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?

"Yes, it isn't slow ", or "Yes, it is slow" ? =) (Sorry for my bad-understanding English) — Larry Foobar, Jun 23 '11 at 21:49
yes it is slow to make yout php code parse and hash static files at each request — regilero, Jun 23 '11 at 21:51
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. — Marc B, Jun 23 '11 at 21:56

score 5 · Answer 1 · edited Jun 23 '11 at 23:21

5

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

edited Jun 23 '11 at 23:21

Larry Foobar

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answered Jun 23 '11 at 21:48

cypher

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`filemtime()` is the way I'd go, too. – Problematic Jun 23 '11 at 21:52
So, it the `Platinum Azure` version, as I see. timestamp uses less resources than hashing... – Larry Foobar Jun 23 '11 at 21:53
Thanks for your answer. I accepted `Platinum Azure`'s questions, because he was first =) – Larry Foobar Jun 23 '11 at 22:11

score 3 · Accepted Answer · answered Jun 23 '11 at 21:46

3

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.

answered Jun 23 '11 at 21:46

Platinum Azure

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7

It's not cruel. He's breaking the cache every time the file changes, which is perfect behavior. – SLaks Jun 23 '11 at 21:49
1

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. – Problematic Jun 23 '11 at 21:50
@SLaks - I'm breaking the cache every time the file changes. But I hash file every load of page. Isn't it cruel? =) – Larry Foobar Jun 23 '11 at 21:51
@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). – Platinum Azure Jun 24 '11 at 14:45

score 2 · Answer 3 · answered Jun 23 '11 at 21:47

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)

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

3 Answers3

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