Merge pull request #2354 from chrislusf/bptree

Add Redis3

11 files changed, 1987 insertions, 0 deletions

diff --git a/weed/util/skiplist/Makefile b/weed/util/skiplist/Makefile
new file mode 100644
index 000000000..af4afe639
--- /dev/null
+++ b/weed/util/skiplist/Makefile
@@ -0,0 +1,6 @@
+all: gen
+
+.PHONY : gen
+
+gen:
+	protoc skiplist.proto --go_out=plugins=grpc:. --go_opt=paths=source_relative
diff --git a/weed/util/skiplist/list_store.go b/weed/util/skiplist/list_store.go
new file mode 100644
index 000000000..0eb1106bc
--- /dev/null
+++ b/weed/util/skiplist/list_store.go
@@ -0,0 +1,32 @@
+package skiplist
+
+type ListStore interface {
+	SaveElement(id int64, element *SkipListElement) error
+	DeleteElement(id int64) error
+	LoadElement(id int64) (*SkipListElement, error)
+}
+
+type MemStore struct {
+	m map[int64]*SkipListElement
+}
+
+func newMemStore() *MemStore {
+	return &MemStore{
+		m: make(map[int64]*SkipListElement),
+	}
+}
+
+func (m *MemStore) SaveElement(id int64, element *SkipListElement) error {
+	m.m[id] = element
+	return nil
+}
+
+func (m *MemStore) DeleteElement(id int64) error {
+	delete(m.m, id)
+	return nil
+}
+
+func (m *MemStore) LoadElement(id int64) (*SkipListElement, error) {
+	element := m.m[id]
+	return element, nil
+}
diff --git a/weed/util/skiplist/name_batch.go b/weed/util/skiplist/name_batch.go
new file mode 100644
index 000000000..71e5aeeba
--- /dev/null
+++ b/weed/util/skiplist/name_batch.go
@@ -0,0 +1,102 @@
+package skiplist
+
+import (
+	"github.com/chrislusf/seaweedfs/weed/glog"
+	"github.com/golang/protobuf/proto"
+	"sort"
+	"strings"
+)
+
+type NameBatch struct {
+	key   string
+	names map[string]struct{}
+}
+
+func (nb *NameBatch) ContainsName(name string) (found bool) {
+	_, found = nb.names[name]
+	return
+}
+func (nb *NameBatch) WriteName(name string) {
+	if nb.key == "" || strings.Compare(nb.key, name) > 0 {
+		nb.key = name
+	}
+	nb.names[name] = struct{}{}
+}
+func (nb *NameBatch) DeleteName(name string) {
+	delete(nb.names, name)
+	if nb.key == name {
+		nb.key = ""
+		for n := range nb.names {
+			if nb.key == "" || strings.Compare(nb.key, n) > 0 {
+				nb.key = n
+			}
+		}
+	}
+}
+func (nb *NameBatch) ListNames(startFrom string, visitNamesFn func(name string) bool) bool {
+	var names []string
+	needFilter := startFrom != ""
+	for n := range nb.names {
+		if !needFilter || strings.Compare(n, startFrom) >= 0 {
+			names = append(names, n)
+		}
+	}
+	sort.Slice(names, func(i, j int) bool {
+		return strings.Compare(names[i], names[j]) < 0
+	})
+	for _, n := range names {
+		if !visitNamesFn(n) {
+			return false
+		}
+	}
+	return true
+}
+
+func NewNameBatch() *NameBatch {
+	return &NameBatch{
+		names: make(map[string]struct{}),
+	}
+}
+
+func LoadNameBatch(data []byte) *NameBatch {
+	t := &NameBatchData{}
+	if len(data) > 0 {
+		err := proto.Unmarshal(data, t)
+		if err != nil {
+			glog.Errorf("unmarshal into NameBatchData{} : %v", err)
+			return nil
+		}
+	}
+	nb := NewNameBatch()
+	for _, n := range t.Names {
+		name := string(n)
+		if nb.key == "" || strings.Compare(nb.key, name) > 0 {
+			nb.key = name
+		}
+		nb.names[name] = struct{}{}
+	}
+	return nb
+}
+
+func (nb *NameBatch) ToBytes() []byte {
+	t := &NameBatchData{}
+	for n := range nb.names {
+		t.Names = append(t.Names, []byte(n))
+	}
+	data, _ := proto.Marshal(t)
+	return data
+}
+
+func (nb *NameBatch) SplitBy(name string) (x, y *NameBatch) {
+	x, y = NewNameBatch(), NewNameBatch()
+
+	for n := range nb.names {
+		// there should be no equal case though
+		if strings.Compare(n, name) <= 0 {
+			x.WriteName(n)
+		} else {
+			y.WriteName(n)
+		}
+	}
+	return
+}
diff --git a/weed/util/skiplist/name_list.go b/weed/util/skiplist/name_list.go
new file mode 100644
index 000000000..4ba26665a
--- /dev/null
+++ b/weed/util/skiplist/name_list.go
@@ -0,0 +1,326 @@
+package skiplist
+
+import (
+	"bytes"
+)
+
+type NameList struct {
+	skipList  *SkipList
+	batchSize int
+}
+
+func newNameList(store ListStore, batchSize int) *NameList {
+	return &NameList{
+		skipList:  New(store),
+		batchSize: batchSize,
+	}
+}
+
+/*
+Be reluctant to create new nodes. Try to fit into either previous node or next node.
+Prefer to add to previous node.
+
+There are multiple cases after finding the name for greater or equal node
+ 1. found and node.Key == name
+    The node contains a batch with leading key the same as the name
+    nothing to do
+ 2. no such node found or node.Key > name
+
+    if no such node found
+      prevNode = list.LargestNode
+
+	// case 2.1
+    if previousNode contains name
+      nothing to do
+
+    // prefer to add to previous node
+    if prevNode != nil {
+		// case 2.2
+		if prevNode has capacity
+			prevNode.add name, and save
+			return
+		// case 2.3
+		split prevNode by name
+    }
+
+	// case 2.4
+	// merge into next node. Avoid too many nodes if adding data in reverse order.
