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

2.5.9 Unicode parser
Important: Consider setting the page fixing option for buffer pools with a poor read hit ratio
and lots of I/O. Balance this setting against the need for real storage in the rest of the
system.
For more information on page fixing and its performance implications, refer to Chapter 4,
“DB2 subsystem performance” on page 127.
DB2 must convert all SQL to Unicode since all SQL statements are now parsed in Unicode
UTF-8 format. This conversion is generally performed by DB2 invoking z/OS Conversion
Services. In addition, the EBCDIC metadata stored in the catalog is converted to Unicode in
CM. After you enable NFM, the metadata is stored in Unicode and the conversion is not
necessary.
If you are using an SBCS code page, the conversion is done directly by DB2. If you have a
more complicated code page, then DB2 invokes z/OS Conversion Services.
For more information on the Unicode parser and its performance implications, refer to
Chapter 4, “DB2 subsystem performance” on page 127.
2.5.10 Optimizer enhancements
Once you migrate to DB2 V8 CM, you can choose to rebind your application plans and
packages to possibly get improvements based on the optimizer enhancements to access
paths. For example, fast column processing is re-enabled if you rebind, and your application
can take advantage of the new stage 1 and indexable predicates.
For more information on application rebinds, refer to Chapter 4, “DB2 subsystem
performance” on page 127.
2.5.11 CF request batching
A new function in z/OS V1.4 and CF level 12, called CF request batching, is the ability to allow
multiple pages to be registered to the CF with a single operation. DB2 V8 takes advantage of
this feature in DB2 V8 during the actions of registering and writing multiple pages to a GBP
and reading multiple pages from a GBP during castout processing. This new feature really
allows for more efficient traffic across the links to and from the CF, and can result in a
reduction of CF processing times and costs associated with data sharing for some workloads.
For more information on CF request batching, refer to Chapter 8, “Data sharing
enhancements” on page 319.
2.6 New-function mode
The performance comparisons are generally dependent on the particular workload.
Preliminary measurements in non-data sharing and non-DRDA environments indicate no
significant difference in CPU time overhead in CM versus NFM.
However, in data sharing, the story is much improved. If you are interested in the performance
impact of a DB2 V7 application migrated to V8 without any application change and significant
configuration change, there can be a noticeable reduction in V8 overhead going from CM to
22 DB2 UDB for z/OS Version 8 Performance Topics