Table T is stored as a pile. It has n rows which are stored in n/k pages.
Secondary index based on column S is to be considered. Column S has b distinct values.
Values are evenly distributed.
Let's consider the query
select * from T where S='something'
The index should be organised as ISAM. Let n be so big that the index would have 2 levels.
Which value of b would cause the use of the index to be more efficient than scanning the whole file?
The seek time for the disk is 6ms, rotation delay 2.4 ms and block transfer time 0.2 ms.