Connection pooling is a strategy to help an application's execution where N connections with the database are opened and overseen in a pool. The application just requests a connection, utilizes it, and afterward drops it back to the pool. At the point when the application requests a connection, the prepared connections are kept accessible to be utilized as part of the pool. The pool deals with the connection life cycle to such an extent that the developer really doesn't have to sit tight for the connection and shift through the stale ones.

Hibernate uses its magic to identify which connection pool provider to use—based on the properties you configure.

The following is the properties configuration for the c3p0 connection pooling:

<property name="hibernate.c3p0.min_size">5</property>
<property name="hibernate.c3p0.max_size">20</property>
<property name="hibernate.c3p0.timeout">300</property>
<property name="hibernate.c3p0.max_statements">50</property>
<property name="hibernate.c3p0.idle_test_period">3000</property>

The following is the example connection pooling properties configuration for the Apache Commons DBCP:

<property name="hibernate.dbcp.initialSize">8</property>
<property name="hibernate.dbcp.maxActive">20</property>
<property name="hibernate.dbcp.maxIdle">20</property>
<property name="hibernate.dbcp.minIdle">0</property>

When using either of the connection pooling mechanisms, we have to place the JAR dependencies in the server classpath manually or by using a dependency management tool such as Maven.

It is also possible to specify the connection provider explicitly with the hibernate.connection.provider_class property, though it is not mandatory.

If we do not configure a connection pool with Hibernate, the default is used. It is visible in the log or console output when we start the application:

org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure

The default connection pool of Hibernate is a good option for the development environment, but when it comes to production, it is recommended to configure the pool based on the requirements and the use cases.

If you are using an application server, you may wish to use the built-in pool (typically, a connection is obtained using the Java Naming and Directory Interface (JNDI)).

To use the server's built-in pool with Hibernate session using JNDI configuration, we need to set the following property in the Hibernate configuration file:

hibernate.connection.datasource=java:/comp/env/jdbc/AB_DB

It is assumed that AB_DB is the JNDI name of the Tomcat JDBC Connection Pool DataSource.

If you cannot or do not wish to use your application server's built-in connection pool, Hibernate supports several other connection pools, such as:

• c3p0
• Proxool

After Apache DBCP, the second most preferred connection pool implementation is c3p0, which easily integrates with Hibernate, and is said to deliver good performance.