JMeter frequency peaks when using ultimate thread group

Question

I use Ultimate Thread Group for performance testing in JMeter. In combination with a timer I want to scale the number of users/threads dynamically while each user has a constant throughput of eg 10 requests/sec.

When the Ultimate Thread Group increases the number of users, the total request rate per second will have a high peak for a short time. After the peak, the request rate is as expected.

For example, I get this trace: Start with 40 users, 10 requests per second for each user: 40 * 10 = 400 requests/second . Increase the number of users up to 60, I expect 60 * 10 = 600 requests/second , but I get a peak of more than 3959 requests/second at the beginning.

summary = 366401 in 00:15:16 =  400.0/s Avg:     1 Min:     0 Max:  1071 Err:     0 (0.00%)
summary +  12000 in 00:00:30 =  400.0/s Avg:     1 Min:     0 Max:    20 Err:     0 (0.00%) Active: 40 Started: 40 Finished: 0
summary = 378401 in 00:15:46 =  400.0/s Avg:     1 Min:     0 Max:  1071 Err:     0 (0.00%)
summary +  12000 in 00:00:30 =  400.0/s Avg:     1 Min:     0 Max:    44 Err:     0 (0.00%) Active: 40 Started: 40 Finished: 0
summary = 390401 in 00:16:16 =  400.0/s Avg:     1 Min:     0 Max:  1071 Err:     0 (0.00%)
summary +  31784 in 00:00:30 = 1061.9/s Avg:     4 Min:     0 Max:   414 Err:     0 (0.00%) Active: 60 Started: 60 Finished: 0
summary = 422185 in 00:16:46 =  419.7/s Avg:     1 Min:     0 Max:  1071 Err:     0 (0.00%)
summary + 118770 in 00:00:30 = 3959.0/s Avg:     5 Min:     0 Max:   493 Err:     0 (0.00%) Active: 60 Started: 60 Finished: 0
summary = 540955 in 00:17:16 =  522.2/s Avg:     2 Min:     0 Max:  1071 Err:     0 (0.00%)
summary +  79419 in 00:00:30 = 2647.3/s Avg:    10 Min:     0 Max:  1435 Err:     0 (0.00%) Active: 60 Started: 60 Finished: 0
summary = 620374 in 00:17:46 =  582.0/s Avg:     3 Min:     0 Max:  1435 Err:     0 (0.00%)
summary +  37227 in 00:00:30 = 1238.1/s Avg:     6 Min:     0 Max:  1354 Err:     0 (0.00%) Active: 60 Started: 60 Finished: 0
summary = 657601 in 00:18:16 =  600.0/s Avg:     3 Min:     0 Max:  1435 Err:     0 (0.00%)
summary +  18000 in 00:00:30 =  600.3/s Avg:     2 Min:     0 Max:   219 Err:     0 (0.00%) Active: 60 Started: 60 Finished: 0
summary = 675601 in 00:18:46 =  600.0/s Avg:     3 Min:     0 Max:  1435 Err:     0 (0.00%)
summary +  18000 in 00:00:30 =  599.9/s Avg:     1 Min:     0 Max:    46 Err:     0 (0.00%) Active: 60 Started: 60 Finished: 0

visualized it looks like this:

Is there a way to avoid this peak? (I also get this peak if I increase the number of users from 60 to 80.80 to 100, ...)

Answer 1

In combination with which "timer"?

I think you're using the wrong timer and the wrong thread group for your scenario, consider moving to Concurrency Thread Group and Throughput Shaping Timer , you can connect them using feedback function so the timer will be the only place which will drive the load pattern.