GATE 2021 CS (CS2) – Question 31

Databases · File Organization and Indexing (B and B+ Trees) · 1 mark · Numerical answer

A sorted data file has 150000 student records and 4096-byte blocks. Disk record pointers are 7 bytes; candidate-key Anum is 12 bytes. A dense index stores Anum and its record pointer in each index record, on the same disk. Records cannot straddle blocks. Find the number of index blocks.

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Correct answer: 698 to 698

Explanation

Each dense index record uses 12+7=19 bytes. A block holds floor(4096/19)=215 complete index records. One entry is needed per student, so the block count is ceil(150000/215)=698. The sort order on another key does not make the candidate-key index sparse.

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