Large exams with 200+ clients

If you want to perform large exams with for example 200+ cuncurrent clients, there are various settings regarding the webserver and database server that have to be increased. In the following, we assume a goal of (number of concurrent exams you wish to perform) = 200.

Hardware recommendations

See Hardware Recommendations.

GLaDOS

In order for GLaDOS to be able to process 200+ tickets at the same time, you have to increase the setting limiting the maximum number of running daemons under System->Settings.

The value n you should choose can be deduced roughly by the formula n = (number of concurrent exams you wish to perform)/5 + 10.

System

Increase the upper limit of the total number of inotify instances and watches per user. You can set this on the fly by

echo 1024 >/proc/sys/fs/inotify/max_user_instances
echo 8192 >/proc/sys/fs/inotify/max_user_watches

Although this will be set back to the default value after the next reboot. To make it permanent, create a new file /etc/sysctl.d/10-glados.conf with contents

# total number of inotify instances per user
fs.inotify.max_user_instances = 1024
fs.inotify.max_user_watches = 8192

The value you should choose for these two settings can be deduced roughly by the formulae:

• max_user_instances = (number of concurrent exams you wish to perform) + 200

• max_user_watches   = (number of concurrent exams you wish to perform)*10 + 1000

Apache

The maximum number of concurrent connections to the webserver have to be increased as well. Edit the file /etc/apache2/mods-enabled/mpm_prefork.conf and change (or add) the directives

<IfModule mpm_prefork_module>
[...]
    MaxRequestWorkers         300
    ServerLimit               300
[...]
</IfModule>

The value n you should choose can be deduced roughly by the formula n = (number of concurrent exams you wish to perform) + 100.

To apply the settings, restart the apache2 service

service apache2 restart

MySQL/ MariaDB

For the database, there is a setting for the maximum number of concurrent connections as well. Create a file /etc/mysql/mariadb.conf.d/60-glados.cnf with contents

# maximum number of concurrent connections
max_connections        = 350

The value n you should choose can be deduced roughly by the formula n = (number of concurrent exams you wish to perform) + (maximum number of running daemons) + 100. For the maximum number of running daemons, see System->Settings.

To apply the settings, restart the mariaDB service

service mariadb restart