redis3 using redis native sorted set

This commit is contained in:
Chris Lu
2021-10-06 18:18:24 -07:00
parent 8668d49c9d
commit 371fead8a5
10 changed files with 817 additions and 205 deletions

View File

@@ -0,0 +1,483 @@
package redis3
import (
"bytes"
"context"
"fmt"
"github.com/chrislusf/seaweedfs/weed/util/skiplist"
"github.com/go-redis/redis/v8"
)
type ItemList struct {
skipList *skiplist.SkipList
batchSize int
client redis.UniversalClient
prefix string
}
func newItemList(client redis.UniversalClient, prefix string, store skiplist.ListStore, batchSize int) *ItemList {
return &ItemList{
skipList: skiplist.New(store),
batchSize: batchSize,
client: client,
prefix: prefix,
}
}
/*
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 *ItemList) 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 {
// case 2.1
if nl.NodeContainsItem(prevNode.Reference(), name) {
return nil
}
// case 2.2
nodeSize := nl.NodeSize(prevNode.Reference())
if nodeSize < nl.batchSize {
return nl.NodeAddMember(prevNode.Reference(), name)
}
// case 2.3
x := nl.NodeInnerPosition(prevNode.Reference(), name)
y := nodeSize - x
addToX := x <= y
// add to a new node
if x == 0 || y == 0 {
if err := nl.ItemAdd(lookupKey, 0, name); err != nil {
return err
}
return nil
}
if addToX {
// collect names before name, add them to X
namesToX, err := nl.NodeRangeBeforeExclusive(prevNode.Reference(), name)
if err != nil {
return nil
}
// delete skiplist reference to old node
if _, err := nl.skipList.DeleteByKey(prevNode.Key); err != nil {
return err
}
// add namesToY and name to a new X
namesToX = append(namesToX, name)
if err := nl.ItemAdd([]byte(namesToX[0]), 0, namesToX...); err != nil {
return nil
}
// remove names less than name from current Y
if err := nl.NodeDeleteBeforeExclusive(prevNode.Reference(), name); err != nil {
return nil
}
// point skip list to current Y
if err := nl.ItemAdd(lookupKey, prevNode.Id); err != nil {
return nil
}
return nil
} else {
// collect names after name, add them to Y
namesToY, err := nl.NodeRangeAfterExclusive(prevNode.Reference(), name)
if err != nil {
return nil
}
// add namesToY and name to a new Y
namesToY = append(namesToY, name)
if err := nl.ItemAdd(lookupKey, 0, namesToY...); err != nil {
return nil
}
// remove names after name from current X
if err := nl.NodeDeleteAfterExclusive(prevNode.Reference(), name); err != nil {
return nil
}
return nil
}
}
// case 2.4
if nextNode != nil {
nodeSize := nl.NodeSize(nextNode.Reference())
if nodeSize < nl.batchSize {
if id, err := nl.skipList.DeleteByKey(nextNode.Key); err != nil {
return err
} else {
if err := nl.ItemAdd(lookupKey, id, name); err != nil {
return err
}
}
return nil
}
}
// case 2.5
// now prevNode is nil
return nl.ItemAdd(lookupKey, 0, name)
}
/*
// 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 *ItemList) DeleteName(name string) error {
lookupKey := []byte(name)
prevNode, nextNode, found, err := nl.skipList.FindGreaterOrEqual(lookupKey)
if err != nil {
return err
}
// case 1
if found && bytes.Compare(nextNode.Key, lookupKey) == 0 {
if _, err := nl.skipList.DeleteByKey(nextNode.Key); err != nil {
return err
}
if err := nl.NodeDeleteMember(nextNode.Reference(), name); err != nil {
return err
}
minName := nl.NodeMin(nextNode.Reference())
if minName == "" {
return nl.NodeDelete(nextNode.Reference())
}
return nl.ItemAdd([]byte(minName), nextNode.Id)
}
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
}
if !nl.NodeContainsItem(prevNode.Reference(), name) {
return nil
}
// case 3
if err := nl.NodeDeleteMember(prevNode.Reference(), name); err != nil {
return err
}
prevSize := nl.NodeSize(prevNode.Reference())
if prevSize == 0 {
if _, err := nl.skipList.DeleteByKey(prevNode.Key); err != nil {
return err
}
return nil
}
nextSize := nl.NodeSize(nextNode.Reference())
if nextSize > 0 && prevSize + nextSize < nl.batchSize {
// case 3.1 merge nextNode and prevNode
if _, err := nl.skipList.DeleteByKey(nextNode.Key); err != nil {
return err
}
nextNames, err := nl.NodeRangeBeforeExclusive(nextNode.Reference(), "")
if err != nil {
return err
}
if err := nl.NodeAddMember(prevNode.Reference(), nextNames...); err != nil {
return err
}
return nl.NodeDelete(nextNode.Reference())
} else {
// case 3.2 update prevNode
// no action to take
return nil
}
return nil
}
func (nl *ItemList) 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 {
if !nl.NodeScanIncluseiveAfter(prevNode.Reference(), startFrom, visitNamesFn) {
