一致性哈希可用于解决服务器均衡问题。 用Golang简单实现了下，并加入了权重。可采用合适的权重配合算法使用。
package main
//一致性哈希(Consistent Hashing)
//author: Xiong Chuan Liang
//date: 2015-2-20
import (
"fmt"
"hash/crc32"
"sort"
"strconv"
"sync"
)
const DEFAULT_REPLICAS = 160
type HashRing []uint32
func (c HashRing) Len() int {
return len(c)
}
func (c HashRing) Less(i, j int) bool {
return c[i] < c[j]
}
func (c HashRing) Swap(i, j int) {
c[i], c[j] = c[j], c[i]
}
type Node struct {
Id int
Ip string
Port int
HostName string
Weight int
}
func NewNode(id int, ip string, port int, name string, weight int) *Node {
return &Node{
Id: id,
Ip: ip,
Port: port,
HostName: name,
Weight: weight,
}
}
type Consistent struct {
Nodes map[uint32]Node
numReps int
Resources map[int]bool
ring HashRing
sync.RWMutex
}
func NewConsistent() *Consistent {
return &Consistent{
Nodes: make(map[uint32]Node),
numReps: DEFAULT_REPLICAS,
Resources: make(map[int]bool),
ring: HashRing{},
}
}
func (c *Consistent) Add(node *Node) bool {
c.Lock()
defer c.Unlock()
if _, ok := c.Resources[node.Id]; ok {
return false
}
count := c.numReps * node.Weight
for i := 0; i < count; i++ {
str := c.joinStr(i, node)
c.Nodes[c.hashStr(str)] = *(node)
}
c.Resources[node.Id] = true
c.sortHashRing()
return true
}
func (c *Consistent) sortHashRing() {
c.ring = HashRing{}
for k := range c.Nodes {
c.ring = append(c.ring, k)
}
sort.Sort(c.ring)
}
func (c *Consistent) joinStr(i int, node *Node) string {
return node.Ip + "*" + strconv.Itoa(node.Weight) +
"-" + strconv.Itoa(i) +
"-" + strconv.Itoa(node.Id)
}
// MurMurHash算法 :https://github.com/spaolacci/murmur3
func (c *Consistent) hashStr(key string) uint32 {
return crc32.ChecksumIEEE([]byte(key))
}
func (c *Consistent) Get(key string) Node {
c.RLock()
defer c.RUnlock()
hash := c.hashStr(key)
i := c.search(hash)
return c.Nodes[c.ring[i]]
}
func (c *Consistent) search(hash uint32) int {
i := sort.Search(len(c.ring), func(i int) bool { return c.ring[i] >= hash })
if i < len(c.ring) {
if i == len(c.ring)-1 {
return 0
} else {
return i
}
} else {
return len(c.ring) - 1
}
}
func (c *Consistent) Remove(node *Node) {
c.Lock()
defer c.Unlock()
if _, ok := c.Resources[node.Id]; !ok {
return
}
delete(c.Resources, node.Id)
count := c.numReps * node.Weight
for i := 0; i < count; i++ {
str := c.joinStr(i, node)
delete(c.Nodes, c.hashStr(str))
}
c.sortHashRing()
}
func main() {
cHashRing := NewConsistent()
for i := 0; i < 10; i++ {
si := fmt.Sprintf("%d", i)
cHashRing.Add(NewNode(i, "172.18.1."+si, 8080, "host_"+si, 1))
}
for k, v := range cHashRing.Nodes {
fmt.Println("Hash:", k, " IP:", v.Ip)
}
ipMap := make(map[string]int, 0)
for i := 0; i < 1000; i++ {
si := fmt.Sprintf("key%d", i)
k := cHashRing.Get(si)
if _, ok := ipMap[k.Ip]; ok {
ipMap[k.Ip] += 1
} else {
ipMap[k.Ip] = 1
}
}
for k, v := range ipMap {
fmt.Println("Node IP:", k, " count:", v)
}
}
/*
分布:
Node IP: 172.18.1.2 count: 115
Node IP: 172.18.1.8 count: 111
Node IP: 172.18.1.3 count: 94
Node IP: 172.18.1.1 count: 84
Node IP: 172.18.1.7 count: 107
Node IP: 172.18.1.6 count: 117
Node IP: 172.18.1.4 count: 92
Node IP: 172.18.1.5 count: 112
Node IP: 172.18.1.0 count: 63
Node IP: 172.18.1.9 count: 105
*/
上面是简单测试后的结果。
