Redirected down a one way: Clearing the Internet Explorer host redirect cache

Submitted by Robert MacLean on Wed, 10/06/2010 - 08:51

Internet Explorer 9 is fast, really, really fast! A lot of that speed comes from the massive caching improvements in IE9 – but this is a bit of a double edge sword, especially for developers when caching gets in the way of what is actually happening. I spent two hours debugging an odd caching issue recently and this is the sad story.

For some testing I needed to setup a redirect, in this case a 301 permanent redirect (handy HTTP status codes cheat sheet in case you don’t remember these). What this would do is enable me to have site alpha (http://localhost:5000/Demo) redirect to site beta (http://localhost:9000/Demo).

Prior to this the scenario look like this:

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Behind the two browser windows is the IE 9 Developer tools and their fantastic new network capture feature. You can easily see that when I hit site alpha I got a 200 result, meaning all good and it loaded.

Once I setup the redirect, you’ll see I get a 304 this is because the data is already cached. Note that even though I typed in the site one URL it immediately loaded site two. This is because the browser had cached the redirect and so skipped the network steps for performance.

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Now the problem, I wanted to turn off the redirect – however the browser cached it and so would ignore the change. Clearing cache, deleting files, rebooting and even using the IE reset option did nothing to solve this Crying face 

The only way to fix it was to fire up the fantastic Fiddler tool and use it’s Clear Cache option with the option to delete persistent cookies, which flushes the WinINET cache.

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Considering that this is supposedly the same as clearing the IE cache I have no idea why this works and IE cache clearing doesn’t but it does work.