Oracle8i JDBC Developer's Guide and Reference
Release 3 (8.1.7)

Part Number A83724-01





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A distributed transaction, sometimes referred to as a global transaction, is a set of two or more related transactions that must be managed in a coordinated way. The transactions that constitute a distributed transaction might be in the same database, but more typically are in different databases and often in different locations. Each individual transaction of a distributed transaction is referred to as a transaction branch.

For example, a distributed transaction might consist of money being transferred from an account in one bank to an account in another bank. You would not want either transaction committed without assurance that both will complete successfully.

In the JDBC 2.0 extension API, distributed transaction functionality is built on top of connection pooling functionality, described under "Connection Pooling". This distributed transaction functionality is also built upon the open XA standard for distributed transactions. (XA is part of the X/Open standard and is not specific to Java.)

The remainder of this overview covers the following topics:

For further introductory and general information about distributed transactions and XA, refer to the Sun Microsystems Specifications for the JDBC 2.0 Optional Package and the Java Transaction API.


Distributed transaction (XA) features require version Oracle8i release 8.1.6 or later of the Oracle database with JServer option.  

Distributed Transaction Components and Scenarios

In reading the remainder of the distributed transactions section, it will be helpful to keep the following points in mind:

Distributed Transaction Concepts

Software that uses distributed transactions cannot use normal connection instance COMMIT, auto-commit, or ROLLBACK functionality, because all COMMIT or ROLLBACK operations in a distributed transaction must be coordinated. Any attempt to use the commit() or rollback() method or enable the auto-commit flag of a connection instance would result in a SQL exception.

When you use XA functionality, the transaction manager uses XA resource instances to prepare and coordinate each transaction branch and then to commit or roll back all transaction branches appropriately.

XA functionality includes the following key components:

Oracle XA Packages

Oracle supplies the following three packages that have classes to implement distributed transaction functionality according to the XA standard:

Classes for XA data sources, XA connections, and XA resources are in both the client package and the server package. (An abstract class for each is in the top-level package.) The OracleXid and OracleXAException classes are in the top-level oracle.jdbc.xa package, because their functionality does not depend on where the code is running.

In middle-tier scenarios, you will import OracleXid, OracleXAException, and the oracle.jdbc.xa.client package.

If you intend your XA code to run in the target Oracle database, however, you will import the oracle.jdbc.xa.server package instead of the client package.

If code that will run inside a target database must also access remote databases, then do not import either package--instead, you must fully qualify the names of any classes that you use from the client package (to access a remote database) or from the server package (to access the local database). Class names are duplicated between these packages.

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