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Re: What can you cache? [was: Byte ranges -- formal spec proposal ]

From: Ari Luotonen <luotonen@netscape.com>
Date: Thu, 18 May 1995 14:35:02 -0700 (PDT)
Message-Id: <199505182135.OAA10111@neon.netscape.com>
To: "Daniel W. Connolly" <connolly@beach.w3.org>
Cc: http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com

> Why not cache CGI-bin responses?

Most of the time CGI responses are entirely dynamic, and not only
return a different document each time they're called, but also have
intended side effects.  In the earliest stages the CERN server used to
cache also CGI responses, but that was a mistake and I changed it so
that only documents with either Expires: and/or Last-modified: header
can be cached.  This is the way both CERN and Netscape proxies do it,
and anything smarter will cause problems.  So, CGI scripts may
explicitly allow caching by giving at least on of those headers,
indicating a non-zero lifetime (L-M less than current time; Expires
greater than current time).

> I believe some proxies (and some clients) cache more aggressively than
> this. For example, I heard that the hensa cache doesn't bother with
> the If-Modified-Since request unless the cache entry is 12 hours or
> 10% of the lifetime of the document (current time - last-modified).

This is not entirely correct.  HENSA doesn't cache CGI responses
unless they have the Exp/L-M header, so this 12hr/10% rule applies to
only static documents.  In general, if you want to get massive savings
from running the proxy, both in response time and bandwidth, you have
to use such settings.  In general, min{12hr,10%} is a very safe
setting.  Both CERN and NS proxies support this kind of configuration.

As an example, there was a rather large Netscape Proxy beta tester
site which saved 75% of its outbound bandwidth with our proxy, with a
6hr/10% setting.  Yes, bandwidth requirement dropped to a quarter of
what it would be without the proxy!

Cheers,
--
Ari Luotonen				ari@netscape.com
Netscape Communications Corp.		http://home.netscape.com/people/ari/
501 East Middlefield Road
Mountain View, CA 94043, USA		Netscape Server Development Team
Received on Thursday, 18 May 1995 16:59:39 EDT

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