We upgraded Moodle from ver 3.6.1 to ver 3.8.9 three months ago. We are using CentOS 7.4.1708, PHP 7.2.16, MySQL 5.7.21, Moove theme
We have a course contains about 5600 participants. When the teacher posts announcement, the Moodle would send duplicated notification email to a portion of students about 150 students repetitive every 30 seconds. The duration is 20 minutes. That means one of the students receive 40 duplicated email. The remaining about 4000 students receive the email twice. It is very irritating.
We found that this situation started happen about one and half month ago. At that time, we installed the plugin - Profile field based cohort membership. Would it be the cause of the problem? It seems working well for the process of student promotion. This plugin should be popular and we found it very useful.
At the same time, we also added the below statements to the httpd.conf
KeepAliveTimeout 3
Timeout 50
Hostnamelookups off
At my.conf, the below statement was added.
skip-name-resolve=1
We don't know if these changes are related to cause of problem or not.
Please advise how to resolve this problem. Thank you very much.