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From Paul Richards <>
Subject Re: proxying
Date Wed, 24 Jan 1996 14:39:24 GMT
In reply to Brian Behlendorf who said
> On Tue, 23 Jan 1996, Paul Richards wrote:
> > Hmm, those are reasonable heuristics to use in the absense of a proper
> > protocol. It doesn't change the fact that http is missing this functionality
> > in a properly formulated manner.
> I don't understand why Expires: doesn't give you what you need.  The fact 
> that it isn't being widely used, or correctly implemented, doesn't mean 
> it doesn't exist.  

Well, I guess I should go read some more docs but I though Expires was
advisory not mandatory, advisory timeouts are pointless. If Expires
is only advisory then you can never be sure that people are seeing
your updated pages and not some stale copy from a cache.

> > It really concerns me 
> > that there's no way to prevent incorrect (i.e. stale) data from being 
> > served from caches. 
> Not true.  If you are paranoid about stale copies, use Proxy: no-cache.  

I'm not paranoid about stale copies to the point that I don't want my
pages cached, I just want to be sure that, with no further effort on
my part, my updated pages will appear everywhere after a time period X.

> be configurable.  The AOL caches, for example, always send IMS requests 
> for HTML documents, but cache GIF images for up to 6 hours (unless they 
> have a Proxy: no-cache).  

You're kind of making my point. There needs to be an "enforced
standard" to deal with the whole caching issue.

> Another note - many sites who rely upon being able to maximize traffic 
> reports are also discouraged from setting Expires: headers because then 
> they can't count how many hits are served out of caches.  There will be 
> discussion on proxy server reporting of locally-served non-IMS hits at 
> the Demographics and Data Collection workshop at the W3C I'll be 
> attending next week - obviously, if servers have at least a hope 
> of being able to get those hit counts they'll be more willing to allow 
> caches to serve files without IMS requests.  I mean, no one cares how 
> many hits your DNS server gets.  :)
> I would definitely like to see some interface to setting Expires: headers 
> in Apache.  A heuristic like Alexei's is interesting, I'd want to cap it 
> at 48 hours or something.  An interface to compare which of the cache 
> sites you are serving to which ones are reporting back numbers would be 
> interesting too - i.e., "I see the AOL caches are reporting hits 
> in a timely manner - I'll be liberal with the expiration dates on the 
> documents I give them" versus "I see Hensa isn't giving me any data, 
> fuck'm, the get no Expires header".  Etc....
> Still, let me know if I'm missing something.

Interesting position, and a different viewpoint I hadn't considered. 

The end users won't be impressed that everyone else's pages come nice
and quickly from the proxy wherease your pages are really slow because
the proxy has to fetch them every time.

I think people need to change their ideas about the "success" factor
of web services, if things keep growing at this rate the concern will
be for bandwidth and how to maximise coverage with minimum network load.
Circumventing caching mechanisms just so you can bump up your hits is
not a good trend to set. 

I think requiring proxy servers to return stats is just silly. I think
there's a bit of an obsession with hit counts.  About the only valid use
I can see for them is in determining that your server's very busy. If
my server was very busy I'd be wanting to offload to caches. All other
reasons for collecting hit counts are bogus because they mean absolutely
nothing in terms of users or whatever.

  Paul Richards. Originative Solutions Ltd.
  Phone: 0370 462071 (Mobile), +44 1225 447500 (work)

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