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Re: Calculating Age Question

From: Paul Hethmon <phethmon@utk.edu>
Date: Mon, 25 Nov 1996 23:45:02 EST
Message-Id: <199610252345.0129221.7@hops.ag.utk.edu>
To: "Roy T. Fielding" <fielding@liege.ICS.UCI.EDU>, HTTP-WG <http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com>
Addressed to: "Roy T. Fielding" <fielding@liege.ICS.UCI.EDU>
              HTTP-WG <@hplb.hpl.hp.com:http-wg@cuckoo.hpl.hp.com>

** Reply to note from "Roy T. Fielding" <fielding@liege.ICS.UCI.EDU> Mon, 25 Nov 1996 19:52:31 -0800 
 
 
> > should be 13? Basically, at each cache, the Age value will   
> > be increased by the response_delay of that cache (plus   
> > resident_time if applicable).   
>   
> Regardless of what it says in the spec, the Age value is not touched  
> by the cache unless resident_time > 0.  In other words, a cache does  
> not age a response that it has never had in its possession.  It is only  
> when resident_time > 0 (the response is coming from the cache and  
> not from an upstream server) that the cache sets the Age value in  
> the message. 
 
Are we making a distinction here between "proxies" and "caches" 
then? It seems the wording in 14.6 still requires caches to 
send the Age header, even if acting more as a proxy. Henrik's code 
that he posted earlier seems to follow this too. 
 
As an implementer, I take the wording to mean calculate the 
Age value and send it everytime even if I've just received the 
response and it's not really in the cache yet. 
 
Putting that aside though, my real question went back to the 
discussion in July between you and Jeff Mogul over the algorithm. I 
guess your point here still reflects that. It does seem the 
algorithm (if all caches send Age) can easily inflate the value. 
More so if there are multiple caches in a chain and the resource 
is kept resident for any length of time in each. 
 
Paul 
 


Paul Hethmon 
phethmon@utk.edu 
phethmon@hethmon.com 
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Received on Monday, 25 November 1996 20:48:16 EST

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