Why such a big TTFB?

Question

MySQL

Good afternoon. The problems of the following nature, when walking around the site, at some point when clicking on the link, it starts loading the page for 30 seconds and only then proceeds, while there is absolutely no sequence in the freezes, it can freeze once a minute, or maybe 10 times in a minute. I sinned about problems with the hoster, but after talking with them and setting up everything that was possible on the server, I realized that the problem is still not in it, and the second site on the same machine works without problems. It's the same with the MySQL side. Now the choice fell on performance problems with PHP or the CodeIgniter engine. Can someone suggest which initial and more obvious direction to look?
Thank you.

Answer 1

I would pledge parts of the engine, fixing the execution time, memory consumption, execution time from system start. There you will see what causes the hang

Answer 2

Very similar to timeout. Some lok, for example. Maybe in sessions? Do you have ajax requests on your site?