Bitmap Indexing Task5

Bitmap indexing operation is one of the most popular techniques in Online Analytical processing(OLAP). Definition: Bitmap indexing is the special type of index which stores data in bit array and providing query service by calculating bitwise logical operation on the bitmaps. Index structure: Bitmap index is consist of one column of a relation and the identifier. To map index, the value of a selected column is used for bitmap as column. based on the identifier, the bit value true or false is put in the bitmap. Bitmap values Identifier Value A Value B 1 1 0 2 0 1 ... ... ... ... ... ... Figure: example of Bitmap index structure

In contrast, the bitmap index is designed for cases where number of distinct values is low, in other words, the values repeat very frequently. For example, the gender field in a customer database usually contains three distinct values: male, female or "unspecified" (NULL). In other words, the cardinality is low for such a column. For such variables, the bitmap index can have a significant space and performance advantage over the commonly used trees

A bitmap index is a specialized variation of a B-tree index. You can use a bitmap index to index columns that can contain one of only a few values, such as marital status or gender. For each highly duplicate value, a bitmap index stores a compressed bitmap for each value that the column might contain. With a bitmap index, storage efficiency increases as the distance between rows that contain the same key decreases. You can use a bitmap index when both of the following conditions are true: • The key values in the index contain many duplicates. • More than one column in the table has an index that the optimizer can use to improve performance on a table scan.

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