kkdai / consistent

Consistent Hashing implement in Golang

Consistent: Consistent Hashing implement in Golang

What is this "Consistent Hashing"

Consistent hashing is a special kind of hashing such that when a hash table is resized and consistent hashing is used, only K/n keys need to be remapped on average, where K is the number of keys, and n is the number of slots. In contrast, in most traditional hash tables, a change in the number of array slots causes nearly all keys to be remapped. (cited from Wiki)

Explanation for how it work

Consistent Hashing has 4 features:

• Balance
• Monotonicity
• Spread
• Load

In this application you will see:

Balance

We use virtual node to make replica for load distribution. (not all node pick the same server).

Monotonicity

Use the hash key function, it will make sure it always pick the same server (in the same quantity of server)

Here is more detail in Chinese

Installation and Usage

Install

go get github.com/kkdai/consistent

Usage

Following is sample code:

package main

import (
	"fmt"
    . "github.com/kkdai/consistent"
)

func main() {
	ch := NewConsistentHashing()
	ch.Add("server1")
	ch.Add("server2")
	ch.Add("server3")
//[server1 server2 server3]

	fmt.Println(ch.ListNodes())
	targetObj := []string{"client1", "client2", "client3", "client4", "client5", "client6"}
	for _, v := range targetObj {
		server, err := ch.Get(v)
		if err == nil {
			fmt.Printf("client: %s in server: %s \n", v, server)
		}
	}
//client: client1 in server: server1
//client: client2 in server: server3
//client: client3 in server: server1
//client: client4 in server: server3
//client: client5 in server: server1
//client: client6 in server: server3

	ch.Add("server4")
	ch.Add("server5")
	for _, v := range targetObj {
		server, err := ch.Get(v)
		if err == nil {
			fmt.Printf("client: %s in server: %s \n", v, server)
		}
	}

//client: client1 in server: server4
//client: client2 in server: server3
//client: client3 in server: server4
//client: client4 in server: server3
//client: client5 in server: server4
//client: client6 in server: server3

}

Inspired By

• 每天进步一点点——五分钟理解一致性哈希算法(consistent hashing)
• https://github.com/stathat/consistent
• Wiki: Consistent Hashing

Project52

It is one of my project 52.

License

This package is licensed under MIT license. See LICENSE for details.