Now that IE 9 has been released and is widely used, we wanted to follow up on some of our previous IE related blog posts to see how things have changed.

1. Using a VPN Still Clobbers IE 9 Performance

We previously reported about the scaling back of the maximum number of concurrent connections in IE 8 when your PC uses a VPN connection. This happened even if the browser traffic didn’t go over that connection.

Unfortunately, IE 9 is affected by VPN connections in the same way:

There is a subtle difference though. IE 8 would dynamically change it’s behavior as you connected or disconnected the VPN. In IE 9 it just seems to look for dialup or VPN connections at startup to determine the connection behavior for the rest of the session. For example, any active dial-up or VPN connection found when IE 9 starts will cause it to use a maximum of two connections per hostname. This limit remains until IE 9 is closed regardless of whether the dialup or VPN connections remain active.

2. IE 9 Mixed Content Warning Improved But Needs PRG

In previous blog posts we’ve covered the mixed content warning issues in IE and the problems it causes. It got even worse in IE 8 as the modal dialog was worded in a way that caused a great deal of confusion with no apparent benefit for ordinary web users.

A big step forward was taken in IE 9 by using a modeless dialog. It displays a simple message to indicate that not all the content was downloaded because some resources used unencrypted HTTP connections:

You can now ignore the message or simply click on the X to dismiss the warning.

Watch out for the ‘Show all content’ button though. Previous mixed content warning dialogs just blocked the download of non-secure content until you clicked the appropriate button. In IE9 ‘Show all content’ causes a complete refresh of the page. If your page was the result of a POST (e.g. form submit) and you didn’t use the POST-Redirect-GET pattern then the user will see this dialog instead of the updated page:

3. Another Reason to Favor IE 9 32-bit over IE 9 64-bit

We previously wrote about why IE 8 64-bit was the not the default version of IE on Windows Vista 64-bit. This was because commonly used plugins such as Flash, Silverlight and Java did not support 64-bit.

IE 9 32-bit remains the default version used on Windows 7 x64 for exactly the same reason:

However, there’s another reason to favor IE 9 32-bit. That’s because IE 9 ships with an advanced JIT compiler that compiles JavaScript into native assembly language code for improved performance. However, this JIT compiler only supports the x86 instruction set at the moment and therefore most Javascript bench marks run much more quickly in IE 9 32-bit than in the 64-bit version.

Here’s what ZDNet had to say about the 32-bit and 64-bit versions of IE 9:

OK, so what conclusions can we draw? Well, let’s begin with the obvious and say that Internet Explorer 9 64-bit is an absolute dog when it comes to JavaScript performance. This is to be expected given that IE 9 64-bit is using an older, slower JavaScript engine, while IE 9 32-bit was using the newer, more efficient Chakra JIT.

4. IE 9 Pinned Sites Are Great But They Disable All Add-ons

One nice feature of IE 9 is the ability to create pinned sites in Windows 7. A pinned site sits on the taskbar like a pinned application and can be quickly accessed when required. The web site can also provide customizations such as jump lists.

Unfortunately, all add-ons including HttpWatch are disabled when you do this. The reason given for this is:

The reason Add-ons don’t run on pinned sites is that we wanted to remove any non-site specific extension points (like toolbars and BHOs) from altering the original browsing experience created by the site.

It doesn’t seem unreasonable to block a debugging tool like HttpWatch, but it’s a shame that productivity tools such as Roboform are not available.

In our last post Asynchronous Google Analytics is Better but Not Faster, we ran some tests using HttpWatch in Firefox 3.6 and IE 8 to see if the asynchronous version of the Google Analytics (GA) script was really faster as many have claimed.

We found the following:

1. Changing from the synchronous to asynchronous GA snippet make no significant difference in page load time over a typical broadband connection
2. When we tried simulating a slow download of the ga.js file, we did find that the asynchronous version of GA isolated the page from this potential performance problem – but only in IE.
3. When we simulated a slow download of the GA image beacon, we did not see a difference between the two versions of GA. In IE, the image always downloaded in the background without holding up the page load event. In Firefox, a slow GA beacon always held up the page load.
4. We found that the asynchronous version of GA completed the GA beacon request much sooner on slow pages allowing the analytics data to be collected even when the user left the page early

Our overall conclusion was that due to point 4) the asynchronous version of GA was worth using because you were more likely to get analytics data from slow pages. The only potential performance benefit we found was in item 2) but we ignored that because:

• It only applied to IE
• There’s a high chance the ga.js file will be cached (unlike the beacon file) before the user visits a page
• In our experience the components of GA always download quickly, often in a 100 ms or less on a typical broadband connection

One of the comments we received was that we should really have tested with IE 6 and 7 as those browsers are more prone to script blocking issues.

