# ex1 - 1 and A 1250, a and R2 will process all records with...

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CPS216 Data-Intensive Computing Systems, Fall 2011 Exercise 1 Question 1 This question is based on the following SQL query over table R(A,B): Select A, MAX(B) From R Where B >= 1000 and B < 2000 Group By A Figure 1 describes the contents of the records in table R(A,B). There are 10000 records in R, with 2500 unique values of A and 5000 unique values of B. (a) Explain how MapReduce can be used most efciently to process this query. That is, explain what the Map phase will do and what the Reduce phase will do. Keep your answer brief and to the point. (b) Suppose the records in table R are stored on 10 nodes, M1-M10, as shown in Figure 2. For example, all records with “A 1 and A 250” are stored on node M1, all records with “A 251 and A 500” are stored on node M2, and so on. The MapReduce computation is done with 10 Mappers and 2 Reducers. The Mappers in the will run on the 10 nodes M1-M10. The Reducers will run on two separate nodes R1-R2 such that R1 will process all records with “A

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Unformatted text preview: 1 and A 1250, a and R2 will process all records with A 1251 and A 2500. In this scenario, how many records will be shued from a Mapper node to a Reducer node in the most ecient MapReduce execution? 1 2499 4997 2499 4997 2499 4998 2499 4998 2500 4999 2500 4999 2500 5000 2500 5000 . . . . x 2x-1 x 2x-1 x 2x x 2x A B For x in 1,2,3,. ..,2499,2500 representation of records in R Algebraic 1 1 1 1 1 2 1 2 2 3 2 3 2 4 2 4 A B Records in R R has a total of T(R)=10000 records Figure 1: Figure showing the contents of records in R Mapper M9 Records with Reducer R1 1 <= A <= 1250 Mapper M1 Records with 1 <= A <= 250 Records with Mapper M2 251 <= A <= 500 Records with 2001 <= A <= 2250 Mapper M10 2251 <= A <= 2500 Records with 1251 <= A <= 2500 Records with Reducer R2 Figure 2: Figure showing the 10 mappers M1-M10 and 2 reducers R1-R2 2...
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ex1 - 1 and A 1250, a and R2 will process all records with...

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