Is a PHP-only "cache engine" ever worth it?

Question

I wrote a rather small skeleton for my web apps and thought that I would also add a small cache for it.

It is rather simple:

• If the current page exists as a file in the cache and the file isn't too old, read it out and exit instead of rebuilding the page

• If the current page isn't cached/outdated recalc the page and save it

However, the bad thing about it is:

• My performance tests with a page that receives 40 relatively long posts via a MySQL query said that with using the cache, it took even longer to handle a single request (1000 tests each)

• How can that happen?

• How can doing a MySQL query, looping through the results the first time, passing the results to the template and then looping through the results for the second time be faster than a filemtime() check and a readout?

• Should I just remove the complete raw-PHP cache and relieve on the availability of some PHP cache like memcached or so?

Answer 1

Premature optimization is the root of all evil. If you don't need a cache, don't use a cache.

That being said, if you are content to not serve up dynamic content per request, you might want to look into using a caching proxy such as varnish and cutting out PHP and the webserver entirely. There's quite a bit of overhead to get to even your first line of PHP, and serving static files through PHP is a little dirty.

If you just want to cache elements, something like memcached or APC's cache is the way to go. APC has the advantage of being more readily available (you should have APC installed on your servers for the opcode cache if you care at all about performance) and memcached has the option of letting you have a cache that's accessible by multiple webservers (and/or multiple caches)