DB2 UDB for z/OS Version 8 Performance Topics - IBM Redbooks

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6.2.2 Conclusion
Figure 6-4 LOAD with default SORTKEYS
In V8, SORT parameters are always enforced, this provides performance improvement
because of shorter I/O in index key sort and parallel index build. However, if the index keys
are already sorted in perfect order or there is only one index in the table space, SORTKEYS
does not provide much advantage.
6.2.3 Recommendations
LOAD with default SORTKEYS performance
V7 one index V8 one index V7 2 indexes V8 2 indexes V7 6 indexes V8 6 indexes
CPU Elapsed time
You take advantage of the high performance of SORT parameters, if more than one index
exists in a table space.
To improve SORT performance during LOAD, you can also specify the appropriate value in
the SORTKEYS option. The SORTKEYS option is an estimate of the number of keys for the
job to sort, so that the index keys are passed in memory and avoid I/Os to the work file. To
read how to estimate the number of keys, refer to topic Improved performance with
SORTKEYS in DB2 UDB for z/OS Version 8 Utility Guide and Reference, SC18-7427.
Also you should not specify sort work data set like SORTWKxx DD statements, while using
SORTKEY, make sure DB2 uses memory instead of sort work data sets.
See the informational APAR II14047 for useful information on the changes of using DFSORT
by DB2 V8 utilities.
Note: With PTF UK03983 for APAR PK04076, LOAD sort is avoided for LOAD SHRLEVEL
NONE if data is sorted and only one index exists.
Chapter 6. Utilities 269