JDBC doesn’t provide connection pooling out of the box. There are connection pooling libraries that layer into JDBC. Most frameworks and application servers do bundle a connection pool out of the box.

Lambda is just a different paradigm than a single monolithic app with a connection pool. I assume that’s what you’re getting at. :)

There are other use cases though. Tools like pgBouncer are fairly useful in a large enterprise where a single database has multiple clients. They provide a single point to coordinate failovers and manage resource limits. I generally prefer a 1:1 relationship between an application and a database, but sometimes you have to play the cards you’re dealt.