bitmapindeksit

Bitmap indexing is a database indexing technique used to improve the performance of queries that involve large datasets. It is particularly effective for columns with low cardinality, meaning columns with a limited number of distinct values. Bitmap indexing works by creating a bitmap for each distinct value in the indexed column. A bitmap is a data structure that uses bits to represent the presence or absence of a value in a row.

When a query is executed, the database engine can use bitwise operations to quickly determine which rows match the query criteria. This is because the bitmaps for each value can be combined using logical operations such as AND, OR, and NOT. For example, if a query asks for rows where the indexed column has a value of 'A' or 'B', the database can combine the bitmaps for 'A' and 'B' using the OR operation.

Bitmap indexing is space-efficient because it only stores a single bit for each row and value combination. However, it can be less efficient for columns with high cardinality, as the number of bitmaps can grow significantly. Additionally, bitmap indexing may not be suitable for columns that are frequently updated, as the bitmaps need to be recalculated whenever the data changes.

Bitmap indexing is commonly used in data warehousing and business intelligence applications, where queries often involve aggregating large amounts of data. It is supported by several database management systems, including Oracle, PostgreSQL, and SQL Server.