Session graph is not constant

Gatling (Open-Source)
1

Hi,

I’m new to Gatling but I like it already especally for the ease of setting up scenarii and the exploitation of the results.

My problem is when I user a ramp in a scenario, the session number per second should be constant (except at start and end) all along the test.
But the curve presents peaks every 35/40 seconds where the number of sessions by second is three to four times the cruise value (which i expect).

My scenario is relatively simple (two requests, one local and one distant) and here is the code to manage the users :
setUp(scn.users(20000).ramp(1000).protocolConfig(httpConf))

What am I doing wrong?

If needed I can post a report to see what’s going on…

Thanks in advance for the help.

Antoine

2

Mmmm, I'm wondering if you might be bitten by this Akka issue:
https://mail.google.com/mail/u/0/?hl=fr#search/akka+scheduler/13c21b7aa32d045a

Could you try to change the ramp duration to something that's not a
multiple of 50 (which is the tick duration set up in application.conf),
please?

3

Here is the gist of the scenario...

really simple : https://gist.github.com/4517979

Thanks again...

4

Could you also provide your simulation.log file, please?

5

I see that your gist uses 2000 users and not 20000 as you first stated.
Is it that you lowered it? Does the problem still occur with 2000 users?

6

Lowering the number of users didn't solve the problem. The report
graph just look different, less peaks which is consistent with the
problem.

Here is a gist to the simulation.log file : https://gist.github.com/4521029

7

IMHO, this is perfectly normal.

Your scenario is so short (only 2 requests, and the first one looks that a static page, so response time should be almost immediate) that your users’ lifespan is directly correlated to the second request response time.

Have a look at ps.psp response time and you’ll realize that it periodically jump from ~150ms to 25s (GC on your server maybe), making your users stay alive much longer.

Cheers,

Stéphane

8

Thanks Stephane.

It was from the server. Nothing to do with gatling… oups :-/

9

No pro, that was an interesting case.