Bottleneck Performance is a trobuled area in the Vusers scenario.we can find out by Monitors only.

Let me define a Performance Bottleneck for you with an example.

Suppose you are driving back from your office and you are on an Interstate let's say I-20. Suddenly you encounter huge amounts of traffic while at Exit 35. However this traffic originates all the way at Exit 33 approximately 2 miles from your exact location. Right after Exit 33 the traffic starts moving fast again.

The Bottleneck in our example is at Exit 33. It is where the problem exists. It is also one of the most complicated issues to take care of in Performance Testing. Testers confuse the point where the application is slowing down with what really causes it. I hope I clarified some of your doubts.