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How to force swf cache update to newer version without whole cache

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Should say: without emptying WHOLE cache.


Hi I have an online elearning system with XMLs, swfs etc...

These are cached locally. When I have a new update the user used to clear their local cache otherwise they wouldn't receive it which is ridiculous.

Now we have a system that replaces EVERYTHING which we call "Break cache" BUT the problem is I don't want to clear the WHOLE cache just one or two file updates.

Is this possible? I have been told it is the html tags we write that operate in the browser that takes care of this but now I'm totally lost. There must be a solution it's only common sense.

Thaks in advance.

Edited by codeBeast

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There are several ways to do this.



A quick ugly fix - just add a querystring to each resource (swf, xml, image, javascript, etc.) that has been updated.


For example, this...

<img src="test.png" />

would become this...

<img src="test.png?v=1" />

and if you change your resource again, it becomes this...

<img src="test.png?v=2" />



A permanent fix - set the cache control headers for the resource. You can just Google Cache-control for whichever language you are using, but the actual response headers will look something like this.

HTTP/1.1 200 OK
Cache-Control: public, must-revalidate, proxy-revalidate, max-age=86400
Expires: Tue, 31 Dec 2019 12:00:00 GMT
Last-Modified: Fri, 08 Feb 2013 00:25:46 GMT
Date: Fri, 08 Feb 2013 00:25:46 GMT
Content-Length: 4346

I don't know what language/webserver you are using - but whenever a request comes in for the resource, you can just compare the date on the Last-modified header with the last modified date for the actual file on disk. If the file has a newer date, then you update the headers and send the new file, otherwise return a 304 status code - which will tell the browser to use its cache. 


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