Magento, long reply from the server

I can not understand why the server responds very long. Everything can work well for 2-3 days, and then the site starts to load in a magical case for a long time. I'm restarting MySQL, but it does not help to restart PHP-fpm, either. I have done many other things, but it does not work. Only a complete restart of the server helps.

How can I understand why the long answer is