We encounter very slow performance from our moodle server during Mid Term survey. We are using Questionnaire plugin for the survey. The survey has 15 questions combination of MCQ single answer and free text for comment.
The survey is conducted at the end of the Lecture with 120 students all together. I was standby in the room, to monitor. During the survey, the system response are very slow although I only see around 75 students login during it at the same time. It took about 1 - 2 mins for me to refresh the page, and check.
Our Moodle version is: 2.3, running on Red Hat 6.4, 64 GB memory, and 32 cores. The database is running MYSQL server 5, and running on physical server and on its own box. The application server has the same specs with the database server. We only have 1 application and 1 database server currently.
At the application server, there are quite number of messages in httpd error_log file:
Can not obtain session lock, referer: http://ourserver/mod/questionnaire/view.php?id=20698
The amount of CPU, Memory and bandwitdh in the application server are normal.
But, at the Database server, there are very high cpu load happening, The memory is ok, only 15%, and network bandwidth are low as well. There is nothing in the MySQL server log file. I didn't turn on the access log file for MySQL server for performance reason.
I am not sure where is the bottleneck. I suspect that is MySQL server performance. But maybe I am wrong. How to fine tune my MySql server to have fast responses.
Appreciate for the great help and response.
Thanks and best Regards,