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

Attention: The ranges of percentages reported in the row DBM1 VS (Virtual Storage) in
MB below 2 GB actually reflect the percent increase moving from V7 to V8 with and
without the virtual buffer pools. Naturally, a decrease in the virtual storage is possible since
the virtual buffer pools move above the 2 GB bar. In the case of large buffer pools, they are
likely to be using hiperpools and data space buffer pools, so this would not apply. You also
see a larger decrease if you compress some of your data, since compression dictionaries
also move above the bar.
We can make the following conclusions about the performance data in Table 4-6:
A general increase in DB2 V8 DBM1 virtual storage below the 2 GB bar in the distributed
environment is observed:
► The virtual storage usage for the DBM1 address space below the 2 GB bar in V8
increases in the range of 24 to 29%. This increase does not take into account the storage
for virtual buffer pools. If it did, then the virtual storage usage for the DBM1 address space
below the 2 GB bar in V8 decreases in the range of 55 to 48%.
This is primarily due to larger thread-related storage structures required by DB2 V8 to
support new functionality such as long names, longer SQL statements, Unicode and 64-bit
addressing.
The DBM1 virtual storage increase per distributed user thread is in the range of 49 to 72%.
The predominant contributors are non-system thread storage and user stack storage.
For the SQLJ workload the virtual storage per active connection increased by 201%.
► Total DBM1 VS without BP - up to 38% increase for the embedded SQL workload
► Per User Thread - up to 73% increase for the SQLJ workload
► Per System Agent - up to 76% increase for the CLI workload
As virtual storage increases, real storage usage will generally increase in order to back the
virtual storage requirement.
User thread storage comparison
The increase in storage is primarily thread-related, as the GETMAINed areas and fixed
storage pools did not change with the different workloads in either V7 or V8.
DB2 V8 uses more storage for each thread in the DBM1 address space due to:
► Thread structures increased in size to support larger names in DB2.
► The RDS OP pool storage that was used at bind time in V7 is now acquired from the
thread's variable storage pool.
► Some DB2 structures must increase in size to support 64-bit addresses.
This section compares the user thread storage in DBM1 below the 2 GB bar and references
Figure 4-5.
Chapter 4. DB2 subsystem performance 151