Sun Microsystems 820433510 manual By calling the con.getAutoCommit and con.getMetaData methods

Working with JDBC Connection Pools

Optionally, the application server can validate connections before they are passed to applications. This validation allows the application server to automatically reestablish database connections if the database becomes unavailable due to network failure or database server crash. Validation of connections incurs additional overhead and slightly reduces performance.

Parameter	Description
Connection Validation	Select the Required checkbox to enable connection validation.
Validation Method	The application server can validate database connections in three ways:
	auto-commit, metadata, and table.
	auto-commit and metadata - The application server validates a connection
	by calling the con.getAutoCommit() and con.getMetaData() methods.
	Auto-commit validation makes use of two methods for validating the
	connection.getAutoCommit() is used to retrieve the current state of
	auto-commit and setAutoCommit() to change the state of auto-commit.
	This allows actual contact with the database to take place.
	getAutomCommit()might or might not contact the database, depending on
	the implementation. Actual physical connection will be wrapped for
	different purposes, such as a connection pool.
	Note – Because many JDBC drivers cache the results of these calls, they do
	not always provide reliable validations. Check with the driver vendor to
	determine whether these calls are cached or not.
	table - The application queries a database table that are specified. The table
	must exist and be accessible, but it doesn't require any rows. Do not use an
	existing table that has a large number of rows or a table that is already
	frequently accessed.
Table Name	If you selected table from the Validation Method combo box, then specify
	the name of the database table here.
On Any Failure	If you select the checkbox labelled Close All Connections, if a single
	connection fails, then the application server closes all connections in the
	pool and then reestablish them. If you do not select the checkbox, then
	individual connections are reestablished only when they are used.
Allow Non Component Callers	Click this check box if you want to enable the pool for use by
	non-component callers such as Servlet Filters and Lifecycle modules.

4.Change transaction isolation settings.

Because a database is usually accessed by many users concurrently, one transaction might update data while another attempts to read the same data. The isolation level of a transaction defines the degree to which the data being updated is visible to other transactions. For details on isolation levels, refer to the documentation of the database vendor.

Chapter 3 • JDBC Resources 49