IE Cache Rules and/or IIS Proxy Server...

[ClearToLand]

I've been (unsuccessfully) searching Google for a web site with a discussion of the Caching Rules for IE. I've looked at the MSKB and learned about Pragma: No-cache and I've installed Proxomitron so that I can capture the exchanges between IE and the web servers. But I don't understand why I have a problem with one web site (I'll hold the name back for now.)

There are a few pieces of dynamic information on each page that change very frequently, but, there are also dozens of little .GIFs that don't. When I refresh the page, I can watch each .GIF get re-downloaded and displayed VERY SLOWLY.

• Why doesn't IE retrieve the static .GIFs from it's cache?
• Can a BlockList be created in Proxomitron to force IE to retrieve the static .GIFs locally?
• How would IIS Proxy Server handle a page with 90% static .GIFs and text, and 10% dynamic text?
  • Would it re-download the ENTIRE page or only the changed objects?
  • Does it have a way to tell the difference?
  • Or is it the rule that if even one text letter changes on a page, the entire page must be re-downloaded?

 

[Garion]

Rules about how objects are cached are managed by the person who manages the web SERVER. Not necessarily the site, but the server. Cacheability rules are passed back and forth in HTTP headers, not in the content of the object. There's really nothing you can do on a per-site basis to over-ride those cache rules. They really aren't IE specific - They are setup for all browsers and web proxies out there. Pretty much any modern browser will accept those cache control directives and follow them.

The concept of a "web page" is really just a rendering thing - How it's displayed your screen. Every object that is part of the page (style sheets, various HTML frames, images, etc.) are all indepdant objects on the web server and that's how the browser treats them. Web admins can set cache control on a per-object basis or use more global paramaters.

Chances are, some misinformed web guy though he should fiddle with the cacheability bits for his site and made everything non-cacheable. That's better than the opposite, however. I can't tell you how often I get a call that "the proxy is broken - I'm seeing someone else's information on XXX site" because idiot admins couldn't figure out that a personalized page should be tagged non-cacheable.

Most browsers use a "Get-If-Modified-Since" (GIMS) that looks at the creation date of the object on the server and compares it to what it has in it's cache. If the object is newer than the cache, it's downloaded, otherwise the object in cache is served.

This stuff is my bread and butter, if you want more details let me know.

- G