Web Caching

Web caching is the practice of storing frequently requested - but infrequently changed - pages, images and other Web objects on a nearby server or even a user's PC.

Information from computers all over the world is available on the World Wide Web. But what happens when a server—or even an entire network - gets too many requests? Performance takes a major hit on that network.

To avoid this, one could buy more servers. But a more efficient way to increase server capacity—especially if the information is relatively static—is to store (or cache) copies of the data on servers in different locations around the Web. Then, when a request comes in for a particular Web page, it can be redirected to a server that's closer to the requester, so the final delivery of the page doesn't have to travel through so many different segments of the Web.

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That's one type of Web cache in which the host is responsible for the caching, even if it is outsourced to a third party such as Cambridge, Mass.-based Akamai Technologies Inc. or Foster City, Calif.-based Inktomi Corp.

Why Caching Matters

In the early days of the Web, when network traffic was much lower, caching wasn't as important. But with hundreds of millions of new computers coming onstream every year and most of them using the Web, caching helps improve quality of service for everyone, provides protection against network surges and reduces overall network traffic.

Sometimes, the Internet service provider is responsible for Web caching. This type of caching could be useful in situations where the same file is requested many times. A good example is a logo that appears on all of a company's Web pages: Each time a user clicks on one of that company's pages, that same logo graphic is called for.

Let's say the company is Google Inc. All of the people at all of the networks that hook into the same Internet service provider could request the Google logo thousands of times a day. Relying on Google to have remote cached sites may be helpful in keeping traffic manageable on Google's network, but it does nothing for the Internet service provider. The provider's servers have to handle all those requests, and caching can come to the rescue. The provider keeps track of what pages and files are being requested and stores local copies of those asked for frequently. When I click on Google.com, the logo comes not from a Google server in Mountain View, Calif., nor from one of Google's outlying cache servers. Instead, my Internet service provider just sends me what it has stored.

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