Питання | Сторінка 140069

Assume that the relation is stored on disk and that the following disk I/O costs apply:

- Sequential page read cost: 0.005 seconds per page

- Random page read cost: 0.015 seconds per page

For index-based access, assume that traversing the index requires one random I/O per level, and that the qualifying records (or their containing pages) are perfectly clustered in the data file.

Match the following scenarious to an access path that is likely to more efficient.

A relation is stored in a file containing 20,000 pages. A primary B⁺-tree index is available with a height of 4. A query returns approximately 0.2% of the records.

A relation with 5,000 pages and a primary index with height 3. A query is issued that retrieves about 1% of the records.

A data file contains 10,000 pages and is accompanied by a primary index with height 3. A query returns about 15% of the records.

A relation is stored in a file with 2,000 pages and has an associated primary index with height 3. A query is executed that retrieves about 80% of the records.

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