After doing some Mariadb optimization (mysqltuner is your friend) and getting rid of all of Zulu history we are now getting much lower CPU load all day. I guess we cannot keep more than a few months of zulu interactions to prevent an overload.
Obviously users are mad that they do not have access to their chat history but the alternative was several incidents a day. Now to keep an eye on the zulu interactions tables to see how fast they grow.