Yep. I worked in a famous-big-company that had a 15 years old service that was dogslow, systemd restarts would take multiple hours.

Everyone was talking about C++ optimizations, mutex everywhere etc - which was in fact a problem.

However.. I seemed to be the first person to actually try to debug what the database was doing, and it was going to disk all the time with a very small cache.. weird..

I see the MySQL settings on a 1TB ram machine and they were... out-of-the-box settings.

With small adjustments I improved the performance of this core system an order of magnitude.