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

The accounting class 1 and class 2 CPU and elapsed times for triggers, stored procedures,
and user-defined functions are accumulated in separate fields and exclude the time
accumulated in other nested activity.
For more details, see Chapter 24. Analyzing performance data in the DB2 UDB for z/OS
Version 8 Administration Guide, SC18-7413.
Inserts activated the trigger 100 times but WHEN condition true once
Figure 3-41 shows the measurement when 100 inserts activated the trigger 100 times but 99
times the WHEN condition evaluated false.
100 Inserts activated Trigger 100 times
but WHEN condition evaluated to true only once
SQL DML TOTAL
-------- --------
SELECT 100
INSERT 100
UPDATE 1
DELETE 0
DESCRIBE 100
DESC.TBL 0
PREPARE 100
OPEN 0
FETCH 0
CLOSE 0
DML-ALL 401
DB2 V7 - workfile activity
BP1 BPOOL ACTIVITY TOTAL
--------------------- --------
BPOOL HIT RATIO (%) 100
GETPAGES 600
GETPAGES-FAILED 0
BUFFER UPDATES 400
SYNCHRONOUS WRITE 0
SYNCHRONOUS READ 0
SEQ. PREFETCH REQS 100
LIST PREFETCH REQS 0
DYN. PREFETCH REQS 0
PAGES READ ASYNCHR. 0
Figure 3-41 SQL and BPOOL activity - Trigger with WHEN true only once
DB2 V8 - workfile activity
BP1 no use reported
The execution of 100 inserts caused the shown amount of work files activity, to actually
execute the update in just one case. The 100 SELECTs shown in the accounting are due to
the WHEN condition which causes 100 SELECTs to a DUMMY TABLE.
In V7 the buffer pool BP1 used by the work files indicates 600 getpages and 400 buffer
updates. In this case there was no activity related to the work files in V8.
Figure 3-42 compares the CPU times when executing triggers in V7 and V8 and the WHEN
condition is evaluated to true only once.
The figure shows that the CPU used for non-nested was reduced 8.3% and the CPU to
execute the trigger is reduced by a more visible 24%.
Chapter 3. SQL performance 89