Planning and Designing XARs

For a great majority of the applications that use XARs, the process of implementing an XAR is simple and straightforward, requiring only that you define the XAR in Enterprise Server. For more information about defining an XAR, see To define an XAR for an enterprise server region.

However, for a more complicated application, you need to plan ahead and design the required XAR(s) to accommodate the complexity of such an application. This can require modification and recompilation of application source code, and compilation of XAR switch module source code, which is provided with our Enterprise Developer product. For more information on this process, see the Planning and Designing XARs topic in your Enterprise Developer documentation.

After building a Micro Focus RM switch module in Enterprise Developer, you can include it in an XAR definition in Enterprise Server. An XAR definition includes an xa_open string, which is where you include specific RM syntax for the underlying RM.

In addition to the RM-specific xa_open string syntax, we provide several options that enable you to fine-tune your XAR definitions to yield maximum efficiency when running applications on Enterprise Server.

XARs support the following RM switch module types:

• SQL Server
• IBM DB2
• Oracle
• Generic one-phase commit for ODBC
• EDB PostgreSQL (early adopter program)

Before configuring an XAR for an enterprise server region, we suggest that you consider the following:

Is the application using MFDBFH datastore(s) with transactional files but no embedded SQL?

If your application does not use any embedded SQL, you are ready to define your MFDBFH XAR(s) as described in Micro Focus Native Database File Handling and Enterprise Server Region Database Management.

Does the application require more than one XAR?

This depends on what database(es) the application accesses, and how the application interacts with it.

Does the application use MFDBFH datastore(s) with transactional files and/or have embedded SQL code that requires more than one XAR of the same RM switch module type?

If your application does not require more than one XAR of the same RM switch module type, and it does not use MFDBFH transactional files, then you are ready to define your XAR(s) in your enterprise server region .

However, in some scenarios, more than one XAR of the same type might be required for CICS, IMS, or IMTK container-managed service interface types that require embedded SQL database access. In another scenario, you might be using MFDBFH to store COBOL transactional files in a database along with executing embedded SQL applications. This likely requires recompilation of application source code. See Working with Multiple XARs for more information.

Is the embedded SQL application coded to use distinct XARs?

Typically, the SQL code is stored in distinct source code modules – some modules used with only one database, and others used with another. Code constructed in this fashion can be compiled for each program module using the XAID compiler directive option set to the value of the appropriate XAR ID. This eliminates the need to change code.

Is it best to use a static or dynamic RM switch module in an XAR?

This depends on how the XAR is accessed by the application(s). See RM Switch Module Registration for more information.

Should transactions be run locally or globally?

This depends on the types of transactions executed. See the LocalTX=(T|F) section in SQL xa_open string Configuration Options for more information.

When and how should user credentials be obtained and applied?

You can configure an XAR to use xa_open-supplied user credentials, or to determine user credentials based on the current user. For more information, see User Impersonation for CICS and JCL and the UserP=(T|F) section in SQL xa_open string Configuration Options.

Are any of the required XARs used in only batch jobs, and you are not using MFDBFH?

If so, consider identifying these XARs as batch-only resources, which can save considerable overhead, and eliminate the need to recompile using the XAID compiler directive option. For more information, see the BatchOnly=(T|F) section in SQL xa_open string Configuration Options.

How do Enterprise Server Service Execution Processes (SEPs) work with XARs?

Each CICS, IMS MPP, or IMTK container-managed SEP implicitly establishes a connection to each enabled XAR in the region; however, when an XAR definition contains BatchOnly=T, these SEPs do not interact with that XAR. For more information, see the BatchOnly=(T|F) section in SQL xa_open string Configuration Options.

Generally, batch SEPs are explicitly provided XAR connections with some variations possible, depending on the batch application. For more information on IKJEFT01 jobs or other batch utilities, see Emulations of Mainframe Utilities in your Enterprise Developer documentation. For more information on DSNALI or DSNRLI applications, see MVS Emulation in your Enterprise Developer documentation.

With IMS BMPs, you can get similar behavior if the DFSRRC00 PARM names a preferred XAR. In this case, IMS BMPs connect only to that XAR; otherwise, the application implicitly establishes a connection to each enabled XAR in the region.

How does CRCN work with XARs?

Because CRCN executes as a CICS transaction, it connect to all enabled XARs that are not defined with BatchOnly=T. At specified time intervals, CRCN pings database connections to ensure their integrity. If a connection is lost, CRCN attempts to reconnect at the next specified time interval. CRCN coordinates this activity with all online SEPs to minimize down time due to lost connections.

For more information about configuring an XAR, see To define an XA Resource (XAR) for an enterprise server region.