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

► REORG utility enhancements
The REORG utility is enhanced to allow you to specify that only partitions placed in Reorg
Pending state should be reorganized. You do not have to specify the partition number or
the partition range. You can also specify that the rows in the table space or the partition
ranges being reorganized should be evenly distributed for each partition range when they
are reloaded. Thus, you do not have to execute an ALTER INDEX statement before
executing the REORG utility. You can specify DISCARD with SHRLEVEL CHANGE. You
can avoid the BUILD2 phase during online REORG by using the new data-partitioned
secondary indexes.
► Online Check Index utility
The new SHRLEVEL CHANGE option specifies that applications can read from and write
to the index, table space, or partition that is to be checked. This option uses techniques
which allow access to the index during almost all of the CHECK process. The processing
is performed on a copy of the data and can use FlashCopy® to obtain a copy in a matter of
seconds.
► Create index dynamic statement invalidation
Create index now invalidates the cached statements associated with the base table
contained in the dynamic statement cache without draining active statements.
► Automatic space management
Many IT people in DB installations consider this a very valuable feature. It potentially
eliminates one of the main causes of failure where rapid growth was not anticipated.
► Minimize impact of creating deferred indexes
Indexes created as deferred are ignored by the DB2 optimizer.
► LOB ROWID transparency
This enhancement includes the capability of hiding the ROWID column from DML and
DDL. This way, applications, running on other platforms, that do not have a ROWID data
type can avoid the special code to handle ROWID and use the same code path for all
platforms.
► Longer table and column names
Architectural changes to DB2 V8 expand the DB2 catalog and SQL with support for long
names (tables and other names up to 128 bytes, column names up to 30 bytes). Support
for longer string constants (up to 32,704 bytes), longer index keys (up to 2,000 bytes), and
longer predicates (up to 32,704 bytes) makes DB2 UDB for z/OS compatible with other
members of the DB2 family.
► SQL statements extended to 2 MB
Complex SQL coding, SQL procedures, and generated SQL, as well as compatibility with
other platforms and conversions from other products, have required the extension of the
SQL statements in DB2. DB2 V8 extends the limit on the size of an SQL statement to 2
MB.
► Multiple DISTINCT clauses in SQL statements
This enhancement allows the DISTINCT keyword to appear in multiple column functions
with different expressions. For example, DB2 V8 now allows:
SELECT SUM(DISTINCT C1), AVG(DISTINCT C2) FROM T1
► More open data sets
With DB2 V8 and z/OS 1.5, a DB2 subsystem can have up to 65,041 open data sets,
instead of 32,767 in V7. This enhancement also reduces the amount of virtual storage
used by DB2 below the 16 MB line, as MVS control blocks related to dynamically allocated
Chapter 1. DB2 UDB for z/OS Version 8 5