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Introduction to DELTA PLUS history files

Two key components of DELTA PLUS are the DELTA PLUS Log and the DELTA PLUS History File. Both the Log and History File are pairs of formatted BSAM data sets used to record all DELTA PLUS updates to an IMS control region. Dual data sets are maintained for both the Log and the History File for recovery and reliability reasons because both are integral to the operation of DELTA PLUS. Both the dual Log data sets and the dual History File data sets must be available before any updates can be made to the IMS control region. Only one Log data set and History File data set is necessary for the Log and History File utilities to function.

When updates are made to the IMS control regions, BMCXLINK records the information associated with that update in the Log and History File data sets. The DELTA PLUS Log data sets contain a copy of the element that was executed and is used at IMS initialization and restart time to apply that update to the IMS system. The DELTA PLUS History File data sets contain a copy of the element, but also contain both the before- and after-image of the resource that was added, deleted, or revised. You can use the DELTA PLUS History File data sets for reporting and generating DELTA Lists and Stage-1 macros that update your SYSGEN input.

You can associate the DELTA PLUS Log and History File data sets with one or more IMS control regions. If you are using grouping (IMS shared queues, n-way data sharing, or grouping of similar systems), then the Log and History File data sets are used by all the IMS systems associated with the Group. Otherwise, they are associated with a single IMS system.

If you are using Groups, you must specify the Log and History File data set names on the Edit Group Options panel. Otherwise, you supply the data set names on the Edit IMSID Options panel. You can allocate and format the Log and History File data sets with panels that are explained in this section.

As with many IMS data sets, the placement of the DELTA PLUS Log and History File data sets should be given careful consideration. Both copies of the Log and History File should not be placed on the same DASD volume.

If the DELTA PLUS Log data sets are to be accessed from multiple CPUs in a shared-DASD environment, they must be protected from simultaneous modifications. A systems-level ENQUEUE using the 8-byte qname of DELTA PLUS and a 44-byte rname containing the Log dsname is used for brief periods to synchronize individual I/O operations within each system. This same ENQUEUE must be propagated to all systems in a shared-DASD environment using a product such as IBM’s GRS package or its equivalent.

Note

During the update process, DELTA PLUS Log data sets determine which DELTA PLUS changes are still active based on the IMS RESLIB being used. DELTA PLUS Log data sets should be backed up and protected in the same manner as the IMS RESLIB.

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DELTA PLUS log and history files




 

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