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

– Column data type changes can be done without losing data availability to data and
indexes. In V5 you could increase the size of VARCHAR columns, the changes in V8
allow you to extend numeric and character columns and to change between CHAR and
VARCHAR.
– Indexes can have columns added, and VARCHAR columns changed from padded to
non padded.
► Partitioning
Several partitioning enhancements are included in DB2 V8 that are useful in almost all real
life environments.
– Online partitioning changes
You can add a new partition to an existing partitioned table space and rotate partitions.
– More partitions
This enhancement increases the maximum number of partitions in a partitioned table
space and index space past the current maximum of 254. The new maximum number
of partitions is 4,096. The DSSIZE and page size determine the maximum number of
possible partitions.
– Data-partitioned secondary indexes
V8 introduces data-partitioned secondary indexes to improve data availability during
partition level utility operations (REORG PART, LOAD PART, RECOVER PART) and
facilitate more complex partition level operations (roll on/off part, rotate part) introduced
by Online Schema Evolution. The improved availability is accomplished by allowing the
secondary indexes on partitioned tables to be partitioned according to the partitioning
of the underlying data.
There is no BUILD2 phase component to REORG SHRLEVEL CHANGE when all
secondary indexes are partitioned, nor is there contention between LOAD PART jobs
executing on different partitions of a table space. A data-partitioned secondary index is
most useful when the query has predicates on both the secondary index columns and
the partitioning columns.
– Separation of partitioning and clustering
Partitioning and clustering were bundled together in versions prior to V8. Now you can
have a partitioned table space without an index and can cluster the data on any index.
These changes may be able to eliminate one index (since you are no longer required to
have a partitioning index) and reduce random I/O (since you can now define any index
as the clustering index).
► System level point-in-time backup and recovery
The system level point-in-time recovery enhancement provides the capability to recover
the DB2 system to any point-in-time, irrespective of the presence of uncommitted units of
work, in the shortest amount of time. This is accomplished by identifying the minimum
number of objects that should be involved in the recovery process, which in turn reduces
the time needed to restore the data and minimizes the amount of log data that needs to be
applied.
For larger DB2 systems with more than 30,000 tables, this enhancement significantly
improves data recovery time, which in turn results in considerably shorter system
downtime.
► BACKUP and RESTORE SYSTEM
These two new utilities provide system level backup, and system level point-in-time
recovery. They activate new functionality available with the new z/OS V1R5
DFSMShsm, which allows a much easier and less disruptive way for fast volume-level
backup and recovery to be used for disaster recovery and system cloning.
4 DB2 UDB for z/OS Version 8 Performance Topics