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

From these measurements we observe that DSNTEP2 under V8 uses 3% more CPU than
DSNTEP2 under V7. DSNTEP4, by exploiting multi-row fetch, uses 10 to 30% less CPU
depending on the number of rows specified.
Class 1 CPU time (MSEC)
1200
800
400
0
DSNTIAUL
5 columns 20 columns
DSNTIAUL is a sample assembler unload program. With DB2 V8, it has been enhanced to:
► Handle SQL statements up to 2 MB in size
► Use multi-row FETCH
You can specify an additional invocation parameter called “number of rows per fetch”. It
indicates the number of rows per fetch that DSNTIAUL is to retrieve. You can specify a
number from 1 to 32,767.
In Figure 9-4 we show the impact of using multi-row fetch in V8, vs. single row fetch in V7, for
5 and for 20 columns. In this test, on average, the DSNTIAUL improvement is 40%.
348 DB2 UDB for z/OS Version 8 Performance Topics
Multi-row Fetch support of DSNTEP4
(10,000 rows fetched / test)
293
937
301
955
190
846
V7
V8
DSNTEP2
V8
DSNTEP2
DSNTEP4
Figure 9-3 Multi-row fetch support of DSNTEP4
V8 DSNTEP4 :
automatic exploitation of
MR Fetch
default MR=100 rows
10% to 35% CPU time
reduction vs. V7 DSNTEP2
V8 DSNTEP2 :
w/o MR exploitation
within 3% CPU time
regression vs. V7 DSNTEP2