Re: Comments on draft-ietf-http-v11-spec-rev-03
Dave Kristol (dmk@bell-labs.com)
Fri, 27 Mar 1998 17:25:32 -0500
Koen Holtman wrote:
> - Section 13.10:
>
> This section introduces a new (as far as I can see) requirement:
>
> # A cache that passes through requests for methods it does not understand
> # should invalidate any entities referred to by the Request-URI.
>
> This may seem like a good safety measure on the surface but I think
> that it is in fact quite damaging. First, designers of new methods
> cannot benefit much from the above rule because 1.0 and 2068 caches
> will not adhere to it. On the other hand, the new rule introduces a
> performance penalty for new methods which do not in fact cause any
> invalidation. One such method would be M-GET, a GET extended with a
> mandatory extension, for example. The performance penalty blocks
> implied by the new rule makes certain ways of extending the protocol
> too expensive and thus shortens the lifetime of the 1.x suite. I want
> the requirement to be removed.
I think I'm the instigator of this change. While your example seems
benign enough, the danger is from methods that change the underlying
object, e.g., M-PUT. The object in the cache would no longer look like
the one at the origin server and must be invalidated. In the absence of
a way to tell intervening caches to invalidate their view of the object
the proxy cache has to do so by default.
I suppose a compromise would be for a cache to mark a cached object as
"must-revalidate" when it sees an unknown method that it passes along.
Cache experts: would that work?
Dave Kristol