The language of the server side of the application. Work speed?

Question

Programming languages

Hello!
Tell me, please,
1) In what language(s) is the server part of the mobile application written (such as a multifunctional messenger)?
2) What determines the speed of applications? Why do some seemingly identical applications run at different speeds?
Thanks ^-^

Answer 1

1. messengers are made using an asynchronous request processing model, for almost every language there are frameworks that implement such a model -> for the java language it is play framework (akka), for js it is node.js, for python it is a tornado, and so on.
2. Different applications obviously have different workloads, as well as different ways of processing data. sub-optimal methods, even at low load can give poor performance.