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

4.2.3 Conclusion
Nondistributed performance
We examined the performance characteristics for a local workload in both data sharing and
non-data sharing environments. The measurement test used the IRWW OLTP workload using
78 concurrent threads with 480 MB of virtual buffer pools in DB2 V7 vs. V8.
There was an 8% increase in real storage usage in DB2 V8 at the LPAR overall level as
compared to DB2 V7.
A batch workload with a small number of threads each doing a single-thread table space scan
with a 1200 MB buffer pool configuration showed only a 3% increase in real storage usage in
DB2 V8 at the overall LPAR level as compared to DB2 V7.
DB2 V8 has significant improvements in virtual storage constraint relief as many of the large
DB2 structures (for example, buffer pools, EDM DBDs, and compression dictionaries) in the
DBM1 address space have moved above the 2 GB bar. The most important factor here is the
percentage of storage used for threads and local DSC compared to other users of DBM1
below 2 GB in V7. This can vary widely among installations.
For the same DB2 configuration (for example, buffer pool sizes), we experienced a 1% to 20%
increase in real storage requirements for medium and large DB2 subsystems. Larger
increases are possible for smaller DB2 subsystems. This is a result of higher defaults,
minimum and maximum buffer pool sizes, RID pool size, Sort pool size, EDM pool size and
bigger threads. Bigger modules, control blocks and working storage also contribute to the
increase in demand for real storage.
How many additional threads, if any, can be supported depends on the Thread Footprint®
which varies by workload depending on the duration of the thread, SQL workload, RELEASE
parameter setting on plan and package bind, effectiveness of thread storage contraction
(CONTSTOR=YES), and storage for pools, control blocks, and work areas moved above the
2 GB bar.
4.2.4 Recommendations
DB2 V8 64-bit support does not totally eliminate virtual storage constraint below the 2 GB bar
in the DBM1 address space. However, V8 provides valuable additional relief, but the relief
varies by installation.
DB2 V8 is able to exploit all available processors’ storage on the latest processor models
(currently 256 GB, current DB2 limit of 1 TB), through:
► Supporting extremely large buffer pools to eliminate I/O
► Exploiting increased ESA Compression
► Using larger thread Sort pool
► Allowing more compressed table spaces and partitions
You must have sufficient real storage to fully back increased storage use usage.
You must still continue to plan for, monitor and tune virtual storage usage below the 2 GB bar.
The DB2 Lab's recommendation is that users should implement a methodology which
incorporates the development and measurement of a production workload to achieve
accurate projections for virtual storage recommendations. The resulting measurements need
to be evaluated using formulas for calculating the thread storage footprint (virtual storage per
thread) and the estimation of the maximum possible threads.
156 DB2 UDB for z/OS Version 8 Performance Topics