What base is suitable for a high-load messenger?

Question

Data storage

What do you think is the most suitable database for a messenger ? Imagine that every day there are about 200,000,000 requests to the database. There is an option for Mongo, but I saw that with more than 500,000 it can no longer cope. I also considered Casandra, but the low support from the community scares me off.

Answer 1

it's 11 rps. well, 34 in the jump. Any will do. This is not a high load

Answer 2

Except basis there are still connections. Rather, the network will fall. Because 90% of the time clients will just hang connected.