Oracle doesn't handle TCP connections, the Oracle Net Listener (a separate process) is responsible for that. It supports connection pooling.

I'm no expert on how this scales compared to Postgres as it is hard to find benchmarks, thanks to Oracle licensing terms.

In oracle its been an option for a long time(since atleast 10g, I think before), shared vs dedicated servers in their language, and in my experience pretty rare to use shared servers.

Shared servers represent a built-in connection pool. They still use one process for each connection.

Oracle uses a thread model in Windows (one "orcle" process, each connection is a thread), but not on Unix/Linux.