I'm trying to test how many simultaneous connections can Openfire handle. I have found a limit at 4000 users. Anything beyond and the response times (for login) start taking several minutes.
I'm testing Openfire 3.6.4 (I'll have to switch to 3.7.1 soon) w/ no connection manager (using tsung framework). No SSL either (yet). The server is an Amazon "machine" having two intel Xeon E5507@2.27GHz cores and 6GB RAM. It is a standard Openfire install, the only thing that I changed was to increase the maximum heap size to 4GB.
When testing with up to 4000 users, tsung reports a rate of about 50 requests per second being processed and a rather constant processing time of 2.5 seconds. If I change the users limit to 5000, there's a linear increase in response time from 2 seconds, all the way up to 3 minutes 30 seconds. For the 5000 users test I cut the incoming rate down to 25 requests/second. Thing look a bit better if I further cut it down to 10 requests/second, but that already looks dangerously low (to me at least).
I would like to know if 4000 is a typical limitation with Openfire or (more likely) if there are settings that I should look into that can improve upon this number. Or maybe we just have to throw more hardware at it?