Re: Last-Modified vs. Expires

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On Tue, 22 Jul 1997 01:34:44 -0700 (PDT) Dean Gaudet wrote:

> The default is .html is static, and the admin has to enable .shtml
> (or whatever extension they want) to get mod_include to start working.
> mod_include's default is no Last-Modified. You have to enable XBitHack
> full and chmod g+x the files to get Last-Modified.

Ask the average webmaster about HTTP-Headers and XBitHack .....
There are a lot more webmaster who know how to use SSI to give their
pages an uniform look and feel.
 
> Anything else would require two passes over the input -- which hurts
> performance. However there might be some cute tricks we can pull... hmm.
> I've got two speed improvements for mod_include on The List anyhow
> (boyer-moore search for the <!--#, and use mmap()), with those in hand I
> could really see making the default do two passes over the input. Then
> not only would you get Last-Modified on truly static content, but I could
> also generate a Content-Length.

This sounds good.

> There is no default Expires, but I can propose one, I'm not sure how
> successful I'll be. What would be a good length?

How will you do this?

If you set an Expires you don't need to set a Last-Modified anymore.
A caching proxy will prefer the Expires anyway.

The better solution to me is to use Expires if it's really a dynamic
object or if it's explicitly set be the webmaster.
And to use Last-Modified for "static" pages with no explicit Expires.

If there is a Last-Modified the cache manager has the possibility to
set his/her refresh pattern to influence how long a cached object will be
considered to be fresh.
This refresh pattern configuration may depend on his/her tradeoff
between freshness and accessabiliy of certain objects (depending on
the connectivity to the Internet and on the connectivity of his/her
provider to the US)

Ernst

PS. I thank you for your great work you are doing for Apache and for
    your interest in improving the co-operation between webservers
    and caching proxies.

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