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

Multi-row FETCH with a static cursor
We apply multi-row fetching to the read programs and check how much we can improve
performance. The 50,000 individual fetch case (listed in Case 1 in Table 3-4 on page 99) is
compared with a multi-fetch program that fetches 100 rows at a time 500 times (listed in
Table 3-6).
Since the 1 million row temporary table is built row by row, regardless of the fetch
implementation, and since we learned that this activity takes up the majority of CPU cycles in
the prior static cursor measurements (whether read or updatable programs), using the
multi-fetch implementation has only improved the DB2 class 2 CPU time by 3% (12.44 vs.
12.05) and the DB2 class 2 elapsed time by 2% (17.21 vs. 16.85).
Table 3-6 Multi-row FETCH static
Multi-row FETCH with a dynamic cursor
The results of applying the same multi-fetch implementation to the dynamic cursor model are
listed in Table 3-7. If we compare them to those of the 50,000 individual fetch program in
Table 3-4 on page 99, Case 1, we see a large performance improvement. Both the DB2 class
2 elapsed time and CPU time have been cut in half: 0.743 vs. 0.340 and 0.849 vs. 0.426.
Reducing the number of trips between the application and database engine by a factor of 100
(50,000 fetches vs. 500 multi-fetches) accounts for the performance gains observed.
Table 3-7 Multi-row FETCH dynamic
Test scenario 4: Single row vs. multi-row FETCH & UPDATE or DELETE
In this case we explored multi-row FETCH followed by UPDATE or DELETE. The multi-row
write programs for update and delete use a row set size of 25 rows and perform 40 fetches
each. The multi-row updates or deletes are also performed 25 rows at a time. So it is
equivalent to 1,000 rows FETCHed and UPDATEd or DELETEd. We then compare it against
single row FETCH and UPDATE or DELETE of 1,000 rows which was done as part of test
scenario 2. Example 3-20 shows our multi-row FETCH and UPDATE program using a static
scrollable cursor. Multi-row FETCH and DELETE programs are prepared similarly.
Example 3-20 Multi-row FETCH program of a static scrollable cursor
DECLARE C1 SENSITIVE STATIC SCROLL CURSOR WITH ROWSET POSITIONING WITH HOLD FOR SELECT
COL1, COL2, COL3, COL4,
COL5,COL6 FROM TABLE
WHERE COL2 < ‘ROWNNNNNNNNN’
104 DB2 UDB for z/OS Version 8 Performance Topics
Static single row
FETCH 50,000
Open 1 million
Class 1 ET / CPU 17.33 / 12.57 16.85 / 12.06
Class 2 ET / CPU 17.21 / 12.44 16.84 / 12.05
Class 3 suspend 4.29 4.34
Static single row
FETCH 50,000
Open 1 million
Class 1 ET / CPU 0.973 / 0.879 0.440 / 0.343
Class 2 ET / CPU 0.849 / 0.743 0.426 / 0.340
Class 3 suspend 0.058 0.064
Static multi-row
FETCH 100 rows 500 times
Open 1 million
Static multi-row
FETCH 100 rows 500 times
Open 1 million