What is a bitmap index?

Question Posted / swapna

4 Answers
22073 Views
Choice Solutions, Infosys, I also Faced
E-Mail Answers

Answers were Sorted based on User's Feedback

What is a bitmap index?..

Answer / 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.

Is This Answer Correct ?

13 Yes

1 No

What is a bitmap index?..

Answer / satendra

Bit map Indexes are used with the columns having low
cardianality like Gender(M/F),Marital Status.The benefit of
it is that it requires a small space comapred to the case
if a B-Tree index is created on the same column of the
table.
Bit map Indexes are useful in the systems where data is not
getting updated frequently.

Is This Answer Correct ?

13 Yes

1 No

What is a bitmap index?..

Answer / pinkey

Bitmap indexes are widely used in data warehousing
environments. The environments typically have large amounts
of data and ad hoc queries, but a low level of concurrent
DML transactions. For such applications, bitmap indexing
provides:

Reduced response time for large classes of ad hoc queries
Reduced storage requirements compared to other indexing
techniques
Dramatic performance gains even on hardware with a
relatively small number of CPUs or a small amount of memory
Efficient maintenance during parallel DML and loads

Is This Answer Correct ?

9 Yes

0 No

What is a bitmap index?..

Answer / rahul roshan

Bitmap indexes have traditionally been considered to work well for data such as Boolean values, which have a modest number of distinct values – in this case, boolean True and False - but many occurrences of those values. This would happen if, for example, you had data on whether or not each resident in a city has internet access. Bitmap indexes use bit arrays (commonly called bitmaps) and answer queries by performing bitwise logical operations on these bitmaps. Bitmap indexes have a significant space and performance advantage over other structures for query of such data. Their drawback is they are less efficient than the traditional B-tree indexes for columns whose data is frequently updated: consequently, they are more often employed in read-only systems that are specialized for fast query - e.g., data warehouses, and generally unsuitable for online transaction processing applications. However, this drawback appears to apply only to their implementation in relational database management systems: certain non-relational DBMSs, notably Intersystems Cache, a hierarchical database, use bitmap indexes for low-cardinality columns in transactional systems.

Is This Answer Correct ?

1 Yes

0 No

Post New Answer