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High Performance Web Sites
book

High Performance Web Sites

by Steve Souders
September 2007
Intermediate to advanced content levelIntermediate to advanced
170 pages
4h 24m
English
O'Reilly Media, Inc.
Content preview from High Performance Web Sites

Empty Cache vs. Primed Cache

Using a far future Expires header affects page views only after a user has already visited your site. It has no effect on the number of HTTP requests when a user visits your site for the first time and the browser's cache is empty. Therefore, the impact of this performance improvement depends on how often users hit your pages with a primed cache. It's likely that a majority of your traffic comes from users with a primed cache. Making your components cacheable improves the response time for these users.

When I say "empty cache" or "primed cache," I mean the state of the browser's cache relative to your page. The cache is "empty" if none of your page's components are in the cache. The browser's cache might contain components from other web sites, but that doesn't help your page. Conversely, the cache is "primed" if all of your page's cacheable components are in the cache.

The number of empty versus primed cache page views depends on the nature of the web application. A site like "word of the day" might only get one page view per session from the typical user. There are several reasons why the "word of the day" components might not be in the cache the next time a user visits the site:

  • Despite her desire for a better vocabulary, a user may visit the page only weekly or monthly, rather than daily.

  • A user may have manually cleared her cache since her last visit.

  • A user may have visited so many other web sites that her cache filled up, and the "word of the day" ...

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Publisher Resources

ISBN: 9780596529307Errata Page