return nil
}
}
for nextNode != nil {
if !nl.NodeScanIncluseiveAfter(nextNode.Reference(), startFrom, visitNamesFn) {
return nil
}
nextNode, err = nl.skipList.LoadElement(nextNode.Next[0])
if err != nil {
return err
}
}
return nil
}
func (nl *ItemList) 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
}
if err := nl.NodeDelete(node.Reference()); err != nil {
return err
}
nodeRef = node.Next[0]
}
return nil
}
func (nl *ItemList) NodeContainsItem(node *skiplist.SkipListElementReference, item string) bool {
key := fmt.Sprintf("%s%dm", nl.prefix, node.ElementPointer)
_, err := nl.client.ZScore(context.Background(), key, item).Result()
if err == redis.Nil {
return false
}
if err == nil {
return true
}
return false
}
func (nl *ItemList) NodeSize(node *skiplist.SkipListElementReference) int {
key := fmt.Sprintf("%s%dm", nl.prefix, node.ElementPointer)
return int(nl.client.ZLexCount(context.Background(), key, "-", "+").Val())
}
func (nl *ItemList) NodeAddMember(node *skiplist.SkipListElementReference, names ...string) error {
key := fmt.Sprintf("%s%dm", nl.prefix, node.ElementPointer)
var members []*redis.Z
for _, name := range names {
members = append(members, &redis.Z{
Score: 0,
Member: name,
})
}
return nl.client.ZAddNX(context.Background(), key, members...).Err()
}
func (nl *ItemList) NodeDeleteMember(node *skiplist.SkipListElementReference, name string) error {
key := fmt.Sprintf("%s%dm", nl.prefix, node.ElementPointer)
return nl.client.ZRem(context.Background(), key, name).Err()
}
func (nl *ItemList) NodeDelete(node *skiplist.SkipListElementReference) error {
key := fmt.Sprintf("%s%dm", nl.prefix, node.ElementPointer)
return nl.client.Del(context.Background(), key).Err()
}
func (nl *ItemList) NodeInnerPosition(node *skiplist.SkipListElementReference, name string) int {
key := fmt.Sprintf("%s%dm", nl.prefix, node.ElementPointer)
return int(nl.client.ZLexCount(context.Background(), key, "-", "("+name).Val())
}
func (nl *ItemList) NodeMin(node *skiplist.SkipListElementReference) string {
key := fmt.Sprintf("%s%dm", nl.prefix, node.ElementPointer)
slice := nl.client.ZPopMin(context.Background(), key).Val()
if len(slice)>0{
s := slice[0].Member.(string)
return s
}
return ""
}
func (nl *ItemList) NodeScanIncluseiveAfter(node *skiplist.SkipListElementReference, startFrom string, visitNamesFn func(name string) bool) bool {
key := fmt.Sprintf("%s%dm", nl.prefix, node.ElementPointer)
if startFrom == "" {
startFrom = "-"
} else {
startFrom = "[" + startFrom
}
names := nl.client.ZRangeByLex(context.Background(), key, &redis.ZRangeBy{
Min: startFrom,
Max: "+",
}).Val()
for _, n := range names {
if !visitNamesFn(n) {
return false
}
}
return true
}
func (nl *ItemList) NodeRangeBeforeExclusive(node *skiplist.SkipListElementReference, stopAt string) ([]string, error) {
key := fmt.Sprintf("%s%dm", nl.prefix, node.ElementPointer)
if stopAt == "" {
stopAt = "+"
} else {
stopAt = "(" + stopAt
}
return nl.client.ZRangeByLex(context.Background(), key, &redis.ZRangeBy{
Min: "-",
Max: stopAt,
}).Result()
}
func (nl *ItemList) NodeRangeAfterExclusive(node *skiplist.SkipListElementReference, startFrom string) ([]string, error) {
key := fmt.Sprintf("%s%dm", nl.prefix, node.ElementPointer)
if startFrom == "" {
startFrom = "-"
} else {
startFrom = "(" + startFrom
}
return nl.client.ZRangeByLex(context.Background(), key, &redis.ZRangeBy{
Min: startFrom,
Max: "+",
}).Result()
}
func (nl *ItemList) NodeDeleteBeforeExclusive(node *skiplist.SkipListElementReference, stopAt string) error {
key := fmt.Sprintf("%s%dm", nl.prefix, node.ElementPointer)
if stopAt == "" {
stopAt = "+"
} else {
stopAt = "(" + stopAt
}
return nl.client.ZRemRangeByLex(context.Background(), key, "-", stopAt).Err()
}
func (nl *ItemList) NodeDeleteAfterExclusive(node *skiplist.SkipListElementReference, startFrom string) error {
key := fmt.Sprintf("%s%dm", nl.prefix, node.ElementPointer)
if startFrom == "" {
startFrom = "-"
} else {
startFrom = "(" + startFrom
}
return nl.client.ZRemRangeByLex(context.Background(), key, startFrom, "+").Err()
}
func (nl *ItemList) ItemAdd(lookupKey []byte, idIfKnown int64, names ...string) error {
if id, err := nl.skipList.InsertByKey(lookupKey, idIfKnown, nil); err != nil {
return err
} else {
if len(names) > 0 {
return nl.NodeAddMember(&skiplist.SkipListElementReference{
ElementPointer: id,
Key: lookupKey,
}, names...)
}
}
return nil
}

