I make a project with "high" I/O for DB. So I immediately started using Redis instead of Postgresql for the high I/O part. (streaming all Nostr events).
Then, I made a try to replace all the shit I've done using Redis by a single SQL query. Guess what, Postgresql is more than enough... it's only between 5 and 15 sql queries/sec. (with almost no data in my DB).
I'll continue to make some tests with much more data in DB to see if Postgresql is still enough (I think it is)