Re: decreased caching efficiency?

[Adrian Chadd <adrian () creative net au>]

On Fri, Oct 20, 2000, Dana Hudes wrote:

> > > When I switch to CGI-based delivery of images the cache will of course 
> > > become pass-through
> > > since there will be no file to cache just a stream of bytes....
> >
> > Is the assumption there that by using CGI you'll automatically tweak a 
> > configuration in a caching proxy?  If so then it's a flawed assumption.
> But there is no file to cache? I don't have enough gear to set up a test with squid myself
> (and that would only be one cache) but how is the engine to know to cache it? 
> My understanding is that CGI-generated content is usually not cached.

BZZT. Another assumption which is actually totally not true.
For example, imagine your photo book. The photos won't change, right ?
The position in your database won't change, right ? So ..

http://www.domain.com/photos?id=31765

ok. 31765 is a static image that won't change. So, you'd be better off
setting its expiry time to something high, wouldn't you?

> > Having had a very quick look at your site, it seems a little strange that 
> > you want to defeat caching of those objects that soak up bandwidth; the 
> > request to perform "click-through" on the advert suggests that you're using 
> > the revenue to pay for your bandwidth costs.  (So, one assumes that the 
> > more the material was cached, the less you'd have to pay, and the less 
> > you'd have to worry about page impressions.)  I particularly like the way 
> > that you require my browser to send a Referer field to be allowed to view 
> > the pictures ;-)
>
> I do indeed use the revenue to pay for bandwidth but the pictures, by and large
> (its a work in progress) have been tuned for file size; still takes time to decompress but hey,
> what can I do. Also the projected load vs. the bandwidth is such that I have a LOT more room left.  The users get a 
> reasaonbly large bitmap in a reasonably small file. ImageMagick is nifty set of programs.  The problem I have is 
> pirates who collect images and use them for other purposes.
> the pictures...well, I actually don't want them hanging around on the user's disk once the browser is no longer on 
> the page.
> I haven't figured out how to make that happen other than expiration of 1 minute or something.

You can't. End of story. This is the internet, people control their end-nodes,
so you have zero chance of this happening. If you *REALLY* want to be evil,
you wrap the images in a java applet so they can't just rightclick on it,
but again that won't stop the smart people. 




Adrian

-- 
Adrian Chadd                    The Law of Software Development and
<adrian () creative net au>     Envelopment at MIT:
    "Every program in development at MIT expands until it can read mail."