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From "Roy T. Fielding" <field...@liege.ICS.UCI.EDU>
Subject Re: outstanding issues for 1.2 code freeze.
Date Tue, 05 Nov 1996 01:50:59 GMT
>>   1) Generalization of BrowserMatch to apply to any header.
> 
> +1. Note that, as Roy said, Vary headers MUST be sent (or we ain't 1.1
> compliant). This is a little more subtle than meets the eye, as we have to
> send Vary even for things that _don't_ match. I'm prepared to put a bit of
> thought into making this as easy as poss for modules if there is consensus to
> proceed. Also note that BrowserMatch as it stands makes us noncompliant with
> 1.1, so I guess we have to do something.

Not too easy -- you don't want to send Vary at all unless the actual content
of the response might change in a way that affects caching.  Something like
nokeepalive or denying bad robots does not qualify.

> BTW, Roy, it occurs to me that a change of server configuration can break
> caches (by changing what we Vary over and probably other ways). Perhaps we
> should include the date of config files (including .htaccess) as part of the
> ETag?

No, don't worry about it.  Vary and ETags are optimizations to improve the
delivery of cached entities.  The likelihood that a change in config files
would significantly affect an already-cached response's validity is so
small that it would never justify stat'ing all of the config files on
every request.

There is no such thing as a perfect cache, but that doesn't mean they
can't be correct 99.9999999% of the time.

......Roy

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