Re: Last-Modified vs. Expires

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On Mon, 21 Jul 1997, Ernst Heiri wrote:

> My Opinion:
> For default (static) pages and for "default" webmasters
> a default Last-Modified header together with reasonable refresh patterns
> of squid is the best solution.
> Expires are better only if they are (may be) set to reasonable values.

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).

- 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)

- 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.

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.

Dean

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