3.3 Overview of Validating Connections in UCP

Connections can be validated using pool properties when the connection is borrowed, and also programmatically using the ValidConnection interface. Both approaches are detailed in this section. Invalid connections can affect application performance and availability.

3.3.1 Validating When Borrowing

A connection can be validated by executing a SQL statement on a connection when the connection is borrowed from the connection pool. Two connection pool properties are used in conjunction in order to enable connection validation:

  • setValidateConnectionOnBorrow(boolean): Specifies whether or not connections are validated when the connection is borrowed from the connection pool. The method enables validation for every connection that is borrowed from the pool. A value of false means no validation is performed. The default value is false.

  • setSQLForValidateConnection(String): Specifies the SQL statement that is executed on a connection when it is borrowed from the pool.

Note:

The setSQLForValidateConnection property is not recommended when using an Oracle JDBC driver. UCP performs an internal ping when using an Oracle JDBC driver. The mechanism is faster than executing an SQL statement and is overridden if this property is set. Instead, set the setValidateConnectionOnBorrow property to true and do not include the setSQLForValidateConnection property.

The following example demonstrates validating a connection when borrowing the connection from the pool. The example uses Connector/J JDBC driver from MySQL:

PoolDataSource  pds = PoolDataSourceFactory.getPoolDataSource();

pds.setConnectionFactoryClassName("com.mysql.jdbc.jdbc2.optional.
   MysqlDataSource");
pds.setURL("jdbc:mysql://host:3306/mysql");
pds.setUser("<user>");
pds.setPassword("<password>");

pds.setValidateConnectionOnBorrow(true);
pds.setSQLForValidateConnection("select * from mysql.user");

Connection conn = pds.getConnection();

3.3.2 Minimizing Connection Validation with setSecondsToTrustIdleConnection() Method

In UCP, when you set the value of the setValidateConnectionOnBorrow(boolean) method to true, then each connection is validated during the checkout. This validation may incur significant overhead in applications that checkout database connections frequently.

To minimize the impact of frequent connection validation, you can now set the setSecondsToTrustIdleConnection(int) method with an appropriate value to trust recently-used or recently-tested database connections. Setting this value skips the connection validation test and improves application performance significantly.

The following table describes the new methods available in Oracle Database 12c Release 2 (12.2.0.1) for using this feature:

Method Description
setSecondsToTrustIdleConnection(int secondsToTrustIdleConnection) Sets the time in seconds to trust a recently-used or recently-tested database connection and skip the validation test during connection checkout.
getSecondsToTrustIdleConnection() Retrieves the value that was set using the setSecondsToTrustIdleConnection(int) method.

When you set the setSecondsToTrustIdleConnection(int) method to a positive value, then the connection validation is skipped, if the connection was used within the time specified in the secondsToTrustIdleConnection(int) method. The default value is 0 seconds, which means that the feature is disabled.

Note:

The setSecondsToTrustIdleConnection(int) method works only if the setValidateConnectionOnBorrow(boolean) method is set to true. If you set the setSecondsToTrustIdleConnection(int) method to a non-zero value, without setting the setValidateConnectionOnBorrow(boolean) method to true, then UCP throws the following exception:

Invalid seconds to trust idle connection value or usage.

3.3.3 Checking If a Connection Is Valid

The oracle.ucp.jdbc.ValidConnection interface provides two methods: isValid and setInvalid. The isValid method returns whether or not a connection is usable and the setInvalid method is used to indicate that a connection should be removed from the pool instance. See "Removing Connections from UCP" for more information on using the setInvalid method.

The isValid method is used to check if a connection is still usable after an SQL exception has been thrown. This method can be used at any time to check if a borrowed connection is valid. The method is particularly useful in combination with a retry mechanism, such as the Fast Connection Failover actions that are triggered after a down event of Oracle RAC. See Using Oracle RAC Features, for more information on Fast Connection Failover.

Note:

The isValid method checks with the pool instance and Oracle JDBC driver to determine whether a connection is still valid. The isValid method results in a round-trip to the database only if both the pool and the driver report that a connection is still valid. The round-trip is used to check for database failures that are not immediately discovered by the pool or the driver.

The isValid method is also helpful when used in conjunction with the connection timeout and connection harvesting features. These features may return a connection to the pool while a connection is still held by an application. In such cases, the isValid method returns false, allowing the application to get a new connection.

The following example demonstrates using the isValid method:

try {  conn = poolDataSouorce.getConnection  ...}catch (SQLException sqlexc)
{
   if (conn == null || !((ValidConnection) conn).isValid())
        
   // take the appropriate action
   
...
conn.close();
}

For XA applications, before calling the isValid() method, you must cast any XAConnection that is obtained from PoolXADataSource to a ValidConnection. If you cast a Connection that is obtained by calling the XAConnection.getConnection() method to ValidConnecion, then it may throw an exception.