Transactions (Oracle GlassFish Server 3.0.1 Application Development Guide)

Oracle GlassFish Server 3.0.1 Application Development Guide

Transactions

The following features pertain to transactions:

Using Non-Transactional Connections

You can specify a non-transactional database connection in any of these ways:

Check the Non-Transactional Connections box on the New JDBC Connection Pool or Edit Connection Pool page in the Administration Console. The default is unchecked. For more information, click the Help button in the Administration Console.
Specify the ----nontransactionalconnections option in the asadmin create-jdbc-connection-pool command. For more information, see the Oracle GlassFish Server 3.0.1 Reference Manual.
Specify the non-transactional-connections option in the asadmin set command. For example:
asadmin set domain1.resources.jdbc-connection-pool.DerbyPool.non-transactional-connections=true
For more information, see the Oracle GlassFish Server 3.0.1 Reference Manual.
Use the DataSource implementation in the GlassFish Server, which provides a getNonTxConnection method. This method retrieves a JDBC connection that is not in the scope of any transaction. There are two variants.
```
public java.sql.Connection getNonTxConnection() throws java.sql.SQLException
```
```
public java.sql.Connection getNonTxConnection(String user, String password) 
   throws java.sql.SQLException
```
Create a resource with the JNDI name ending in __nontx. This forces all connections looked up using this resource to be non transactional.

Typically, a connection is enlisted in the context of the transaction in which a getConnection call is invoked. However, a non-transactional connection is not enlisted in a transaction context even if a transaction is in progress.

The main advantage of using non-transactional connections is that the overhead incurred in enlisting and delisting connections in transaction contexts is avoided. However, use such connections carefully. For example, if a non-transactional connection is used to query the database while a transaction is in progress that modifies the database, the query retrieves the unmodified data in the database. This is because the in-progress transaction hasn’t committed. For another example, if a non-transactional connection modifies the database and a transaction that is running simultaneously rolls back, the changes made by the non-transactional connection are not rolled back.

Here is a typical use case for a non-transactional connection: a component that is updating a database in a transaction context spanning over several iterations of a loop can refresh cached data by using a non-transactional connection to read data before the transaction commits.

Using JDBC Transaction Isolation Levels

For general information about transactions, see Chapter 15, Using the Transaction Service and Chapter 21, Administering Transactions, in Oracle GlassFish Server 3.0.1 Administration Guide. For information about last agent optimization, which can improve performance, see Transaction Scope.

Not all database vendors support all transaction isolation levels available in the JDBC API. The GlassFish Server permits specifying any isolation level your database supports. The following table defines transaction isolation levels.

Table 14–1 Transaction Isolation Levels


Transaction Isolation Level	Description
`read-uncommitted`	Dirty reads, non-repeatable reads, and phantom reads can occur.
`read-committed`	Dirty reads are prevented; non-repeatable reads and phantom reads can occur.
`repeatable-read`	Dirty reads and non-repeatable reads are prevented; phantom reads can occur.
`serializable`	Dirty reads, non-repeatable reads and phantom reads are prevented.

You can specify the transaction isolation level in the following ways:

Select the value from the Transaction Isolation drop-down list on the New JDBC Connection Pool or Edit Connection Pool page in the Administration Console. For more information, click the Help button in the Administration Console.
Specify the ----isolationlevel option in the asadmin create-jdbc-connection-pool command. For more information, see the Oracle GlassFish Server 3.0.1 Reference Manual.
Specify the transaction-isolation-level option in the asadmin set command. For example:
asadmin set domain1.resources.jdbc-connection-pool.DerbyPool.transaction-isolation-level=serializable
For more information, see the Oracle GlassFish Server 3.0.1 Reference Manual.

Note that you cannot call setTransactionIsolation during a transaction.

You can set the default transaction isolation level for a JDBC connection pool. For details, see Creating a JDBC Connection Pool.

To verify that a level is supported by your database management system, test your database programmatically using the supportsTransactionIsolationLevel method in java.sql.DatabaseMetaData, as shown in the following example:

InitialContext ctx = new InitialContext();
DataSource ds = (DataSource)
ctx.lookup("jdbc/MyBase");
Connection con = ds.getConnection();
DatabaseMetaData dbmd = con.getMetaData();
if (dbmd.supportsTransactionIsolationLevel(TRANSACTION_SERIALIZABLE)
{ Connection.setTransactionIsolation(TRANSACTION_SERIALIZABLE); }

For more information about these isolation levels and what they mean, see the JDBC API specification.

Note –

Applications that change the isolation level on a pooled connection programmatically risk polluting the pool, which can lead to errors.