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YSLOW suggests: For static components: implement "Never expire" policy by setting far future Expires header.... if you use a far future Expires header you have to change the component's filename whenever the component changes. At Yahoo! we often make this step part of the build process: a version number is embedded in the component's filename, for example, yahoo_2.0.6.js. http://developer.yahoo.com/performance/rules.html

I'd like to take advantage of caching for my mostly static pages and reload the js files when the version # changes. I've set a version # for my .js files but my main.html page has Expires set to the future so it doesn't reload and therefore doesn't reload the js files. Ideally I'd like to tell the browser (using a psychic technique) to reload main.html when a new version of the site is released. I could make my main.html page always reload but then I loose the caching benefit. I'm not looking for the ctrl-F5 answer as this needs to happen automatically for our users.

I think the answer is: main.html can't be cached, but I'd like to hear what are others doing to solve this problem. How are you getting the best caching vs. reload benefits.

Thanks.

JStark
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  • I think you're right - *main.html can't be cached*. Or at least not the entire page. – Jason McCreary Dec 27 '11 at 19:37
  • Make sure you're server support 304 Not Modified, so at least no content has to be re-downloaded if the page hasn't changed. If you want more you could look into html5's appcache. That does the trick you want, but you need some JS to 'reload' the page if the appcache has changed. Otherwise the page will update the next time the page is requested. Probably doesn't make much sense to you, what I just said. – Gerben Dec 27 '11 at 19:42

2 Answers2

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Your analysis is correct. Web performance best practices suggest a far future expiration date for static components (i.e., those which don't change often), and using a version number in the URL manages those changes nicely.

For the main page (main.html), you would not set a far future expiration date. Instead, you could not set an expiration, or set it for a minimal amount of time, for example +24 hours.

BrianC
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Guess it depends on why you want to cache the HTML page - to improve user load-times or reduce server load.

Even with a long expiry time you might find that it's not actually cached at the client for very long (Yahoo studies show that files don't live in the cache for very long), so a shorter expiry time e.g. 1 day, might not be an issue.

If it's to reduce backend load, it might be worth looking at whether a proxy like Varnish would help i.e. it caches the pages from the origin server at serves them when requested. This way you could control how long pages are cached with a finer level of control.

Andy Davies
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