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From Niklas Edmundsson <ni...@acc.umu.se>
Subject Re: [PATCH]: mod_cache: don't store headers that will never be used
Date Mon, 30 Jul 2007 08:40:59 GMT
On Sun, 29 Jul 2007, Graham Leggett wrote:

> What may make this workable is the combination of "The body is NOT stale" 
> with "max-age=0". The danger of not writing the headers is that an entity, 
> once stale, will not be freshened when the spec says it should, and will 
> cause a thundering herd of conditional requests to a backend server. This 
> issue has been badly understood by some in the past, who suggested that the 
> ability to update cached entities be removed. We need to make very sure that 
> by fixing one problem we don't introduce another.

You missed the condition that the header wasn't expired, right? To 
reiterate:
- The body is NOT stale (ie. HTTP_NOT_MODIFIED when revalidating)
- The on-disk header hasn't expired.
- The request has max-age=0

Since the on-disk header hasn't expired AND the body is unchanged, 
you'll have the same data in the cache except for the Expires header.

/Nikke
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  Niklas Edmundsson, Admin @ {acc,hpc2n}.umu.se      |     nikke@acc.umu.se
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