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

5.3.2 Performance
– Invalidation occurs during ALTER.
► Static BIND does not avoid an index that is in RBDP:
– Indexes in RBDP can still be chosen, and will get a resource unavailable condition at
execution time.
Dynamic partition management
The enhancements related to partitions are:
► Add, rotate, and rebalance partitions
Execute the ALTER TABLE ADD PARTITION statement to add a partition to a partitioned
table space and you are ready to go. You can start inserting/loading rows into the new
partition immediately.
Rotating partitions allows old data to “roll-off” while reusing the partition for new data with
the ALTER TABLE ROTATE PARTITION FIRST TO LAST statement. When rotating, you
can specify that all the data rows in the oldest (or logically first) partition are to be deleted,
and then specify a new table space high boundary (limit key) so that the partition
essentially becomes the last logical partition in sequence, ready to hold the data that is
added. The emptied partition is available immediately, no REORG is necessary. Logical
and physical partition numbering is now different. Refer to the columns DSNUM and
LOGICAL_PART in catalog tables SYSTABLEPART and SYSCOPY for the actual physical
to logical partition number correspondence. Recover to previous PIT is blocked as
SYSCOPY and SYSLGRNX entries are deleted.
Rebalancing partitions is done by means of the REORG TABLESPACE utility. Specifying
the REBALANCE option when specifying a range of partitions to be reorganized allows
DB2 to set new partition boundaries for those partitions, so that all the rows that
participate in the reorganization are evenly distributed across the reorganized partitions.
However, if the columns used in defining the partition boundaries have many duplicate
values perfect rebalancing may not be possible.
Note that adding and rotating partitions will automatically convert index controlled to table
controlled partitioning.
► Alter partition boundaries
In DB2 V6, the ability to modify limit keys for table partitions was introduced. The
enhancement in DB2 V8 introduces the same capability for table-based partitioning with
the ALTER TABLE ALTER PARTITION ENDING AT statement. The affected data partitions
are placed into Reorg Pending state (REORP) until they have been reorganized.
In this section we describe the online schema performance measurements.
Performance measurement description
The environment we used in this measurement:
► z/OS V1R3
► DB2 for z/OS V8 in NFM
► IBM z900 Series 2064 4-way processor
► ESS 2105-800 with FICON channels
Performance measurement results
Alter Column Data Types
In a non-partitioned table with 17 columns and 2 indexes the following alters were executed:
Chapter 5. Availability and capacity enhancements 233