Netscape reload of animated gifs, and negotiation

[Brian Behlendorf <br...@organic.com>]

So here at organic we've long ago stopped using file name suffixes (i.e.,
referring to logo.gif as just "logo") relying upon content negotiation
mechanisms to fill in the details.  I'm sure other sites do that these days
too.  When we did an upgrade to 1.2 about a month ago, we noticed some sites
started getting hit very heavily - looking deeper we noticed a huge stream of
requests for particular gifs, as fast as possible, from a small number of
clients at any given time.  In particular, some of the navigation bar images in
the harley davidson site, and even more particular, the animated icons.

This wasn't happening before the 1.2 upgrade.  What changed?  The best we could
tell was that the images started having Expires: headers on them, with a date
and time exactly equal to the current date and time. I presume this is because
of content negotiation (Alexei alluded to that when I asked him).  The funny
thing was that netscape was loading an animated image, would go through the
animation, determine the image was "stale", and attempt to reload it.  Since
some of the animations are a fraction of a second long (a "rumbling engine" for
one of the icons) this effectively meant the browser was trying to access it as
fast as possible.  

It took me until today to hazard a guess that the Expires headers could be
turned off with a "CacheNegotiatedDocs" directive.  Once I added that then all
was back to normal.  It's just weird that it had "started" happening.

Not a bug, but we should prominently explain the situation somewhere on the
site and how to fix it using CacheNegotiatedDocs (and what the implications of
*that* are).  Maybe there's a better solution long term?

	Brian


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