+	if nextNode is not nil and nextNode has capacity
+	  delete nextNode.Key
+      nextNode.Key = name
+      nextNode.batch.add name
+      insert nodeNode.Key
+	  return
+
+	// case 2.5
+    if prevNode is nil
+      insert new node with key = name, value = batch{name}
+      return
+
+*/
+func (nl *NameList) WriteName(name string) error {
+
+	lookupKey := []byte(name)
+	prevNode, nextNode, found, err := nl.skipList.FindGreaterOrEqual(lookupKey)
+	if err != nil {
+		return err
+	}
+	// case 1: the name already exists as one leading key in the batch
+	if found && bytes.Compare(nextNode.Key, lookupKey) == 0 {
+		return nil
+	}
+
+	if !found {
+		prevNode, err = nl.skipList.GetLargestNode()
+		if err != nil {
+			return err
+		}
+	}
+
+	if nextNode != nil && prevNode == nil {
+		prevNode, err = nl.skipList.loadElement(nextNode.Prev)
+		if err != nil {
+			return err
+		}
+	}
+
+	if prevNode != nil {
+		prevNameBatch := LoadNameBatch(prevNode.Value)
+		// case 2.1
+		if prevNameBatch.ContainsName(name) {
+			return nil
+		}
+
+		// case 2.2
+		if len(prevNameBatch.names) < nl.batchSize {
+			prevNameBatch.WriteName(name)
+			return nl.skipList.ChangeValue(prevNode, prevNameBatch.ToBytes())
+		}
+
+		// case 2.3
+		x, y := prevNameBatch.SplitBy(name)
+		addToX := len(x.names) <= len(y.names)
+		if len(x.names) != len(prevNameBatch.names) {
+			if addToX {
+				x.WriteName(name)
+			}
+			if x.key == prevNameBatch.key {
+				if err := nl.skipList.ChangeValue(prevNode, x.ToBytes()); err != nil {
+					return err
+				}
+			} else {
+				if err := nl.skipList.Insert([]byte(x.key), x.ToBytes()); err != nil {
+					return err
+				}
+			}
+		}
+		if len(y.names) != len(prevNameBatch.names) {
+			if !addToX {
+				y.WriteName(name)
+			}
+			if y.key == prevNameBatch.key {
+				if err := nl.skipList.ChangeValue(prevNode, y.ToBytes()); err != nil {
+					return err
+				}
+			} else {
+				if err := nl.skipList.Insert([]byte(y.key), y.ToBytes()); err != nil {
+					return err
+				}
+			}
+		}
+		return nil
+
+	}
+
+	// case 2.4
+	if nextNode != nil {
+		nextNameBatch := LoadNameBatch(nextNode.Value)
+		if len(nextNameBatch.names) < nl.batchSize {
+			if err := nl.skipList.Delete(nextNode.Key); err != nil {
+				return err
+			}
+			nextNameBatch.WriteName(name)
+			if err := nl.skipList.Insert([]byte(nextNameBatch.key), nextNameBatch.ToBytes()); err != nil {
+				return err
+			}
+			return nil
+		}
+	}
+
+	// case 2.5
+	// now prevNode is nil
+	newNameBatch := NewNameBatch()
+	newNameBatch.WriteName(name)
+	if err := nl.skipList.Insert([]byte(newNameBatch.key), newNameBatch.ToBytes()); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+/*
+// case 1: exists in nextNode
+if nextNode != nil && nextNode.Key == name {
+	remove from nextNode, update nextNode
+	// TODO: merge with prevNode if possible?
+	return
+}
+if nextNode is nil
+	prevNode = list.Largestnode
+if prevNode == nil and nextNode.Prev != nil
+	prevNode = load(nextNode.Prev)
+
+// case 2: does not exist
+// case 2.1
+if prevNode == nil {
+	return
+}
+// case 2.2
+if prevNameBatch does not contain name {
+	return
+}
+
+// case 3
+delete from prevNameBatch
+if prevNameBatch + nextNode < capacityList
+	// case 3.1
+	merge
+else
+	// case 3.2
+	update prevNode
+
+
+*/
+func (nl *NameList) DeleteName(name string) error {
+	lookupKey := []byte(name)
+	prevNode, nextNode, found, err := nl.skipList.FindGreaterOrEqual(lookupKey)
+	if err != nil {
+		return err
+	}
+
+	// case 1
+	var nextNameBatch *NameBatch
+	if nextNode != nil {
+		nextNameBatch = LoadNameBatch(nextNode.Value)
+	}
+	if found && bytes.Compare(nextNode.Key, lookupKey) == 0 {
+		if err := nl.skipList.Delete(nextNode.Key); err != nil {
+			return err
+		}
+		nextNameBatch.DeleteName(name)
+		if len(nextNameBatch.names) > 0 {
+			if err := nl.skipList.Insert([]byte(nextNameBatch.key), nextNameBatch.ToBytes()); err != nil {
+				return err
+			}
+		}
+		return nil
+	}
+
+	if !found {
+		prevNode, err = nl.skipList.GetLargestNode()
+		if err != nil {
+			return err
+		}
+	}
+
+	if nextNode != nil && prevNode == nil {
+		prevNode, err = nl.skipList.loadElement(nextNode.Prev)
+		if err != nil {
+			return err
+		}
+	}
+
+	// case 2
+	if prevNode == nil {
+		// case 2.1
+		return nil
+	}
+	prevNameBatch := LoadNameBatch(prevNode.Value)
+	if !prevNameBatch.ContainsName(name) {
+		// case 2.2
+		return nil
+	}
+
+	// case 3
+	prevNameBatch.DeleteName(name)
+	if len(prevNameBatch.names) == 0 {
+		if err := nl.skipList.Delete(prevNode.Key); err != nil {
+			return err
+		}
+		return nil
+	}
+	if nextNameBatch != nil && len(nextNameBatch.names) + len(prevNameBatch.names) < nl.batchSize {
+		// case 3.1 merge nextNode and prevNode
+		if err := nl.skipList.Delete(nextNode.Key); err != nil {
+			return err
+		}
+		for nextName := range nextNameBatch.names {
+			prevNameBatch.WriteName(nextName)
+		}
+		return nl.skipList.ChangeValue(prevNode, prevNameBatch.ToBytes())
+	} else {
+		// case 3.2 update prevNode
+		return nl.skipList.ChangeValue(prevNode, prevNameBatch.ToBytes())
+	}
+
+	return nil
+}
+
+func (nl *NameList) ListNames(startFrom string, visitNamesFn func(name string) bool) error {
+	lookupKey := []byte(startFrom)
+	prevNode, nextNode, found, err := nl.skipList.FindGreaterOrEqual(lookupKey)
+	if err != nil {
+		return err
+	}
+	if found && bytes.Compare(nextNode.Key, lookupKey) == 0 {
+		prevNode = nil
+	}
+	if !found {
+		prevNode, err = nl.skipList.GetLargestNode()
+		if err != nil {
+			return err
+		}
+	}
+
+	if prevNode != nil {
+		prevNameBatch := LoadNameBatch(prevNode.Value)
+		if !prevNameBatch.ListNames(startFrom, visitNamesFn) {
+			return nil
+		}
+	}
+
+	for nextNode != nil {
+		nextNameBatch := LoadNameBatch(nextNode.Value)
+		if !nextNameBatch.ListNames(startFrom, visitNamesFn) {
+			return nil
+		}
+		nextNode, err = nl.skipList.loadElement(nextNode.Next[0])
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func (nl *NameList) RemoteAllListElement() error {
+
+	t := nl.skipList
+
+	nodeRef := t.startLevels[0]
+	for nodeRef != nil {
+		node, err := t.loadElement(nodeRef)
+		if err != nil {
+			return err
+		}
+		if node == nil {
+			return nil
+		}
+		if err := t.deleteElement(node); err != nil {
+			return err
+		}
+		nodeRef = node.Next[0]
+	}
+	return nil
+
+}
