SMF DDCONS Specification
Within the SMFPRMxx member of SYS1.PARMLIB, the DDCONS option is used to control SMF EXCP section consolidation. The DDCONS option alleviates long shutdown times experienced by long running tasks that dynamically allocate and unallocate thousands of data sets.
rm
Within the SMFPRMxx member of SYS1.PARMLIB, the DDCONS option is used to control SMF EXCP section consolidation. The DDCONS option alleviates long shutdown times experienced by long running tasks that dynamically allocate and unallocate thousands of data sets.
Prior to the DDCONS option, EXCP section consolidation was an integral part of the SMF address space record-building process. This consolidation process saves space in the SMF records by consolidating segments with the same DDNAME and device address. The process is time consuming, however, especially at step and job end when thousands of dynamic allocations and unallocations have occurred.
DDCONS(YES) is the default and allows SMF EXCP segment consolidation to occur. DDCONS(NO) completely inactivates the consolidation process and allows the long-running tasks discussed above to shut down quickly. The down side of DDCONS(NO) is that SMF type 30 interval, step, and job end records can become significantly larger because of the increased numbers of EXCP segments recorded. The efficiency realized by the MVS SMF modules is offset by more space required by SMF dump data sets, longer processing time required by SMF dump routines, and longer processing times required by SMF post processors such as
MICS
.IBM has suggested a technique that gains the benefits of DDCONS(NO) while minimizing the down side of the larger SMF type 30 records. The technique is to use DDCONS(YES) as the default in SYS1.PARMLIB(SMFPRMxx), and to use the SET command to change the value dynamically to DDCONS(NO) when shutdown of long-running tasks is required. This strategy takes advantage of the fact that the DDCONS option sets a flag that is checked by SMF whenever EXCP consolidation would typically occur. Since the only time that SMF consolidation is time consuming is at step end, changing to DDCONS(NO) before shutdown allows EXCP segment consolidation to occur over the life of the step, but avoids the overhead that is incurred at step end.