What is a bitmap index?

Answer Posted / a.jyothsna

In a bitmap index, a bitmap for each key value is used
instead of a list of rowids.
Each bit in the bitmap corresponds to a possible rowid. If
the bit is set, then it means that the row with the
corresponding rowid contains the key value. A mapping
function converts the bit position to an actual rowid, so
the bitmap index provides the same functionality as a
regular index even though it uses a different
representation internally. If the number of different key
values is small, then bitmap indexes are very space
efficient. Bitmap indexing is of great benefit to data
warehousing applications.

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