- MPM: Multi Processing Module
- Prefork: Forking process in advance (like pool)
test under Apache2.4 on Ubuntu
# on terminal session #1
$ ab -c 5 -n 100 -v 3 -H $AUTH_HEADER http://127.0.0.1/mpos/v1/stores/10# on the other terminal session
$ top
# pressed "V" for tree view

https://stackoverflow.com/questions/2712825/what-is-mod-php