should I worried about ram and CPU usage ? is there plan where I don't have to worry about it ? some thing like google cloud firestore / realtimedb, or mongodb cloud serverless.

Not sure why you would be worried about this, does your project currently have enough users for you to worry about DB load? are your queries optimised enough? (using indexes and stored procedures for better performance)

Yes, a lot of users. Tried hosting my own database on hetzner ryezn, still high load. I move to firestore, so I don't have to deal cpu load anymore. It costs me about $150 a month on firestore. The queries is very optimized, because mostly the query is coming from nosql database, which doesn't have any "where" at all excep for the key. Let alone join and stuff. It's mostly select * from sometable where key="something" and insert into sometable.

NoSQL still requires indexes for optimisation, but if your queries are running well without these then I don't see where this would be an issue for Supabase. How you design your database tables will help too. When you say a lot of users, how many are you talking about?

I am talking about spike like 10k connection / minute possibly more. Imagine all of the students of your town, and your neighborhood, took exam at the same time. Firestore / any Nosql database, afaik create indexes automatically for the node name. mostly my query is something like this

get("subjectsID/studentsID/answers")

I hope you've seen this https://discord.com/channels/839993398554656828/839993398554656831/892501025804652574