W3C home > Mailing lists > Public > ietf-http-wg-old@w3.org > September to December 1995

Re: Rethinking content negotiation (Was: rethinking caching)

From: David Robinson <drtr1@cus.cam.ac.uk>
Date: Thu, 21 Dec 95 17:39 GMT
Message-Id: <m0tSoy0-000DJLC@ursa.cus.cam.ac.uk>
To: http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
>>I like this syntax. The URI header would work, but this is short and
>>to the point.

>I think this syntax is insufficient.  This is pretty much the information
>that was contained in the HTTP/1.0-01 draft (AKA HTTP/1.1 before there was a
>1.1) and it was presumably changed because others felt likewise.  Using that
>scheme would require that the caching proxy keep the exact header(s) stored
>for the specified vary quanity for comparison purposes.  This is a huge
>burden on a proxy because it doesn't just have to save headers once, it has
>to save headers for each request that doesn't have the exact same paramters
>as previous requests.

Firstly, I'm not convinced that it's a _huge_ burden; does anyone have
any statistics on Accept: headers?

>An example might be useful here, if not longwinded.  This demonstrates the
>insufficent-ness of the old URI:, and a Vary: header scheme as well.
>[Example of Accept: header]

Yes, there are cases where a Vary: header will not provide enough information
for a cache. But are you arguing against the implementation of the
Vary: header? I am suggesting that it is a useful feature for varying
resources. You seem to be arguing that it may not be enough for caching
of content-negotatiated resources. Does that matter?

>(I completely ignore the vary by User-Agent here, but until we invent the
>psychic proxy, no proxy can solve for server's varying content outside of the
>content negotiation scheme without listing all 2000 user agents that come
>through its doors.)

I'm not quite sure what you mean, but half of the point of the Vary: header
was to inform about the server's varying content outside the content
negotiation scheme.

 David Robinson.
Received on Thursday, 21 December 1995 09:52:51 UTC

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