Re: Last-Modified vs. Expires

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On Mon, 21 Jul 1997 13:34:23 -0700 (PDT) Dean Gaudet wrote:

> What we have on the table are a bunch of mods for apache which do various
> things to generate Last-Modifieds for SSI files (essentially the only
> dynamic content apache ships with).

But is SSI is *the* method for designing webages with standard components.
Including e.g. a standard footer in static web page turns the result
for each caching proxy into a dynamic object.
 
> - already in the code is "XBitHack Full" which uses the g+x permission bit
> to indicate that the Last-Modified header can use the date of the file
> being served. (i.e. the file uses things like #include header/footer,
> and they're "static" too)

How many webmasters using SSI to include static parts into a webpage
are really using this mechanisme?
 
> - proposed is an "XBitHack FullNegated" which does the same as Full but
> does it on files without g+x set (a much more common situation, but
> has the potential of breaking things)
>
> - someone sent in a patch which reads the include file twice and generates
> a Last-Modified header using the most recent age of all the pieces.
> This one is too performance intensive to do by default though imho.

And what is the loss of performance if the same static object has to
transfered many times by many servers? - Yes Apache will have some loss
of performance but the WWW users will gain a lot of performance!
 
> The last two are unlikely to be accepted into the core... but I wanted to
> get some input from people using/developing caches in case there are some
> salient points that I've missed.
>
> > Most webmaster don't care (know) a lot about this strange parameters
> > which are used by this strange people at the other end of a small line
> > to "over there".
>
> Even those that do know about Expires, don't always do the right thing.
> I've talked with webmasters who know of Expires and set it to, say 1 day,
> on the essentially static .gifs used to decorate their pages. The
> reasoning: "but if I need to change it in a hurry I don't want to have a 1
> month expires on it!". My comment is usually, "well you can change the
> URL", which is met with a blank stare.

You can't change webmaster who will prevent their pages from caching -
but you can influence the (majority?) of webmaster who don't care about
cachability in making squid as cache compatible as possible (reasonable)
in its default configuration.

Ernst

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Received on Tue Jul 29 2003 - 13:15:42 MDT