what is the best tool (open or commercial) currently available, that lets me send customized requests to a web server and get back a response to check the performance?
i will be sending it a load of more than 20K per second, but i need to get numbers for each call made. also, the numbers might be in some microseconds or nanoseconds. How in this small measurement unit, can i work out a baseline and a benchmark?
If you're using Apache, Apache AB is a benchmarking to test how many requests your serve can serve per second and how well it handles load and concurrency. It's an open-source project - check it out here.
In addition, wikipedia has a nice list of benchmarking software for testing servers.