Change the thread count of test plan in JMeter, at run time

Question

I want to change the number of threads for a JMeter test plan at runtime.

I have Googled my problem and found a proposed solution to use JMeter plugins. But in this solution I would have to schedule the thread group before running the test plan, which I don't want. I also found another potential solution which changes the property, but doesn't affect test plan behavior at run time.

Ultimately, what I am trying to do is change the thread number given in a thread group and have it immediately increase or decrease the number of threads in the current running test plan.

Is this possible?

Answer 1

IMHO that's just a fancy feature that has no real benefit when doing proper performance testing. In order to generate relevant test output (report), you need repeatability, and clearly defined test methodology and scenarios. In order to compare impact of any application/server/infrastructure changes, you need repeatability.

What do you mean by

We can't predict the user of our site

That's why we do performance testing at the first place. To find out what is our application/infrastructure limit.
I.e. the most significant metric you can produce is how your application response time changes when number of parallel users change. But not change erratically, in run time.

With jMeter plugins' Ultimate thread group you can cover any imaginable scenario.

Answer 2

The short answer is: no, you cannot change the number of threads dynamically during runtime. Each thread count value is only read once when the test plan is first compiled and is not resolved again after this point, so it remains fixed.