What stack to choose for a realtime application?

Question

Programming languages

All hello
I want to find something sane for a real-time application (something like a social network with messages, friends and noble maidens).
PYSY everything is for educational purposes, I just want to get in and start rummaging around in real-time applications, how and with what they are prepared
What I would like:
A database with a change feed (like rethinkdb) or something similar that will allow you to conveniently organize this realtime
In order to be able to scale the application relatively easily, users around the world are assumed, and because of this, you need to minimize delays and you need to be ready for a large number of users.
What I tried:
.NET + signalR + MySQL - There is a difficulty with scaling to multiple servers, if you deploy multiple instances of servers with an application, then you need to somehow sync data between them.
The next experiment was
nodeJs + socket.io + rethinkdb - the database can be in a cluster, you can deploy several instances with the application, change subscriptions and all that, but rethinkdb became an open source project - and this somehow didn’t do any good, there is problems with the database itself, it does not withstand many connections, and starts to slow down when there is a lot of data (this is from articles on the internet).
Then I tried Firebase (cloud firestore + cloud functions) - and here everything is already generally good with scaling, but these features are in beta and firestore is missing a lot (for example, a normal api for working with arrays) and this is all very crutch. I also tried realtime database, but it has its own problems, such as indexes . I
also looked at AWS (AppSync), but did not have time to poke and I will be glad if someone tells something and shares their experience of using it.
And I was thinking about something like local data organization, synchronizing the necessary data between servers and synchronizing them with some kind of database
Everyone, thank you in advance for your attention

Answer 1

nodejs + socket.io + redis

Answer 2

Clojure + Aleph and Datomic :)

Answer 3

https://crossbar.io/