Understand the hanging of the site on MySQL

Good afternoon.
Suddenly, the site began to hang and return a 524 error.
A good acquaintance of the sysadmin said that the matter was in the database, but even he could not understand the true reason. Says that the base loads the processor by 200%. When the mysql service is stopped, the load drops.

P.S. Need a good specialist in databases, in particular MySQL, not a human combine)