1Z0-515 · Question #54
Identify the benefit of using bitmap join indexes. Select one.
The correct answer is C. Faster query performance for some queries. Oracle benchmarks claim that bitmap join indexes can run a query more than eight times faster than traditional indexing methods. However, this speed improvement is dependent upon many factors, and the bitmap join is not a panacea. Some restrictions on using the bitmap join…
Question
Identify the benefit of using bitmap join indexes. Select one.
Options
- AFaster query performance for all queries.
- BReduced space for indexes.
- CFaster query performance for some queries.
- DLower memory usage.
How the community answered
(21 responses)- A5% (1)
- B5% (1)
- C76% (16)
- D14% (3)
Explanation
Oracle benchmarks claim that bitmap join indexes can run a query more than eight times faster than traditional indexing methods. However, this speed improvement is dependent upon many factors, and the bitmap join is not a panacea. Some restrictions on using the bitmap join index include: The indexed columns must be of low cardinality--usually with less than 300 distinct values. The query must not have any references in the WHERE clause to data columns that are not contained in the index. The overhead when updating bitmap join indexes is substantial. For practical use, bitmap join indexes are dropped and rebuilt each evening about the daily batch This means that bitmap join indexes are useful only for Oracle data warehouses that remain read- only during the processing day.
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