About a month the site slows down very much, how to calculate the reason?

Question

Highload

Our online store has been operating for about six years. It is self-written (php + SQL). All the years worked, there were no problems. But the last month or two there has been such a trend that he is very stupid. Pages take a long time to load, especially in the admin panel. Everything is ok with hosting, there were no changes. Tell me how to calculate the reason for the long response. We don't have the qualifications ourselves. There is a suspicion that the matter is in the overgrown database. Some tables have become very "big". But very often pages slow down when loading which does not access these heavy tables.
Can anyone tell me what tools to measure any indicators?

Answer 1

1) Look at the top queries to the database, the heaviest the most frequent.
2) Arrange indexes.
3) Cache the results of heavy and frequent queries.
4) Analyze the load, maybe there is not enough processor or memory.
Perhaps the problem is blocking.

Answer 2

If it brings you money - look for consulting, you yourself now, apparently, will not be able to overcome the
mysql situation https://ru.linkedin.com/in/vfedorkov
postgres postgresql-consulting.ru