Databases Reference
In-Depth Information
be multidimensionally clustered, though they may be. Region, year, and product are
columns of the respective dimension tables, which can be indexed using regular or
dimension indexes (if the dimension tables are multidimensionally clustered tables).
When we access the fact table on REGION, DATEOFSALE, and PRODUCT_CLASS
values, dimension index scans of the dimension indexes on these columns can be done,
and then index ANDing of the resulting location identifiers is performed. Again, once
we have a list of blocks, a minirelational scan can be done on each block to get the
records.
8.5
Storage Considerations
Figure 8.10 illustrates several MDC cells, each containing a number of storage blocks.
Usually, except by pure chance, the number of rows in the cell will not exactly fill a
whole number of storage blocks. As a result, in most cases each cell will contain one par-
tially filled storage block. The greater the number of cells there are, the more partially
filled blocks, and therefore, the more space wasted.
Figure 8.10
Partially filled blocks within cells.
Having a large number of partially filled blocks will result in a large amount of
wasted storage and significantly larger table sizes. The large table sizes counteract the
