How to check server load?

Question

PHP

There are two PHP scripts that make REST requests to another server.
We need to see which one behaves better under load.
What parameters to look at (response time, memory load, CPU)? What utilities to use?
Thanks

Answer 1

ab, as the easiest option, yandex-tank, if beautiful reports are needed (loadosophia for example).

Answer 2

apache benchmark? :)

Answer 3

choose for every taste: siege (almost analogous to ab), wrk, gatling etc...

Answer 4

Also JMeter, if you want to do a load farm yourself.
There is Blitz - a cloud solution with a free plan. They have their own API that allows you to write complex test plans.

Answer 5

use mod_status in apache

Answer 6

loaddy.com
loadimpact.com
synthetics not ok. It is better to check with "close to reality" tools