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From Ruediger Pluem <>
Subject Re: mod_deflate Vary header
Date Fri, 04 Nov 2005 22:54:05 GMT

On 11/04/2005 07:36 AM, Florian Zumbiehl wrote:


>>Maybe I'm pessimistic, but I think, omitting the Vary header for
>>uncompressed ressources will lead to "poisoned" caches, which statistically
>>nearly always will request the uncompressed variant and so actually
>>*add* load to your server's bandwidth.
> Hu? Erm, could it be that you are thinking of load-reducing caches put
> directly in front of the web server? In that case, I wonder how the web
> server's bandwidth could be the bottleneck?!
> To put this straight: I was thinking about web servers behind
> V.90/ISDN/ADSL lines where _that_ line  usually will be the bottleneck
> on any connections to the outside world and about caching proxies
> in that outside world ...

Yes, but if you do compression because some of your clients have low bandwith
connections (but are capable of receiving compressed pages) and access your
server via a proxy then not sending the Vary header can "poison" the cache in a way
you do not want. Because if the client which causes the proxy to cache the response
is not capable to receive compressed pages will cause the proxy to cache *only* the
uncompressed version of the page.



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