Bitmap indices are commonly used by DBMS's to accelerate decision support queries. A bitmap index is a collection of bitmaps in which each bit is mapped to a record ID (RID). A bit in a bitmap is set if the corresponding RID has property P (i.e., the RID represents a customer that lives in New York), and is reset otherwise. A significant advantage of bitmap indices is that complex logical selection operations can be performed very quickly, by performing bit-wise AND, OR, and NOT operations. Bitmap are also compact representations of densely populated sets. By using bitmap compression techniques, they are also compact representations of sparsely populated sets.
展开▼
