Saw this today, and noticed they used httpd as one of the projects they collected data about:
http://neverworkintheory.org/2016/06/09/too-many-knobs.html http://cseweb.ucsd.edu/~tixu/papers/fse15.pdf Hard to make a quick conclusion, but I do believe in the general statement of enumerations > numeric config options and having good defaults.