\ No newline at end of file
diff --git a/weed/util/skiplist/name_list_serde.go b/weed/util/skiplist/name_list_serde.go
new file mode 100644
index 000000000..be9f06698
--- /dev/null
+++ b/weed/util/skiplist/name_list_serde.go
@@ -0,0 +1,71 @@
+package skiplist
+
+import (
+	"github.com/chrislusf/seaweedfs/weed/glog"
+	"github.com/golang/protobuf/proto"
+)
+
+func LoadNameList(data []byte, store ListStore, batchSize int) *NameList {
+
+	nl := &NameList{
+		skipList:  New(store),
+		batchSize: batchSize,
+	}
+
+	if len(data) == 0 {
+		return nl
+	}
+
+	message := &SkipListProto{}
+	if err := proto.Unmarshal(data, message); err != nil {
+		glog.Errorf("loading skiplist: %v", err)
+	}
+	nl.skipList.maxNewLevel = int(message.MaxNewLevel)
+	nl.skipList.maxLevel = int(message.MaxLevel)
+	for i, ref := range message.StartLevels {
+		nl.skipList.startLevels[i] = &SkipListElementReference{
+			ElementPointer: ref.ElementPointer,
+			Key:            ref.Key,
+		}
+	}
+	for i, ref := range message.EndLevels {
+		nl.skipList.endLevels[i] = &SkipListElementReference{
+			ElementPointer: ref.ElementPointer,
+			Key:            ref.Key,
+		}
+	}
+	return nl
+}
+
+func (nl *NameList) HasChanges() bool {
+	return nl.skipList.hasChanges
+}
+
+func (nl *NameList) ToBytes() []byte {
+	message := &SkipListProto{}
+	message.MaxNewLevel = int32(nl.skipList.maxNewLevel)
+	message.MaxLevel = int32(nl.skipList.maxLevel)
+	for _, ref := range nl.skipList.startLevels {
+		if ref == nil {
+			break
+		}
+		message.StartLevels = append(message.StartLevels, &SkipListElementReference{
+			ElementPointer: ref.ElementPointer,
+			Key:            ref.Key,
+		})
+	}
+	for _, ref := range nl.skipList.endLevels {
+		if ref == nil {
+			break
+		}
+		message.EndLevels = append(message.EndLevels, &SkipListElementReference{
+			ElementPointer: ref.ElementPointer,
+			Key:            ref.Key,
+		})
+	}
+	data, err := proto.Marshal(message)
+	if err != nil {
+		glog.Errorf("marshal skiplist: %v", err)
+	}
+	return data
+}
\ No newline at end of file
diff --git a/weed/util/skiplist/name_list_test.go b/weed/util/skiplist/name_list_test.go
new file mode 100644
index 000000000..b3a686553
--- /dev/null
+++ b/weed/util/skiplist/name_list_test.go
@@ -0,0 +1,73 @@
+package skiplist
+
+import (
+	"math/rand"
+	"strconv"
+	"testing"
+)
+
+const (
+	maxNameCount = 100
+)
+
+func String(x int) string {
+	return strconv.Itoa(x)
+}
+
+func TestNameList(t *testing.T) {
+	list := newNameList(memStore, 7)
+
+	for i := 0; i < maxNameCount; i++ {
+		list.WriteName(String(i))
+	}
+
+	counter := 0
+	list.ListNames("", func(name string) bool {
+		counter++
+		print(name, " ")
+		return true
+	})
+	if counter != maxNameCount {
+		t.Fail()
+	}
+
+	// list.skipList.println()
+
+	deleteBase := 5
+	deleteCount := maxNameCount - 3 * deleteBase
+
+	for i := deleteBase; i < deleteBase+deleteCount; i++ {
+		list.DeleteName(String(i))
+	}
+
+	counter = 0
+	list.ListNames("", func(name string) bool {
+		counter++
+		return true
+	})
+	// list.skipList.println()
+	if counter != maxNameCount-deleteCount {
+		t.Fail()
+	}
+
+	// randomized deletion
+	list = newNameList(memStore, 7)
+	// Delete elements at random positions in the list.
+	rList := rand.Perm(maxN)
+	for _, i := range rList {
+		list.WriteName(String(i))
+	}
+	for _, i := range rList {
+		list.DeleteName(String(i))
+	}
+	counter = 0
+	list.ListNames("", func(name string) bool {
+		counter++
+		print(name, " ")
+		return true
+	})
+	if counter != 0 {
+		t.Fail()
+	}
+
+}
diff --git a/weed/util/skiplist/skiplist.go b/weed/util/skiplist/skiplist.go
new file mode 100644
index 000000000..52e6c606a
--- /dev/null
+++ b/weed/util/skiplist/skiplist.go
@@ -0,0 +1,563 @@
+package skiplist
+
+// adapted from https://github.com/MauriceGit/skiplist/blob/master/skiplist.go
+
+import (
+	"bytes"
+	"fmt"
+	"math/bits"
+	"math/rand"
+	"time"
+)
+
+const (
+	// maxLevel denotes the maximum height of the skiplist. This height will keep the skiplist
+	// efficient for up to 34m entries. If there is a need for much more, please adjust this constant accordingly.
+	maxLevel = 25
+)
+
+type SkipList struct {
+	startLevels [maxLevel]*SkipListElementReference
+	endLevels   [maxLevel]*SkipListElementReference
+	maxNewLevel int
+	maxLevel    int
+	listStore   ListStore
+	hasChanges  bool
+	// elementCount int
+}
+
+// NewSeedEps returns a new empty, initialized Skiplist.
+// Given a seed, a deterministic height/list behaviour can be achieved.
+// Eps is used to compare keys given by the ExtractKey() function on equality.
+func NewSeed(seed int64, listStore ListStore) *SkipList {
+
+	// Initialize random number generator.
+	rand.Seed(seed)
+	//fmt.Printf("SkipList seed: %v\n", seed)
+
+	list := &SkipList{
+		maxNewLevel: maxLevel,
+		maxLevel:    0,
+		listStore:   listStore,
+		// elementCount: 0,
+	}
+
+	return list
+}
+
+// New returns a new empty, initialized Skiplist.
+func New(listStore ListStore) *SkipList {
+	return NewSeed(time.Now().UTC().UnixNano(), listStore)
+}
+
+// IsEmpty checks, if the skiplist is empty.
+func (t *SkipList) IsEmpty() bool {
+	return t.startLevels[0] == nil
+}
+
+func (t *SkipList) generateLevel(maxLevel int) int {
+	level := maxLevel - 1
+	// First we apply some mask which makes sure that we don't get a level
+	// above our desired level. Then we find the first set bit.
+	var x = rand.Uint64() & ((1 << uint(maxLevel-1)) - 1)
+	zeroes := bits.TrailingZeros64(x)
+	if zeroes <= maxLevel {
+		level = zeroes
+	}
+
+	return level
+}
+
+func (t *SkipList) findEntryIndex(key []byte, minLevel int) int {
+	// Find good entry point so we don't accidentally skip half the list.
+	for i := t.maxLevel; i >= 0; i-- {
+		if t.startLevels[i] != nil && bytes.Compare(t.startLevels[i].Key, key) < 0 || i <= minLevel {
+			return i
+		}
+	}
+	return 0
+}
+
+func (t *SkipList) findExtended(key []byte, findGreaterOrEqual bool) (prevElementIfVisited *SkipListElement, foundElem *SkipListElement, ok bool, err error) {
+
+	foundElem = nil
+	ok = false
+
+	if t.IsEmpty() {
+		return
+	}
+
+	index := t.findEntryIndex(key, 0)
+	var currentNode *SkipListElement
+
+	currentNode, err = t.loadElement(t.startLevels[index])
+	if err != nil {
+		return
+	}
+	if currentNode == nil {
+		return
+	}
+
+	// In case, that our first element is already greater-or-equal!