View File

@@ -0,0 +1,75 @@
package redis3
import (
"github.com/chrislusf/seaweedfs/weed/glog"
"github.com/chrislusf/seaweedfs/weed/util/skiplist"
"github.com/go-redis/redis/v8"
"github.com/golang/protobuf/proto"
)
func LoadItemList(data []byte, prefix string, client redis.UniversalClient, store skiplist.ListStore, batchSize int) *ItemList {
nl := &ItemList{
skipList: skiplist.New(store),
batchSize: batchSize,
client: client,
prefix: prefix,
}
if len(data) == 0 {
return nl
}
message := &skiplist.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] = &skiplist.SkipListElementReference{
ElementPointer: ref.ElementPointer,
Key: ref.Key,
}
}
for i, ref := range message.EndLevels {
nl.skipList.EndLevels[i] = &skiplist.SkipListElementReference{
ElementPointer: ref.ElementPointer,
Key: ref.Key,
}
}
return nl
}
func (nl *ItemList) HasChanges() bool {
return nl.skipList.HasChanges
}
func (nl *ItemList) ToBytes() []byte {
message := &skiplist.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, &skiplist.SkipListElementReference{
ElementPointer: ref.ElementPointer,
Key: ref.Key,
})
}
for _, ref := range nl.skipList.EndLevels {
if ref == nil {
break
}
message.EndLevels = append(message.EndLevels, &skiplist.SkipListElementReference{
ElementPointer: ref.ElementPointer,
Key: ref.Key,
})
}
data, err := proto.Marshal(message)
if err != nil {
glog.Errorf("marshal skiplist: %v", err)
}
return data
}

View File

@@ -4,11 +4,10 @@ import (
"context"
"fmt"
"github.com/chrislusf/seaweedfs/weed/glog"
"github.com/chrislusf/seaweedfs/weed/util/skiplist"
"github.com/go-redis/redis/v8"
)
const maxNameBatchSizeLimit = 1000
const maxNameBatchSizeLimit = 1000000
func insertChild(ctx context.Context, redisStore *UniversalRedis3Store, key string, name string) error {
@@ -29,7 +28,7 @@ func insertChild(ctx context.Context, redisStore *UniversalRedis3Store, key stri
}
}
store := newSkipListElementStore(key, client)
nameList := skiplist.LoadNameList([]byte(data), store, maxNameBatchSizeLimit)
nameList := LoadItemList([]byte(data), key, client, store, maxNameBatchSizeLimit)
if err := nameList.WriteName(name); err != nil {
glog.Errorf("add %s %s: %v", key, name, err)
@@ -64,7 +63,7 @@ func removeChild(ctx context.Context, redisStore *UniversalRedis3Store, key stri
}
}
store := newSkipListElementStore(key, client)
nameList := skiplist.LoadNameList([]byte(data), store, maxNameBatchSizeLimit)
nameList := LoadItemList([]byte(data), key, client, store, maxNameBatchSizeLimit)
if err := nameList.DeleteName(name); err != nil {
return err
@@ -97,7 +96,7 @@ func removeChildren(ctx context.Context, redisStore *UniversalRedis3Store, key s
}
}
store := newSkipListElementStore(key, client)
nameList := skiplist.LoadNameList([]byte(data), store, maxNameBatchSizeLimit)
nameList := LoadItemList([]byte(data), key, client, store, maxNameBatchSizeLimit)
if err = nameList.ListNames("", func(name string) bool {
if err := onDeleteFn(name); err != nil {
@@ -126,7 +125,7 @@ func listChildren(ctx context.Context, redisStore *UniversalRedis3Store, key str
}
}
store := newSkipListElementStore(key, client)
nameList := skiplist.LoadNameList([]byte(data), store, maxNameBatchSizeLimit)
nameList := LoadItemList([]byte(data), key, client, store, maxNameBatchSizeLimit)
if err = nameList.ListNames(startFileName, func(name string) bool {
return eachFn(name)

