Here are statistics that I gathered. I'm almost done modifying the program to use 1 timer thread instead of 1 per bot as well as writing to the socket from the writer thread. This should reduce the number of threads from 6k (2k x 3) to 2k plus change. It appears that +RTS -k3k does make a difference. As per Simon, 2-4k avoids the thread being garbage collected because each thread gets its own block in the storage manager. Simon, did I get that right? BTW, how does garbage-collecting a thread works in this scenario? My threads are very long-running. The total is the number of bots launched, lobby is how many bots connected to the lobby. Failed is mostly due to connection reset by peer errors. The Windows C++ server uses IOCP and running a firewall was apparently interfering with that somehow. I hate Windows :-(. --- Test#1 +RTS -k3k as per Simon. Keep-alive timeout of 9 minutes. Total: 1961, Lobby: 1961, Failed: 0 Total: 2000, Lobby: 2000, Failed: 1 This test went smoothly and got to 2k connections very quickly. Maybe within 30 minutes or so. I did not gather CPU usage, etc. statistics. --- Test #2, No thread stack increase, 1 minute keep-alive timeout, more network traffic With a 1 minute timeout things run veeery slow. 86 physical and 158Mb of VM with 1k bots, CPU 50-60%. Data sent/received is 60-70 packets and 6-7kb/sec. Killed after a while. The statistics are phys/VM, CPU usage in % and #packets/transfer speed Total: 1345, Lobby: 1326, Failed: 0, 102/184, 50%, 90/8kb Total: 1395, Lobby: 1367, Failed: 2 Total: 1421, Lobby: 1394, Failed: 4 Total: 1490, Lobby: 1463, Failed: 4, 108/194, 50%, 110/11Kb Total: 1574, Lobby: 1546, Failed: 4, 113/202, 50%, 116/11kb --- Test #3, Rebuilding app with basic logging only (level 10). Stil veeery slow. Started ~6pm Total: 121, Lobby: 118, Failed: 1 Total: 521, Lobby: 509, Failed: 13, 46/104, 20-30%, 35/3kb Total: 1055, Lobby: 1044, Failed: 13, 94/168, 50% Total: 1325, Lobby: 1313, Failed: 13 Total: 1566, Lobby: 1553, Failed: 13, 126/215, 70-80%, Total: 1692, Lobby: 1680, Failed: 13, 136/228, 80% Total: 1728, Lobby: 1715, Failed: 13, 140/234, 85% Total: 1746, Lobby: 1733, Failed: 13, 140/235, 50-85%, 6:39pm Total: 1818, Lobby: 1805, Failed: 13, 145/240, 60-85%, Total: 1896, Lobby: 1883, Failed: 13, 153/250, 60-85%, 7:01pm Total: 1933, Lobby: 1919, Failed: 13, 155/255, 70-85%, 7:12pm System has 216Mb of spare physical memory at this point but the app seems to spend most of the time collecting garbage. Total: 1999, Lobby: 1986, Failed: 13, 162/262, 65-86%, 7:41pm -- http://wagerlabs.com/