6. DATA SOURCES › 6.2 Data Collector and Processing Considerations › 6.2.1 SMF Recording Options › 6.2.1.5 DDCONS Specification

6.2.1.5 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.

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 CA 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 normally
occur.  Since the only time that SMF consolidation is time
consuming is at step end, changing to DDCONS(NO) just prior
to shutdown allows EXCP segment consolidation to occur over
the life of the step, but avoids the overhead that is
incurred at step end.