Further Considerations

Whilst the CRCN transaction is monitoring the resource managers, you should consider the following:

Static or dynamic XA registration?

Dynamic XA is more efficient than static XA, because the xa transaction is effectively started when the application accesses the resource manager; however static XA might be required if:

• the application is not intercepting lost connections, or does not take appropriate action to signal to the system administrator that the connection to an RM has been lost, such as when a transaction ABENDs, or sends severe errors to the console; or:
• there is a possibility that the connection to an RM is lost on a single SEP.

  If this SEP is running CRCN, CRCN will detect the connection loss and send a request to all SEPs to disconnect/reconnect to the RM.

  If this SEP is running an application, the application should detect the connection loss, abend, and consequently signal the RM failure to the administrator. However, this SEP cannot signal to CRCN that the connection has been lost, because with dynamic registration, the RM must register itself with the TM (in this case, Enterprise Server). If the connection to this RM has been lost, the RM will not register, and the enterprise server region will not attempt any xa-verb processing against this RM, and therefore no error can be raised.

Long-running tasks

If there are long-running tasks in the system, ensure that they regularly pass the control back to the system. For a CICS transaction, this means executing an EXEC CICS so that the system gets the opportunity to process the xa request sent to each process by CRCN. Failure to pass control back to the system causes the process emitting the request to wait until its request has been processed in all SEPs. If these requests are not processed immediately, CRCN waits until they are.