How to find a script that slows down a site?

Question

linux

The site + admin panel began to slow down a lot. It is not exactly clear after what manipulations, which I am trying to find out and fix.
The site is operational, but the server responds on average 30+ seconds. FastCGI is fine, other sites on the host work without problems. It is obvious that this time the script is being processed, which causes the delay. I checked all the corrections made, rolled back but I do not find the problem.
Is it possible to somehow track which script is being processed for so long?
Or perhaps it should be done differently?
Thanks for the help!

Answer 1

Purely speculative analytics can also lead to the right decision.
How long have brakes been around? It is worth looking at the files changed during this time (at least just identify them with find).
Which tables in the database are very swollen? What scripts use them? It is possible that requests that used to have time to go through and make room for new ones are now somewhat slower and create a traffic jam (for example, an autocomplete ajax request that is repeated every time you press each key, in conditions of a slow response, it may feel like the site is hanging at all).

Answer 2

https://ru.wordpress.org/plugins/p3-profiler/

Answer 3

https://ru.wordpress.org/plugins/query-monitor/ and other similar plugins.
I recommend watching the report .
FastCGI itself is a memory-guzzling crutch. Now, if PHP-FPM, then this is another matter.

Answer 4

+ admin? Then plugins
And the scripts are easy to look at - Network tab in Dev Tools + F5 and see what is loaded when everything hangs

Answer 5

Use xhprof

Answer 6

I would first run through the GTMetrix test, Y-Slow is also included in it. At the output, the script gives a list of recommendations for acceleration, with links to braking places.
gtmetrix.com