I can find it in system monitor.
but, [systemctl list-unit-files | grep mysql ] did not show anything.
After googled, I found it belong to akonadi which seems to be a component of KDE.
use following to kill the process
pkill -f akonadi
Then
edit ~/.config/akonadi/akonadiserverrc
change to following
StartServer=false
reference:
https://askubuntu.com/questions/762062/akonadi-services-and-mysqld-use-too-much-memory-in-kubuntu-16-04
strang mysqld process in KDE,Centos7.7
原文：https://www.cnblogs.com/johnsonshu/p/12210547.html