Your Browser Cache, and Web Sites With Dual Addresses

As you surf the web, and read various web sites, you’ll occasionally notice oddities. Following one link, you’ll see one version of a web site; following a second link, you’ll see the same web page, but with different content.

Obviously, the web page was updated, between the first time that you visited it, and the second time. Nothing odd there.

But here’s the oddity. You visit the web site a third time, using the first link, and you see the same, older content. Then you check the second link again, and it shows the newer content again.

What’s going on here?

It’s simple, really, and this example, which uses Blogger, also applies to the real world. With Blogger, “http://www.bloggerstatusforreal.blogspot.com/” and “http://bloggerstatusforreal.blogspot.com/refer to the same blog, which is “bloggerstatusforreal“.

On your computer, “http://www.bloggerstatusforreal.blogspot.com/” and “http://bloggerstatusforreal.blogspot.com/” are stored in your cache, separately. Let’s look at a hypothetical example.

  1. Your browser cache has a 1 week expiry.
  2. You read
    http://bloggerstatusforreal.blogspot.com/
    2006/12/your-browser-cache-and-web-sites-with.html

    today. You cache today’s copy, under bloggerstatusforreal.blogspot.com.

  3. I update “Your Browser Cache, and Web Sites With Dual Addresses” tomorrow.
  4. The following day, you read
    http://www.bloggerstatusforreal.blogspot.com/
    2006/12/your-browser-cache-and-web-sites-with.html

    You cache tomorrows copy, under http://www.bloggerstatusforreal.blogspot.com.

  5. You then reread
    http://bloggerstatusforreal.blogspot.com/
    2006/12/your-browser-cache-and-web-sites-with.html

    Since it’s only 2 days old, you’ll read it from cache. The cached copy precedes the update in step 3.

Step 5 will show an older copy of the web page, even though you do it after step 4. Next week, bloggerstatusforreal.blogspot.com will expire a day sooner than www.bloggerstatusforreal.blogspot.com. The problem may repeat, in reverse.

So expect to see alternating differences, one version being more current than the other, forever.

If you ask for advice from the experts, and they advise you to clear your cache, this is why. Both versions of the blog, on your computer, will be refreshed simultaneously, and then be in synchronisation with each other. This allows more reliable troubleshooting.

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