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

Percent of CPU overhead
Average CPU overhead for 15 Queries
Query CPU overhead using NOT PADDED vs. PADDED keys
Two varchar keys in two indexes are altered from padded to not padded
8
7
6
5
4
3
2
1
0
VC10 VC20 VC30 VC40 VC50
Figure 5-13 Query CPU overhead using NOT PADDED vs. PADDED index
There is a cost associated with the use of not padded keys as together with the key also the
length bytes are saved. As the VARCHARs become longer the CPU overhead decreases.
The impact on index leaf pages and index getpages is shown in Figure 5-14.
P
P
CPU overhead
P:
Projection
Chapter 5. Availability and capacity enhancements 239