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

► The elapsed time is 22 times smaller (about 95%) and CPU time 68 times smaller (about
98%) when we compare V7 DEGREE(1) with V8 using the MQT.
Figure 3-11 Query rewrite for simple query
Query rewrite for join
Figure 3-12 reports the performance of a query rewrite for a join.
The query rewrite for join is similar to the simple query. The plan table for V7 shows the join of
the three tables (633k, 1.5 M and 1.3 M rows) using nested loop join. The execution in DB2
V8 uses the MQT201 that reads 171 rows with a large reduction in the elapsed and CPU
time. Summary of the measurements of query rewrite for join:
► V7 DEGREE(1)
28.02 sec. elapsed, 16.52 sec. CPU
► V7 DEGREE(ANY)
14.25 sec. elapsed, 17.9 sec. CPU
► V8 using MQT
0.9 sec. elapsed, 0.07 sec. CPU
In this example, there is a reduction of 31 times (about 96%) in elapsed time and 236 times
(about 99%) in CPU time when we compare V7 DEGREE(1) with V8 using the MQT.
48 DB2 UDB for z/OS Version 8 Performance Topics
Query rewrite for a simple query
V7 PLAN_TABLE
TNAME TABLE_TYPE ACCESSTYPE
EVE T R
V8 PLAN_TABLE
TNAME TABLE_TYPE ACCESSTYPE
MQT091 M R
30
25
20
15
10
5
0
V7 DEGREE(1)
V7 DEGREE(ANY)
V8 using MQT
22X
70X
Elapsed sec CPU sec