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From Graham Leggett <minf...@sharp.fm>
Subject Re: mod_deflate and vary accept-encoding
Date Sun, 15 Aug 2010 10:44:22 GMT
On 13 Aug 2010, at 8:25 PM, Bryan McQuade wrote:

> In looking at the source for mod_deflate:
>
> http://www.google.com/codesearch/p?hl=en#lfs-jRjrQ3s/trunk/modules/ 
> filters/mod_deflate.c&l=524
>
> It appears to insert Vary Accept-Encoding header into every candidate
> response by default, which is what you would expect.
>
> But the instructions here: http://httpd.apache.org/docs/2.0/mod/mod_deflate.html
>
> suggest adding a line to manually add Vary Accept-Encoding to  
> responses:
> # Make sure proxies don't deliver the wrong content
> Header append Vary User-Agent env=!dont-vary
>
> Is this "Header append Vary User-Agent env=!dont-vary" necessary or
> does mod_deflate now add the Vary Accept-Encoding header by default?

One extra thing on varying on the useragent string - we (very large UK  
based media website) recently sampled about a week's worth of User- 
Agent strings, and came up with roughly 1 million unique strings,  
which in the process renders caching meaningless.

Ideally people shouldn't be varying on useragent, and we shouldn't be  
suggesting people to do so in any documentation if we can avoid it.

Regards,
Graham
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