Understanding locust users and spwan rate

Question

I am trying to understand the exact relationship between the number of users and the spawn rate in locust which I could not find anywhere in the documentation.

So assume that I set the number of users to be 100, the spawn rate to be 50 users per second, and the test duration to be 10 seconds.

Is this a correct interpretation that in 2 seconds (100/50) all the required 100 users are ready and for the next 8 seconds we have 100 constant users running the tasks?

Furthermore, if I use the LoadTestShape class where I can change the number of users and the spawn rate at every tick so that for the next tick I increase the number of users to 150, does it take 1 second to spawn another 50 users to reach 150, or it spawns a whole new batch of 150 users in 3 seconds?

Answer 1

Is this a correct interpretation that in 2 seconds (100/50) all the required 100 users are ready and for the next 8 seconds we have 100 constant users running the tasks?

Yes.

Furthermore, if I use the LoadTestShape class where I can change the number of users and the spawn rate at every tick so that for the next tick I increase the number of users to 150, does it take 1 second to spawn another 50 users to reach 150, or it spawns a whole new batch of 150 users in 3 seconds?

With LoadTestShape you set the target user count (total) and the rate at which you want to approach that number, so option #1.

Note that the exact rate of the ramp up is not 100% guaranteed. If you set the new rate to occur after X seconds, you cant be sure you’ll have all 150 users running at X+1 seconds.