Smart solution for expires headers

We want to set expires headers for used images, css and javascript to improve pagespeed, but we are aware of the cachingproblem when modifying a css or js script.

Is it possible to add a meta or other tag in the file which loads the xhtml which tells the browser to refresh every element, no matter what caching is set on existing开发者_Go百科 images, css or js?

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As far as I know, there's no such shortcut.

And even if it was - what would be the point? Sending such a header would defeat the purpose of the future expiration header in the first place.

When setting expiration headers, you need to add some sort of asset versioning to to your elements, such as <link rel="stylesheet" href="css/style.css?v=2">

Changing the path to the asset would achieve the same goal.

Yes this is a hassle. But cache invalidation is a hard problem, there's really no easy way around it.

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What you probably want to do is version your static content. so say you have a main.css file then you can version this by renaming it to main_0.css (just an example) and then you would set the cache expire to a year. if you ever need to update main.css just increment the version number and update your references. Then all clients will get the latest version.

There are several solutions that can do this versioning for you, but this is the basic principle..

I have always found theese resources very usefull when having cache related questions:

1. http://code.google.com/intl/no/speed/page-speed/docs/caching.html
2. http://code.google.com/intl/no/speed/page-speed/docs/filters.html

Hope this helps.

EDIT

Here is a versioning solution (mod_pagespeed) that does what i explained above:

1. http://code.google.com/intl/no/speed/page-speed/docs/filter-cache-extend.html

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Is it possible to add a meta or other tag in the file which loads the xhtml which tells the browser to refresh every element, no matter what caching is set on existing images, css or js?

Not as far as I'm aware.

We want to set expires headers for used images, css and javascript to improve pagespeed

This is a good thing in my opinion.

but we are aware of the cachingproblem when modifying a css or js script.

If you're making drastic changes to CSS or JS then you ought to be staging the changes anyway. Manage these changes by having the new CSS and JS on a different path and change the references in your HTML when making the change. This allows you to:

• instantly roll out / back
• make selective rollouts by dynamically generating those references
• web logs now provide clear audit trail for following up bug reports
• avoid any issues with short term caching of CSS and JS