Re: Caching policy?

N.G.Smith (
Fri, 01 Sep 1995 09:42:57 +0000

>Is there a recommended caching policy for proxies? The algorithm that
>suggests itself to me is to check the expiry date for the cached document
>and if it's still in date use it, otherwise send a conditional GET.

If every document arrived with an expiry date then this would be fine.
Unfortunately precious few do and so other heuristic rules are often
used to guess when a conditional GET is required. The rule most
commonly used is based on a proportion of the time since the document
was Last-Modified. This assumes that a recently modified document is
likely to change again soon, while a document that has not been touched
in ages will remain fairly static. A maximum upper bound is often used
to make sure that conditional GETs happen on a regular basis even if
the Last-Modified date was a long time ago.

>I assume that there have been discussions of this: is there a reference to
>a summary anywhere?

Discussion of these issues used to happen on, but the
list of Mailing Lists at W3C [1] suggests that www-proxy is `previous'
rather than `current'. Archives of the list only exist to January 1995.
Has the list been discontinued?

Neil Smith
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