2.14 seconds without Adsense, 6.97 seconds with Adsense. Time to clean it up, Adsense!
I did a detailed analysis of Adsense performance on one of my sites. I'm not really surprised at the enormous overhead of Adsense.
The page I analyzed had a total of about 62K of original text content unzipped, truly about four pages of text, including navigation headers and footers. (All my content is GZIPPED)
Because of the large amount of content, this page dynamically chooses to show 3 Adsense TEXT tower units in one column and 3 Link Units. The format is similar to the Google SERPs, ads in a unobtrusive column, and link units mostly on the footer. For my sites, smaller pages dynamically show fewer Ad Units. (Link Units at the bottom of the page do add a twinge of income! Try it.)
So for my 62K of original CONTENT; Adsense required 139.5K of downloaded scripts and data to show 15 text ads and 3 Link Units. Each Ad Unit might consist of about 17 words! Each Link Unit might have about 14 words to display. So to show a total of 297 characters of text Adsense downloaded 139,500 bytes of data.
Yes some of this overhead may be cached, but for most websites it's the FIRST IMPRESSION that counts. There's no caching for the first impression!
It works out to 69% of the page load time is due to Adsense!
69% of the bytes downloaded are due to Adsense! This page that loads in 6.97 seconds on a DSL connection would load in 2.14 seconds without Adsense!
I hate to think about what Adsense is doing to Dial Up users! One Third of US Internet Still at Dialup Speed [webmasterworld.com]
With a trivial alteration to the Adsense "code", we all insert in our pages, 719 milliseconds of download time could be eliminated. Adsense needlessly queries the "Not Modified" status of the show_ads.js file multiple times. THIS IS A COMPLETE WASTE OF TIME. It's also needless extra load on the Adsense servers!
Please ASA, I have a detailed spreadsheet breaking this all down. I'd be happy to send you a copy.
One thing Adsense knows is the faster a page renders the more earnings it produces. But Adsense keeps loading the Units down with Tweaky features; Time to stop, and slim down!
I have to thank the creator of the Firebug tool facilitating the collection of this detailed data.