MySQL 8.021 = 100% CPU when many UPDATE queries to 1 table
As a rule, Databases do not run slowly.  Queries do.

update set value=0 in client_table;

Look at the actual query (not the paraphrasing above).
Look at the &quot;where clause&quot; on that query.
Is it supported by indexes or is your database having to scan through the entire table to find the record you want to update?  That would easily account for the excessive CPU load (you may well find that the entire table is sitting in memory).
Running updates in a loop is also questionable.
Have you retrieved a list of record 'ID's and are now looping through them, making a change to each?
Relational DBMSs like to work on &quot;sets&quot; of rows that can extend to millions of rows.  &quot;Sniping&quot; at individual rows where you could process them all in a single, set-based, query will be slower.