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From Dirk-Willem van Gulik <>
Subject Re: very rough caching change patch - centralize vary/http knowledge
Date Wed, 07 May 2008 19:13:25 GMT

On May 7, 2008, at 7:01 PM, Roy T. Fielding wrote:
> On May 7, 2008, at 9:25 AM, Dirk-Willem van Gulik wrote:
>> But to me allowing caching modules some knowledge of HTTP is  
>> probably good - as
>> optimizing the generic case is simply not worthwhile - the very  
>> point of caches
>> is that they understand something of the biz-processes to go beyond  
>> what a the
>> operating system and what not can yield.
> Please keep in mind that Vary is an instruction from the origin  
> server to
> external caches that it does not control.  A cache within an origin  
> server
> or reverse proxy/gateway is free to ignore Vary if so configured.   
> Thus, an
> internal cache may have two sets of instructions -- one "internal  
> vary"
> that guides its operation and another Vary header field that is  
> intended
> for external recipients of a message.

Which is why I intentionally stopped short of hiding this completely  
in the cache_utils - but instead let the caching modules 'choose' if  
they follow up, change, have their own and/or use (or totally ignore)  

Or am I misreading you - and are you suggesting that we should have an  
extra layer in there - i.e. bury the vary aspect for the storage part  
of the cache - and have a separate layer for the 'is this equal' logic  
(rather than having them bundled in one, as it is now) ?


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