Scaling a PHP MySQL Web Application

Is that demo code for the caching system not broken? It looks to me like, if the cache gets rebuilt, the output is only sent to the file, and there's no output sent to the browser. I can't test that right now, and there are a few functions there I've never used, but that is what it looks like.

Also: I don't like system that just check for the age of the cache, and not a more elaborate system that, using a single simple DB query, checks if the input data has changed, before regenerating the file. That looks way more useful to me. But, of course, you have to hand code that query for each page.

I always take issue with people talking about replication as a solution to scalability. It better to think of replication as a solution for availability.

I think part2 is far better suited for the typical knowledge level on HN:

http://www.oracle.com/technetwork/articles/dsl/white-php-par...

BTW their demonstration code where they hit filemtime constant to see if a file is outdated is also a bad recommendation since there is OS overhead, especially exaggerated if you use NAS. Instead use time of day for an zero-load way to check if sometime is out of date, and only update during times of lower load.