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From "William A. Rowe, Jr." <>
Subject [Fwd: Re: Invalidation after updates or deletions]
Date Tue, 18 Jul 2006 15:46:08 GMT
Cache validation is not my expertise although I've enjoyed participating
in the banter over how to support 1 to 3 hit cache lookups of variants
which also vary ;-)  This thread is certainly of interest to those of you
working in the area of cache invalidation, current in discussion and raised
by Mark Nottingham on the HTTP-WG discussion list.

One thing occurred to me.  mod_ftp treats ftp 'commands' as http 'methods'.
So RETR is equivilant to a GET.  His point about "and unrecognised request
methods" reminds me there is no way for a module to reflect that a method
it handled was idempotent or otherwise harmless to the ETag and content of
the cache.  If your module implements PATCH, as this modifies the resource,
there is no harm since it's unrecognized by the cache.  If your module
implements GET-HTML-HEAD, we have a problem since cache doesn't recognize
and your module can't inform.

It would be cool to have an idempotence flag in the next major release for
handlers/filters to say that the arbitrary method operation munged the origin,
or it did not. Thoughts?


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