In an application server environment, should one prefer javax.sql.DataSource or javax.sql.ConnectionPoolDataSource?

Question

An existing question expresses something similar, but I want to call out a slightly different nuance here.

The basic question: All application servers give the ability to

Answer 1

Just to shed some light: I'm using Postgres, and the API doc from PGConnectionPoolDataSource is quite clear for me:

public class PGConnectionPoolDataSource
extends org.postgresql.ds.jdbc4.AbstractJdbc4ConnectionPoolDataSource
implements javax.sql.ConnectionPoolDataSource

PostgreSQL implementation of ConnectionPoolDataSource. The app server or middleware vendor should provide a DataSource implementation that takes advantage of this ConnectionPoolDataSource. If not, you can use the PostgreSQL implementation known as PoolingDataSource, but that should only be used if your server or middleware vendor does not provide their own. Why? The server may want to reuse the same Connection across all EJBs requesting a Connection within the same Transaction, or provide other similar advanced features.