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Is Ramp-up time in Jmeter affects concurrency ? I have 100 Threads in thread group and Ramp up time as 20. Will these 100 threads concurrent if ramp-up time is 20 Seconds?

As per theory, I have observed that Jmeter initiates thread after few seconds(depending on ramp up time).

If ramp up time is greater than 1 second, can I assume that number of threads set into the thread group are not concurrent??

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set ramp up time to zero to start all the thread at same time.

difference in starting time between threads = Ramp up time/ no of threads.

If you have ramp up time = 20 and no of threads = 100 then each thread with start with time gap of 0.2 (20/100) sec from previous thread

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It depends.

JMeter acts as follows:

  • JMeter starts defined number of threads during ramp-up period
  • Threads start executing samplers upside down (or according to Logic Controllers)
  • When thread doesn't have any more samplers to execute or loops to iterate - it's being shut down

So if your test is short enough you may easily run into a situation when 1st thread has already finished its work and 20th thread hasn't been started yet.

You can check your actual concurrency using i.e. Active Threads Over Time Listener

Active Threads Over Time

Remember the following:

  • Active Threads Over Time listener isn't shipped with JMeter, you'll need to install JMeter plugins. See Installing plugins article for instructions
  • Active Threads Over Time listener assumes JMeter is saving number of currently active threads. In order to trigger the saving add the following line to user.properties file (it's located in JMeter's "bin" folder)

    jmeter.save.saveservice.thread_counts=true
    

    You'll need to restart JMeter to pick the property up. See Apache JMeter Properties Customization Guide for more information on JMeter properties and ways of working with them

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If you have 100 Threads in thread group and Ramp up time as 20, these 100 threads aren't concurrent. To maintain concurrency for 100 threads you have to use either loop counts or Durations (Scheduler in Thread Group).

You may try with the "Ultimate Thread Group" (JMeter plugins) instead of only "Thread group". To check this, you can use "Active Threads Over Time"(JMeter plugins) listeners.

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As per your configuration, each thread(user) will start their action after 20/100 =0.2 seconds. i.e. after first thread has initiated, second thread will start after 0.2 seconds.

If you want to verify the same from Jmeter, on the top right corner threads are shown once you start the action.

  • I got your point Harsh, but will those threads be concurrent?? – Pravin W Apr 19 '16 at 6:09
  • Nope. Concurrent means all the threads will start on the same time.But here threads will start after 0.2 seconds of duration. so this is not a concurrent – Harsh Mehta Apr 19 '16 at 6:11

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