I've seen PHP applications use 30% of their CPU in the “realpath cache”, which at the time was a super-slow (O(n²) in this case) home-grown hash table for cachi

I've seen PHP applications use 30% of their CPU in the “realpath cache”, which at the time was a super-slow (O(n²) in this case) home-grown hash table for caching the result of realpath(), which was called all the time because someone decided include_once() needed to run its paths through realpath() in case someone included a file multiple time through symlinks. And I guess they couldn't trust inode numbers or Windows didn't have them or something… I hope it's gone. I really do hope it's gone :-)