+	if findGreaterOrEqual && compareElement(currentNode, key) > 0 {
+		foundElem = currentNode
+		ok = true
+		return
+	}
+
+	for {
+		if compareElement(currentNode, key) == 0 {
+			foundElem = currentNode
+			ok = true
+			return
+		}
+
+		// Which direction are we continuing next time?
+		if currentNode.Next[index] != nil && bytes.Compare(currentNode.Next[index].Key, key) <= 0 {
+			// Go right
+			currentNode, err = t.loadElement(currentNode.Next[index])
+			if err != nil {
+				return
+			}
+			if currentNode == nil {
+				return
+			}
+		} else {
+			if index > 0 {
+
+				// Early exit
+				if currentNode.Next[0] != nil && bytes.Compare(currentNode.Next[0].Key, key) == 0 {
+					prevElementIfVisited = currentNode
+					var currentNodeNext *SkipListElement
+					currentNodeNext, err = t.loadElement(currentNode.Next[0])
+					if err != nil {
+						return
+					}
+					if currentNodeNext == nil {
+						return
+					}
+					foundElem = currentNodeNext
+					ok = true
+					return
+				}
+				// Go down
+				index--
+			} else {
+				// Element is not found and we reached the bottom.
+				if findGreaterOrEqual {
+					foundElem, err = t.loadElement(currentNode.Next[index])
+					if err != nil {
+						return
+					}
+					ok = foundElem != nil
+				}
+
+				return
+			}
+		}
+	}
+}
+
+// Find tries to find an element in the skiplist based on the key from the given ListElement.
+// elem can be used, if ok is true.
+// Find runs in approx. O(log(n))
+func (t *SkipList) Find(key []byte) (prevIfVisited *SkipListElement, elem *SkipListElement, ok bool, err error) {
+
+	if t == nil || key == nil {
+		return
+	}
+
+	prevIfVisited, elem, ok, err = t.findExtended(key, false)
+	return
+}
+
+// FindGreaterOrEqual finds the first element, that is greater or equal to the given ListElement e.
+// The comparison is done on the keys (So on ExtractKey()).
+// FindGreaterOrEqual runs in approx. O(log(n))
+func (t *SkipList) FindGreaterOrEqual(key []byte) (prevIfVisited *SkipListElement, elem *SkipListElement, ok bool, err error) {
+
+	if t == nil || key == nil {
+		return
+	}
+
+	prevIfVisited, elem, ok, err = t.findExtended(key, true)
+	return
+}
+
+// Delete removes an element equal to e from the skiplist, if there is one.
+// If there are multiple entries with the same value, Delete will remove one of them
+// (Which one will change based on the actual skiplist layout)
+// Delete runs in approx. O(log(n))
+func (t *SkipList) Delete(key []byte) (err error) {
+
+	if t == nil || t.IsEmpty() || key == nil {
+		return
+	}
+
+	index := t.findEntryIndex(key, t.maxLevel)
+
+	var currentNode *SkipListElement
+	var nextNode *SkipListElement
+
+	for {
+
+		if currentNode == nil {
+			nextNode, err = t.loadElement(t.startLevels[index])
+		} else {
+			nextNode, err = t.loadElement(currentNode.Next[index])
+		}
+		if err != nil {
+			return err
+		}
+
+		// Found and remove!
+		if nextNode != nil && compareElement(nextNode, key) == 0 {
+
+			if currentNode != nil {
+				currentNode.Next[index] = nextNode.Next[index]
+				if err = t.saveElement(currentNode); err != nil {
+					return err
+				}
+			}
+
+			if index == 0 {
+				if nextNode.Next[index] != nil {
+					nextNextNode, err := t.loadElement(nextNode.Next[index])
+					if err != nil {
+						return err
+					}
+					if nextNextNode != nil {
+						nextNextNode.Prev = currentNode.Reference()
+						if err = t.saveElement(nextNextNode); err != nil {
+							return err
+						}
+					}
+				}
+				// t.elementCount--
+				if err = t.deleteElement(nextNode); err != nil {
+					return err
+				}
+			}
+
+			// Link from start needs readjustments.
+			startNextKey := t.startLevels[index].Key
+			if compareElement(nextNode, startNextKey) == 0 {
+				t.hasChanges = true
+				t.startLevels[index] = nextNode.Next[index]
+				// This was our currently highest node!
+				if t.startLevels[index] == nil {
+					t.maxLevel = index - 1
+				}
+			}
+
+			// Link from end needs readjustments.
+			if nextNode.Next[index] == nil {
+				t.endLevels[index] = currentNode.Reference()
+				t.hasChanges = true
+			}
+			nextNode.Next[index] = nil
+		}
+
+		if nextNode != nil && compareElement(nextNode, key) < 0 {
+			// Go right
+			currentNode = nextNode
+		} else {
+			// Go down
+			index--
+			if index < 0 {
+				break
+			}
+		}
+	}
+	return
+}
+
+// Insert inserts the given ListElement into the skiplist.
+// Insert runs in approx. O(log(n))
+func (t *SkipList) Insert(key, value []byte) (err error) {
+
+	if t == nil || key == nil {
+		return
+	}
+
+	level := t.generateLevel(t.maxNewLevel)
+
+	// Only grow the height of the skiplist by one at a time!
+	if level > t.maxLevel {
+		level = t.maxLevel + 1
+		t.maxLevel = level
+		t.hasChanges = true
+	}
+
+	elem := &SkipListElement{
+		Id:    rand.Int63(),
+		Next:  make([]*SkipListElementReference, t.maxNewLevel, t.maxNewLevel),
+		Level: int32(level),
+		Key:   key,
+		Value: value,
+	}
+
+	// t.elementCount++
+
+	newFirst := true
+	newLast := true
+	if !t.IsEmpty() {
+		newFirst = compareElement(elem, t.startLevels[0].Key) < 0
+		newLast = compareElement(elem, t.endLevels[0].Key) > 0
+	}
+
+	normallyInserted := false
+	if !newFirst && !newLast {
+
+		normallyInserted = true
+
+		index := t.findEntryIndex(key, level)
+
+		var currentNode *SkipListElement
+		var nextNodeRef *SkipListElementReference
+
+		for {
+
+			if currentNode == nil {
+				nextNodeRef = t.startLevels[index]
+			} else {
+				nextNodeRef = currentNode.Next[index]
+			}
+
+			var nextNode *SkipListElement
+
+			// Connect node to next
+			if index <= level && (nextNodeRef == nil || bytes.Compare(nextNodeRef.Key, key) > 0) {
+				elem.Next[index] = nextNodeRef
+				if currentNode != nil {
+					currentNode.Next[index] = elem.Reference()
+					if err = t.saveElement(currentNode); err != nil {
+						return
+					}
+				}
+				if index == 0 {
+					elem.Prev = currentNode.Reference()
+					if nextNodeRef != nil {
+						if nextNode, err = t.loadElement(nextNodeRef); err != nil {
+							return
+						}
+						if nextNode != nil {
+							nextNode.Prev = elem.Reference()
+							if err = t.saveElement(nextNode); err != nil {
+								return
+							}
+						}
+					}
+				}
+			}
+
+			if nextNodeRef != nil && bytes.Compare(nextNodeRef.Key, key) <= 0 {
+				// Go right
+				if nextNode == nil {
+					// reuse nextNode when index == 0
+					if nextNode, err = t.loadElement(nextNodeRef); err != nil {
+						return
+					}
+				}
+				currentNode = nextNode
+				if currentNode == nil {
+					return
+				}
+			} else {
+				// Go down
+				index--
+				if index < 0 {
+					break
+				}
+			}
+		}
+	}
+
+	// Where we have a left-most position that needs to be referenced!
