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:
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:
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:
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:
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:
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.
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: