While reading about Doctrine's cache mechanism (which applies to other stuff than database queries, by the way), my eye was caught by a little message at the end (last section) about cache slams. I have used cache mechanisms extensively over the last few years, but (maybe luckily) never happened to witness a "cache slam". There's a link to a blog (by an unnamed author) that explains that. To make it short, you can have race conditions in APC (and
There's a nice article from Makina-Corpus on the topic here: http://www.makina-corpus.org/blog/separate-cache-backends-drupal6-and-drupal7 Notably, the cache_backport module in Drupal 6 backports the cache handlers from Drupal 7 (replaces cacherouter, in a way).