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Hash ring provides consistent hashing based on the libketema
library.
You can either install it using the Node Package Manager (NPM)
npm install hashring
Or fork this repository to your machine
git clone git://github.com/3rd-Eden/node-hashring.git hashring
The constructor is designed to handle multiple arguments types as the hash ring
can be used for different use cases. You have the ability to use a String
to
add a single server, a Array
to provide multiple servers or an Object
to
provide servers with a custom weight. The weight can be used to give a server a
bigger distribution in the hash ring. For example you have 3 machines, 2 of
those machines have 8 gig memory and one has 32 gig of memory because the last
server has more memory you might it to handle more keys than the other server.
So you can give it a weight of 2 and the other servers a weight of 1.
Creating a hash ring with only one server
var hashring = require('hashring'); var ring = new hashring('192.168.0.102:11212');
Creating a hash ring with multiple servers
var hashring = require('hashring'); var ring = new hashring([ '192.168.0.102:11212', '192.168.0.103:11212', '192.168.0.104:11212']);
Creating a hash ring with multiple servers and weights
var hashring = require('hashring'); var ring = new hashring({ '192.168.0.102:11212': 1 , '192.168.0.103:11212': 2 , '192.168.0.104:11212': 1 });
Creating a hash ring with multiple servers an vnodes selected per nodes
var hashring = require('hashring'); var ring = new hashring({ '192.168.0.102:11212': {"vnodes": 5} , '192.168.0.103:11212': {"vnodes": 10} , '192.168.0.104:11212': {"vnodes": 7} });
Optionaly you could add the weigth property to the object.
By default the hash ring uses a JavaScript crc32 implementation hashing algorithm. But this can be overwritten by adding a second argument to the constructor. This can be anything that is supported as hashing algorithm by the crypto module.
var hashring = require('hashring'); var ring = new hashring('192.168.0.102:11212', 'md5');
I have chosen crc32 as default algorithm because a creates a nice dense ring distribution. Another good alternative and common used hashing algorithm is md5. The JavaScript crc32 algorithm is faster than md5. So If you are doing allot of operations per seconds these small differences can really matter.
In these examples I assume that you already setup a hashring
instance, with
the variable name ring
like I did the in the examples illustrated above.
a.k.a key -> node look up, this is where all the magic is happening.
ring.get('foo'); // => '192.168.0.104:11212' ring.get('pewpew'); // => '192.168.0.103:11212'
If you are experiencing downtime with one of your servers, you might want to
hot swap
with a new server.
ring.replace('192.168.0.104:11212','192.168.0.112:11212'); ring.get('foo'); // => '192.168.0.112:11212'
Adds a new server to the hash ring, but please note that this could cause a shift in current key -> server distribution.
ring.add('192.168.0.102:11212');
Remove a server from the generated hash ring.
ring.remove('192.168.0.102:11212');
Iterates over the nodes for a give key, can be used to create redundancy support.
ring.range('key', 3);
Clean up the internal hash ring, kill the cache, kill nodes, nuke the planet.
range.end();
For a more extensive documentation: Read the source, it's not rocket sience.