IE 9 Browser Network Capture Tool – Not a reliable Network Capture Tool to measure Latency.

14 Feb

Recently one of the business executive from Catchpoint posted the link in Performance Specialist list in LinkedIn about the potential issue with IE Browser network capture tools where in network capture tool in IE was showing high response time for one of resource when in fact the response time for that resource was in fraction of milliseconds.I found this case very interesting given that given that I have seen lot many performance Engineers and Users using these tools to identify the performance issues. Catch point had made its point very clear, that there are certain cases where in the browser network capture tools do not show us the correct network capture time and the time shown by these tools are impacted by elements of the page.

Given that they had also provided with the test case as how to reproduce this issue,I thought that let me try and see if I can reproduce the issue, so I pulled out their script and loaded it in my Dreamweaver to check this.I was curious to know and understand as what factors of the page were responsible for this abnormal behavior.

I made some changes to the script and pointed the IFrame source to my local Test PHP page hosted on my local Apache server.The point of making this change was to ensure that there is no actual network issues impacting the test case.In addition to this I changed the loop frequency in order to check at what level of DOM manipulation will this issue surface and has major impact on the network capture feature of the browsers.

addDomLoadEvent(function() {
   var title = document.getElementById('title');
       var span;
      for(var i = 0; i <= 1000; i++) {
        span = document.createElement('span');
        span.innerHTML = i;
        document.getElementById('ctn').appendChild(span);
        }

The above piece of code is taken from Catch Point’s test case and only changes I made was to change value of the loop i.e, I ensure that its creating 10,20,50,1000,5000 and 10000 span elements on the fly and they are aligned inline without styles applied to it.After making changes, I ensured that I am taking the network capture with browser’s developers tools for IE9 ,Firefox 9,Chrome 15, and Safari 5.1.

For Creating 10 Span elements, response time reported by IE Capture tools is 32ms.

IE 10

For Creating 20 Span elements, response time reported by IE Capture tools is 31ms.

IE 20

For Creating 100 Span elements, response time reported by IE Capture tools is 46ms.

IE 100

For Creating 1000 Span elements,response time reported by IE Capture tools is 250ms.

IE 1000

For Creating 5000 Span elements,response time reported by IE Capture tools is 820ms.

IE 5000

For Creating 10000 Span elements,response time reported by IE Capture tools is 1.66 sec.

IE 10000

As you see, more the span elements we create ,more the Iframe’s response time. Since the test case was executed in the local environment with absolutely nothing in network to download, we would have expected the response time of IFrame to be same in all cases.Unfortunately it was not.So I think its fair to conclude that IE 9 network capture tool cannot be used to measure the response time at least for sure iframe elements and possibly for those elements which generate the network requests in the heavily DOM operated environments.

I would like to also add that this test case is not about writing perfect javascript but more of knowing and understanding whether Browser’s capture tools are in fact independent of its rendering and parsing architecture.Finally with this test case we can conclude that at least in IE 9, browser’s network capture tool do depend on its rendering and parsing architecture which at times might give users a incorrect picture of network latency.

Hope some one from Microsoft take a note of this behavior and fix this behavior.

In addition to this there are also many other interesting findings which I came across, maybe sometimes later I will write a note on that in another post.

Finally thanks to Catchpoint for highlighting this issue.

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2 Responses to “IE 9 Browser Network Capture Tool – Not a reliable Network Capture Tool to measure Latency.”

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    • kiranbadi1991 March 2, 2012 at 6:32 pm #

      Hey Ashley,

      Thanks.Will ping them in case of requirements.

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