Dear community
We finally resolved the problem with the response times. Had something to do with the OJS, but it was actually a hardware problem at the end. Our system is running on a RedHat Enterprise virtual machine with a relatively small system disc (high available disc) and a storage disc.
This storage is an NFS mount. The stalling problem occurred when we had relatively high traffic. OJS is logging all views and downlods into the usageEventLog daily files. To write the statistics in there, the file is locked for a short time, written, and unlocked again. During high traffic a lot of apache processes want to write their logs parallel into the usageEventLogs - and the NFS mount is not handling the file-locks very quick. Therefore the processes (users) had to wait in the queue to get write-permissions leading to the awesome delay times.
As the usageEventLogs is the only file having this high parallel-write-issues we moved this file only (not to have any problems with the available disc space) to the system disc where the Linux itself is managing the file-locks. As this is done way more efficient, the queue can be processed way quicker - the stalling problem could be resolved with this fix.
Thanks for your help, as I havn’t any experience with NFS mounts I could not find this problem in the past. However, I’m glad we could fix it and use the OJS with the expected performance :).
Furthermore: using the OJS web_cache=ON and disabled the scheduled_tasks in the config.inc.php config file of the OJS, handling the scheduled tasks and the remove of the cached files via some cron's not to bother the apache with these tasks during user visits.
All best from Austria,
Reto