Application Performance/Memory consumption by Java EE App

I've been asked a question during recent interview that goes lik开发者_如何学JAVAe:

In a Java EE app, when load increases its performance goes down, and at some point application stops responding.

What are the steps you'll take to figure out the root cause of this problem?

I had some answers in mind like:

1. I will ensure application is using Connection pool
2. SQLs are fine tuned
3. Session is not getting loaded heaviliy

However the interviewer was not convinced, and he later asked: How will you figure out which part of the application is exactly causing this problem? Will you use any tool or something? I thought for a moment about Profiler, but was not too sure.

Need some help on this?

Well, I doubt if this would have satisfied the interviewer, but the method I use is random stack sampling. The slower things go, the quicker it pinpoints the reason.

In J2EE, this seems to tell how to do that.