Praveen Kumar wrote:I am sure that response time is one of the main thing we need consider when you are tuning the web app. In addition too we need to consider many other things.
I think you're still missing the point. It's too early to talk about tuning an application if you don't even know what the goal is, and for that you (or more likely, product management) has to define what the performance requirements are. Mayne the application meets them all already, so there's nothing to do?
When the users start battering down the doors screaming that the app's too freaking slow or the servers catch fire because they're consuming resources like it's 2012, then you get out the performance tools, measure where the problems are, and address them. Premature optimization not only wastes resources, it makes the application harder to maintain. And more often than not, based on 20+ years of doing this for a living, the optimizations will be in the wrong place, so you'll end up having to measure and tune anyway. So might as well keep the app maintainable,
Customer surveys are for companies who didn't pay proper attention to begin with.
Your question is so broad that it is impossible to answer.
I recommend installing jamon in your dev, test and prod tiers so that you can capture data when you start to have performance issues (sql performance as well as ejb and page request performance). Having said that jamon can help you with much more than performance. It allows you to see when errors are occurring, if your testers are covering your code properly, how your users use your application and more. And it is easy to setup without changing your code.
As people above have already mentioned, you need to identify what the performance goals are. Especially, in web application environment, you can get freeware tools like YSlow, PageSpeed etc or even go to "www.webpagetest.org" and see how your application is performing currently. Based on the resulting statistics, you can determine what to optimize and how much to optimize.
Without such starting points, I dont think anyone would be able to answer this question - as performance in itself is a very vast topic.