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Question
Computer Science
Posted 2 months ago
Suppose you have a file with 
1
0
0
0
0
0
 pages to be sorted with general external merge sort 
(
without tournament sort and without blocked disk access improvements
)
.
 Assume that you have 
2
0
0
 buffer pages available in memory that can be used for sorting. Answer the
following questions:
a
)
 How many sorted runs will the general external merge sort produce at the end of the first pass?
b
)
 How many passes will it take to sort the file completely? c
)
What is the total I
/
O cost 
(
 the number of disk access made
)
 of sorting the file 
?
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Answer from Sia
Posted 2 months ago
Answer to part a)
Given file size: 1,000,000 pages
Buffer size: 200 pages
Number of runs: Total pages / Buffer size
Calculation: 1,000,000 / 200 = 5000 runs
Conclusion: The general external merge sort will produce 5000 sorted runs at the end of the first pass
At the end of the first pass, the general external merge sort will produce 5000 sorted runs.
Answer to part b)
Number of runs after the first pass: 5000
Buffer size: 200 pages (199 for input, 1 for output)
Number of runs that can be merged in each pass: 199
Calculation of passes: ceil(log_199(5000))
Using logarithm to calculate the number of passes needed
Conclusion: It will take 4 passes to completely sort the file
It will take 4 passes to completely sort the file.
Answer to part c)
Number of runs: 5000
Number of passes: 4
I/O cost per pass: 2 * Total pages (read + write)
Total I/O cost: Number of passes * I/O cost per pass
Calculation: 4 * 2 * 1,000,000 = 8,000,000 disk accesses
Conclusion: The total I/O cost of sorting the file is 8,000,000 disk accesses
The total I/O cost of sorting the file is 8,000,000 disk accesses.

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