hash css and js files to break cache. Is it slow?

Question

I have some script that generates templates of a page. Also, this scripts renders <script> and <link rel='stylesheet'> tags in the HTML.

I'd like to add cache-breaking feature with "?v=xxxxx" parameter.

I do it in such a way:

foreach ($scripts as &$script) {

    // get script file name
    $script = "{$this->_js_folder}/{$script}";

    // get it's realpath
    $realfile = realpath(substr($script,1));

    // hashing the file
    $hash = md5_file($realfile);

    // adding cache-breaking number
    $script .= '?v='.$hash;

} //: foreach

Isn't it slow, to hash about a dozen files every time user refreshes the page?

Shimmy

"Yes, it isn't slow ", or "Yes, it is slow" ? =) (Sorry for my bad-understanding English) – Shimmy

yes it is slow to make yout php code parse and hash static files at each request – Loss

Why would you do this? Browsers/Servers already cooperate to only transfer data if it was modified since the last retrieval. That's what the If-Modified-Since header and 304 status codes are for. – Lithuanian

Answer 1

That's cruel to your users to break the cache every time. How often do you change those files?

At any rate, I would suggest using a timestamp-- far faster than md5.

Tolley

It's not cruel. He's breaking the cache every time the file changes, which is perfect behavior. – Incredible

I don't think he's suggesting breaking cache every time, but using the md5 checksum of the file so that it will break if the file is changed. – Hesitation

@Incredible - I'm breaking the cache every time the file changes. But I hash file every load of page. Isn't it cruel? =) – Shimmy

@SLaks: Sorry. When I hear "cache-breaking" it usually means to try to make the page effectively uncacheable (or at least completely pointless to cache). – Tolley

Answer 2

Personally, I wouldn't hash the file, that's a waste of resources. Instead of it, i would add the last-modified timestamp into the v?=.... I mean something like this:

foreach ($scripts as &$script) {

    // get script file name
    $script = "{$this->_js_folder}/{$script}";

    // get it's realpath
    $realfile = realpath(substr($script,1));

    // getting last modified timestamp
    $timestamp = filemtime($realfile);

    // adding cache-breaking number
    $script .= '?v='.$timestamp;

} //: foreach

Tick

filemtime() is the way I'd go, too. – Hesitation

So, it the Platinum Azure version, as I see. timestamp uses less resources than hashing... – Shimmy

Thanks for your answer. I accepted Platinum Azure's questions, because he was first =) – Shimmy

Answer 3

Depending on how you update your site, you should probably use the date modified instead.

However, if you always re-upload every file, this is not a good idea.
However, you should then be able to cache the hash in memory (and perhaps also check the timestamp)

Incredible