So, here are the condensed results of running the same tests in IE 6 and 7:

Do Pages Load Faster With Asynchronous Google Analytics in IE 6 and 7?

As before there was no significant performance advantage. Here are the IE 6 time charts with an empty cache:

And the IE 7 charts with a primed cache:

Would Google Performance Problems Have Less Impact With Asynchronous Google Analytics in IE 6 and IE 7?

We found that IE 6 and 7 behaved the same as IE 8 when we simulated the slow download of the GA image beacon. It didn’t matter which version of the GA script we used. The image always downloaded in the background without affecting the page load time:

When we tried slowing the download of the ga.js file, we found that IE 6 and IE 7 benefited from the asynchronous version of GA in the same way as IE 8:

Is Data More Likely to be Recorded by Asynchronous Google Analytics During Early Page Exits in IE 6 and IE 7?

Again, we saw the same behavior as IE 8. Using the asynchronous version of GA increased the chance of collecting analytics data when a user left a page early.

Conclusion

We found no differences in our tests with IE 6 and IE 7 compared to IE 8. Asynchronous GA is worth using because it increases the chance of gathering data from slow pages, but you shouldn’t expect to see faster page load times unless you encounter a slow, uncached ga.js file in IE.

So why doesn’t asynchronous GA deliver significant performance gains as widely claimed? We believe it is down to the following factors:

1. The synchronous version of the GA script is included at the bottom of the <body> tag minimizing it’s impact on the rest of the page
2. The files used by GA typically download so quickly that in most cases any improvement has minimal impact on the overall page load time
3. The asynchronous loading techniques don’t seem to work in Firefox for either component and only help with the ga.js file in IE

In December 2009, Google launched the asynchronous version of the Google Analytics script. The update aimed to address potential script blocking problems that have been extensively researched and reported by Steve Souders at Google.

Steve’s blog post about the new asynchronous loading of Google Analytics identified three potential benefits:

1. Your pages should load faster
2. Availability or performance problems at Google should have less impact on your site
3. Analytics data is more likely to be collected if a user leaves a page early

Before applying the change to our web site we decide to compare the new and old versions of the Google Analytics scripts using HttpWatch 7.0 .

The following sections describe what has changed in the asynchronous Google Analytics script and the tests we performed to compare it to the traditional synchronous version.

What has Changed?

Google Analytics collects data using two components on a page:

• A javascript file script file that is loaded from http://www.google-analytics.com/ga.js
• A 1×1 pixel image beacon (http://www.google-analytics.com/__utm.gif) that passes data back to Google in query string parameters

You enable Google Analytics on a web page by calling a page tracking function in ga.js. This function automatically gathers analytics data, such as operating system and browser versions, then generates the call to the image beacon.

The difference between the two ways of loading Google Analytics is in the way that the script file is loaded. In the traditional synchronous version, two small script tags are added at the end the page’s <body> tag:

...
  <script type="text/javascript">
    var gaJsHost = (("https:" == document.location.protocol) ?
    "https://ssl." : "http://www.");
    document.write(unescape("%3Cscript src='" + gaJsHost +
    "google-analytics.com/ga.js' type='text/javascript'%3E%3C/script%3E"));
  </script>
 
  <script type="text/javascript">
    var pageTracker = _gat._getTracker("XX-XXXXXX-X"); // Your GA id
    pageTracker._trackPageview();
  </script>
</body>
...

The first script tag ensures that the correct HTTP or HTTPS version of the qa.js file is loaded. The second script tag then calls into the javascript file triggering the beacon image download.

These two script tags are placed at the end of the body tag to ensure that they don’t hold up the download of any other resources on the page. The disadvantage of doing this is that the analytics call may not be triggered if the user exits the page before it has completely downloaded.

The asynchronous version of the Google Analytics loading code uses a single script tag at the end of the page’s <head> :

...
 
  <script>
    var _gaq = _gaq || [];
    _gaq.push(['_setAccount', 'XX-XXXXXX-X']);
    _gaq.push(['_trackPageview']);
 
    (function() {
      var ga = document.createElement('script');
      ga.type = 'text/javascript';
      ga.async = true;
      ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www')
        + '.google-analytics.com/ga.js';
      var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
 
    })();
  </script>
 
</head>
...

