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From "Graham Leggett" <minf...@sharp.fm>
Subject Re: mod_cache: Don't update when req max-age=0?
Date Mon, 21 May 2007 15:17:14 GMT
On Mon, May 21, 2007 4:49 pm, Niklas Edmundsson wrote:

> Does anybody see a problem with changing mod_cache to not update the
> stored headers when the request has max-age=0, the body turns out
> not to be stale and the on-disk header hasn't expired?
>
> The rationale behind this is that there are hordes of stupid "download
> managers" that always issue this kind of request, and multiple in
> parallell to the same file at that. This hammers the entire
> cache-layer by causing headers to be rewritten for each request.
>
> Since max-age=0 requests can't be fulfilled without revalidating the
> object they don't benefit from this header rewrite, and requests with
> max-age!=0 that can benefit from the header rewrite won't be affected
> by this change.
>
> Am I making sense? Have I missed something fundamental?

At first glance, doing this I think will break RFC2616 compliance, and if
it does break RFC compliance then I think it should not be default
behaviour. However if it does solve a real problem for admins, then having
a directive allowing the admin to enable this behaviour does make sense.

Zooming out a little bit, this seems to fall into the category of "RFC
violations that allow the cache to either hit the backend less, or hit the
backend not at all, for the benefit of an admin who knows whet they are
doing".

A simple set of directives that allow an admin to break RFC compliance
under certain circumstances in order to achieve certain goals does make
sense.

Regards,
Graham
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