View File

@@ -2,11 +2,12 @@ package redis3
import (
"context"
"github.com/chrislusf/seaweedfs/weed/util/skiplist"
"fmt"
"github.com/go-redis/redis/v8"
"github.com/stvp/tempredis"
"strconv"
"testing"
"time"
)
var names = []string{
@@ -53,20 +54,21 @@ func TestNameList(t *testing.T) {
store := newSkipListElementStore("/yyy/bin", client)
var data []byte
for _, name := range names {
nameList := skiplist.LoadNameList(data, store, maxNameBatchSizeLimit)
nameList := LoadItemList(data, "/yyy/bin", client, store, maxNameBatchSizeLimit)
nameList.WriteName(name)
nameList.ListNames("", func(name string) bool {
// println(name)
return true
})
if nameList.HasChanges() {
data = nameList.ToBytes()
}
println()
// println()
}
nameList := skiplist.LoadNameList(data, store, maxNameBatchSizeLimit)
nameList := LoadItemList(data, "/yyy/bin", client, store, maxNameBatchSizeLimit)
nameList.ListNames("", func(name string) bool {
println(name)
return true
@@ -74,6 +76,99 @@ func TestNameList(t *testing.T) {
}
func xBenchmarkNameList(b *testing.B) {
server, err := tempredis.Start(tempredis.Config{})
if err != nil {
panic(err)
}
defer server.Term()
client := redis.NewClient(&redis.Options{
Network: "unix",
Addr: server.Socket(),
})
store := newSkipListElementStore("/yyy/bin", client)
var data []byte
for i := 0; i < b.N; i++ {
nameList := LoadItemList(data, "/yyy/bin", client, store, maxNameBatchSizeLimit)
nameList.WriteName(strconv.Itoa(i)+"namexxxxxxxxxxxxxxxxxxx")
if nameList.HasChanges() {
data = nameList.ToBytes()
}
}
}
func xBenchmarkRedis(b *testing.B) {
server, err := tempredis.Start(tempredis.Config{})
if err != nil {
panic(err)
}
defer server.Term()
client := redis.NewClient(&redis.Options{
Network: "unix",
Addr: server.Socket(),
})
for i := 0; i < b.N; i++ {
client.ZAddNX(context.Background(),"/yyy/bin", &redis.Z{Score: 0, Member: strconv.Itoa(i)+"namexxxxxxxxxxxxxxxxxxx"})
}
}
func TestNameListAdd(t *testing.T) {
server, err := tempredis.Start(tempredis.Config{})
if err != nil {
panic(err)
}
defer server.Term()
client := redis.NewClient(&redis.Options{
Addr: "localhost:6379",
Password: "",
DB: 0,
})
client.FlushAll(context.Background())
N := 364800
ts0 := time.Now()
store := newSkipListElementStore("/y", client)
var data []byte
nameList := LoadItemList(data, "/y", client, store, 100000)
for i := 0; i < N; i++ {
nameList.WriteName(fmt.Sprintf("%8d", i))
}
ts1 := time.Now()
for i := 0; i < N; i++ {
client.ZAddNX(context.Background(),"/x", &redis.Z{Score: 0, Member: fmt.Sprintf("name %8d", i)})
}
ts2 := time.Now()
fmt.Printf("%v %v", ts1.Sub(ts0), ts2.Sub(ts1))
/*
keys := client.Keys(context.Background(), "/*m").Val()
for _, k := range keys {
println("key", k)
for i, v := range client.ZRangeByLex(context.Background(), k, &redis.ZRangeBy{
Min: "-",
Max: "+",
}).Val() {
println(" ", i, v)
}
}
*/
}
func BenchmarkNameList(b *testing.B) {
server, err := tempredis.Start(tempredis.Config{})
@@ -83,16 +178,17 @@ func BenchmarkNameList(b *testing.B) {
defer server.Term()
client := redis.NewClient(&redis.Options{
Network: "unix",
Addr: server.Socket(),
Addr: "localhost:6379",
Password: "",
DB: 0,
})
store := newSkipListElementStore("/yyy/bin", client)
var data []byte
for i := 0; i < b.N; i++ {
nameList := skiplist.LoadNameList(data, store, maxNameBatchSizeLimit)
nameList := LoadItemList(data, "/yyy/bin", client, store, maxNameBatchSizeLimit)
nameList.WriteName("name"+strconv.Itoa(i))
nameList.WriteName(fmt.Sprintf("name %8d", i))
if nameList.HasChanges() {
data = nameList.ToBytes()
@@ -102,52 +198,6 @@ func BenchmarkNameList(b *testing.B) {
func BenchmarkRedis(b *testing.B) {
server, err := tempredis.Start(tempredis.Config{})
if err != nil {
panic(err)
}
defer server.Term()
client := redis.NewClient(&redis.Options{
Network: "unix",
Addr: server.Socket(),
})
for i := 0; i < b.N; i++ {
client.ZAddNX(context.Background(),"/yyy/bin", &redis.Z{Score: 0, Member: "name"+strconv.Itoa(i)})
}
}
func xBenchmarkNameList(b *testing.B) {
server, err := tempredis.Start(tempredis.Config{})
if err != nil {
panic(err)
}
defer server.Term()
client := redis.NewClient(&redis.Options{
Addr: "localhost:6379",
Password: "",
DB: 0,
})
store := newSkipListElementStore("/yyy/bin", client)
var data []byte
for i := 0; i < b.N; i++ {
nameList := skiplist.LoadNameList(data, store, maxNameBatchSizeLimit)
nameList.WriteName("name"+strconv.Itoa(i))
if nameList.HasChanges() {
data = nameList.ToBytes()
}
}
}
func xBenchmarkRedis(b *testing.B) {
client := redis.NewClient(&redis.Options{
Addr: "localhost:6379",
Password: "",
@@ -155,6 +205,6 @@ func xBenchmarkRedis(b *testing.B) {
})
for i := 0; i < b.N; i++ {
client.ZAddNX(context.Background(),"/xxx/bin", &redis.Z{Score: 0, Member: "name"+strconv.Itoa(i)})
client.ZAddNX(context.Background(),"/xxx/bin", &redis.Z{Score: 0, Member: fmt.Sprintf("name %8d", i)})
}
}

