How does jmeter starts sending requests to server

Question

If Thread: 100, Rampup: 1 and Loop count: 1 is the configuration, how will jmeter start sending requests to the server?

Request will be sent 1 req/sec or all requests will be sent all at once to server?

Answer 1

JMeter will send requests as fast as it can, to wit:

1. It will start all threads (virtual users) you define in Thread Group within the ramp-up period (in your case - 100 threads in 1 second)
2. Each thread (virtual user) will start executing Samplers which are present in the Thread Group upside down (or according to the Logic Controllers)
3. When there are no more samplers to execute or loops to iterate the thread will be shut down
4. When there are no more active threads left - JMeter test will end.

With regards to requests per second - it mostly depends on your application response time, i.e.

• if you have 100 virtual users and response time is 1 second - you will get 100 requests/second

• if you have 100 virtual users and response time is 2 seconds - you will get 50 requests/second

• if you have 100 virtual users and response time is 500 milliseconds - you will get 200 requests/second
• etc.

I would recommend increasing (and decreasing) the load gradually, this way you will be able to correlate increasing load with increasing throughput/response time/number of errors, etc. while releasing all threads at once will not tell you the full story (unless you're doing a form of spike testing, in this case consider using Synchronizing Timer)

Answer 2

JMeter's ramp-up period set as 1 means to start all 100 threads in 1 second.

This isn't recommended settings as describe below

The ramp-up period tells JMeter how long to take to "ramp-up" to the full number of threads chosen. If 10 threads are used, and the ramp-up period is 100 seconds, then JMeter will take 100 seconds to get all 10 threads up and running. Each thread will start 10 (100/10) seconds after the previous thread was begun. If there are 30 threads and a ramp-up period of 120 seconds, then each successive thread will be delayed by 4 seconds.

Ramp-up needs to be long enough to avoid too large a work-load at the start of a test, and short enough that the last threads start running before the first ones finish (unless one wants that to happen).

Start with Ramp-up = number of threads and adjust up or down as needed.

See also Can i set ramp up period 0 in JMeter?

bear in mind that with low rampup and many threads, you may be limited by local resources, so your results may be a measurement of client capability rather than server.