I am doing API load testing with JMeter. I have a Macbook Air (client) connected with ethernet to a machine being tested with the load (server).
I wanted to do a simple test. Hit the server with 5 requests per second (RPS). I create a concurrency thread group with 60 threads, a throughput shaping timer with 5 RPS for one minute, my HTTP request and hit the play button and run the test.
I expect to see my Hits per Second listener indicating a flat line of 5 hits per second, instead I see a variable rate, starting with 5 and then dropping to 2 and then later to 4... Sometimes there is more than the specified 5 RPS (e.g. 6 RPS) the point is that it's not a constant 5. It's too much of a variable rate - it's all over the place. And I don't get any errors.
My server, takes between 500ms to 3s to return an answer based on how much load is present - this is what I am testing. What I want to achieve with this test is to return as much as possible a response in 500ms time under load and I am not getting that. I have to start wondering if it's JMeter's fault in some way, but that's a topic for another day.
When I replace my HTTP sample request with a dummy sampler, I get the RPS I desire.
I thought I had a problem with JMeter resources, so I change heap size/memory to 1GB, use the -XX:+ DisableExplicitGC and -d64 flag and run in CLI mode. I never got any errors, not before setting the flags and not after. Also, I believe that 5 RPS is a small number so I don't expect resources to be a problem.
Something worth noting is that sometimes, the threads start executing towards the end of the test rather than at the start, I find this very odd behaviour.
What's next? Time to move to a new tool?
