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Date: Mon, 01 May 2006 15:14:57 -0500
From: "William A. Rowe, Jr." <wrowe@rowe-clan.net>
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Subject: Re: Possible new cache architecture
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Brian Akins wrote:
> Graham Leggett wrote:
> 
>> That's two hits to find whether something is cached.
> 
> You must have two hits if you support vary.

Well, one to three hits.  One, if you use an arbitrary page (MRU or most
frequently referenced would be most optimial, but it really doesn't matter)
and then determine what varies, and if you are in the right place, or what
that right place is (page by language, or whatever fields it varied by.)

Three hits or more if your variant also varies ;)

>> How are races prevented?
> 
> shouldn't be any.  something is in the cache or not.  if one "piece" of 
> an http "object" is not valid or in cache, the object is invalid. 
> Although other variants may be valid/in cache.

And, of course, inserting the hit once it's composed is important, and can
happen in parallel (3 clients looking for the same, and then fetching the
same page from the origin).  But it's harmless if the insertion is mutex
protected, and the insertion can only happen once the page is fetched
complete.