Why use a database connection pool?

To encrypt the queries that are sent from the app to the database
Opening connections is costly; a pool reuses a limited set of them (Correct option)
To split the data of the application across several servers
To cache the results of queries that are repeated often

Opening connections is expensive; a pool reuses a bounded set and protects the DB from too many connections

Opening a database connection takes time (network handshake, authentication) and each open connection uses memory on the database server.

A pool keeps a fixed number of connections open and lends them to requests, which return them when done.

Size it so that all app instances together stay under the database's max connections.

Reuse connections with a pool; don't open one per query.