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

Step 3 is repeated for each master data table. A count should also be
returned for the DSO table without any joins (and local predicates only), and
finally a count of the total filtering from the entire query. These counts will be
used to compare all filtering combinations. See Figure 10-7 for these counts.
Step 4 - Compare with Actual Access Path
Tables Accessed
PDIVISION -
AZOSASALE00
SCO_AREA -
AZOSASALE00
SPROFIT_CTR -
AZOSASALE00
XZMATLPLNT -
AZOSASALE00
XZRLNSP -
AZOSASALE00
Count
with
Filtering
12432
1042733
3164
2264
Figure 10-7 Compare with actual access path
Final
Filtering
The original DSO table contains 7,084,349 rows. After local predicates are
applied, the result is 1,042,733 rows, and the final count for the query
including all filtering is four rows.
4. Compare the filtering provided by each master data table joined to the DSO.
In this example we can see that SCO_AREA provides no filtering (because
the count equals the count of local DSO predicates only), but all other master
data tables provide strong filtering. It is clear, however, that XZMATLPLNT
joined to AZOSASALE00 provides the strongest filtering (8 rows returned,
when the entire query only returns 4 rows).
Any indexing, clustering, and partitioning decisions should take into
consideration the patterns of all queries against the DSO (if possible), although
— for this example only — the decisions should be made to support a table join
sequence of table XZMATLPLNT accessed first, and joined to AZOSASALE00.
210 Best Practices for SAP BI using DB2 9 for z/OS
8
4
4
4
4
4
ODS table 7,084,349.
After local predicates
1,042,733 (14.7%)
No Filtering
2 table count is closest
to the final count