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Data & Analytics · Advanced

Bitmap Index

An index storing a bit array per distinct value, efficient for low-cardinality columns in read-heavy analytic workloads.

Definition

Bitmap indexes, a notable Oracle feature, combine quickly with AND and OR across several columns, which makes them suitable for star-schema queries. They are poor for OLTP because updates lock large portions of the bitmap.

Example

A bitmap index on Gender or Region in a data warehouse fact table.

Exam tip

Bitmap = low cardinality and read-mostly; B-tree = high cardinality and OLTP.

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