It sets up the parameters required to make the call into ga.js but doesn’t invoke the function directly. A script element is added to the document allowing asynchronous download without blocking other elements of the page. The HTML 5 async attribute is also set on the script tag for browsers that support it.

Once the ga.js file is loaded and executed it looks for an array variable called _gaq and executes the function with the previously specified arguments.

Do Pages Load Faster With Asynchronous Google Analytics?

To try this out we created a version of our Download page using both versions of the Google Analytics loading code. We first tried the synchronous version with an empty cache in IE to simulate a new visitor to the page:

And then with the asynchronous version:

The page load times were dominated by other components on the page. Using the asynchronous version of Google Analytics didn’t really make any difference.

We tried the same tests with a primed cache to see if there would be a greater impact when the page was loaded during a repeat visit. First the synchronous version:

and then the asynchronous version:

Again there was practically no difference in the page load time of the page allowing for variability in our tests.

The reason for that is that calls to Google Analytics are incredibly fast (usually around a 100ms or less) and the download of the image beacon doesn’t block other components because it uses a different hostname.

We tried Firefox 3.6 and got almost the same results.

Conclusion: Google Analytics is so fast that you won’t see any significant improvement with the asynchronous loading version.

Would Google Performance Problems Have Less Impact With Asynchronous Google Analytics?

For this test we needed to simulate performance problems at Google. We did this by modifying the standard script snippets to call our own ASP.NET versions of the Google files that served the same content but added a 5 second delay.

For example, here’s the ASPX file we used to serve up a local copy of ga.js:

<%@ Page Language="C#" Debug="true" %>
<%@ Import Namespace=System.IO %>
<%
  System.Threading.Thread.Sleep(6000);
  Response.AddHeader("Content-Type", "text/javascript");
  Response.WriteFile( ".\\ga.js");
  Response.End();
%>

We did something similar with the Google __utm.gif file so that we could add delays to either component.

Using our slow simulation of ga.js in IE 8 we found that the page’s onload event was delayed with the synchronous version of the Google Analytics:

This caused the IE 8 to display the spinning icon in the current tab:

and a “Waiting…” message in the status bar:

indicating to the user that the page was not fully downloaded.

We then tried using the slow version of the __utm.gif image file. This didn’t cause a problem in IE 8 as the page loaded successfully but continued to download the image beacon in the background even with the synchronous version of Google Analytics:

Firefox 3.6 didn’t cope as well. Delaying the download of the beacon file with the synchronous loading code had the same effect as delaying the ga.js file – the page load was delayed, the spinning tab icon was displayed and the status line indicated that it was waiting for data.

We then tried the asynchronous version of the analytics loading code. Delaying either the ga.js or utm.gif file had no effect on the loading of the page in IE; effectively hiding the issue from the web site visitor:

Surprisingly, the asynchronous version of the analytics code made no difference to Firefox 3.6 when we simulated slow downloads of the Google components:

Conclusion: Using the asynchronous load made IE 8 more robust to performance problems in the loading of qa.js. Otherwise it made no difference. In reality, ga.js is often cached anyway making it the less likely of the two components to be subject to performance problems.

Is Data More Likely to be Recorded by Asynchronous Google Analytics During Early Page Exits?

To test this potential benefit we changed our test pages to include a slow loading script file at the top of the body tag. The idea was to emulate what might happen on your page if a third party component, such as an ad script, started to slow down.

The script tag we added called an ASPX file than delayed 6 seconds before returning an empty script block:

<body>
  <script type="text/javascript" src='http://veryslowdownload/ad.aspx'></script>

This stopped our page being displayed for six seconds.

Using the synchronous version of the loading code in IE 8 and Firefox 3.6, we found that the Google Analytics beacon image was not downloaded if the user gave up and went elsewhere:

The asynchronous loading of Google Analytics solved this problem in both browsers. The image beacon was downloaded almost immediately even though the page was blocked by the slow script tag:

Conclusion: The asynchronous version of Google Analytics helps to ensure that analytics data is gathered in IE and Firefox when the user leaves a page early.

Should I Use the Asynchronous Version of Google Analytics?

Yes, but not for the reasons you might expect. It’s unlikely to make any difference to how quickly your pages load.

The main reason to use it is that you are more likely to get analytics data if a user leaves a page early.