Connection pooling

• Hibernate's own connection pooling algorithm is, however, quite rudimentary.

You should use a third party pool for best performance and stability.
Just replace the hibernate.connection.pool_size property with connection pool specific settings.
This will turn off Hibernate's internal pool.

C3P0 is an open source JDBC connection pool distributed along with Hibernate in the lib directory.
Hibernate will use its org.hibernate.connection.C3P0ConnectionProvider for connection pooling if you set hibernate.c3p0.* properties.
If you would like to use Proxool, refer to the packaged hibernate.properties

The following is an example hibernate.properties file for c3p0:
hibernate.connection.driver_class = org.postgresql.Driver
hibernate.connection.url = jdbc:postgresql://localhost/mydatabase
hibernate.connection.username = myuser
hibernate.connection.password = secret
hibernate.c3p0.min_size=5
hibernate.c3p0.max_size=20
hibernate.c3p0.timeout=1800
hibernate.c3p0.max_statements=50
hibernate.dialect = org.hibernate.dialect.PostgreSQLDialect

http://docs.jboss.org/hibernate/core/3.6/reference/en-US/html/session-configuration.html#configuration-optional

• hibernate.c3p0.min_size – Minimum number of JDBC connections in the pool. Hibernate default: 1

hibernate.c3p0.max_size – Maximum number of JDBC connections in the pool. Hibernate default: 100
hibernate.c3p0.timeout – When an idle connection is removed from the pool (in second). Hibernate default: 0, never expire.
hibernate.c3p0.max_statements – Number of prepared statements will be cached. Increase performance. Hibernate default: 0 , caching is disable.
hibernate.c3p0.idle_test_period – idle time in seconds before a connection is automatically validated. Hibernate default: 0

Toad test to see connections
http://www.mkyong.com/hibernate/how-to-configure-the-c3p0-connection-pool-in-hibernate/

• Using a properties (flat text) file. For instance

jdbc-0.proxool.alias=property-test
jdbc-0.proxool.driver-url=jdbc:hsqldb:.
jdbc-0.proxool.driver-class=org.hsqldb.jdbcDriver
jdbc-0.user=sa
jdbc-0.password=
jdbc-0.proxool.maximum-connection-count=10
jdbc-0.proxool.house-keeping-test-sql=select CURRENT_DATE

http://proxool.sourceforge.net/configure.html