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ETags OffBy 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-Modified-Since and 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

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).


Turn ETags Off

This goes in your root .htaccess file but if you have access to httpd.conf that is better.

This code uses the FileETag and the Header directive to remove all ETags from being sent.

Header unset ETag
FileETag None

Example ETag Request and Response

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

With ETags

ETags OnThe 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.

Without ETags

ETags Off

Tags

September 10th, 2007

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