Survey of Etag usage

Posted by Sam Soltano on 16 August 2012 in News, ETag, Site Elements

An Etag is an HTTP header element that enables a web server to save bandwidth in subsequent calls of the same page. When a browser sends the Etag of a cached page, the server knows whether a new version of that page is available and sends only a short response if that is not the case.

Etags are recommended by Google and Yahoo, although Yahoo has some warnings about using the default Etags generated by popular web servers in case of multi-server sites.

Our new survey shows that Etags are used by 16.9% of all sites. There are two versions of Etags: strong Etags indicate a byte-for-byte identical page in the browser cache, whereas weak Etags indicate only a semantically equivalent page. 98.7% of all Etags used are strong, which is a bit surprising as "semantically equivalent" seems to be sufficient for page caching purposes. The reason for that might be that strong Etags are the default type, and weak Etags have to be explicitly declared as such.

The ranking breakdown survey shows that high traffic sites use less Etags, which might have to do with the problems of Etags on server farms. If high-traffic sites use Etags, they use more of the weak type than average sites.

The content management system breakdown report for Etags shows which CMSs tend to use Etags and which ones stay away. Google's Blogger is one of the popular systems that is configured to use Etags, and so is the majority of Drupal sites. whereas WordPress and Joomla sites rarely use them.

The server-side language breakdown report shows Ruby sites as most likely to use Etags, certainly due to the fact that this is the default behavior of Ruby-on-Rails.

The breakdown by web server shows large differences. An interesting observation, for example, is that 90.7% of sites running on Google servers use Etags, but only 0.4% of sites running on Yahoo Traffic Server.

Detailed data on Etag usage will also be included in all our reports in the future.

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Please note, that all trends and figures mentioned in that article are valid at the time of writing. Our surveys are updated frequently, and these trends and figures are likely to change over time.

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