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EJB Distributed Transactions

Learn about EJB transactions, distributed across multiple sites, ensuring ACID properties. Dive into programmatic vs. declarative demarcation techniques, isolation levels, and updates to multiple databases.

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EJB Distributed Transactions

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  1. EJB Transactions

  2. Distributed Transactions • EJB allows application developers to write applications that atomically update data in multiple databases • may be distributed across multiple sites • sites may use EJB Servers from different vendors • The enterprise Bean Provider and the client application programmer are not exposed to the complexity of distributed transactions.

  3. ACID Properties • Atomicity. In a transaction involving two or more discrete pieces of information, either all of the pieces are committed or none are. • Consistency. A transaction either creates a new and valid state of data, or, if any failure occurs, returns all data to its state before the transaction was started. • Isolation. A transaction in process and not yet committed must remain isolated from any other transaction. • Durability. Committed data is saved by the system such that, even in the event of a failure and system restart, the data is available in its correct state.

  4. Programmatic vs. Declarative Transaction Demarcation • Bean-managed transaction demarcation • enterprise bean code demarcates transactions using javax.transaction.UserTransaction • accesses between UserTransaction.begin and UserTransaction.commit calls are part of a transaction • Container-managed transaction demarcation • container demarcates transactions per instructions provided by the Application Assembler in the deployment descriptor

  5. Container-Managed Transaction Demarcation • NotSupported - container invokes enterprise Bean method with an unspecified transaction context • Required - container invokes enterprise Bean method with a valid transaction context • Supports • If the client calls with a transaction context, same as Required • If the client calls without a transaction context, same as NotSupported

  6. Container-Managed Transaction Demarcation - 2 • RequiresNew - container invokes enterprise Bean method with a new transaction context • Mandatory - container invokes enterprise Bean method with the client’s transaction context • Never - container invokes an enterprise Bean method without a transaction context • client is required to call without a transaction context

  7. Isolation Levels • Describes the degree to which access to a resource manager by a transaction is isolated from other concurrently executing transactions • Part of the EJB 1.0 specification -- has been eliminated in EJB 1.1! • API for managing an isolation level is resource-manager specific • bean provider may specify the same or different isolation levels for each resource manager

  8. Updates to Multiple Databases Client Server X Y DB A DB C DB B • Multiple databases • Single transaction

  9. Updates to Multiple Databases in Same Transaction EJB Server EJB Server client Y X DB B DB A

  10. EJB Server client DB X begin commit TP Y EJB Server Updates to Multiples Databases on Multiple Servers

  11. Two-Phase Commit (2PC) • JDBC 1.2 does not support XA two phase commit • impossible for an EJB server using JDBC 1.2 to directly support for distributed transactions • Distributed transactions requires the existence of database drivers that support XA 2PC • in most cases, developers are relying on the vendor to provide database drivers

  12. Relationship to JTA and JTS • Java Transaction API (JTA) • Java Transaction Service (JTS)

  13. Java Transaction API (JTA)

  14. Java Transaction API (JTA) • JTA specifies the interfaces between a transaction manager and the other parties involved in a distributed transaction processing system • application programs • resource managers • application server

  15. Java Transaction Service (JTS) • Java binding of the CORBA Object Transaction Service (OTS) 1.1 specification • Provides transaction interoperability using the standard IIOP protocol for transaction propagation between servers • Intended for vendors who implement transaction processing infrastructure for enterprise middleware • may be used by an EJB Server vendor as the underlying transaction manager

  16. EJB Relationship to JTA and JTS • Does not require the EJB Container to support the JTS interfaces • Requires that the EJB Container support the javax.transaction.UserTransaction • interface defined in JTA • Does not require support for • JTA resource manager (XAResource) • application server interfaces

  17. Summary • Transaction-based systems can be implemented simply using EJB • Transactions are not simple -- transaction behavior is affected by choice of • session bean or entity bean • statefull or stateless session bean • bean-managed vs. container-managed transaction demarcation • transaction attributes • lots more stuff!

  18. References • [ 1 ] Java Transaction API (JTA). http://java.sun.com/products/jta. • [ 2 ] Java Transaction Service (JTS). http://java.sun.com/products/jts. • [ 3 ] OMG Object Transaction Service. http://www.omg.org/corba/sectrans.htm#trans.

  19. For More Information... • Telephone 412 / 268-5800 • Fax 412 / 268-5758 • Email rcs@sei.cmu.edu • World Wide Web http://www.sei.cmu.edu • U.S. mail Customer Relations Software Engineering Institute Carnegie Mellon Pittsburgh, PA 15213-3890

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