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

► Configuration
– DB2 for z/OS V8 NFM
– Non-data sharing
– z/OS Release 1.5
– DFSMSdss V1R5
– IBM z900 Series 2064 4-way processor
– ESS 800 DASD
– FlashCopy V2
► Workload for measurement
– 20 M rows, 6 indexes, 1 table space with 10 partitions
► Measurement scenarios
– CHECK INDEX SHRLEVEL(REFERENCE), CHECK INDEX SHRLEVEL(CHANGE)
against
Partitioned Index
Non-partitioned index
All indexes (6) of the table space
– Concurrent CHECK INDEX SHRLEVEL(REFERENCE) PART of all partitions of the
table space versus single CHECK INDEX SHRLEVEL(CHANGE) against
Partitioned index
Non-partitioned index
CHECK INDEX measurement results and study
We look at several measurements using and not using FlashCopy, and executing CHECK
INDEX on concurrent partitions.
SHRLEVEL CHANGE with FlashCopy vs. SHRLEVEL REFERENCE
This test case measures the CPU and elapsed time to compare CHECK INDEX with option
SHRLEVEL CHANGE using FlashCopy V2 to CHECK INDEX with option SHRLEVEL
REFERENCE. The results of this test case are shown in Figure 6-2. SHRLEVEL CHANGE
using FlashCopy reduces the elapsed time dramatically.
The observations of this study are as follows:
► With the SHRLEVEL CHANGE option, DB2 uses parallel tasks in the execution of the
utility. In the case of a partitioned index (PI), the UNLOAD, SORT and CHECKIDX tasks
are processed in parallel in each partition of the table space. In the case of a
non-partitioned index (NPI), the UNLOAD and SORT tasks are processed in parallel, like
for PI, but the CHECKIDX and MERGE phases do not use parallel processing.
► Most CPU time improvement in SHRLEVEL CHANGE of partitioned index comes from the
CHECKIDX phase. Also SHRLEVEL CHANGE of non-partitioned index improves CPU
time in the CHECKIDX phase in comparison with SHRLEVEL REFERENCE, but the total
CPU time increases in SHRLEVEL CHANGE because of SORT and MERGE phases. The
MERGE phase exists only in the case of a non-partitioned index and SHRLEVEL
CHANGE.
If we only look at the CHECKIDX phase, we can say that SHRLEVEL CHANGE improved
CPU time significantly both in PI and NPI. SHRLEVEL CHANGE makes the total elapsed
time decrease dramatically both in PI and NPI. A PI can benefit from the performance
improvement of online CHECK INDEX more than an NPI.
► CHECK INDEX 6 indexes of the table space with SHRLEVEL CHANGE has 18 tasks.
– UNLOAD 6 indexes in parallel
Chapter 6. Utilities 265