In 2015, if you do not have a connection pool solution you should NOT start here. This project is not maintained. There is no support for a thread to wait if a connection is not available. Under load proxool will exceed the max connections and create more. However, it will NOT clean these up and it will leak. If you set the connection max high enough you probably won't run into this problem. But it's design gaps are very noticeable. Even the last proxool 0.9 is not necessarily drop in plug and play from 0.8.3. We had issues in changes proxool code did around jndi into 0.9. Suggest you look elsewhere for a project that is maintained and has a better design. It was good for it's time, but is not production suitable for high load environments today.
Thanks for Proxool, it's the best!