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

DSNTIAUL without multi-row fetch
The results of the performance measurement between HPU and DB2 V8 DSNTIAUL are
summarized in Table 10-6 for the case where DSNTIAUL is not using multi-row fetch.
Table 10-6 HPU V2.2 vs. DB2 V8 DSNTIAUL (no multi-row)
Test case HPU V2.2 DB2 V8 DSNTIAUL % Difference
CPU Elapsed CPU Elapsed CPU Elapsed
Case 1 11.89 62 186.99 239 1472.66 285.48
Case 2 9.44 61 N/A N/A N/A N/A
Case 3 13.57 59 186.77 238 1276.34 303.38
Case 4 9.67 46 148.46 166 1435.26 260.86
Case 5 18.00 58 184.71 236 926.16 306.89
Case 6 13.93 46 146.33 163 950.46 254.34
Case 7 12.87 45 8.23 45 -36.05 0
Case 8 17.80 59 191.34 237 974.94 301.69
Case 9 12.51 45 1.75 22 -86.01 -51.11
Case 10 2.39 22 1.75 22 -26.77 0
Parallel 15.33 24 N/A N/A N/A N/A
DSNTIAUL can use an index so one would assume that DSNTIAUL may have a slight
advantage over the UNLOAD utility. However, the measurement cases illustrate otherwise.
DSNTIAUL was the larger consumer of CPU time and also typically had the longer elapsed
time, although two test cases showed DSNTIAUL being the better performer. However, when
you compare DSNTIAUL with HPU, the results are extraordinary. HPU outperformed
DSNTIAUL by using less than 10% of the CPU time.
Nearly every unload product is written with the assumption that users will unload a large
percentage of the available data, usually in the 50 - 100% range. In these instances, it may be
better to scan the entire table rather than using an index.
However, there are times when you may want to unload a small percentage of the rows,
perhaps 10 - 20% and you know an index exists that allows access to the table data. In this
case, a scan of the table may result in worse performance than if an SQL statement were
executed directly by DB2; you may then see better performance with DSNTIAUL than with
HPU.
If you are using HPU and you have a query where using the SQL might perform better than a
table space scan, use the DB2 FORCE parameter. This causes HPU to pass the query to
DB2 for execution and may result in better performance. This is evident in case 10 which is
the same as case 9 except DB2 FORCE is used. The results are once again dramatic; there
is a 6X improvement in CPU time with the exact same elapsed time.
Note: DSNTIAUL cannot unload from an image copy data set so the results are N/A for
case 2.
Chapter 10. Performance tools 375