Consider the expression
(a) Sort-merge join
(b) Block nested loops
where r has 1,000 tuples, 20 tuples per page; s has 2,000 tuples, 4 tuples per page; and the main memory bu er for this operation is 22 pages long.
Relation r has 50 pages and s has 500 pages. In each case we ignore the cost of outputting the result, as it is the same for both methods.
(a)
Thus, assuming that merging can be done during the last phase of sorting, the total cost should not exceed 3200 page transfers.
(b) Assuming that r is scanned in the outer loop, the cost is 50 + (50/20)*500 = 1300.
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