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Best Practices for SAP BI using DB2 9 for z/OS - IBM Redbooks

Best Practices for SAP BI using DB2 9 for z/OS - IBM Redbooks

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Figure 6-14 is displayed once you have clicked the Explain icon on the menu bar<br />

(Figure 6-13 on page 87) and you have selected the Table In<strong>for</strong>mation tab. This<br />

tab displays the partitions that have been created by your repartitioning process.<br />

Figure 6-14 Table In<strong>for</strong>mation tab - reflects partitions after running a simple query<br />

6.2.2 Advantages of partitioning/repartitioning<br />

In conjunction with <strong>SAP</strong> compression (see 6.4, “<strong>SAP</strong> compression <strong>for</strong> loads” on<br />

page 96), partitioning the E-Face and F- fact tables provides significant benefits<br />

<strong>for</strong> query per<strong>for</strong>mance:<br />

► Partitioning enhances the ability of queries to execute in parallel, thus<br />

reducing overall elapsed time.<br />

► When users specify a restriction based upon time, then <strong>SAP</strong> <strong>BI</strong> generates<br />

predicates against the partition limit keys to allow partition elimination.<br />

Partition elimination is the process of <strong>DB2</strong> avoiding access to unnecessary<br />

partitions regardless of the E- fact table index used or whether a tablespace<br />

scan is used on the E- fact table. This has the benefit of allowing time-based<br />

filtering (at the partition level) to be combined with filtering from another<br />

dimension without requiring index ANDing or a Cartesian product of multiple<br />

dimensions be<strong>for</strong>e the E- fact table.<br />

88 <strong>Best</strong> <strong>Practices</strong> <strong>for</strong> <strong>SAP</strong> <strong>BI</strong> <strong>using</strong> <strong>DB2</strong> 9 <strong>for</strong> z/<strong>OS</strong>

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