Performance testing for existing web app - Useful tools?

You might want to take a look at BrowserMob (http://browsermob.com/). You can upload your Selenium IDE test scripts and get them to run on your site. It's founder is the creator of Selenium RC, Patrick Lightbody.

Depending on the complexity of your application, you may be able to use JMeter, by the ASF.

It's a purely Java based load-testing application with a number of graphing plug-ins, protocol supports, controllers, reporting frameworks and such. You can choose what data to log, how to graph it, how to output it to file and so on. It'll even put it into CSV or a variety of XML based formats.

It's ugly but workable, unless your application is heavy with JavaScript... It doesn't include a VM capable of running it and you'll have to do things like AJAX using hacks (Such as Regexes and handcrafted responses. Icky.) It's open source so you can add additional controllers if you need too.

Still, to do what you want (Record actions, replay, graph/store results) it should suffice.

The Net Tab in Firebug can help you measure and find out what exactly is affecting the load time of the website. You don't even need to have access to the server to use it.YSlow Gives you very cool tips for improving the overall load and feel of a specified site.I personaly use the Net tab to identify possible load times, may it be large images, javascripts css or bad latencies.I never heard of an automated tool for doing this, AFAIK selenium helps you build integration tests which helps you ensure certain parts of the application works as expected, but I'm not sure if it can also be used as a profiling tool.I hope this helps