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Trail map 1. Installation Content 2. The Sample Application 3. Deploying and Testing the Sample Application 4. Making the Sample Application Persistent 5. Recovery From Failure 6. Where Next? Navigation Home Additional Trails Distributed Transaction Processing The X/Open DTP Model The OMG OTS Model Transactions in J2EE Configuring ATS Configuring the Recovery Manager ORB Portability Transactional Object For Java
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Overview of the X/Open DTP model The X/Open Distributed Transaction Processing (DTP) model is a distributed transaction processing model proposed by the Open Group, a vendor consortium. This model is a standard among most of the commercial vendors in transaction processing and database domains. This model consists of the follwng components (illustrated in Figure 1) an Application Program (AP), which defines transaction boundaries and specifies actions that constitute a transaction Resource Managers (RMs) such as databases or file access systems, which provide access to resources a Transaction Manager (TM), which assigns identifiers to transactions, monitors their progress, and takes responsibility for transaction completion and for coordinating failure recovery Communication Resource Managers (CRMs), which control communication between distributed applications within or across TM domains Figure 1 - The X/Open DTP model ##### Interface between functional components There are six interfaces between software components in the X/Open DTP model. AP-RM. The AP-RM interfaces give the AP access to resources. X/Open interfaces, such as SQL and ISAM provide AP portability. The X/Open DTP model imposes few constraints on native RM APIs. The constraints involve only those native RM interfaces that define transactions. AP-TM. The AP-TM interface (the TX interface) provides the AP with an Application Programming Interface (API) by which the AP coordinates global transaction management with the TM. For example, when the AP calls tx_begin( ) the TM informs the participating RMs of the start of a global transaction. After each request is completed, the TM provides a return value to the AP reporting back the success or otherwise of the TX call. TM-RM. The TM-RM interface (the XA interface) lets the TM structure the work of RMs into global transactions and coordinate completion or recovery. The XA interface is the bidirectional interface between the TM and RM. The functions that each RM provides for the TM are called the xa_*() functions. For example the TM calls xa_start( ) in each participating RM to start an RM-internal transaction as part of a new global transaction. Later, the TM may call in sequence xa_end() xa_prepare( ) and xa_commit() to coordinate a (successful in this case) two-phase commit protocol. The functions that the TM provides for each RM are called the ax_*( ) functions. For example an RM calls ax_reg( ) to register dynamically with the TM. TM-CRM. The TM-CRM interface (the XA+ interface) supports global transaction information flow across TM Domains. In particular TMs can instruct CRMs by use of xa_*() function calls to suspend or complete transaction branches, and to propagate global transaction commitment protocols to other transaction branches. CRMs pass information to TMs in subordinate branches by use of ax_*( ) function calls. CRMs also use ax_*( ) function calls to request the TM to create subordinate transaction branches, to save and retrieve recovery information, and to inform the TM of the start and end of blocking conditions. AP-CRM. X/Open provides portable APIs for DTP communication between APs within a global transaction. The API chosen can significantly influence (and may indeed be fundamental to) the whole architecture of the application. For this reason, these APIs are frequently referred to in this specification and elsewhere as communication paradigms.In practice, each paradigm has unique strengths, so X/Open offers the following popular paradigms: the TxRPC interface (see the referenced TxRPC specification) the XATMI interface (see the referenced XATMI specification) the CPI-C interface (see the referenced CPI-C specification). X/Open interfaces, such as the CRM APIs listed above, provide application portability. The X/Open DTP model imposes few constraints on native CRM APIs. CRM-OSI TP. This interface (the XAP-TP interface) provides a programming interface between a CRM and Open Systems Interconnection Distributed Transaction Processing (OSI TP) services. XAP-TP interfaces with the OSI TP Service and the Presentation Layer of the seven-layer OSI model. X/Open has defined this interface to support portable implementations of application-specific OSI services. The use of OSI TP is mandatory for communication between heterogeneous TM domains. For details of this interface, see the referenced XAP-TP specification and the OSI TP standards. Although the aim of the Open Group was providing portable interfaces, only the XA interface appears to be accepted and implemented by a wide range of vendors. XA is a bidirectional interface between resource managers and transaction managers. This interface specifies two sets of functions. The first set, called as xa_*() functions are implemented by resource managers for use by the transaction manager. Table 1 - XA Interface of X/Open DTP Model for the transaction manager
Function | Purpose
xa_start | Directs a resource manager to associate the subsequent requests by application programs to a transaction identified by the supplied identifier.
xa_end | Ends the association of a resource manager with the transaction.
xa_prepare | Prepares the resource manager for the commit operation. Issued by the transaction manager in the first phase of the two-phase commit operation.
xa_commit | Commits the transactional operations. Issued by the transaction manager in the second phase of the two-phase commit operation.
xa_recover | Retrieves a list of prepared and heuristically committed or heuristically rolled back transactions
xa_forget | Forgets the heuristic transaction associated with the given transaction identifier
The second set of functions, called as ax_*() functions, are implemented by the transaction manager for use by resource managers. Table 2 - XA Interface of X/Open DTP Model for resource managers
Function | Purpose
ax_reg() | Dynamically enlists with the transaction manager.
ax_unreg() | Dynamically delists from the transaction manager.
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