Friday, March 13, 2009

Your Browser and Upstream Caches

Many problems which are reported by bloggers have simple resolution procedures.
Clear cache in the browser, and restart the browser.
Some problems are slightly more complex.
Clear both cache and cookies, and restart the browser.
and, at the center of each procedure, we see
Clear cache.


Cache, or local storage of Internet content, is at the center of many problems with blogs and web sites. If a copy of your blog is in a cache somewhere, the computers that access the cached copy will continue to display that copy, until told to get a fresh copy. If you just updated your blog, folks accessing the cached copy won't see your changes. One way to ensure that you see fresh copies of everything is to clear cache, which forces fresh retrieval of everything.

For all of its simplicity, clearing cache isn't a universal solution, and neither is it consistently productive - even for problems which are generally known to respond to clearing of cache.

Have you ever noticed that, after you access a new web site, any subsequent visits to that web site seem faster?

That's not your imagination, that's your browser using cached content. Caching reduces load time, and it reduces network and server load, by not retrieving directly from a web site, every time you visit that web site. If you clear cache gratuitously, you increase network and server load for everybody, and slow down everybody's Internet experience.

Besides slowing down the Internet for everybody, clearing cache won't consistently solve your problems. If you clear your cache, that ensure that you get a fresh copy of your blog (and other web sites). It has nothing to do with what your readers see. And you can only clear the cache that you control.

Such instructions - to clear cache - cover clearing of cache in the browser, because everybody uses a browser (almost everybody, anyway). Some networks, particularly larger ones, may have a caching proxy server, for both efficiency and security. When you clear your cache in your browser, you won't always think of a local proxy server.

Besides you (or your local network, which you may or may not control) having a caching proxy, there's another possibility. Your ISP may be providing a "Download Accelerator" service. One component of such a service may include a local cache of popular web sites, on your computer, and / or on servers in the ISPs server farm.

If you clear the cache in your browser, and there is an upstream cache on your computer, on your network, or on a server at your ISP, the contents of the upstream cache remains undisturbed. When you request a fresh copy of your blog in your browser, and you just cleared cache in your browser, your browser asks upstream for a copy of the blog. If the blog is in an upstream cache, that's where your browser gets the new copy. Not from the Blogger / Google server.

So if there was a problem with your blog, the problem was just solved by Blogger, and you were instructed to clear cache to ensure that you are able to view your blog with the problem resolved, and if you have an upstream cache, your clearing cache in your browser won't do anything to help.

Here is where, instead of clearing cache, you need to bypass cache temporarily - when you bypass cache, you guarantee a dynamic retrieval from the Blogger / Google server. This is, unfortunately, a temporary measure - unless you explicitly bypass cache each time, until all upstream caches expire, and each cache explicitly requests a fresh copy of the blog.

And here is one of the capricious and random details about web surfing. Every different blogger / blog reader in the world will have a different cache / computer / network infrastructure affecting their surfing activities. And the differences will explain one person responding with
You rock! I'm Following your web site in the future!!
and another
Your advice was useless. Why do you even bother?


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1 comment:

Susan said...

You do rock.