Randomising number of repeats for different users in Gatling

Question

I'm currently trying to write a scenario in Gatling where I would like an action to be repeated between 1 and 8 times. The randomness should be on a per user basis, so for example one user may get 3 repeats and another gets 7.

I'm wanting the scenario to work like this to simulate the fact that I don't know for certain how many times a user will repeat an action.

I tried the following:

class MySimulation extends Simulation {
  private val myScenario = scenario("Scenario")
    .repeat(Random.nextInt(8) + 1) {
      // some stuff
    }

  setUp(myScenario.inject(rampUsers(100) during (60 seconds)))
}

However what this ends up doing is compiling to one random number, and then using that for every single user. So if the random number generation gets 5, each user will end up repeating 5 times, which is not what I want.

Is there a way in Gatling so that each user gets a different random number for the repeat function? Or will it only work with constant numbers?

Answer 1

The way you attempted didn't work as your scenario as defined is a builder that is executed once at startup - so Random.nextInt is only called once.

But there are a few ways you could achieve what you want.

The easiest (since you just want a random number) would be to use the gatling EL to randomly take an element of a sequence.

firstly, define a scala val with the range of numbers you want

private val times = 1 to 8

then put your range into the session and use the EL to get a random value from the collection

.exec(_.set("times", times))
.repeat("${times.random()}" ) {
  // some stuff
}

Alternatively, you could define a custom feeder - this approach lets you do things like random strings

private val times = Iterator.continually( Map( "times" -> Random.nextInt(8) + 1))

Then just feed and use the "times" value

.feed(times)
.repeat("${times}") {
  // some stuff
}