During installation of CA Datacom, a default DBMSTLST module is assembled. This default assemble determines the various buffers that are allocated for use when running DBUTLTY. For many of the important database functions performed by DBUTLTY, the buffers specified by DBMSTLST determine the performance metrics of the DBUTLTY execution, such as, elapsed time, I/Os, and CPU usage.
The default buffer allocations for DBMSTLST are quite small to keep the amount of 31-bit space that is necessary to execute the DBUTLTY program at a minimum. However, in most sites today, there is adequate 31-bit memory available and, using these small default allocations is wasting resources and slowing performance of the DBUTLTY functions.
The following are the default buffer allocations for DBMSTLST:
CXXNO=10 DATANO=15 DXXNO=16 IXXNO=8
During various testing, we have determined that different DBUTLTY functions perform better with additional buffers specifications. You can experiment with having different copies of the DBMSTLST module stored in different user libraries. Then, at DBUTLTY execution time, use the library with the DBMSTLST that performs best for that utility function.
For most sites, the multiple DBMSTLST module approach is too complicated and time consuming. While the amount of buffers needed by each DBUTLTY function varies, consider the following as a minimal number of buffers in DBTMLST :
CXXNO=10 DATANO=128 DXXNO=64 IXXNO=32
For sites with available space, some additional performance can be gained with the following slightly higher buffers numbers:
CXXNO=10 DATANO=256 DXXNO=512 IXXNO=256
After a new installation process, immediately rerun the install job that builds the DBMSTLST module and specify the expanded buffer setting you select.
Business Value
Having the additional buffer sizes when not needed does not slow the processing of the utility. However, having the additional buffers for the functions that need them could greatly improve processing time and resource consumption for DBUTLTY.
Additional Considerations
Certain DBUTLTY functions, such as BACKUP, EXTRACT, and REORG, allow the specification of the SEQBUFS= in the DBUTLTY control cards. For these utility functions, specifying a value for SEQBUFS overrides the number of buffers specified in the DBMSTLST DATANO parameter. In z/OS sites, if the SEQBUFS is not specified, the value is set to 128. The BACKUP, EXTRACT, and REORG functions are guaranteed to have at least 128 data buffers for their processing.
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