Physical Database Design

2.3 Bitmap Indexing 25

Thus, we see that the composite index time reduces the exhaustive scan time by a fac-

tor of about 55 to 1. Multiplying 55 times 750 target rows to get a rough estimate, we

see that at approximately 41,250 target rows and higher, a table scan becomes the

more efficient method of satisfying this query. The overall plot of I/O time is shown

in Figure 2.4.

2.3 Bitmap Indexing

One of the most basic rules of thumb for index design in data warehouses is to create

indexes on each column of each of the dimension tables and all the corresponding for-

eign keys in the fact table. This facilitates any joins required between the fact table ...