Databases Reference
In-Depth Information
Join shown on the left. This Bitmap operator is identified as
Opt_Bitmap1007
, as you can
verify in the operator's Properties window, and the
Opt_
prefix indicates that optimized
bitmap filtering is, in fact, being used. The second Bitmap operator, not shown on this
part of the plan, is identified as
Opt_Bitmap1008
. The probe input of the Hash Join is
a Table Scan operator on the
FactInternetSales
fact table, which is also shown in
Figure 6-9. Finally, the predicate section of this Table Scan operator's properties, as
shown in Figure 6-10, shows that both the
Opt_Bitmap1007
and
Opt_Bitmap1008
bitmap filters are being applied to the fact table to remove non-qualifying rows before
the Hash Join.
Figure 6-10:
Fact table Table Scan operator properties.
Finally, bitmap filtering can significantly improve the performance of data warehouse
queries by pushing the filters down into the scan of the fact table early in the query plan,
so that subsequent operators have fewer rows to process.
