Tool for measuring webserver performance
I am maintaining a website running apache webserver.I want to measure the webserver performance to know whether my webserver will be able to handle for a given set of users.I checked the open source tools like httperf,flood etc..I can see a man page of options for this tools but i dont know exact procedure to run them for measuring performance.So please answer my questions:
1. Which is the best open source tool available for testing webserver performance?
2. What is the exact procedure to run the tool?
3. How to take care of dynamic websites like those using php,cgi etc? Are there any special toools available?
4. Which tools does the open source websites like sourceforge.net etc use?
5. Suppose if my website is not able to handle a given set of users what are the alternatives to upgrade my website?
BTW: I am asking all the questions after googling for hours.