Pool size and connection number


i read this article:

i’m reuse database connection in different routes.

i have only One connection in my backend and all queries and updates are running via this connection. Also there are some connections for monitoring mongodb atlas.

i think we can say 10*3 (node number) + 1 = 31 connections.

i also read this article:

kyle said: The pool size is the option which determines how many queries may be run using the same connection in parallel, similar to the number of lanes in a tunnel.

and this post: What is connection limit meant for?

@Jason_Tran said “The connection limit in Atlas represents the maximum number of simultaneous connections that the mongos 4 or mongod 3 will accept”.

so i’m confused. i have only one connection and also monitoring connections.

we assume i’m using M10 cluster which has max 1500 connections and I want mongodb server can handle
1400 simultaneous queries and updates.

what should be maxPoolSize? 31? because i have one connection in my backend.

Or 1400 + 10(monitor) = 1410 Because mongodb server must handle 1400 simultaneous queries and updates.

what is best practice maxPoolSize?

I have more a question about this post How to increase MongoDB connection pool size? - mongodb - The Parse Community

Core Maintainer: “However, keep in mind that the DB connection string may also influence the pool size”

what does it mean?

where should i define pool size? in options object or in connection string?