Sun GlassFish Enterprise Server 2.1 Administration Guide

Editing a JDBC Connection Pool

The Edit JDBC Connection Pool page provides the means to change all of the settings for an existing pool except its name.

  1. Change general settings.

    The values of the general settings depend on the specific JDBC driver that is installed. These settings are the names of classes or interfaces in the Java programming language.



    DataSource Class Name 

    The vendor-specific class name that implements the DataSource and / or XADataSource APIs. This class is in the JDBC driver.

    Resource Type 

    Choices include javax.sql.DataSource (local transactions only), javax.sql.XADataSource (global transactions), and java.sql.ConnectionPoolDataSource (local transactions, possible performance improvements).

  2. Change pool settings.

    A set of physical database connections reside in the pool. When an application requests a connection, the connection is removed from the pool, and when the application releases the connection, it is returned to the pool.



    Initial and Minimum Pool Size 

    The minimum number of connections in the pool. This value also determines the number of connections placed in the pool when the pool is first created. 

    Maximum Pool Size 

    The maximum number of connections in the pool. 

    Pool Resize Quantity 

    When the pool scales up and scales down towards the maximum and minimum pool sizes respectively, it is resized in batches. This value determines the number of connections in the batch. Making this value too large delays connection creation and recycling; making it too small will be less efficient. 

    Idle Timeout 

    The maximum time in seconds that a connection can remain idle in the pool. After this time expires, the connection is removed from the pool. 

    Max Wait Time 

    The amount of time the application requesting a connection will wait before getting a connection timeout. Because the default wait time is long, the application might appear to hang indefinitely. 

  3. Change connection validation settings.

    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.



    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.



    Non-transactional Connections 

    Click the check box if you want Application Server to return all non-transactional connections. 

    Transaction Isolation 

    Makes it possible to select the transaction isolation level for the connections of this pool. If left unspecified, the connections operate with default isolation levels provided by the JDBC driver. 

    Guaranteed Isolation Level 

    Only applicable if the isolation level has been specified. If you select the Guaranteed checkbox, then all connections taken from the pool have the same isolation level. For example, if the isolation level for the connection is changed programmatically (with con.setTransactionIsolation) when last used, this mechanism changes the status back to the specified isolation level.

  5. Change properties.

    In the Additional Properties table, it is possible to specify properties, such as the database name (URL), user name, and password. Because the properties vary with database vendor, consult the vendor’s documentation for details.