+	for i := level; i >= 0; i-- {
+
+		didSomething := false
+
+		if newFirst || normallyInserted {
+
+			if t.startLevels[i] == nil || bytes.Compare(t.startLevels[i].Key, key) > 0 {
+				if i == 0 && t.startLevels[i] != nil {
+					startLevelElement, err := t.loadElement(t.startLevels[i])
+					if err != nil {
+						return err
+					}
+					if startLevelElement != nil {
+						startLevelElement.Prev = elem.Reference()
+						if err = t.saveElement(startLevelElement); err != nil {
+							return err
+						}
+					}
+				}
+				elem.Next[i] = t.startLevels[i]
+				t.startLevels[i] = elem.Reference()
+				t.hasChanges = true
+			}
+
+			// link the endLevels to this element!
+			if elem.Next[i] == nil {
+				t.endLevels[i] = elem.Reference()
+				t.hasChanges = true
+			}
+
+			didSomething = true
+		}
+
+		if newLast {
+			// Places the element after the very last element on this level!
+			// This is very important, so we are not linking the very first element (newFirst AND newLast) to itself!
+			if !newFirst {
+				if t.endLevels[i] != nil {
+					endLevelElement, err := t.loadElement(t.endLevels[i])
+					if err != nil {
+						return err
+					}
+					if endLevelElement != nil {
+						endLevelElement.Next[i] = elem.Reference()
+						if err = t.saveElement(endLevelElement); err != nil {
+							return err
+						}
+					}
+				}
+				if i == 0 {
+					elem.Prev = t.endLevels[i]
+				}
+				t.endLevels[i] = elem.Reference()
+				t.hasChanges = true
+			}
+
+			// Link the startLevels to this element!
+			if t.startLevels[i] == nil || bytes.Compare(t.startLevels[i].Key, key) > 0 {
+				t.startLevels[i] = elem.Reference()
+				t.hasChanges = true
+			}
+
+			didSomething = true
+		}
+
+		if !didSomething {
+			break
+		}
+	}
+
+	if err = t.saveElement(elem); err != nil {
+		return err
+	}
+	return nil
+
+}
+
+// GetSmallestNode returns the very first/smallest node in the skiplist.
+// GetSmallestNode runs in O(1)
+func (t *SkipList) GetSmallestNode() (*SkipListElement, error) {
+	return t.loadElement(t.startLevels[0])
+}
+
+// GetLargestNode returns the very last/largest node in the skiplist.
+// GetLargestNode runs in O(1)
+func (t *SkipList) GetLargestNode() (*SkipListElement, error) {
+	return t.loadElement(t.endLevels[0])
+}
+
+// Next returns the next element based on the given node.
+// Next will loop around to the first node, if you call it on the last!
+func (t *SkipList) Next(e *SkipListElement) (*SkipListElement, error) {
+	if e.Next[0] == nil {
+		return t.loadElement(t.startLevels[0])
+	}
+	return t.loadElement(e.Next[0])
+}
+
+// Prev returns the previous element based on the given node.
+// Prev will loop around to the last node, if you call it on the first!
+func (t *SkipList) Prev(e *SkipListElement) (*SkipListElement, error) {
+	if e.Prev == nil {
+		return t.loadElement(t.endLevels[0])
+	}
+	return t.loadElement(e.Prev)
+}
+
+// ChangeValue can be used to change the actual value of a node in the skiplist
+// without the need of Deleting and reinserting the node again.
+// Be advised, that ChangeValue only works, if the actual key from ExtractKey() will stay the same!
+// ok is an indicator, wether the value is actually changed.
+func (t *SkipList) ChangeValue(e *SkipListElement, newValue []byte) (err error) {
+	// The key needs to stay correct, so this is very important!
+	e.Value = newValue
+	return t.saveElement(e)
+}
+
+// String returns a string format of the skiplist. Useful to get a graphical overview and/or debugging.
+func (t *SkipList) println() {
+
+	print("start --> ")
+	for i, l := range t.startLevels {
+		if l == nil {
+			break
+		}
+		if i > 0 {
+			print(" -> ")
+		}
+		next := "---"
+		if l != nil {
+			next = string(l.Key)
+		}
+		print(fmt.Sprintf("[%v]", next))
+	}
+	println()
+
+	nodeRef := t.startLevels[0]
+	for nodeRef != nil {
+		print(fmt.Sprintf("%v: ", string(nodeRef.Key)))
+		node, _ := t.loadElement(nodeRef)
+		if node == nil {
+			break
+		}
+		for i := 0; i <= int(node.Level); i++ {
+
+			l := node.Next[i]
+
+			next := "---"
+			if l != nil {
+				next = string(l.Key)
+			}
+
+			if i == 0 {
+				prev := "---"
+
+				if node.Prev != nil {
+					prev = string(node.Prev.Key)
+				}
+				print(fmt.Sprintf("[%v|%v]", prev, next))
+			} else {
+				print(fmt.Sprintf("[%v]", next))
+			}
+			if i < int(node.Level) {
+				print(" -> ")
+			}
+
+		}
+		nodeRef = node.Next[0]
+		println()
+	}
+
+	print("end --> ")
+	for i, l := range t.endLevels {
+		if l == nil {
+			break
+		}
+		if i > 0 {
+			print(" -> ")
+		}
+		next := "---"
+		if l != nil {
+			next = string(l.Key)
+		}
+		print(fmt.Sprintf("[%v]", next))
+	}
+	println()
+}
diff --git a/weed/util/skiplist/skiplist.pb.go b/weed/util/skiplist/skiplist.pb.go
new file mode 100644
index 000000000..adb121bfc
--- /dev/null
+++ b/weed/util/skiplist/skiplist.pb.go
@@ -0,0 +1,438 @@
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// versions:
+// 	protoc-gen-go v1.25.0
+// 	protoc        v3.12.3
+// source: skiplist.proto
+
+package skiplist
+
+import (
+	proto "github.com/golang/protobuf/proto"
+	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
+	protoimpl "google.golang.org/protobuf/runtime/protoimpl"
+	reflect "reflect"
+	sync "sync"
+)
+
+const (
+	// Verify that this generated code is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(20 - protoimpl.MinVersion)
+	// Verify that runtime/protoimpl is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(protoimpl.MaxVersion - 20)
+)
+
+// This is a compile-time assertion that a sufficiently up-to-date version
+// of the legacy proto package is being used.
