By removing the ETag header, you disable caches and browsers from being able to validate files, so they are forced to rely on your Cache-Control and Expires header. Basically you can remove
If-None-Match requests and their
304 Not Modified Responses.
Entity tags (ETags) are a mechanism to check for a newer version of a cached file.
Easy Apache Speed Tips Articles
- Turn On Compression
- Add Future Expires Header
- Add Cache-Control Headers
- Turn Off ETags
- Remove Last-Modified Header
- Use Multiple SubDomains
Please don't turn off ETags and Last-Modified headers for your .html files, leave one of them ON. (I use Last-Modified for .html).
This goes in your root .htaccess file but if you have access to
httpd.conf that is better.
Header unset ETag FileETag None
Notice that the ETag performs the same service that Last-Modified header performs.
Response for /i/yahoo.gif
HTTP/1.1 200 OK Last-Modified: Tue, 12 Dec 2006 03:03:59 GMT ETag: "10c24bc-4ab-457e1c1f" Content-Length: 12195
Later, if the browser has to validate a component, it uses the If-None-Match header to pass the ETag back to the origin server. If the ETags match, a 304 status code is returned reducing the response by 12195 bytes for this example.
GET /i/yahoo.gif HTTP/1.1 Host: us.yimg.com If-Modified-Since: Tue, 12 Dec 2006 03:03:59 GMT If-None-Match: "10c24bc-4ab-457e1c1f" HTTP/1.1 304 Not Modified
The problem with ETags is that they typically are constructed using attributes that make them unique to a specific server hosting a site. ETags won't match when a browser gets the original component from one server and later tries to validate that component on a different server, a situation that is all too common on Web sites that use a cluster of servers to handle requests. By default, both Apache and IIS embed data in the ETag that dramatically reduces the odds of the validity test succeeding on web sites with multiple servers.
September 10th, 2007