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

The second program, shown in Example 3-15, declares an ASENSITIVE SCROLLABLE
cursor, which is the default in DECLARE CURSOR of V8. ASENSITIVE scrollable cursors
allow DB2 to choose the maximum sensitivity of a cursor as possible, and in this case the
following SELECT statement does not indicate read-only cursor (that is, a UNION or UNION
ALL, ORDER BY, FOR READ ONLY, FOR FETCH ONLY) so DB2 determines dynamic as the
maximum sensitivity.
Example 3-15 Read program of dynamic cursor
DECLARE C1 ASENSITIVE SCROLL CURSOR WITH HOLD FOR SELECT
COL1, COL2, COL3, COL4, COL5,
COL6, COL7, COL8, COL9, COL10
FROM TABLE
WHERE COL2 < ‘ROWNNNNNNNNN’;
DO I = 1 TO 50000;
FETCH NEXT C1 INTO
:COL1,:COL2,:COL3,:COL4,:COL5,
:COL6,:COL7,:COL8,:COL9,:COL10;
END;
The measurements have been done varying the number of FETCHes and the number of
qualified rows opened as a cursor. This is done to show how the performance is affected by
different result set sizes (the size of the temporary table in the case of the static cursor
examples). The summary of our test cases is:
► Use ISO(CS) and CD(NO) as a bind parameter
For the read program these options provide maximum performance and concurrency.
► 50k or 10 FETCHes
► FETCH of 10 columns for a total of 50 bytes
► Qualified 1 million or 100k rows opened as a cursor
In the program shown in Example 3-17, we specified 1,000,000 or 100,000 in
‘ROWnnnnnnnnn’ row-id.
Table 3-4 shows the test results for static and dynamic cursors from the output of the DB2 PE
trace record.
Table 3-4 Read cursor - Static vs. dynamic
Trace data Static Dynamic
Class 1
ET/CPU
Class 2
ET/CPU
Class 3
suspend
Fetch 50k
Open 1M
Fetch 10
Open 1M
Fetch 50k
Open 100k
Fetch 50k
Open 1M
Fetch 10
Open 1M
Fetch 50k
Open 100k
17.33/12.57 16.76/11.91 5.73 / 2.57 0.973/0.879 0.072/0.011 0.971/0.885
17.21/12.44 16.75/11.90 5.61/ 2.43 0.849/0.743 0.069/0.009 0.849/0.748
4.29 4.4 3.02 0.058 0.054 0.059
Since the primary interest in this performance study is the DB2 Class 2 CPU time and
elapsed time, the PL/I programs were designed with minimum Class 1 (application) CPU and
elapsed time in mind. Therefore, the Class 1 CPU and elapsed times in all measurements is
composed mainly of the DB2 Class 2 CPU and elapsed times. The typical business
Chapter 3. SQL performance 99