+const _ = proto.ProtoPackageIsVersion4
+
+type SkipListProto struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	StartLevels []*SkipListElementReference `protobuf:"bytes,1,rep,name=start_levels,json=startLevels,proto3" json:"start_levels,omitempty"`
+	EndLevels   []*SkipListElementReference `protobuf:"bytes,2,rep,name=end_levels,json=endLevels,proto3" json:"end_levels,omitempty"`
+	MaxNewLevel int32                       `protobuf:"varint,3,opt,name=max_new_level,json=maxNewLevel,proto3" json:"max_new_level,omitempty"`
+	MaxLevel    int32                       `protobuf:"varint,4,opt,name=max_level,json=maxLevel,proto3" json:"max_level,omitempty"`
+}
+
+func (x *SkipListProto) Reset() {
+	*x = SkipListProto{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_skiplist_proto_msgTypes[0]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *SkipListProto) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*SkipListProto) ProtoMessage() {}
+
+func (x *SkipListProto) ProtoReflect() protoreflect.Message {
+	mi := &file_skiplist_proto_msgTypes[0]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use SkipListProto.ProtoReflect.Descriptor instead.
+func (*SkipListProto) Descriptor() ([]byte, []int) {
+	return file_skiplist_proto_rawDescGZIP(), []int{0}
+}
+
+func (x *SkipListProto) GetStartLevels() []*SkipListElementReference {
+	if x != nil {
+		return x.StartLevels
+	}
+	return nil
+}
+
+func (x *SkipListProto) GetEndLevels() []*SkipListElementReference {
+	if x != nil {
+		return x.EndLevels
+	}
+	return nil
+}
+
+func (x *SkipListProto) GetMaxNewLevel() int32 {
+	if x != nil {
+		return x.MaxNewLevel
+	}
+	return 0
+}
+
+func (x *SkipListProto) GetMaxLevel() int32 {
+	if x != nil {
+		return x.MaxLevel
+	}
+	return 0
+}
+
+type SkipListElementReference struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	ElementPointer int64  `protobuf:"varint,1,opt,name=element_pointer,json=elementPointer,proto3" json:"element_pointer,omitempty"`
+	Key            []byte `protobuf:"bytes,2,opt,name=key,proto3" json:"key,omitempty"`
+}
+
+func (x *SkipListElementReference) Reset() {
+	*x = SkipListElementReference{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_skiplist_proto_msgTypes[1]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *SkipListElementReference) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*SkipListElementReference) ProtoMessage() {}
+
+func (x *SkipListElementReference) ProtoReflect() protoreflect.Message {
+	mi := &file_skiplist_proto_msgTypes[1]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use SkipListElementReference.ProtoReflect.Descriptor instead.
+func (*SkipListElementReference) Descriptor() ([]byte, []int) {
+	return file_skiplist_proto_rawDescGZIP(), []int{1}
+}
+
+func (x *SkipListElementReference) GetElementPointer() int64 {
+	if x != nil {
+		return x.ElementPointer
+	}
+	return 0
+}
+
+func (x *SkipListElementReference) GetKey() []byte {
+	if x != nil {
+		return x.Key
+	}
+	return nil
+}
+
+type SkipListElement struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	Id    int64                       `protobuf:"varint,1,opt,name=id,proto3" json:"id,omitempty"`
+	Next  []*SkipListElementReference `protobuf:"bytes,2,rep,name=next,proto3" json:"next,omitempty"`
+	Level int32                       `protobuf:"varint,3,opt,name=level,proto3" json:"level,omitempty"`
+	Key   []byte                      `protobuf:"bytes,4,opt,name=key,proto3" json:"key,omitempty"`
+	Value []byte                      `protobuf:"bytes,5,opt,name=value,proto3" json:"value,omitempty"`
+	Prev  *SkipListElementReference   `protobuf:"bytes,6,opt,name=prev,proto3" json:"prev,omitempty"`
+}
+
+func (x *SkipListElement) Reset() {
+	*x = SkipListElement{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_skiplist_proto_msgTypes[2]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *SkipListElement) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*SkipListElement) ProtoMessage() {}
+
+func (x *SkipListElement) ProtoReflect() protoreflect.Message {
+	mi := &file_skiplist_proto_msgTypes[2]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use SkipListElement.ProtoReflect.Descriptor instead.
+func (*SkipListElement) Descriptor() ([]byte, []int) {
+	return file_skiplist_proto_rawDescGZIP(), []int{2}
+}
+
+func (x *SkipListElement) GetId() int64 {
+	if x != nil {
+		return x.Id
+	}
+	return 0
+}
+
+func (x *SkipListElement) GetNext() []*SkipListElementReference {
+	if x != nil {
+		return x.Next
+	}
+	return nil
+}
+
+func (x *SkipListElement) GetLevel() int32 {
+	if x != nil {
+		return x.Level
+	}
+	return 0
+}
+
+func (x *SkipListElement) GetKey() []byte {
+	if x != nil {
+		return x.Key
+	}
+	return nil
+}
+
+func (x *SkipListElement) GetValue() []byte {
+	if x != nil {
+		return x.Value
+	}
+	return nil
+}
+
+func (x *SkipListElement) GetPrev() *SkipListElementReference {
+	if x != nil {
+		return x.Prev
+	}
+	return nil
+}
+
+type NameBatchData struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	Names [][]byte `protobuf:"bytes,1,rep,name=names,proto3" json:"names,omitempty"`
+}
+
+func (x *NameBatchData) Reset() {
+	*x = NameBatchData{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_skiplist_proto_msgTypes[3]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *NameBatchData) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*NameBatchData) ProtoMessage() {}
+
+func (x *NameBatchData) ProtoReflect() protoreflect.Message {
+	mi := &file_skiplist_proto_msgTypes[3]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use NameBatchData.ProtoReflect.Descriptor instead.
