Thank you guys for your quick response. I am new to Kamailio so all your information are very helpful for me.  My setting:  children=8  in kaimailio.cfg . I did not change it and leave it by default on my 4 cores system.  My thought: I think it may related to Mysql since cpu and iowait is low and the problem happens only when I add more subscribers to mysql database. I will try according to : 1: Dmitri  combination of mysql and htable as mysql cache 2: Mathias tune MySQL server 3: I think ram database should help on this. But it seems these is little document on redis. I am looking into SQLite3 memory mode but if there is any related reference / link will be appreciated. Thanks with regards, David David 2017年9月28日 下午02:59，Daniel-Constantin Mierla &lt;miconda(a)gmail.com&gt; 写道： Hello, it seems that interaction with mysql is a bottleneck. What is the value of children parameter in kamailio.cfg? Cheers, Daniel On 28.09.17 04:00, Jiankai Zhu wrote: My goal: make sure when using kamailio as engine I can achieve: on systems with 4GB memory, Kamailio can serve a population over 300 000 online subscribers <from: https://www.kamailio.org/w/features/ > Test bed: CPU: 4 cores , 4G RAM Kamailio 5 with Mysql.  Test source：another server running SIPp 10k subscriber in Mysql .  6000 Register Per Second ,  reuse 10k user to register , it works fine.  If register 50 every second for per user it seem 300 k subscribers should work.  (about 300% cpu used of totally 400% cpu. All requests finished without retransmit and fail. ) add 90k subscriber into Mysql . 100k subscirbers in Mysql . 1000 Register Per Second , a lot of failure and can not work .  (cpu are not used much at that time. IO is not high.) My question :  What is the root cause of bad performance when there is 100k subscribers' data in the Mysql database.  How can I deploy a kamailio with 300k  subscriber in database, and support 6000 register per second at the same time ? Maybe use ram database instead of Mysql?    Thanks with regards, David _______________________________________________ Kamailio (SER) - Users Mailing List sr-users(a)lists.kamailio.org https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users -- Daniel-Constantin Mierla www.twitter.com/miconda -- www.linkedin.com/in/miconda Kamailio Advanced Training - www.asipto.com Kamailio World Conference - www.kamailioworld.com