Find the cause and fix the server overload.

Diagnosed server load, over 12 million database queries per day, which led to 20 minutes of CPU time and over 8 million SELECT/UPDATE/other type queries.
Optimized SQL queries, reduced the volume of record scanning and data transfer, which allowed for a decrease in load on the CPU and database. Changes were also made to the query logic on the application side.

Result:
The server has been stabilized, CPU load reduced by more than 10 times, the database is no longer overloaded, and the website's performance has become stable and fast.