IBM Information Management System (IMS)

 View Only

 Does IMS use an algebraic or logical comparison when deciding where to insert a dependent segment with a key field defined with SEQ,U?

Don Leahy's profile image
Don Leahy posted Thu June 19, 2025 10:41 AM

We have a DEDB with a direct dependent segment that typically has many occurrences.  The segment has a key field defined as SEQ,U in the DBD.  It uses TYPE=P.

We are experimenting with the idea of using a negative number for the key, but IMS seems to ignore the sign of the field.  As a result, a segment with key  x'0002003011303013214035371D' is inserted after a segment with  x'0002002111902324021906632D'   This makes sense if the comparison is logical not algebraic (which would take the sign into account).

Thanks.  We are not married to this idea; if IMS does indeed use a logical comparison then we will try something else. 

Don Leahy's profile image
Don Leahy posted Tue July 08, 2025 11:38 AM

We are not pursuing this approach any more.  The intent was to store the segments in descending date/time sequence.  We can achieve this by converting the key to its 9s complement before the ISRT call.   This is just a proof of concept for us; the objective is to speed up direct dependent segment ISRTS when the twin chain is long.      

Related Content