I found it under Server -> session handling, and currently it set store in DB. I will change to store it File.
I have also tried the mysqlturner, and modified some of the setting in my.cnf, but the performance is still the same.
So, while checking in the internet I found out this article:
This article is suggested to open the max_syn_backlog in the sysctl.conf file from the TCP network.
I have tried it in my dev. server and it speed up the processing almost three times. Does you have any experience with max_syn_Backlog? Is there any side impact to moodle? I plan to implement it on my database server which located internally.
Thanks a lot for your response.