Most advices I have seen say that I'll probably want to code it myself, but I was wondering about the latency of that solution? I'll likely have a SQL store and that would be a good argument to use postgres...
We have switched to an Phoenix (elixir) server which listens to the database, then clients subscribe via websockets. We're opensourcing it here: https://github.com/supabase/realtime
It's still in very early stages (although I am using it in production). Basically the Phoenix server listens to PostgreSQL's replication functionality and converts the byte stream into JSON, which it then broadcasts over websockets. This is great since you can scale the Phoenix servers without any additional load on your DB. Also it doesn't require wal2json (a Postgres extension). The beauty of listening to the replication functionality is that you can make changes to your database from anywhere - your api, directly in the DB, via a console etc - and you will still receive the changes via Phoenix.
It's similar to Apache Kafka but very light on resources and easy to selfhost.
Ow yeah, the throughput is around 150 k msg/s. Without much configuration.