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

Sparse index (SI) performance
Large elapsed time reduction
Elapsed Time (s)
Thousands
Figure 3-20 Sparse index performance
4
3
2
1
0
I10
I14
I22
S22A S22C VP12
I26 S22B VP11 VP13
QUERY NO
The performance measurements considering the use of sparse indexes in star join show:
► 77 queries on two workloads are measured.
► Among the 41 queries that exploit sparse index (SI), most of queries show 50% - 80%
elapsed time reduction. Top queries:
– Query VP13 elapsed without SI = 3634 sec. and with SI = 561.9 sec. (84% reduction)
– Query I10 elapsed time without SI = 3399 sec. and with SI = 1838 sec. (45% reduction)
– Query VP12 elapsed without SI = 3143 sec. and with SI = 498.7 sec. (84% reduction)
– Query I22 elapsed time without SI = 3142 sec. and with SI = 1625 sec. (48% reduction)
► With parallelism, they show an additional 30% - 60% elapsed time reduction.
► Performance improves more when more sorts are involved.
Star join access path
Figure 3-21 shows a comparison on CPU times between DB2 V7 and DB2 V8.
without SI
with SI
These measurement results were based on all the DB2 V8 supported features, including the
in memory work file.
Chapter 3. SQL performance 61