What is the highest number of threads that is reasonable to simultaneously run in Jmeter?

Question

I want to use the highest possible number of threads (to use less computers) but without making the bottleneck to be in the client.

Answer 1

I used JMeter since 2004 and i launched lot of load tests.

With PC Windows 7 64 bits 4Go RAM iCore5.

I think JMeter can support 300 to 400 concurrent threads for Http (Sampler) protocol with only one "Aggregate Report Listener" who writes in the log file results and timers between call pages.

For a big load test you could configure JMeter with slaves (load generators) like this http://jmeter-plugins.org/wiki/HttpSimpleTableServer/

I have already done tests with 11 PC slaves to simulate 5000 threads.

Answer 2

It'll depend on the hardware you run on as well as the underlying script. I've always felt that this fuzziness is the biggest problem with traditional load testing tools. If you've got a small budget ($200 or so gets you a LOT of testing), check out my company's load testing service, BrowserMob.

Besides our Real Browser Users (RBUs) which control thousands on actual browsers for the purpose of performance and load testing, we also have traditional virtual users (VUs). Scripts are written in JavaScript and can make various HTTP calls.

The reason I bring it up is that I always felt that the game of trying to figure out how many VUs you can fit on your load gen hardware is dangerous. It's so easy to get bad results without realizing it.

To solve that for BrowserMob, we took an extremely conservative approach on the number of VUs and RBUs per CPU core: no more than 1 browser or 50 threads per CPU core, and sometimes much less. In the world of cloud computing, CPU cycles are so cheap that it just doesn't make sense to try to overload machines.

Answer 3

One of the issues we had with running JMeter on Windows XP was the Windows XP TCP Connection Limit. Limit should be removed in order to run use the JMeter to workstation’s full potential More info here. AFAIK, does not apply to other OS.

Answer 4

I have not used JMeter, but the answer probably depends on your hardware. Best bet might be to establish metrics of performance, guess at the number of threads and then run a binary search as follows.

Source was Wikipedia.

Number guessing game...

This rather simple game begins something like "I'm thinking of an integer between forty and sixty inclusive, and to your guesses I'll respond 'High', 'Low', or 'Yes!' as might be the case." Supposing that N is the number of possible values (here, twenty-one as "inclusive" was stated), then at most questions are required to determine the number, since each question halves the search space. Note that one less question (iteration) is required than for the general algorithm, since the number is already constrained to be within a particular range.

Even if the number we're guessing can be arbitrarily large, in which case there is no upper bound N, we can still find the number in at most steps (where k is the (unknown) selected number) by first finding an upper bound by repeated doubling. For example, if the number were 11, we could use the following sequence of guesses to find it: 1, 2, 4, 8, 16, 12, 10, 11

One could also extend the technique to include negative numbers; for example the following guesses could be used to find −13: 0, −1, −2, −4, −8, −16, −12, −14, −13

Answer 5

JMeter can simulate a very High Load provided you use it right.

Don't listen to Urban Legends that say JMeter cannot handle high load.

Now as for answer, it depends on:

• your machine power

• your jvm 32 bits or 64 bits

• your jvm allocated memory -Xmx

• your test plan ( lot of beanshell, post processor, xpath ... Means lots of cpu)

• your os configuration (tunable)

• Gui / non gui mode

So there is no theorical answer but following Best Practices will ensure JMeter performs well.

Note that with jmeter you can distribute load through remote testing, read:

• Remote Testing > 15.4 Using a different sample sender

And finally use cloud based testing if it's not enough.

Read this for tuning tips:

• http://www.ubik-ingenierie.com/blog/jmeter_performance_tuning_tips/

Read this book for doing load testing and using JMeter correctly.

Answer 6

The JMeter Wiki reports cases where JMeter was used with as much as 1000 threads. I have used it with at most 100 threads, but the Links in the Wiki suggest resource reductions I never tried.