View File

@@ -10,7 +10,7 @@ import (
)
type SkipListElementStore struct {
prefix string
Prefix string
client redis.UniversalClient
}
@@ -18,13 +18,13 @@ var _ = skiplist.ListStore(&SkipListElementStore{})
func newSkipListElementStore(prefix string, client redis.UniversalClient) *SkipListElementStore {
return &SkipListElementStore{
prefix: prefix,
Prefix: prefix,
client: client,
}
}
func (m *SkipListElementStore) SaveElement(id int64, element *skiplist.SkipListElement) error {
key := fmt.Sprintf("%s%d", m.prefix, id)
key := fmt.Sprintf("%s%d", m.Prefix, id)
data, err := proto.Marshal(element)
if err != nil {
glog.Errorf("marshal %s: %v", key, err)
@@ -33,12 +33,12 @@ func (m *SkipListElementStore) SaveElement(id int64, element *skiplist.SkipListE
}
func (m *SkipListElementStore) DeleteElement(id int64) error {
key := fmt.Sprintf("%s%d", m.prefix, id)
key := fmt.Sprintf("%s%d", m.Prefix, id)
return m.client.Del(context.Background(), key).Err()
}
func (m *SkipListElementStore) LoadElement(id int64) (*skiplist.SkipListElement, error) {
key := fmt.Sprintf("%s%d", m.prefix, id)
key := fmt.Sprintf("%s%d", m.Prefix, id)
data, err := m.client.Get(context.Background(), key).Result()
if err != nil {
if err == redis.Nil {