fix(sampleRate): fix sample rate calculation

Author: peteyycz

lib/providers/httpTransaction/index.js

@@ -26,6 +26,7 @@ function HttpTransaction(eventBus, options) {
   this.partials = {};
   this.traces = [];
   this.rpmMetrics = {};
+  this.totalRequestCount = 0;
 
   this.on(HttpTransaction.CLIENT_RECV, this.onClientReceive);
   this.on(HttpTransaction.CLIENT_SEND, this.onClientSend);
@@ -150,9 +151,11 @@ HttpTransaction.prototype.onServerSend = function (data) {
     type: HttpTransaction.SERVER_SEND
   });
 
-  var isSampled = trace.isSampled || this.sampleRate > Math.random();
+  var isSampled = trace.isSampled || (1 / this.sampleRate) > Math.random();
   if (data.mustCollect || isSampled) {
+    trace.isForceSampled = !!trace.isSampled;
     delete trace.isSampled;
+
     this.traces.push(trace);
   }
 
@@ -169,6 +172,7 @@ HttpTransaction.prototype.collectStatusCode = function (trace) {
 };
 
 HttpTransaction.prototype.onServerReceive = function (data) {
+  this.totalRequestCount++;
   var headers = data.headers;
   var spanId = headers['x-span-id'];
   var parentId = headers['x-parent'];
@@ -222,8 +226,10 @@ HttpTransaction.prototype._send = function (options) {
     var dataBag = {};
     dataBag.sampleRate = this.sampleRate;
     dataBag.samples = cloneDeep(this.traces);
+    dataBag.totalRequestCount = this.totalRequestCount;
 
-    this.sampleRate = Math.floor(dataBag.samples.length / this.sampleSize) || 1;
+    this.sampleRate = Math.floor(this.totalRequestCount / this.sampleSize) || 1;
+    this.totalRequestCount = 0;
 
     this.traces = [];
 

lib/providers/httpTransaction/index.spec.js

@@ -23,6 +23,7 @@ describe('The HttpTransaction module', function () {
 
   it('can be instantiated', function () {
     var httpTransaction = HttpTransaction.create(eventBus, {});
+    expect(httpTransaction.totalRequestCount).to.be.eql(0);
     expect(httpTransaction).to.be.ok;
   });
 
@@ -48,6 +49,45 @@ describe('The HttpTransaction module', function () {
     expect(httpTransaction.partials[traceId].events[0].data).to.eql(data);
   });
 
+  it('emits a send event onto the event bus', function () {
+    var emitStub = this.sandbox.stub(eventBus, 'emit');
+
+    var httpTransaction = HttpTransaction.create(eventBus, {
+      service: 'aladdin'
+    });
+
+    var options = {
+      isSync: false
+    };
+
+    var totalRequestCount = 10000;
+    var sampleSize = 60;
+    var sampleRate = 1;
+    var newSampleRate = Math.floor(totalRequestCount / sampleSize);
+
+    var databag = {
+      sampleRate: sampleRate,
+      samples: [
+        1
+      ],
+      totalRequestCount: totalRequestCount
+    };
+
+    httpTransaction.totalRequestCount = totalRequestCount;
+    httpTransaction.sampleSize = sampleSize;
+    httpTransaction.traces = [
+      1
+    ];
+
+    httpTransaction._send(options);
+
+    expect(httpTransaction.totalRequestCount).to.be.eql(0);
+    expect(httpTransaction.sampleRate).to.be.eql(newSampleRate);
+
+    expect(emitStub).to.be.calledOnce;
+    expect(emitStub).to.be.calledWith(eventBus.HTTP_TRANSACTION_STACK_TRACE, databag);
+  });
+
   describe('events', function () {
 
     it('stores the "ClientReceive" events w/ `x-span-id`', function () {
@@ -179,6 +219,8 @@ describe('The HttpTransaction module', function () {
           ]
         }
       });
+
+      expect(httpTransaction.totalRequestCount).to.be.eql(1);
     });
 
     it('stores the "ServerRecieve" events with parent and timing data', function () {
@@ -282,6 +324,7 @@ describe('The HttpTransaction module', function () {
         span: url,
         host: host,
         trace: id,
+        isForceSampled: false,
         service: service,
         statusCode: 301,
         events: [{