Added the capability to select virtual nodes per shard.

This feature enable to do a progressive miss on shard added, so you could
modify the amount of new vnodes progressively getting a better distribution
of misses on shard added

lib/hashring.js

@@ -23,15 +23,27 @@ var createHash = require('crypto').createHash
 
 function HashRing (args, algorithm, options) {
   var nodes = []
-    , weights = {};
+    , weights = {}
+    , vnodes = {};
 
    switch (Object.prototype.toString.call(args)){
     case '[object String]':
       nodes.push(args);
       break;
     case '[object Object]':
-      weights = args;
       nodes = Object.keys(args);
+      for(var i in args){
+          if(typeof args[i] === "number"){
+              weights[i] = args[i];
+          }else{
+              if(args[i].weigth != undefined){
+                weights[i] = args[i].weigth;
+              }
+              if(args[i].vnodes != undefined){
+                vnodes[i] = args[i].vnodes;
+              }
+          }
+      }
       break;
     case '[object Undefined]':
       break;
@@ -49,6 +61,7 @@ function HashRing (args, algorithm, options) {
 
   this.nodes = nodes || [];
   this.weights = weights;
+  this.vnodes = vnodes;
   this.algorithm = algorithm || 'crc32';
 
   // overwrite the hashKey method if crc32 is chosen
@@ -105,11 +118,10 @@ HashRing.prototype.generateRing = function generateRing () {
 
     // The factor is based on the weight, the more weight the more space a item
     // will get in our hash ring
-    factor = Math.floor((this.options.vnode_count * len * weight) / totalweight);
-
+    var vnodes_count = this.vnodes[node] || this.options.vnode_count
+    factor = Math.floor((vnodes_count * len * weight) / totalweight);
     for (j = 0; j < factor; j++) {
       tmp = this.hashKey(node + '-' + j);
-
       for (k = 0; k < 3; k++) {
         key = this.hashValue(tmp, function hash (x) {
           return x + k * 4;
@@ -120,7 +132,6 @@ HashRing.prototype.generateRing = function generateRing () {
       }
     }
   }
-
   // Sort the keys, nummeric !important. I forgot it at first and took me
   // 2 hours to debug \o/
   this.sortedKeys.sort(function sort (a, b) {
@@ -207,7 +218,7 @@ HashRing.prototype.replaceServer = function replaceServer (oldServer, newServer)
  * @api public
  */
 
-HashRing.prototype.addServer = function addServer (server, weights) {
+HashRing.prototype.addServer = function addServer (server, weights, vnodes) {
   if (this.nodes.indexOf(server) !== -1) return; // prevents duplicates
 
   // add weights
@@ -217,6 +228,12 @@ HashRing.prototype.addServer = function addServer (server, weights) {
     }
   }
 
+  // add vnodes
+  if (vnodes) {
+    for(var key in vnodes) {
+      this.vnodes[key] = vnodes[key];
+    }
+  }
   if (!Array.isArray(server)) {
     server = [server];
   }
@@ -247,6 +264,10 @@ HashRing.prototype.removeServer = function removeServer (server) {
     delete this.weights[server];
   }
 
+  if (this.vnodes[server]) {
+    delete this.weights[server];
+  }
+
   // clear all old caches and regenerate
   this.ring = {};
   this.cache = {};

tests/hashring.test.js

@@ -38,7 +38,25 @@ module.exports = {
     ring.sortedKeys.length.should.be.above(1);
     Object.keys(ring.weights).should.have.length(3);
   }
+, 'Constructing with a object with pernode vnodes': function(){
+    var ring = new Hashring({
+        '192.168.0.102:11212': {"vnodes":40}
+      , '192.168.0.103:11212': {"vnodes":50}
+      , '192.168.0.104:11212': {"vnodes":5}
+    });
+    ring.nodes.should.have.length(3);
+    ring.sortedKeys.length.should.be.equal((40+50+5)*3)
+
+   ring = new Hashring({
+        '192.168.0.102:11212': {"vnodes":4}
+      , '192.168.0.103:11212': {"vnodes":3}
+      , '192.168.0.104:11212': {"vnodes":5}
+    });
+    ring.nodes.should.have.length(3);
+    ring.sortedKeys.length.should.be.equal((4+3+5)*3)
 
+
+  }
 , 'Constructing with a different algorithm': function () {
     var ring = new Hashring('192.168.0.102:11212', 'md5');