Documentation
¶
Overview ¶
package consistent 提供了一致性哈希的计算功能，以用于分布式请求的负载均衡。 比如有三台机器，分别为cacheA,cacheB,cacheC， 我们可以通过提供的功能来分配大量用户的大批量请求。
我们可以通过New来创建一致性哈希，通过Add、Remove来增加、删除服务器，通过Get来获取提供服务的物理机。 需要注意的是,如果增删服务器，hash值将会重新计算（remap），会造成注册的服务器重建相关业务。
相关技术的材料，可以查看：
wikipedia: http://en.wikipedia.org/wiki/Consistent_hashing csdn: http://blog.csdn.net/cywosp/article/details/23397179/ csdn: http://blog.csdn.net/caigen1988/article/details/7708806 go语言实现: https://segmentfault.com/a/1190000000414004
Index ¶
- Variables
- type Consistent
- func (c *Consistent) Add(elt string)
- func (c *Consistent) Get(name string) (string, error)
- func (c *Consistent) GetMachineNum() int
- func (c *Consistent) GetN(name string, n int) ([]string, error)
- func (c *Consistent) GetTwo(name string) (string, string, error)
- func (c *Consistent) Members() []string
- func (c *Consistent) Remove(elt string)
- func (c *Consistent) Set(elts []string)
- func (c *Consistent) SetReplicas(replicasNum int)
- Bugs
Examples ¶
Constants ¶
This section is empty.
Variables ¶
View Source
var ErrEmptyCircle = errors.New("empty circle")
ErrEmptyCircle is the error returned when trying to get an element when nothing has been added to hash.
Functions ¶
This section is empty.
Types ¶
type Consistent ¶
Consistent 通过成员变量，保留一致性哈希环的struct.
func NewConsistent ¶
func NewConsistent() *Consistent
NewConsistent 基于默认的replicas定义，创建一个新的对象。
要改变replicas的值，可以在添加服务器节点之前，通过SetReplicas方法修改。
Example ¶
package main
import (
"fmt"
"github.com/alex023/basekit/hash/consistent"
"log"
)
func main() {
c := consistent.NewConsistent()
c.Add("cacheA")
c.Add("cacheB")
c.Add("cacheC")
users := []string{"user_mcnulty", "user_bunk", "user_omar", "user_bunny", "user_stringer"}
for _, u := range users {
server, err := c.Get(u)
if err != nil {
log.Fatal(err)
}
fmt.Printf("%s => %s\n", u, server)
}
}
Output: user_mcnulty => cacheA user_bunk => cacheA user_omar => cacheA user_bunny => cacheC user_stringer => cacheC
func (*Consistent) Add ¶
func (c *Consistent) Add(elt string)
Add 增加一个物理机到hash表中
Example ¶
package main
import (
"fmt"
"github.com/alex023/basekit/hash/consistent"
"log"
)
func main() {
c := consistent.NewConsistent()
c.Add("cacheA")
c.Add("cacheB")
c.Add("cacheC")
users := []string{"user_mcnulty", "user_bunk", "user_omar", "user_bunny", "user_stringer"}
fmt.Println("initial state [A, B, C]")
for _, u := range users {
server, err := c.Get(u)
if err != nil {
log.Fatal(err)
}
fmt.Printf("%s => %s\n", u, server)
}
c.Add("cacheD")
c.Add("cacheE")
fmt.Println("\nwith cacheD, cacheE [A, B, C, D, E]")
for _, u := range users {
server, err := c.Get(u)
if err != nil {
log.Fatal(err)
}
fmt.Printf("%s => %s\n", u, server)
}
}
Output: initial state [A, B, C] user_mcnulty => cacheA user_bunk => cacheA user_omar => cacheA user_bunny => cacheC user_stringer => cacheC with cacheD, cacheE [A, B, C, D, E] user_mcnulty => cacheE user_bunk => cacheA user_omar => cacheA user_bunny => cacheE user_stringer => cacheE
func (*Consistent) Get ¶
func (c *Consistent) Get(name string) (string, error)
Get 按照顺时针取值原则，获取name的哈希值最接近的物理服务器，即circle[i-1]<hash(name)<=circle[i]，返回circle[i]对应的物理服务。
func (*Consistent) GetN ¶
func (c *Consistent) GetN(name string, n int) ([]string, error)
GetN returns the N closest distinct elements to the name input in the circle.
func (*Consistent) GetTwo ¶
func (c *Consistent) GetTwo(name string) (string, string, error)
GetTwo returns the two closest distinct elements to the name input in the circle.
func (*Consistent) Remove ¶
func (c *Consistent) Remove(elt string)
Remove removes an element from the hash.
Example ¶
package main
import (
"fmt"
"github.com/alex023/basekit/hash/consistent"
"log"
)
func main() {
c := consistent.NewConsistent()
c.Add("cacheA")
c.Add("cacheB")
c.Add("cacheC")
users := []string{"user_mcnulty", "user_bunk", "user_omar", "user_bunny", "user_stringer"}
fmt.Println("initial state [A, B, C]")
for _, u := range users {
server, err := c.Get(u)
if err != nil {
log.Fatal(err)
}
fmt.Printf("%s => %s\n", u, server)
}
c.Remove("cacheC")
fmt.Println("\ncacheC removed [A, B]")
for _, u := range users {
server, err := c.Get(u)
if err != nil {
log.Fatal(err)
}
fmt.Printf("%s => %s\n", u, server)
}
}
Output: initial state [A, B, C] user_mcnulty => cacheA user_bunk => cacheA user_omar => cacheA user_bunny => cacheC user_stringer => cacheC cacheC removed [A, B] user_mcnulty => cacheA user_bunk => cacheA user_omar => cacheA user_bunny => cacheB user_stringer => cacheB
func (*Consistent) Set ¶
func (c *Consistent) Set(elts []string)
批量设置物理服务器到hash中。如果输入值与hash已经存在的值不一致，则以输入值为准。
Set sets all the elements in the hash. If there are existing elements not present in elts, they will be removed.
func (*Consistent) SetReplicas ¶
func (c *Consistent) SetReplicas(replicasNum int)
修改constent的replicas属性，务必在Add方法之前使用
Notes ¶
Bugs ¶
没有实现热替换。某台服务器失效后，hash值需要全部重新计算，导致业务系统影响很大。
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