Connection pooling is a technique in Java that enables a pool of connections to be created and reused across multiple clients or threads. In traditional database access mechanisms, a new connection is established each time a client requests access to the database. This is not efficient as opening and closing connections are expensive operations. Hence, connection pooling is used to minimize the overhead of repeatedly establishing and destroying connections.

Connection pooling works by creating a pool of pre-established connections to the database. When a client requests a connection, it is given an available connection from the pool. Once the client is done with the connection, it is returned to the pool instead of being closed. This allows other clients to reuse the same connection from the pool instead of creating a new one.

1. Reduced overhead: Connection pooling reduces the overhead of opening and closing a connection each time a request is made to the database. This results in significant performance improvements and optimizes resource usage.

2. Scalability: Connection pooling offers better scalability by allowing multiple clients to use a single connection. As more clients request access to the database, additional connections are added to the pool on-demand.

3. Improved reliability: Connection pooling improves the reliability of the application by reducing the likelihood of connection-related issues such as connection timeouts, connection leaks, and database connection errors.

Overall, connection pooling is a useful technique for managing database connections in Java-based applications. It offers significant performance benefits and improves the reliability and scalability of the application.