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What's the catch about caching?

One of the biggest frustrations for the novice website developer is to catch errors, change them, and then have those changes seemingly do absolutely no good whatsoever. It turns out those changes may have done some good, but the browser is displaying the old page. It thinks it is being clever and helping us out, so it caches our pages for speed. When the page gets changed, it does not display differently until the browser is refreshed.

Lesson learned, problem solved, right? Wrong! Now, sometimes when it is announced that there is something new on our site, people go there and see the same old, same old. Then they send an email roughly saying "just what are you talking about?" Again, this is a caching difficulty, as is the problem that one sometimes notices on message boards, when the newly posted message doesn't seem to "take" -- it is not there.

Caching is used widely across the Internet to cut down the amount of time it takes to request information. It works by keeping a temporary copy of information that has been requested locally for a defined amount of time.

The most common forms of caching web pages occur with your web browser and with your Internet Service Provider (ISP, such as Verizon, AOL, Earthlink, etc.). Most web browsers cache pages when you visit a web site so that the next time you go to that page it appears to load faster, because it is using a local copy rather than requesting a new copy be sent across the Internet.

Some people know about the browser caching, but still get taken aback by ISP caching. ISP caching works in much the same way as browser caching. Once you have visited a website your ISP may cache those pages so that they appear to load faster the next time you visit them. The main problem with this is that unlike your browser cache you can not delete these temporary files, instead you have to wait until your ISPs cache expires and it requests fresh copies of the files. This can be very frustrating if you are trying to develop or make changes to your website -- or even to look at new information.

Unfortunately there is very little that can be done about ISP caching except to change your ISP. Most ISPs do not cache pages for more than half an hour or so but there are some that take considerably longer. AOL and Compuserve are the ISPs that seem to keep them for a very long time -- sometimes even more than 24 hours, though they claim they do not.

If you are getting unusual results and suspect that caching may be your problem, first hope that problem is simple, and clear your browser's cache. (If for some reason you don't want to do that and you have multiple browsers on your computer, you can just go to the page with another browser).

Here are some ways to clear your browser's cache:

Internet Explorer

  1. Press the Refresh button or use the menu options View, Refresh.
    This will update any Web page stored in your disk cache with the latest content on the Web.
  2. If Refresh fails to display the updated page, empty your Internet Explorer disk cache.

    For Internet Explorer version 4.0:

    • On the View menu of your Internet Explorer toolbar, click Internet Options.
    • Click the General tab.
    • In the Temporary Internet files area, click Delete Files, then click OK.
    • Click OK to close Internet Options.

    For Internet Explorer version 5.0, 5.5, 6.0:

    • On the Tools menu of your Internet Explorer toolbar, click Internet Options.
    • Click the General tab.
    • In the Temporary Internet files area, click Delete Files, then click OK.
    • Click OK to close Internet Options.

Netscape

  1. Press the Reload button or use the menu options View, Reload.
    Netscape checks with the server to see if an update has occurred before bringing a page from cache. If any change to the page has occurred, a fresh version is transmitted from the Web; otherwise, a copy is quickly retrieved from cache
  2. If Reload fails to display the updated page, press the Reload button while holding down the Ctrl key (Option key on Macintosh).
    Netscape retrieves a fresh version from the Web whether the page has been updated or not. Cache is not used. This type of reload is useful if you suspect the cached copy of a page has been corrupted.
  3. If Reload while holding down Ctrl fails, empty your Netscape disk cache:

    For Netscape version 4.7, 6.0, 7.0:

    • On the Edit menu of your Netscape toolbar, click Preferences.
    • Click the Advanced category and select Cache.
    • Click the Clear Disk Cache button and the Clear Memory Cache button.
    • Click OK.


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