How and with what to profile python, postgresql, hardware, etc?

Question

Profiling

Here we have an abstract application in a vacuum. Flask, postgresql, redis.
How to profile? How to find out what "rests" performance? I often read about this on habr / etc, but I did not find anything understandable.
From knowledge - I turned on the log of slow postgres requests - everything is fine, everything is fast, by indexes.
How do you figure out when you can put up with performance and sigh to buy more servers, and when to look for bottles necks?

Answer 1

If you need to watch in production, then strictly newrelic is an excellent service.
And when developing, you can start with this: www.vrplumber.com/programming/runsnakerun is a good profiler for Python. Run a load test and see what is eating how much.

Answer 2

First, understand what load you expect. And do load testing.