Add global sampling rate

lib/statsd.js

@@ -12,9 +12,10 @@ var dgram = require('dgram'),
  *   @option cacheDns    {boolean} An optional option to only lookup the hostname -> ip address once
  *   @option mock        {boolean} An optional boolean indicating this Client is a mock object, no stats are sent.
  *   @option global_tags {Array=} Optional tags that will be added to every metric
+ *   @option sampleRate {Float} Global Sampling rate, default: 1 (No sampling)
  * @constructor
  */
-var Client = function (host, port, prefix, suffix, globalize, cacheDns, mock, global_tags) {
+var Client = function (host, port, prefix, suffix, globalize, cacheDns, mock, global_tags, sampleRate) {
   var options = host || {},
          self = this;
 
@@ -27,7 +28,8 @@ var Client = function (host, port, prefix, suffix, globalize, cacheDns, mock, gl
       globalize   : globalize,
       cacheDns    : cacheDns,
       mock        : mock === true,
-      global_tags : global_tags
+      global_tags : global_tags,
+      sampleRate : sampleRate
     };
   }
 
@@ -38,6 +40,7 @@ var Client = function (host, port, prefix, suffix, globalize, cacheDns, mock, gl
   this.socket      = dgram.createSocket('udp4');
   this.mock        = options.mock;
   this.global_tags = options.global_tags || [];
+  this.sampleRate = options.sampleRate || 1;
 
   if(options.cacheDns === true){
     dns.lookup(options.host, function(err, address, family){
@@ -196,6 +199,7 @@ Client.prototype.send = function (stat, value, type, sampleRate, tags, callback)
       buf,
       merged_tags = [];
 
+  sampleRate = sampleRate || this.sampleRate;
   if(sampleRate && sampleRate < 1){
     if(Math.random() < sampleRate){
       message += '|@' + sampleRate;
@@ -231,7 +235,7 @@ Client.prototype.send = function (stat, value, type, sampleRate, tags, callback)
  */
 Client.prototype.close = function(){
     this.socket.close();
-}
+};
 
 exports = module.exports = Client;
 exports.StatsD = Client;

test/test_statsd.js

@@ -84,19 +84,21 @@ describe('StatsD', function(){
       assert.equal(global.statsd, undefined);
       assert.equal(statsd.mock, undefined);
       assert.deepEqual(statsd.global_tags, []);
+      assert.deepEqual(statsd.sampleRate, 1);
       assert.ok(!statsd.mock);
     });
 
     it('should set the proper values when specified', function(){
       // cachedDns isn't tested here; see below
-      var statsd = new StatsD('host', 1234, 'prefix', 'suffix', true, null, true, ['gtag']);
+      var statsd = new StatsD('host', 1234, 'prefix', 'suffix', true, null, true, ['gtag'], 0.6);
       assert.equal(statsd.host, 'host');
       assert.equal(statsd.port, 1234);
       assert.equal(statsd.prefix, 'prefix');
       assert.equal(statsd.suffix, 'suffix');
       assert.equal(statsd, global.statsd);
       assert.equal(statsd.mock, true);
       assert.deepEqual(statsd.global_tags, ['gtag']);
+      assert.deepEqual(statsd.sampleRate, 0.6);
     });
 
     it('should set the proper values with options hash format', function(){
@@ -108,7 +110,8 @@ describe('StatsD', function(){
         suffix: 'suffix',
         globalize: true,
         mock: true,
-        global_tags: ['gtag']
+        global_tags: ['gtag'],
+        sampleRate: 0.6
       });
       assert.equal(statsd.host, 'host');
       assert.equal(statsd.port, 1234);
@@ -117,6 +120,7 @@ describe('StatsD', function(){
       assert.equal(statsd, global.statsd);
       assert.equal(statsd.mock, true);
       assert.deepEqual(statsd.global_tags, ['gtag']);
+      assert.deepEqual(statsd.sampleRate, 0.6);
     });
 
     it('should attempt to cache a dns record if dnsCache is specified', function(done){
@@ -229,6 +233,72 @@ describe('StatsD', function(){
     });
   });
 
+  describe('#global_sample_rate', function(){
+    it('should not sample if it is not specified', function(finished){
+      udpTest(function(message, server){
+        assert.equal(message, 'test:1|c');
+        server.close();
+        finished();
+      }, function(server){
+        var address = server.address(),
+            statsd = new StatsD(address.address, address.port);
+
+        statsd.increment('test');
+      });
+    });
+
+    it('should sample if global sample rate is specified', function(finished){
+      var called = false;
+      udpTest(function(message, server){
+        assert.equal(message, 'foo.test.bar:42|c|@0.6');
+        assert.equal(called, true);
+        server.close();
+        finished();
+      }, function(server){
+        var address = server.address(),
+          statsd = new StatsD(address.address, address.port, 'foo.', '.bar', true, false, false, [], 0.6);
+
+        statsd.increment('test', 42, function(){
+          called = true;
+        });
+      });
+    });
+
+    it('should sample if metric sample rate is specified', function(finished){
+      var called = false;
+      udpTest(function(message, server){
+        assert.equal(message, 'foo.test.bar:42|c|@0.5');
+        assert.equal(called, true);
+        server.close();
+        finished();
+      }, function(server){
+        var address = server.address(),
+          statsd = new StatsD(address.address, address.port, 'foo.', '.bar');
+
+        statsd.increment('test', 42, 0.5, function(){
+          called = true;
+        });
+      });
+    });
+
+    it('should honor metric sampleRate if both global and metric sample rate is specified', function(finished){
+      var called = false;
+      udpTest(function(message, server){
+        assert.equal(message, 'foo.test.bar:42|c|@0.5');
+        assert.equal(called, true);
+        server.close();
+        finished();
+      }, function(server){
+        var address = server.address(),
+          statsd = new StatsD(address.address, address.port, 'foo.', '.bar', true, false, false, [], 0.6);
+
+        statsd.increment('test', 42, 0.5, function(){
+          called = true;
+        });
+      });
+    });
+  });
+
   describe('#timing', function(finished){
     it('should send proper time format without prefix, suffix, sampling and callback', function(finished){
       udpTest(function(message, server){