Subset pointers

Subset pointers help you avoid unproductive get calls when you need to access the last part of a long segment chain.

These pointers divide a chain of segment occurrences under the same parent into two or more groups, or subsets. You can define as many as eight subset pointers for any segment type, dividing the chain into as many as nine subsets. Each subset pointer points to the start of a new subset.

Restrictions:  When you unload and reload a DEDB containing subset pointers, IMS does not automatically retain the position of the subset pointers. When unloading the DEDB, you must note the position of the subset pointers, storing the information in a permanent place. (For example, you could append a field to each segment, indicating which subset pointer, if any, points to that segment.) Or, if a segment in a twin chain can be uniquely identified, identify the segment a subset pointer is pointing to and add a temporary indication to the segment for reload. When reloading the DEDB, you must redefine the subset pointers, setting them to the segments to which they were previously set.