+func (*NameBatchData) Descriptor() ([]byte, []int) {
+	return file_skiplist_proto_rawDescGZIP(), []int{3}
+}
+
+func (x *NameBatchData) GetNames() [][]byte {
+	if x != nil {
+		return x.Names
+	}
+	return nil
+}
+
+var File_skiplist_proto protoreflect.FileDescriptor
+
+var file_skiplist_proto_rawDesc = []byte{
+	0x0a, 0x0e, 0x73, 0x6b, 0x69, 0x70, 0x6c, 0x69, 0x73, 0x74, 0x2e, 0x70, 0x72, 0x6f, 0x74, 0x6f,
+	0x12, 0x08, 0x73, 0x6b, 0x69, 0x70, 0x6c, 0x69, 0x73, 0x74, 0x22, 0xda, 0x01, 0x0a, 0x0d, 0x53,
+	0x6b, 0x69, 0x70, 0x4c, 0x69, 0x73, 0x74, 0x50, 0x72, 0x6f, 0x74, 0x6f, 0x12, 0x45, 0x0a, 0x0c,
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+	0x61, 0x12, 0x14, 0x0a, 0x05, 0x6e, 0x61, 0x6d, 0x65, 0x73, 0x18, 0x01, 0x20, 0x03, 0x28, 0x0c,
+	0x52, 0x05, 0x6e, 0x61, 0x6d, 0x65, 0x73, 0x42, 0x33, 0x5a, 0x31, 0x67, 0x69, 0x74, 0x68, 0x75,
+	0x62, 0x2e, 0x63, 0x6f, 0x6d, 0x2f, 0x63, 0x68, 0x72, 0x69, 0x73, 0x6c, 0x75, 0x73, 0x66, 0x2f,
+	0x73, 0x65, 0x61, 0x77, 0x65, 0x65, 0x64, 0x66, 0x73, 0x2f, 0x77, 0x65, 0x65, 0x64, 0x2f, 0x75,
+	0x74, 0x69, 0x6c, 0x2f, 0x73, 0x6b, 0x69, 0x70, 0x6c, 0x69, 0x73, 0x74, 0x62, 0x06, 0x70, 0x72,
+	0x6f, 0x74, 0x6f, 0x33,
+}
+
+var (
+	file_skiplist_proto_rawDescOnce sync.Once
+	file_skiplist_proto_rawDescData = file_skiplist_proto_rawDesc
+)
+
+func file_skiplist_proto_rawDescGZIP() []byte {
+	file_skiplist_proto_rawDescOnce.Do(func() {
+		file_skiplist_proto_rawDescData = protoimpl.X.CompressGZIP(file_skiplist_proto_rawDescData)
+	})
+	return file_skiplist_proto_rawDescData
+}
+
+var file_skiplist_proto_msgTypes = make([]protoimpl.MessageInfo, 4)
+var file_skiplist_proto_goTypes = []interface{}{
+	(*SkipListProto)(nil),            // 0: skiplist.SkipListProto
+	(*SkipListElementReference)(nil), // 1: skiplist.SkipListElementReference
+	(*SkipListElement)(nil),          // 2: skiplist.SkipListElement
+	(*NameBatchData)(nil),            // 3: skiplist.NameBatchData
+}
+var file_skiplist_proto_depIdxs = []int32{
+	1, // 0: skiplist.SkipListProto.start_levels:type_name -> skiplist.SkipListElementReference
+	1, // 1: skiplist.SkipListProto.end_levels:type_name -> skiplist.SkipListElementReference
+	1, // 2: skiplist.SkipListElement.next:type_name -> skiplist.SkipListElementReference
+	1, // 3: skiplist.SkipListElement.prev:type_name -> skiplist.SkipListElementReference
+	4, // [4:4] is the sub-list for method output_type
+	4, // [4:4] is the sub-list for method input_type
+	4, // [4:4] is the sub-list for extension type_name
+	4, // [4:4] is the sub-list for extension extendee
+	0, // [0:4] is the sub-list for field type_name
+}
+
+func init() { file_skiplist_proto_init() }
+func file_skiplist_proto_init() {
+	if File_skiplist_proto != nil {
+		return
+	}
+	if !protoimpl.UnsafeEnabled {
+		file_skiplist_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*SkipListProto); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_skiplist_proto_msgTypes[1].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*SkipListElementReference); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_skiplist_proto_msgTypes[2].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*SkipListElement); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_skiplist_proto_msgTypes[3].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*NameBatchData); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+	}
+	type x struct{}
+	out := protoimpl.TypeBuilder{
+		File: protoimpl.DescBuilder{
+			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
+			RawDescriptor: file_skiplist_proto_rawDesc,
+			NumEnums:      0,
+			NumMessages:   4,
+			NumExtensions: 0,
+			NumServices:   0,
+		},
+		GoTypes:           file_skiplist_proto_goTypes,
+		DependencyIndexes: file_skiplist_proto_depIdxs,
+		MessageInfos:      file_skiplist_proto_msgTypes,
+	}.Build()
+	File_skiplist_proto = out.File
+	file_skiplist_proto_rawDesc = nil
+	file_skiplist_proto_goTypes = nil
+	file_skiplist_proto_depIdxs = nil
+}
diff --git a/weed/util/skiplist/skiplist.proto b/weed/util/skiplist/skiplist.proto
new file mode 100644
index 000000000..2991ad830
--- /dev/null
+++ b/weed/util/skiplist/skiplist.proto
@@ -0,0 +1,30 @@
+syntax = "proto3";
+
+package skiplist;
+
+option go_package = "github.com/chrislusf/seaweedfs/weed/util/skiplist";
+
+message SkipListProto {
+  repeated SkipListElementReference start_levels = 1;
+  repeated SkipListElementReference end_levels = 2;
+  int32 max_new_level = 3;
+  int32 max_level = 4;
+}
+
+message SkipListElementReference {
+  int64 element_pointer = 1;
+  bytes key = 2;
+}
+
+message SkipListElement {
+  int64 id = 1;
+  repeated SkipListElementReference next = 2;
+  int32 level = 3;
+  bytes key = 4;
+  bytes value = 5;
+  SkipListElementReference prev = 6;
+}
+
+message NameBatchData {
+  repeated bytes names = 1;
+}
\ No newline at end of file
diff --git a/weed/util/skiplist/skiplist_serde.go b/weed/util/skiplist/skiplist_serde.go
new file mode 100644
index 000000000..e528b8a3d
--- /dev/null
+++ b/weed/util/skiplist/skiplist_serde.go
@@ -0,0 +1,51 @@
+package skiplist
+
+import "bytes"
+
+func compareElement(a *SkipListElement, key []byte) int {
+	if len(a.Key) == 0 {
+		return -1
+	}
+	return bytes.Compare(a.Key, key)
+}
+
+func (node *SkipListElement) Reference() *SkipListElementReference {
+	if node == nil {
+		return nil
+	}
+	return &SkipListElementReference{
+		ElementPointer: node.Id,
+		Key:            node.Key,
+	}
+}
+
+func (t *SkipList) saveElement(element *SkipListElement) error {
+	if element == nil {
+		return nil
+	}
+	return t.listStore.SaveElement(element.Id, element)
+}
+
+func (t *SkipList) deleteElement(element *SkipListElement) error {
+	if element == nil {
+		return nil
+	}
+	return t.listStore.DeleteElement(element.Id)
+}
+
+func (t *SkipList) loadElement(ref *SkipListElementReference) (*SkipListElement, error) {
+	if ref.IsNil() {
+		return nil, nil
+	}
+	return t.listStore.LoadElement(ref.ElementPointer)
+}
+
+func (ref *SkipListElementReference) IsNil() bool {
+	if ref == nil {
+		return true
+	}
+	if len(ref.Key) == 0 {
+		return true
+	}
+	return false
+}
\ No newline at end of file
diff --git a/weed/util/skiplist/skiplist_test.go b/weed/util/skiplist/skiplist_test.go
new file mode 100644
index 000000000..a35bef6f3
--- /dev/null
+++ b/weed/util/skiplist/skiplist_test.go
@@ -0,0 +1,295 @@
+package skiplist
+
+import (
+	"bytes"
+	"fmt"
+	"math/rand"
+	"strconv"
+	"testing"
+)
+
+const (
+	maxN = 10000
+)
+
+var (
+	memStore = newMemStore()
+)
+
+func TestReverseInsert(t *testing.T) {
+	list := NewSeed(100, memStore)
+
+	list.Insert([]byte("zzz"), []byte("zzz"))
+	list.Delete([]byte("zzz"))
+
+	list.Insert([]byte("aaa"), []byte("aaa"))
+
+	if list.IsEmpty() {
+		t.Fail()
+	}
+
+}
+
+
+func TestInsertAndFind(t *testing.T) {
+
+	k0 := []byte("0")
+	var list *SkipList
+
+	var listPointer *SkipList
+	listPointer.Insert(k0, k0)
+	if _, _, ok, _ := listPointer.Find(k0); ok {
+		t.Fail()
+	}
+
+	list = New(memStore)
+	if _, _, ok, _ := list.Find(k0); ok {
+		t.Fail()
+	}
+	if !list.IsEmpty() {
+		t.Fail()
+	}
+
+	// Test at the beginning of the list.
