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SDEP validation

The logical integrity of SDEP pointers can be verified when you execute the analysis function. You can specify an implicit value for the SDEP_VALIDATION keyword on the GLOBAL command. This keyword value is used by all analysis functions within the job step. To override the GLOBAL command value, explicitly specify the SDEP_VALIDATION keyword on the ANALYZE command. Any of the following modes of pointer validation can be selected by using the SDEP_VALIDATION keyword:

Related topics

Verifying-area-integrity

  • SDEP_VALIDATION=FULL constructs a complete cross-reference of every pointer and segment occurrence. The analysis function checks every pointer to ensure that a segment occurrence appears at the referenced location. The complete chain of sequential dependents that are associated with the root segment are identified. The analysis function verifies that each segment occurrence is referenced by one (and only one) pointer.
  • SDEP_VALIDATION=QUICK (the default) generates a checksum for all sequential dependents within the area. The checksum consists of the sum of the RBAs for each segment occurrence minus the RBAs of all SDEP pointers. Because there should be exactly one pointer to each segment, a non-zero value indicates a pointer problem.
  • SDEP_VALIDATION=OFF bypasses logical verification of sequential dependent pointers. The product still reads the SDEP control intervals to perform physical validation and to gather statistics.
  • SDEP_VALIDATION=NONE bypasses all processing of the SDEP control intervals. The product does not perform physical validation and does not gather statistics.

Active SDEP boundaries

The boundaries of the active sequential dependent portion of the area are defined by the logical begin (LB) and logical end (LE) values that are stored within the DMAC. The interpretation of these values depends on the type of analysis that is being executed.

During online analysis, other applications might be updating the database. When analysis starts, the LB value is obtained from the in-core copy of the DMAC that is used by the IMS control region. Because new SDEP segments can be added during analysis, BMC AMI Fast Path Online Analyzer for IMS ignores the LE in the DMAC and computes its own value for the LE as the LB plus one full cycle. This value is the largest that the LE could possibly become during the analysis. As the root segments are scanned, the 8-byte SDEP pointers are evaluated against this range. If the SDEP pointer is less than LB, it is treated as a null pointer (ignored). If the SDEP pointer is greater than the computed LE, it is reported as an error. BMC AMI Fast Path Online Analyzer for IMS obtains the updated values of the LB and LE from the in-core copy of the DMAC used by the IMS control region just before it scans the SDEP blocks.

During concurrent analysis, other applications might be updating the database. Because of this discrepancy window, which is characteristic of concurrent mode, the LB and LE values stored in the DMAC might be completely out of date by the time of the analysis. The analysis function scans SDEP segments only if they fall within the recorded boundaries. All 8-byte SDEP pointers outside of these boundaries are treated as null pointers (ignored). SDEP segments that are added after the DMAC has been obtained will cause SDEP pointer problems and/or orphaned segments to be reported.

Warning

Important

SDEP_VALIDATION=QUICK should not be used in concurrent mode.

Orphaned sequential dependents

If a root segment is deleted, its sequential dependent segments become 'orphans.' The segments still exist within the active sequential dependent portion of the area, but they are not referenced by a valid SDEP pointer.

The SDEP validation modes handle orphaned sequential dependents as follows:

  • SDEP_VALIDATION=NONE and SDEP_VALIDATION=OFF do not detect orphaned segments and will not report them as errors.
  • SDEP_VALIDATION=QUICK reports a pointer error if an orphaned segment exists. This mode of pointer validation cannot distinguish between orphaned segments and other problems, and it is not recommended if orphaned segments are known to exist in the area.
  • SDEP_VALIDATION=FULL identifies the individual segments as orphans.

You can use the ORPHANED_SDEP_MSG keyword to control the severity that is associated with this condition and the generation of messages.

Warning

Important

If you are running IMS version 6.1 or later, any SDEP with a time stamp less than the logical begin time stamp is treated as deleted. SDEP_VALIDATION=QUICK can report a pointer problem after SDEP scan/delete has been run. This condition occurs if a root segment is deleted and that root segment was previously the owner of one of the logically deleted SDEP segments.

 

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Fast Path Online Suite 4.1