A connection pool is a cache of database connection objects. The objects represent physical database connections that can be used by an application to connect to a database. At run time, the application requests a connection from the pool. If the pool contains a connection that can satisfy the request, it returns the connection to the application. If no connections are found, a new connection is created and returned to the application. The application uses the connection to perform some work on the database and then returns the object back to the pool. The connection is then available for the next connection request.

Connection pools promote the reuse of connection objects and reduce the number of times that connection objects are created. Connection pools significantly improve performance for database-intensive applications because creating connection objects is costly both in terms of time and resources. Tasks such as network communication, reading connection strings, authentication, transaction enlistment, and memory allocation all contribute to the amount of time and resources it takes to create a connection object. In addition, because the connections are already created, the application waits less time to get the connection.

Connection pools often provide properties that are used to optimize the performance of a pool. The properties control behaviors such as the minimum and maximum number of connections allowed in the pool or the amount of time a connection can remain idle before it is returned to the pool. The best configured connection pools balance quick response times with the memory spent maintaining connections in the pool. It is often necessary to try different settings until the best balance is achieved for a specific application.

Applications that are database-intensive, generally benefit the most from connection pools. As a policy, applications should use a connection pool whenever database usage is known to affect application performance.

A connection pool provides the following benefits:

• Reduces the number of times new connection objects are created.

• Promotes connection object reuse.

• Quickens the process of getting a connection.

• Reduces the amount of effort required to manually manage connection objects.

• Minimizes the number of stale connections.

• Controls the amount of resources spent on maintaining connections.

UCP provides a connection pool implementation for caching JDBC connections. Java applications that are database-intensive use the connection pool to improve performance and better utilize system resources.

A UCP JDBC connection pool can use any JDBC driver to create physical connections that are then maintained by the pool. The pool can be configured and provides a full set of properties that are used to optimize pool behavior based on the performance and availability requirements of an application. For more advanced applications, UCP provides a pool manager that can be used to manage a pool instance.

The pool also leverages many high availability and performance features available through an Oracle Real Application Clusters (Oracle RAC) database. These features include Fast Connection Failover (FCF), Run-time connection Load Balancing (RLB), and Connection Affinity.