Consistent-hash NPM

consistent-hash

This is a dependency-free javascript-only implementation of consistent hashing hash ring. Uses strings for hash keys, and hashes using a PJW hash variant.

This implementation is pretty fast, and has a nice key distribution.

    var ConsistentHash = require('consistent-hash')
    var hr = new ConsistentHash()
    hr.add('server1')
    hr.add('server2')

    var serverToUse = hr.get('resourceName')

Installation

    npm install consistent-hash

API

hr = new ConsistentHash( options )

Options:

range - hash ring control point modulo range, default 100003. Use a prime number.
weight - the default number of control points to create for each node added, default 40.

The number of nodes supported is range / controlPoints, default 2500. For 10x more nodes, use range 1,000,003.

Properties:

nodeCount - number of nodes on the hash ring
keyCount - number of control points (tokens) around the hash ring

hr.add( node ,weight )

Register a node as also managing the resource. The node's share of the resources will be proportionate to its weight. The default weight is 40, and control points are randomly created between 0 and range - 1. Returns hr.

Adding the same node more than once increases its weight.

weight - how many resource instances this node should manage compared to the other nodes (default 1). Higher weights will be assigned more resources. Three nodes A, B and C with weights 1, 2 and 3 will each handle 1/6, 1/3 and 1/2 of the resources, respectively.
points - the array of control points to use for this node.

hr.remove( node )

Remove all instances of this node from the hash ring and free its control points. Freed control points may get allocated to newly added nodes. Returns hr.

hr.get( resourceName ,count )

Locate the node that handles the named resource. Returns a node previously added with add(), or null if no nodes.

If a count is specified, it returns an array of count distinct nodes; first the one that handles the named resource, then the following closest nodes around the hash ring.