How to find out why the server takes a long time to respond?

Question

Computer networks

The problem is that when you enter into the address bar of the site, he thinks the browser for a very long time, and only after 3-6 seconds it starts loading the page. Sometimes there is a 504 gateway timeout.
How to solve the problem, except for moving to another hosting?

Answer 1

vps? enable php, nginx, apache, mysql profiling. Watch the logs of long queries, look for a bottleneck. if not vps, but something cheaper, then it's probably time to move.

Answer 2

If shared-hosting - then only by moving.
You can, of course, dig deeper into the code, tweak it, but it's more expensive in terms of man-hours.
If VPS - then at least write whose and what tariff. What is the load? Can you dos'yat? Or cron scripts spawned. Screenshots top/htop let's.