Why does performance degrade when many UPDATE, INSERT or DELETE statements are
issued on a table that has an associated bitmap index?
A.
The DML operations re-create the bitmap index blocks
B.
Additional time is taken to remove NULL values from the bitmap index after a DML
operation
C.
The bitmap index is rebuilt automatically after a DML operation
D.
The smallest amount of a bitmap that can be locked is a bitmap segment
What is that mean? Can anyone explain?
When the table has bitmap index, it means that it has a limited choice. You can think of combo box in HTML. The problem in bitmap index is it has to be rebuilt once it is updated. There’s no way to update the index. What gets worse is that the index is rebuilt not by one row but by one bitmap segment. This is associated with how the bitmap index is built.
The bottom line is that when you use bitmap index, you have to be careful. Don’t use bitmap index on the column that can be frequently updated.
D