Question
Which of the following file organizations is/are I/O efficient for the scan operation in DBMS?
Official answer and solution
- Official answer
- A and B
- From
- Official GATE 2024 answer key
Solution
Compare sequential page reads of data files (Sorted and Heap) against random record lookups via unclustered indexes during a full table scan.
A scan operation retrieves all records in a relation:
- In both Sorted (A) and Heap (B) file organizations, all data pages of the file are read sequentially from disk, requiring only page I/Os (where is the number of data blocks), which is I/O optimal.
- Traversing an Unclustered tree index (C) or Unclustered hash index (D) to fetch every record can cause a separate random disk block I/O per record (up to block I/Os for records), which is highly I/O inefficient.
Final answer
Options (A), (B)
The answer is the one in the official GATE answer key. The solution is this site's own explanation.
Source
- Paper
- GATE 2024 Computer Science and Information Technology - Set 2 (CS2)
- Question
- 26 of 65
- Section
- Computer Science and Information Technology
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