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

Test case HPU V2.2 DB2 V8 UNLOAD % Difference
CPU Elapsed CPU Elapsed CPU Elapsed
Parallel 15.33 24 68.08 31 344.09 29.16
Even if an index is available, the UNLOAD utility does not take advantage of it.
You can see that in all cases, HPU outperforms the DB2 V8 UNLOAD utility in CPU time.
However, in most cases, the UNLOAD utility elapsed time is slightly better.
In case 2, where the unload is performed using an image copy, the UNLOAD utility takes
almost 4 times more CPU than HPU although the elapsed time for the UNLOAD utility is
almost 7% better than HPU.
In case 4, the elapsed time for both HPU and the UNLOAD utility is the same, but HPU
outperforms the UNLOAD utility using 1/4 the CPU time.
When parallelism is used, HPU outshines the DB2 UNLOAD utility. The CPU time for the
UNLOAD utility is almost 3.5 times more than HPU and the elapsed time for the UNLOAD
utility is 29% higher than HPU.
Case 10 is the same as Case 9 except the measurement for HPU involved the use of DB2
FORCE. This HPU parameter indicates that DB2 must be used to extract the requested rows.
This is generally preferred when the SELECT statement uses a filtering predicate that is
efficiently processed through SQL, and the filter factor is high.
Note: The DB2 UNLOAD utility in case 1 unloads the entire table space. Case 3 unloads
the entire table; since it is the same as case 1, the Unload is not reported for case 3.
The graphical depiction of the results is in Figure 10-1 and Figure 10-2. The results are
dramatic for the DB2 HPU tool.
Figure 10-1 shows Case 1 through Case 5.
Chapter 10. Performance tools 373