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

Single row vs. multi-row FETCH
To test multi-row FETCH in static and dynamic scrollable cursors, we used two PL/I programs.
BIND options and sensitivity options for the DECLARE CURSOR and FETCH statements are
kept the same as the single row read cursor program. Each of the multi-row read programs
fetches 100 rows (the row set size) with a single fetch and performs a total of 500 fetches to
be compared against the original read program doing 50,000 individual fetches.
Example 3-18 shows a sample of our program for multi-row FETCH using a static scrollable
cursor.
Example 3-18 Multi-row FETCH program of a static scrollable cursor
DECLARE C1 INSENSITIVE SCROLL CURSOR WITH ROWSET POSITIONING WITH HOLD FOR SELECT
COL1, COL2, COL3, COL4, COL5,
COL6, COL7, COL8, COL9, COL10
FROM TABLE
WHERE COL2 < ‘ROWNNNNNNNNN’;
FETCH INSENSITIVE FIRST ROWSET FROM C1 FOR 100 ROWS INTO
:COL1,:COL2,:COL3,:COL4,:COL5,
:COL6,:COL7,:COL8,:COL9,:COL10;
DO I = 1 TO 499;
FETCH INSENSITIVE NEXT ROWSET
C1 INTO
:COL1,:COL2,:COL3,:COL4,:COL5,
:COL6,:COL7,:COL8,:COL9,:COL10;
END;
Example 3-19 shows a sample of our program for multi-row FETCH using a dynamic
scrollable cursor.
Example 3-19 Multi-row FETCH program of a dynamic scrollable cursor
DECLARE C1 ASENSITIVE SCROLL CURSOR WITH ROWSET POSITIONING WITH HOLD FOR SELECT
COL1, COL2, COL3, COL4, COL5,
COL6, COL7, COL8, COL9, COL10
FROM TABLE
WHERE COL2 < ‘ROWNNNNNNNNN’;
FETCH FIRST ROWSET FROM C1 FOR
100 ROWS INTO
:COL1,:COL2,:COL3,:COL4,:COL5,
:COL6,:COL7,:COL8,:COL9,:COL10;
DO I = 1 TO 499;
FETCH NEXT ROWSET
C1 INTO
:COL1,:COL2,:COL3,:COL4,:COL5,
:COL6,:COL7,:COL8,:COL9,:COL10;
END;
In this test case we have not measured a different number of FETCHes or a different number
of qualified rows, because the purpose of this case is the comparison of multi-row FETCH
with single row FETCH. The summary of this test case is:
► Use ISO(CS) and CD(NO) as a bind parameter
These options provide maximum performance and concurrency for read programs.
► 100 rows (rowset) of 500 FETCHes
► Qualified 1 million at open cursor
Chapter 3. SQL performance 103