes a float64 value from the bytes field of the receiver. If
// the bytes field is not 8 bytes in length or the tag is not FLOAT an error
// will be returned.
func (v *Value) GetFloat() (float64, error) {
	if tag := v.GetTag(); tag != ValueType_FLOAT {
		return 0, fmt.Errorf("value type is not FLOAT: %s", tag)
	}
	if len(v.Bytes) != 8 {
		return 0, fmt.Errorf("float64 value should be exactly 8 bytes: %d", len(v.Bytes))
	}
	_, u := encoding.DecodeUint64(v.Bytes)
	return math.Float64frombits(u), nil
}

// GetInt decodes an int64 value from the bytes field of the receiver. If the
// bytes field is not 8 bytes in length or the tag is not INT an error will be
// returned.
func (v Value) GetInt() (int64, error) {
	if tag := v.Tag; tag != ValueType_INT {
		return 0, fmt.Errorf("value type is not %s: %s", ValueType_INT, tag)
	}
	if len(v.RawBytes) != 8 {
		return 0, fmt.Errorf("uint64 value should be exactly 8 bytes: %d", len(v.RawBytes))
	}
	_, u, err := encoding.DecodeUint64(v.RawBytes)
	if err != nil {
		return 0, err
	}
	return int64(u), nil
}

// GetFloat decodes a float64 value from the bytes field of the receiver. If
// the bytes field is not 8 bytes in length or the tag is not FLOAT an error
// will be returned.
func (v Value) GetFloat() (float64, error) {
	if tag := v.Tag; tag != ValueType_FLOAT {
		return 0, fmt.Errorf("value type is not %s: %s", ValueType_FLOAT, tag)
	}
	if len(v.RawBytes) != 8 {
		return 0, fmt.Errorf("float64 value should be exactly 8 bytes: %d", len(v.RawBytes))
	}
	_, u, err := encoding.DecodeUint64(v.RawBytes)
	if err != nil {
		return 0, err
	}
	return math.Float64frombits(u), nil
}

// ValueInt returns the value decoded as an int64. This method will panic if
// the value cannot be decoded as an int64.
func (kv *KeyValue) ValueInt() int64 {
	if kv.Value == nil {
		return 0
	}
	if i, ok := kv.Value.(*int64); ok {
		return *i
	}
	b := kv.ValueBytes()
	if len(b) == 0 {
		return 0
	}
	_, uint64val := roachencoding.DecodeUint64(b)
	return int64(uint64val)
}

// loadAppliedIndex retrieves the applied index from the supplied engine.
func (r *Range) loadAppliedIndex(eng engine.Engine) (uint64, error) {
	var appliedIndex uint64
	if r.isInitialized() {
		appliedIndex = raftInitialLogIndex
	} else {
		appliedIndex = 0
	}
	v, _, err := engine.MVCCGet(eng, keys.RaftAppliedIndexKey(r.Desc().RaftID),
		proto.ZeroTimestamp, true, nil)
	if err != nil {
		return 0, err
	}
	if v != nil {
		_, appliedIndex = encoding.DecodeUint64(v.Bytes)
	}
	return appliedIndex, nil
}

// loadAppliedIndex retrieves the applied index from the supplied engine.
func (r *Replica) loadAppliedIndex(eng engine.Engine) (uint64, error) {
	var appliedIndex uint64
	if r.isInitialized() {
		appliedIndex = raftInitialLogIndex
	} else {
		appliedIndex = 0
	}
	v, _, err := engine.MVCCGet(eng, keys.RaftAppliedIndexKey(r.Desc().RangeID),
		roachpb.ZeroTimestamp, true, nil)
	if err != nil {
		return 0, err
	}
	if v != nil {
		var err error
		_, appliedIndex, err = encoding.DecodeUint64(v.GetRawBytes())
		if err != nil {
			return 0, err
		}
	}
	return appliedIndex, nil
}

// outputDotFile generates a .dot file describing the current state of
// the gossip network. nodes is a map from network address to gossip
// node. edgeSet is empty on the first invocation, but
// its content is set to encompass the entire set of edges in the
// network when this method returns. It should be resupplied with each
// successive invocation, as it is used to determine which edges are
// new and which have been deleted and show those changes visually in
// the output graph. New edges are drawn green; edges which were
// removed over the course of the last simulation step(s) are drawn in
// a lightly-dashed red.
//
// The format of the output looks like this:
//
//   digraph G {
//   node [shape=record];
//        node1 [fontsize=12,label="{Node 1|MH=3}"]
//        node1 -> node3 [color=green]
//        node1 -> node4
//        node1 -> node5 [color=red,style=dotted]
//        node2 [fontsize=24,label="{Node 2|MH=2}"]
//        node2 -> node5
//        node3 [fontsize=18,label="{Node 3|MH=5}"]
//        node3 -> node5
//        node3 -> node4
//        node4 [fontsize=24,label="{Node 4|MH=4}"]
//        node4 -> node2
//        node5 [fontsize=24,label="{Node 5|MH=1}"]
//        node5 -> node2
//        node5 -> node3
//   }
//
// Returns the name of the output file and a boolean for whether or not
// the network has quiesced (that is, no new edges, and all nodes are
// connected).
func outputDotFile(dotFN string, cycle int, network *simulation.Network, edgeSet map[string]edge) (string, bool) {
	f, err := os.Create(dotFN)
	if err != nil {
		log.Fatalf("unable to create temp file: %s", err)
	}
	defer f.Close()

	// Determine maximum number of incoming connections. Create outgoing
	// edges, keeping track of which are new since last time (added=true).
	outgoingMap := make(edgeMap)
	var maxIncoming int
	quiescent := true
	// The order the graph file is written influences the arrangement
	// of nodes in the output image, so it makes sense to eliminate
	// randomness here. Unfortunately with graphviz it's fairly hard
	// to get a consistent ordering.
	for _, simNode := range network.Nodes {
		node := simNode.Gossip
		incoming := node.Incoming()
		for _, iNode := range incoming {
			e := edge{dest: node.GetNodeID()}
			key := fmt.Sprintf("%d:%d", iNode, node.GetNodeID())
			if _, ok := edgeSet[key]; !ok {
				e.added = true
				quiescent = false
			}
			delete(edgeSet, key)
			outgoingMap.addEdge(iNode, e)
		}
		if len(incoming) > maxIncoming {
			maxIncoming = len(incoming)
		}
	}

	// Find all edges which were deleted.
	for key, e := range edgeSet {
		e.added = false
		e.deleted = true
		quiescent = false
		nodeID, err := strconv.Atoi(strings.Split(key, ":")[0])
		if err != nil {
			log.Fatal(err)
		}
		outgoingMap.addEdge(roachpb.NodeID(nodeID), e)
		delete(edgeSet, key)
	}

	f.WriteString("digraph G {\n")
	f.WriteString("node [shape=record];\n")
	for _, simNode := range network.Nodes {
		node := simNode.Gossip
		var missing []roachpb.NodeID
		var totalAge int64
		for _, otherNode := range network.Nodes {
			if otherNode == simNode {
				continue // skip the node's own info
			}
			infoKey := otherNode.Addr.String()
			// GetInfo returns an error if the info is missing.
			if info, err := node.GetInfo(infoKey); err != nil {
				missing = append(missing, otherNode.Gossip.GetNodeID())
				quiescent = false
			} else {
				_, val, err := encoding.DecodeUint64(info)
				if err != nil {
					log.Fatalf("bad decode of node info cycle: %s", err)
//.........这里部分代码省略.........