A data file consisting of 1,50,000 student-records is stored on a hard disk with block size of 4096 bytes. The data file is sorted on the primary key RollNo. The size of a record pointer for this disk is 7 bytes. Each student-record has a candidate key attribute called ANum of size 12 bytes. Suppose an index file with records consisting of two fields, ANum value and the record pointer to the corresponding student record, is built and stored on the same disk. Assume that the records of data file and index file are not split across disk blocks. The number of blocks in the index file is ________.

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Official answer: 698

File Organization and Indexing

Type of Index: The data file is ordered by RollNo, so creating an index on a non-ordering key ANum requires a secondary index, which must be dense (one entry per record in the data file).
Total Index Entries:
$n = 150,000$
Size of an Index Record ( $R_i$ ):
$R_i = \text{Size of ANum} + \text{Size of Record Pointer} = 12 + 7 = 19\text{ bytes}$
Blocking Factor of Index ( $Bfr_i$ ): Since records cannot span across block boundaries:
$Bfr_i = \left\lfloor \frac{\text{Block Size}}{R_i} \right\rfloor = \left\lfloor \frac{4096}{19} \right\rfloor = 215\text{ records/block}$
Total Blocks for Index File:
$\text{Number of blocks} = \left\lceil \frac{150,000}{215} \right\rceil = \left\lceil 697.674 \right\rceil = 698\text{ blocks}$

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This File Organization and Indexing previous year question is Q21 of the GATE CSE 2021 Set 2 paper. Find more GATE CSE PYQs on File Organization and Indexing in Databases, or browse all GATE CSE PYQs.

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File Organization and Indexing in GATE CSE

File Organization and Indexing has 17 GATE CSE PYQs across 17 papers from 2011 to 2026. 2 of them are 1-mark NAT questions like this one, and it is the only one in GATE CSE 2021 Set 2.

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Independent practice explanation verified by the GateAI team. GATE is conducted by the IITs; question text follows the official paper.