| PoolCallback | Represents a callback used to release or remove a PooledConnection back into the pool. |
| PooledConnection | Represents a connection that is managed in a pool. |
| PooledConnectionFactory | Represents a factory that creates PooledConnection. |
| Pool | A map of pool ids to Connections. |
| PoolCleaner | Thread that wakes up periodically and closes expired, unused connections. |