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From d...@ast.cam.ac.uk (David Robinson)
Subject Re: cache verification
Date Sun, 10 Mar 1996 15:34:00 GMT
Alexei wrote:
>I agree. That's not the problem. The problem is when there *is* no 
>Expires header. Currently the proxy module generates its own, based on 
>the Last-Modified header (*0.1 is the default), and uses that. The 
>probelm is *this* behavior. I agree that when an Expires header is 
>present, it should not check, but when one is not, it should always send 
>a conditional GET, just to check, since it has no way of knowing. This is 
>the way CERN works, and every other proxy I'm aware of.

1: I stole the Last-modified factor from the CERN server, so your last
   statement is false.

2: You can achieve the behaviour you want by setting the last-modified
  factor to zero; then all documents without an Expiry header will 'expire'
  immediately.

3: The behaviour of not checking the remote server is very useful;
   for a lot of people a cache that always checks the origin server can
   be worse than useless for small documents. (small = few hundred bytes).

Paul wrote:
>... I agree, if there's no Expire it should probably be treated as 0 and
>a GET done.

There is no overriding reason to treat a missing Expire as 'expire now'.
In a lot of cases that is the wrong assumption to make; most documents
don't expire immediately. Of course, that's not say that this isn't the
right assumption to make sometimes.

 David.


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