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

FOR UPDATE OF COL6;
FETCH SENSITIVE FIRST ROWSET FROM C1 FOR 25 ROWS INTO
:COL1,:COL2,:COL3,:COL4,:COL5,:COL6;
UPDATE TABLE SET COL6 = :COL6+10 WHERE CURRENT OF C1;
DO I = 1 TO 39;
FETCH SENSITIVE NEXT ROWSET FROM C1 INTO
:COL1,:COL2,:COL3,:COL4,:COL5,:COL6;
UPDATE TABLE SET COL6 = :COL6 +10 WHERE CURRENT OF C1;
END;
(Same for Deletes)
Example 3-21 shows our multi-row FETCH and UPDATE program using a dynamic scrollable
cursor.
Example 3-21 Multi-row FETCH program of a dynamic scrollable cursor
DECLARE C1 SENSITIVE DYNAMIC SCROLL CURSOR WITH ROWSET POSITIONING WITH HOLD FOR SELECT
COL1, COL2, COL3, COL4, COL5,
COL6 FROM TABLE
WHERE COL2 < ‘ROWNNNNNNNNN’
FOR UPDATE OF COL6;
FETCH SENSITIVE FIRST ROWSET FROM C1 FOR 25 ROWS INTO
:COL1,:COL2,:COL3,:COL4,:COL5,:COL6;
UPDATE TABLE SET COL6 = :COL6+10 WHERE CURRENT OF C1;
DO I = 1 TO 39;
FETCH SENSITIVE NEXT ROWSET FROM C1 INTO
:COL1,:COL2,:COL3,:COL4,:COL5,:COL6;
UPDATE TABLE SET COL6 = :COL6 +10 WHERE CURRENT OF C1;
END;
(Same for Deletes)
The summary of this test case is:
► Use ISO (RS) as a bind parameter
These options protect data integrity (not for performance).
► 40 FETCHes followed by UPDATE on a rowset of 25 rows
► 40 FETCHes followed by DELETE on a rowset of 25 rows
► Qualified 1 million rows at open cursors
Multi-row FETCH and UPDATE or DELETE with a static cursor
We now move to the static updatable programs and apply multi-row update and delete
function. The results are shown in Table 3-8. We can see the same performance apply to this
type of program, the bulk of the performance overhead is attributable to the building of the
temporary table, resulting in negligible differences in DB2 class 2 elapsed and CPU times:
16.43 vs. 16.39 and 11.49 vs. 11.44.
Table 3-8 Multi-row FETCH and UPDATE or DELETE static
Static single row
UPDATE or
DELETE 1k each
Open 1M
Class 1 ET / CPU 16.44 / 11.51 16.40 / 11.45
Class 2 ET / CPU 16.43 / 11.49 16.39 / 11.44
Class 3 suspend 4.50 4.51
Static multi-row
UPDATE or DELETE 25 rows
x 40 times each
Open 1M
Chapter 3. SQL performance 105