I need to test if our system can perform N requests per second. Technically, it's 2 requests to one API, 2 requests to another, and 6 requests to third one. But the important thing that they should happen simultaneously - so 10 requests per second. So, in JMeter I've created three Thread Groups, first defines number of threads 1, and ramp-up time 0. Second thread group is the same, and third thread group defines number of threads 6 and ramp-up time 0. But that doesn't really guarantee it's going to run them per second How do I emulate that? And how do I see the results -- if it was able to perform or wasn't?
Thanks!
As with any network test, there's always going to be problems, especially with latency - even if you could send exactly 6 per second, they're going to be sent sequentially (that's just how packets get sent) and may not all hit in that second, plus processing time.
Generally when performance metrics specific x per second, it's measured over a period of time. Your API may even have a buffer - so you could technically send 6 per second, but process 5 per second, with a buffer of 20, meaning it'd be fine for 20 seconds of traffic, as you'd have sent 120, which would take 120/5 = 24 seconds to process. But any more than that would overflow the buffer. So to just send exactly 6 in a second to test is insufficient.
In the thread group, you're right setting number of threads (users) to 6. Then run it looping forever (tick it or put it in a while loop) and add a listener like aggregate report and results tree. The results you can use to check the right stuff is being sent and responded to (assuming you validate the responses) and in the aggregate report, you can see how many of each activity is happening per hour (obviously multiply by 3600 for seconds, but because of this inaccuracy it's best to run it for a good length of time).
The initial load test can now be run, and as a more accurate test, you can leave it running for longer (soak test) to see if any other problems surface - buffer overflows, memory leaks, or other unexpected events.