test

Sun Java System Application Server Enterprise Edition 8.2 Developer's Guide

Using JDBC Transaction Isolation Levels

For general information about transactions, see Chapter 12, Using the Transaction Serviceand the Sun Java System Application Server Enterprise Edition 8.2 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 Application Server permits specifying any isolation level your database supports. The following table defines transaction isolation levels.

Table 11–1 Transaction Isolation Levels

Transaction Isolation Level  

Description  

TRANSACTION_READ_UNCOMMITTED

Dirty reads, non-repeatable reads and phantom reads can occur. 

TRANSACTION_READ_COMMITTED

Dirty reads are prevented; non-repeatable reads and phantom reads can occur. 

TRANSACTION_REPEATABLE_READ

Dirty reads and non-repeatable reads are prevented; phantom reads can occur. 

TRANSACTION_SERIALIZABLE

Dirty reads, non-repeatable reads and phantom reads are prevented. 

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 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:

java.sql.DatabaseMetaData db;
if (db.supportsTransactionIsolationLevel(TRANSACTION_SERIALIZABLE)
   { Connection.setTransactionIsolation(TRANSACTION_SERIALIZABLE); }

For more information about these isolation levels and what they mean, see the JDBC 3.0 API specification.

Note –

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