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Can See Pittsburgh Results on Mother's Computer But Not Mine

Posted By: Michael Petch
Date: Friday, 24 February 2012, at 12:44 a.m.

In Response To: Can See Pittsburgh Results on Mother's Computer But Not Mine (Paul Weaver)

There can be a difference. It depends on what the server supports and the client. But in general when a browser requests a page and the server says "Here is your contents, and by the way it was last modified on a particular date X (And it may also say, hey this page expires on date Y"). The browser makes decisions on this data. Browser will cache pages and resources to speed things up. If you load a page and the expiry date has been reached (usually before hand) your browser will request the page again. If the page had a last modified indicator set on a previous request it can then send a special request to the server saying when the page is loaded again by saying "Hey man, you told me this page was last modified on date X, can you give me the new page if it has been modified since".

With F5 your browser tries to honour the expiry times and requests the server send back content if it has been modified since last getting it.

With Control-F5 all the expiry data and the last modfiied on info (in the cache) is cleared for the resources on the page being refreshed, effectively bypassing anything in the cache.

Clearing the entire cache wipes out all this info for all the sites that have been navigated to.

Things can go wrong on servers that dish out dynamic pages (constantly updated) and say "Hey I was last modified on Date X", but don't change that date when content is updated or incorrectly respond to requests saying "I haven't changed the content of the page since the last time you asked about" butthe server had changed it. In these circumstances (or any that get the cache confused) control-F5 or complete browser clearing is required.

There are some cases with some ISP's, and AOL use to be notorious for it. They use to use transparent proxies that sat between you and the web server you were talking to. Unfortunately their caches were set up improperly or buggy. Often times you could clear the entire cache (or control-F5) on your computer and constantly get old content even though people on other ISPs and or proxies had no issue at all. Often times you had to wait for the ISP's cache to clear the content and then eventually you'd get a newer copy.

The wonderful world of the WWW ;-)

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