Sun-microsystems GLASSFISH ENTERPRISE 820433510 Manual de usuario descargar pdf (Pagina 49)

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

dierent 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 specied. 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 denes 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.

Working with JDBC Connection Pools

Chapter 3 • JDBC Resources 49

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Sun-microsystems GLASSFISH ENTERPRISE 820433510 Manual de usuario Pagina 49