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

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6.4.2 Data validation<br />

► <strong>SAP</strong> compression places summarized records in the E- fact table.<br />

– The E- fact table can be partitioned (at the time the InfoCube is designed)<br />

to optimize query per<strong>for</strong>mance. If the InfoCube is not compressed, <strong>SAP</strong><br />

partitioning will not take effect.<br />

– Data from overlapping packages (based upon time characteristics) is<br />

consolidated into E, and thus rows are somewhat pre-summarized.<br />

– Similarly, data from overlapping packages (based upon time<br />

characteristics) is consolidated into E, and thus rows are somewhat<br />

pre-summarized.<br />

– <strong>SAP</strong> compression simplifies query optimization of the InfoCube because<br />

the optimizer does not have to factor in filtering from the package ID.<br />

► <strong>SAP</strong> compression resets the reference point <strong>for</strong> non-cumulative key figures.<br />

This can improve query per<strong>for</strong>mance, since fewer rows are needed to<br />

calculate key figure value queries <strong>for</strong> dates near to the reference point.<br />

► <strong>SAP</strong> compression sometimes reduces data storage requirements when rows<br />

from more than one package have the same time value (packages 1 and 2<br />

were loaded on the same day, <strong>for</strong> example). In situations in which the F- fact<br />

table contains packages that do not overlap time periods, <strong>SAP</strong> compression<br />

may not reduce disk storage requirements. But even in this situation, <strong>SAP</strong><br />

compression is always recommended because of the other advantages.<br />

Data in the F- fact table must be carefully checked (via an acceptance and<br />

approval process) prior to compression. Compression results in the package ID<br />

in the F- fact table being replaced with a 00 or a 99 (see 6.4.3, “Cumulative data<br />

versus non-cumulative key figures” on page 98) and all records summarized into<br />

the E- fact table.<br />

The replacement of the package ID means that these summarized records may<br />

not be deleted from the InfoCube after <strong>SAP</strong> compression <strong>using</strong> the<br />

corresponding package ID. For this reason, it is important that the data be<br />

carefully checked and validated prior to being summarized and prior to being<br />

compressed.<br />

However, data can be deleted from the infoCube after <strong>SAP</strong> compression by other<br />

characteristics such as time. If packages have been consolidated due to<br />

overlapping time, then package deletion may not be possible.<br />

Chapter 6. <strong>Best</strong> practices <strong>for</strong> InfoCubes 97

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