Mongrel is designed to help developers get things done. While it also makes deploying Ruby Web applications easier, it is the debugging features that developers love the most. Most folks are not accustomed to having this level of debugging from their Web server, though, so this section will cover all the various things you can find out about your Rails application using Mongrel.
The debugging capabilities in Mongrel were born out of frustration and necessity. It's frustrating tracking down certain types of defects in a Rails application, and when people have these problems they blame Mongrel. It's necessary to have strong debugging in order to determine if the problem is caused by Mongrel or by other code.
Using these techniques makes it easier to find memory leaks, open file leaks, various thread issues, and problems with proxy configurations. The tools aren't the greatest but they'll help quite a bit in a pinch.