Pool_size for multiple applications that use the same db

I have a multi tenant application: one admin app and multiple, tens, of clients. All they use a single database, and a single Repo module - “MyLib.MainRepo”

“MyLib.MainRepo” lives in a library and a library is used by each application and admin app too.

On each a server they can be 3-4 clients running together.

Q: what should I set “pool_size” to in my case? Higher than 10, or lower?

When, say, there’re 3-4 clients/applications running on the same server, should I set “pool_size” to 3 in each applications, so that this way they all will sum up to 10? Or still to 10 in each one?

A VPS server has 1 or 2 cores, I think, on my current plan.

I usually go for Ecto pool_size equalling System.schedulers_online() in my configs. Found out that this way my app actually stresses my machine (and for some the work I did I needed maximum speed due to ingesting millions of records).