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

► The performance benchmarks for non-data sharing and data sharing environments have
shown slight differences.
► For the online transaction distributed workload, the increase in CPU can be up to 20% with
an ITR reduction up to 12%. Batch DRDA can take advantage of multi-row fetch, so it can
even show an improvement of 20%.
For details on these results, see Chapter 4, “DB2 subsystem performance” on page 127.
2.1.7 New-function mode
After you have run in CM for the appropriate length of time determined by your needs, you
decide when it is time to get to the next step which is enabling-new-function mode (ENFM).
You run a job to do so, and now you are ready to enable new-function mode (NFM). ENFM
affects the changes to the catalog, including adding long name support to the catalog,
converting to Unicode, changing system-defined indexes to not-padded, and changing the
page size for some of the catalog table spaces to 8 KB, 16 KB, and so on. Once this job is
started, you cannot fallback to DB2 V7 or to DB2 V8 CM; the capability to fallback is removed
and enforced once you enable new function mode.
While you are in ENFM, you cannot begin to use any new function yet, but you are no longer
in CM either.
We recommend you consider a minimum amount of changes as you flow through the
migration path to NFM. Be sure to start with the same DSNZPARM settings, and then slowly
begin making changes to your environment one parameter at a time. Similarly, when you
finally reach NFM, slowly begin exploiting some of the new features. This slow path is the best
path for risk mitigation and to evaluate the performance impact of the new features.
A measurement of the IRWW non-data sharing workload has shown no significant difference
in CPU time between CM and no new function NFM.
Coexistence with data sharing
Data sharing coexistence exists only in CM. Coexistence means having both V7 and V8 CM
subsystems in a single data sharing group. ENFM is a group wide event since it affects a
single catalog. As soon as you enable new-function mode on one of the members, it occurs
for all of the members in the group.
DB2 catalog and directory
Once the DB2 catalog and directory are converted to V8 mode, the size of these structures
can be slightly affected. Many existing VARCHAR columns are altered to VARCHAR(128).
Since most of the columns that are being changed are already VARCHAR, the effect should
be minimal. The maximum length is changing, and not the data that is already there. Some
columns are changed from CHAR(8) to VARCHAR(24). The columns that used to be CHAR
and are changed to VARCHAR get bigger by two bytes. The system-defined catalog indexes,
since they are NOT PADDED, may actually get smaller.
Some catalogs rarely get reorganized, so for those that do not, there may be a reclaiming of
space. As a result, it is possible when you migrate to NFM that the size of the catalog may be
slightly reduced.
Typically, we experienced a small amount of DB2 catalog and directory growth, but not more
than 10%.
14 DB2 UDB for z/OS Version 8 Performance Topics