Re: Last-Modified vs. Expires

dgaudet-list-squid-dev@arctic.org writes:

>> I have recently been thinking it would be very good to be able
>> to mark a URL as "absolutely static." That is, the origin server
>> guarantees that the content will never change. So even if the
>> client issued a 'pragma: no-cache' or 'max-stale=0' in the request,
>> the cache could ALWAYS immediately return a hit for the object.
>> Of course, we would generally have HTML remain dynamic as it is
>> now, and apply the static feature to images and such.
>
>I don't think there's anything like this yet. You could experiment with
>it easily w/apache without any more code. Use the mod_headers module and
>something like this:
>
><Files ~ "\.gif$">
> Header add Cache-control never-expires
></Files>
>
>> This is one big difference between NNTP and HTTP. Usenet has quite
>> efficient distribution because each artcile is only transmitted once
>> between a pair of NNTP servers. Its certainly not the case with
>> the Web. This was all became very apparent during the Mars pathfinder
>> mission. It would have been so nice to be able to have JPL mark
>> all their images as static, which I'm quite sure they were anyway.
>
>Were there images marked with Last-Modified but no Expires? In that case
>does squid requery on every hit, or does it implement its own staleness
>timer?

I don't know if the images had expires. They certainly had last-modified.

But the point is that even with expires or last-modified, the
'pragma: no-cache' request causes a cache miss. A surpsising
number of requests include no-cache. I'm not sure why, maybe
everyone hits reload all the time, or maybe some user agents
always include it.

So what I'm after is a way to safely ignore no-cache. To give
the cache a way to say "I'm going to ignore your stupid no-cache
request because I KNOW this object will never EVER change."

Duane W.

--
wessels@nlanr.net                           Think Globally, Cache Locally.