This is an example of the Network effect. The more people that use a system the more valuable the system becomes.
The Price of Missing
It gets worse because downloading a file over a new TCP connection with Google is slower than downloading a file over an existing TCP connection with your website! This is due to TCP’s slow start and congestion control. Newly created connections transmit data slower than existing connections do. (This is why persistent connections are so important!)
The Odds of Winning
Well, according to the great folks at BuiltWith, only 13% of all websites use some kind of 3rd party CDN. Of those websites using a CDN, 25.56% of them are using Google’s Ajax Library API. So only 3.89% of all websites surveyed are using Google’s AJAX Library API.
sites serving the library
from Google’s CDN
Getting More Data
So maybe the odds aren’t good. But is it still worth it to potentially help some people?
- If you are using a CDN and the visitor does not have cached copy, they download the site 1/3 of a second slower than if they had downloaded all the content from your web server.
- If you are using a CDN and the visitor does have cached copy, they download all of the content 1/3 of a second faster than if they had downloaded all the content from your web server.
That does not make sense. It makes even less sense as the download speed of your visitors increases. Try to avoid serving 20 or 30 kilobytes of content at the cost of using a 3rd party just doesn’t make sense.
I will discuss the very select group of sites that should use CDNs, as well as some other interesting data discovered while surveying the Alexa 2000 in posts early next week.