+	for i := 0; i < maxN; i++ {
+		key := []byte(strconv.Itoa(maxN - i))
+		list.Insert(key, key)
+	}
+	for i := 0; i < maxN; i++ {
+		key := []byte(strconv.Itoa(maxN - i))
+		if _, _, ok, _ := list.Find(key); !ok {
+			t.Fail()
+		}
+	}
+
+	list = New(memStore)
+	// Test at the end of the list.
+	for i := 0; i < maxN; i++ {
+		key := []byte(strconv.Itoa(i))
+		list.Insert(key, key)
+	}
+	for i := 0; i < maxN; i++ {
+		key := []byte(strconv.Itoa(i))
+		if _, _, ok, _ := list.Find(key); !ok {
+			t.Fail()
+		}
+	}
+
+	list = New(memStore)
+	// Test at random positions in the list.
+	rList := rand.Perm(maxN)
+	for _, e := range rList {
+		key := []byte(strconv.Itoa(e))
+		// println("insert", e)
+		list.Insert(key, key)
+	}
+	for _, e := range rList {
+		key := []byte(strconv.Itoa(e))
+		// println("find", e)
+		if _, _, ok, _ := list.Find(key); !ok {
+			t.Fail()
+		}
+	}
+	// println("print list")
+	list.println()
+
+}
+
+func Element(x int) []byte {
+	return []byte(strconv.Itoa(x))
+}
+
+func TestDelete(t *testing.T) {
+
+	k0 := []byte("0")
+
+	var list *SkipList
+
+	// Delete on empty list
+	list.Delete(k0)
+
+	list = New(memStore)
+
+	list.Delete(k0)
+	if !list.IsEmpty() {
+		t.Fail()
+	}
+
+	list.Insert(k0, k0)
+	list.Delete(k0)
+	if !list.IsEmpty() {
+		t.Fail()
+	}
+
+	// Delete elements at the beginning of the list.
+	for i := 0; i < maxN; i++ {
+		list.Insert(Element(i), Element(i))
+	}
+	for i := 0; i < maxN; i++ {
+		list.Delete(Element(i))
+	}
+	if !list.IsEmpty() {
+		t.Fail()
+	}
+
+	list = New(memStore)
+	// Delete elements at the end of the list.
+	for i := 0; i < maxN; i++ {
+		list.Insert(Element(i), Element(i))
+	}
+	for i := 0; i < maxN; i++ {
+		list.Delete(Element(maxN - i - 1))
+	}
+	if !list.IsEmpty() {
+		t.Fail()
+	}
+
+	list = New(memStore)
+	// Delete elements at random positions in the list.
+	rList := rand.Perm(maxN)
+	for _, e := range rList {
+		list.Insert(Element(e), Element(e))
+	}
+	for _, e := range rList {
+		list.Delete(Element(e))
+	}
+	if !list.IsEmpty() {
+		t.Fail()
+	}
+}
+
+func TestNext(t *testing.T) {
+	list := New(memStore)
+
+	for i := 0; i < maxN; i++ {
+		list.Insert(Element(i), Element(i))
+	}
+
+	smallest, _ := list.GetSmallestNode()
+	largest, _ := list.GetLargestNode()
+
+	lastNode := smallest
+	node := lastNode
+	for node != largest {
+		node, _ = list.Next(node)
+		// Must always be incrementing here!
+		if bytes.Compare(node.Key, lastNode.Key) <= 0 {
+			t.Fail()
+		}
+		// Next.Prev must always point to itself!
+		prevNode, _ := list.Prev(node)
+		nextNode, _ := list.Next(prevNode)
+		if nextNode != node {
+			t.Fail()
+		}
+		lastNode = node
+	}
+
+	if nextNode, _ := list.Next(largest); nextNode != smallest {
+		t.Fail()
+	}
+}
+
+func TestPrev(t *testing.T) {
+	list := New(memStore)
+
+	for i := 0; i < maxN; i++ {
+		list.Insert(Element(i), Element(i))
+	}
+
+	smallest, _ := list.GetSmallestNode()
+	largest, _ := list.GetLargestNode()
+
+	lastNode := largest
+	node := lastNode
+	for node != smallest {
+		node, _ = list.Prev(node)
+		// Must always be incrementing here!
+		if bytes.Compare(node.Key, lastNode.Key) >= 0 {
+			t.Fail()
+		}
+		// Next.Prev must always point to itself!
+		nextNode, _ := list.Next(node)
+		prevNode, _ := list.Prev(nextNode)
+		if prevNode != node {
+			t.Fail()
+		}
+		lastNode = node
+	}
+
+	if prevNode, _ := list.Prev(smallest); prevNode != largest {
+		t.Fail()
+	}
+}
+
+func TestFindGreaterOrEqual(t *testing.T) {
+
+	maxNumber := maxN * 100
+
+	var list *SkipList
+	var listPointer *SkipList
+
+	// Test on empty list.
+	if _, _, ok, _ := listPointer.FindGreaterOrEqual(Element(0)); ok {
+		t.Fail()
+	}
+
+	list = New(memStore)
+
+	for i := 0; i < maxN; i++ {
+		list.Insert(Element(rand.Intn(maxNumber)), Element(i))
+	}
+
+	for i := 0; i < maxN; i++ {
+		key := Element(rand.Intn(maxNumber))
+		if _, v, ok, _ := list.FindGreaterOrEqual(key); ok {
+			// if f is v should be bigger than the element before
+			if v.Prev != nil && bytes.Compare(v.Prev.Key, key) >= 0 {
+				fmt.Printf("PrevV: %s\n    key: %s\n\n", string(v.Prev.Key), string(key))
+				t.Fail()
+			}
+			// v should be bigger or equal to f
+			// If we compare directly, we get an equal key with a difference on the 10th decimal point, which fails.
+			if bytes.Compare(v.Key, key) < 0 {
+				fmt.Printf("v: %s\n    key: %s\n\n", string(v.Key), string(key))
+				t.Fail()
+			}
+		} else {
+			lastNode, _ := list.GetLargestNode()
+			lastV := lastNode.GetValue()
+			// It is OK, to fail, as long as f is bigger than the last element.
+			if bytes.Compare(key, lastV) <= 0 {
+				fmt.Printf("lastV: %s\n    key: %s\n\n", string(lastV), string(key))
+				t.Fail()
+			}
+		}
+	}
+
+}
+
+func TestChangeValue(t *testing.T) {
+	list := New(memStore)
+
+	for i := 0; i < maxN; i++ {
+		list.Insert(Element(i), []byte("value"))
+	}
+
+	for i := 0; i < maxN; i++ {
+		// The key only looks at the int so the string doesn't matter here!
+		_, f1, ok, _ := list.Find(Element(i))
+		if !ok {
+			t.Fail()
+		}
+		err := list.ChangeValue(f1, []byte("different value"))
+		if err != nil {
+			t.Fail()
+		}
+		_, f2, ok, _ := list.Find(Element(i))
+		if !ok {
+			t.Fail()
+		}
+		if bytes.Compare(f2.GetValue(), []byte("different value")) != 0 {
+			t.Fail()
+		}
+	}
+}