Mapr (HP) Hadoop Developer Certification Questions and Answers (Dumps and Practice Questions)

Question : When will you create Custom Combiner?



1. When you want to reduce the amount of network traffic during shuffle phase

2. If reducer is not a associative and commutative than , we should use Custom combiner else we could use Reducer as a Combiner

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4. 1,2

5. 1,2,3


Correct Answer : Get Lastest Questions and Answer :
Explanation: The combiner function is used as an optimization for the MapReduce job. The combiner function runs on the output of the map phase and is used as a
Filtering or an aggregating step to lessen the number of intermediate keys that are being passed to the reducer. In most of the cases the reducer class is set
to be the combiner class. The difference lies in the output from these classes. The output of the combiner class is the intermediate data that is passed to
the reducer whereas the output of the reducer is passed to the output file on disk.





Question : Select correct statement regarding combiner?



1. A combiner is called after all the Mappers finish and before the results are shuffled and transmitted over the network.

2. In Custom combiner output of the Combiner not necessarily match with the input of Reducer

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4. 1,2

5. 1,2,3


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Explanation: Combiner will not always improve the performance. It only improve performance if after shuffling data and before sending data over
network can be reduced using combiner.




Question : If our Hadoop Job is CPU bound and Reducer is a Commutative and Associative. Then using reducer as a combiner will certainly improve the
performance.

1. True
2. False

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Explanation: If your job is CPU bound , hence no benefit on the network IO. Hence, using reducer as a combiner will not give any advantage for
this JOB.

Related Questions

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Question : Arrange following in correct order of execution
A. call to main() method
B. Instantiation of new Configuration object
D. job.waitForCompletion()
C. Calling ToolRunner.run() static method


1. A,B,C,D
2. D,C,B,A
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4. B,A,C,D
5. A,C,D,B


Question : Select the correct statement for Driver class



1. Driver class needs to check input argument if input directory path is provided or not.

2. We have to configure mapper.reducer in Driver class only

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4. 1,3

5. 1,2,3


Question : Sometimes, before running your MapReduce job. You configure the below environment variable
LD_LIBRARY_PATH
Why?


1. It defines a list of directories where your executables are located

2. It points to all the jars in the Hadoop distribu3on required to compile and run your MapReduce programs

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4. 1,3

5. 1,2,3


Question : In MapReduce jobs all the values must implemented following interfaces



1. Comparable

2. Writable

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4. 1,2
5. 1,2,3



Question : In MapReduce jobs all the keys must implemented following interfaces


1. Comprable

2. Witable

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4.



Question : Put the following java classes in order, as they act when mapper is executed.
A. InputKey
B. InputSplit
C. RecordReader
D. InputFormat


1. D,B,C,A
2. A,B,C,D
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4. A,D,C,B