UNIX MPMs that actually _work_ in Apache 2: worker prefork (old)
Yeah, but what if you want to run PHP or mod_perl?
Sure, PHP or mod_perl ~might~ work for you if you're lucky and you don't compile in the wrong third-party library, but you'll be in a world of pain if you don't.
It's very hard to bolt threading onto an existing system that links to legacy libraries. Java managed to provide a thread-safe environment by having a painful API to link to C code, "100% Pure Java" xenophobia -- and it still took them 5 years to make a JVM which was reliable enough for government work.
On Linux I've done some benchmarking and found that worker isn't any faster than prefork at serving static pages. (Is it any different on other platforms, such as Solaris?) In principle you might save RAM by running prefork, but in this day and age you can fit 16 GB in a 1U pretty easily and it's cheaper than hiring a programmer who doesn't know how to track down race conditions, never mind one that does.
