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

the PARTITION BY clause in the CREATE TABLE statement. Since the partitioning index is
no longer required, another index may also be used as a clustering index.
Remember that index-controlled partitioning is still supported in DB2 V8 but several new
enhancements are only supported when using table-controlled partitioning.
We now review index terminology and classification.
Indexes on table-controlled partitioned tables can be classified as follows:
► Based on whether or not an index is physically partitioned:
– Partitioned index: The index is made up of multiple physical partitions (not just index
pieces)
– Non-partitioned index: The index is a single physical data set (or multiple pieces)
► Based on whether or not the columns in the index correlate with the partitioning columns
of the table (the left most partitioning columns of the index are those specified in the
PARTITION BY clause of the table):
– Partitioning index: The columns in the index are the same as (and have the same
collating sequence), or start with the columns in the PARTITION BY clause of the
CREATE TABLE statement.
– Secondary index: Any index in which the columns do not coincide with the partitioning
columns of the table.
– Data-partitioned secondary indexes: Any index defined with the PARTITIONED option
(see later).
► Based on whether or not the index determines the clustering of the data. Note that when
using table-controlled partitioning:
– Clustering index: The index determines the order in which the rows are stored in the
partitioned table.
– Non-clustering index: The index does not determine the data order in the partitioned
table.
5.5.1 Partitioned table space without index
5.5.2 Clustering index
Because the table definition of a table-controlled partitioned table is complete after executing
the CREATE TABLE statement, no partitioning index is required. So you can have a
table-controlled partitioned table without a partitioning index. Due to the non-unique nature of
DPSIs it is advised to specify predicates on partitioning key columns in order to enable
partition pruning from queries using predicates for DPSI columns.
In DB2 V8, any index on a table-controlled partitioned table can be the clustering index,
including a secondary index. If predicates used to access the table controlled partitioned table
do not refer to the partitioning columns, a clustering index can now be defined for these
predicates.
5.5.3 Clustering index always
If no explicit clustering index is specified for a table, the V8 REORG utility recognizes the first
index created on each table as the implicit clustering index when ordering data rows.
Chapter 5. Availability and capacity enhancements 247