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

► Measurement data collected with DB2 Performance Expert V2
– Accounting trace class 1,2,3
– Statistics trace class 1,3,4,5,6,8
Measurement methodology
► One table defined in one segmented table space is used for all measurements.
► All the measurements involved only table space scans (1 index is defined).
► First time effect
Bring up the DB2 subsystem before each measurement to clear the data in the buffer pool,
eliminating the inconsistency of different buffer hit ratios from run to run.
► No concurrency issues
There is no other program accessing the table space during the measurements.
► Read programs are bound with ISOLATION(CS) and CURRENT DATA(NO)
► Update programs are bound with ISOLATION(RS)
► Each program issues one commit after closing the cursor
Measurement cases
► Read cursor (single row fetch) - Static vs. dynamic
► Update cursor (single row fetch and update) - Static vs. dynamic
► Multi-row FETCH using static or dynamic cursors - Single row vs. multi-row
► Multi-row FETCH and UPDATE or DELETE using static or dynamic cursors - Single row
vs. multi-row
3.12.4 Test description and study
The following is the description of our four test cases and study from our measurement data.
The programs are all written in PL/I.
Test scenario 1: Read cursor - Static vs. dynamic
This test uses two types of FETCH programs. The intent is to compare insensitive with
asensitive cursors for static and dynamic.
The first program, shown in Example 3-14, declares an insensitive scrollable cursor to retrieve
data from the table. It means this program is strictly read-only (does not allow positioned
update and delete).
Example 3-14 Read program of static cursor
DECLARE C1 INSENSITIVE 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 INSENSITIVE NEXT C1 INTO
:COL1,:COL2,:COL3,:COL4,:COL5,
:COL6,:COL7,:COL8,:COL9,:COL10;
END;
98 DB2 UDB for z/OS Version 8 Performance Topics