IBM SC34-7012-01 manual Implications of interval control START requests, Procedure

Procedure

vArrange for all transactions to access files in a sequence agreed in advance. This could be a suitable subject for installation standards. Be extra careful if you allow updates through multiple paths.

vEnforce explicit installation enqueueing standards so that all applications do the following:

1.Enqueue by the same character string

2.Use those strings in the same sequence.

vAlways access records within a file in the same sequence. For example, where you update several file or database records, ensure that you access them in ascending sequence.

Ways of doing this include the following:

1.The terminal operator always enters data in the existing data set sequence.

This method requires special terminal operator action, which may not be practical within the constraints of the application. (For example, orders may be taken by telephone in random product number sequence.)

2.The application program first sorts the input transaction contents so that the sequence of data items matches the sequence on the data set.

This method requires additional application programming, but imposes no external constraints on the terminal operator or the application.

3.The application program issues a SYNCPOINT command after processing each data item entered in the transaction.

This method requires less additional programming than the second method. However, issuing a synchronization point implies that previously processed data items in the transaction are not to be backed out if a system or transaction failure occurs before the entire transaction ends. This may not be valid for the application, and raises the question as to which data items in the transaction were processed and which were backed out by CICS. If the entire transaction must be backed out, synchronization points should not be issued, or only one data item should be entered per transaction.

Of the three methods, the second (sorting data items into an ascending sequence by programming) is most widely accepted.

If you allow updates on a data set through the base and one or more alternate index (AIX) paths, or through multiple AIX paths, sequencing record updates may not provide protection against transaction deadlock. You are not protected because the different base key sequences will probably not all be in ascending (or descending) order. If you do allow updates through multiple paths, and if you need to perform several record updates, always use a single path or the base. Define such a procedure in your installation standards.

Implications of interval control START requests

Interval control START requests initiate another task—for example, to perform updates accumulated by the START-issuing task; this allows the user to continue accumulating data without waiting for the updates to be applied.

The PROTECT option on a START request ensures that, if the task issuing the START fails during the unit of work, the new task will not be initiated, even though its start time may have passed. (See “START requests” on page 76 for more information about the PROTECT option.)

Consider also the possibility of a started task that fails. Unless you include abend processing in the program, only the master terminal will know about the failure.

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