The journal file looks like this:
Aug 21 09:44:39 servername.ipaddress.plesk.page systemd[1]: mariadb.service: A process of this unit has been killed by the OOM killer.
Aug 21 09:44:41 servername.ipaddress.plesk.page systemd[1]: mariadb.service: Main process exited, code=killed, status=9/KILL...