Question 1

Determine which best describes when the reduce method is first called in a MapReduce job?

AReducers start copying intermediate key-value pairs from each Mapper as soon as it has completed. The programmer can configure in the job what percentage of the intermediate data should arrive before the reduce method begins.

BReducers start copying intermediate key-value pairs from each Mapper as soon as it has completed. The reduce method is called only after all intermediate data has been copied and sorted.

CReduce methods and map methods all start at the beginning of a job, in order to provide optimal performance for map-only or reduce-only jobs.

DReducers start copying intermediate key-value pairs from each Mapper as soon as it has completed. The reduce method is called as soon as the intermediate key-value pairs start to arrive.

Answer : B

Question 2

You have written a Mapper which invokes the following five calls to the OutputColletor.collect method:

output.collect (new Text (''Apple''), new Text (''Red'') ) ;

output.collect (new Text (''Banana''), new Text (''Yellow'') ) ;

output.collect (new Text (''Apple''), new Text (''Yellow'') ) ;

output.collect (new Text (''Cherry''), new Text (''Red'') ) ;

output.collect (new Text (''Apple''), new Text (''Green'') ) ;

How many times will the Reducer's reduce method be invoked?

Answer : B

reduce()gets called once for each [key, (list of values)] pair. To explain, let's say you called:

out.collect(new Text('Car'),new Text('Subaru');

out.collect(new Text('Car'),new Text('Honda');

out.collect(new Text('Car'),new Text('Ford');

out.collect(new Text('Truck'),new Text('Dodge');

out.collect(new Text('Truck'),new Text('Chevy');

Thenreduce()would be called twice with the pairs

reduce(Car, <Subaru, Honda, Ford>)

reduce(Truck, <Dodge, Chevy>)

Question 3

To process input key-value pairs, your mapper needs to lead a 512 MB data file in memory. What is the best way to accomplish this?

ASerialize the data file, insert in it the JobConf object, and read the data into memory in the configure method of the mapper.

BPlace the data file in the DistributedCache and read the data into memory in the map method of the mapper.

CPlace the data file in the DataCache and read the data into memory in the configure method of the mapper.

DPlace the data file in the DistributedCache and read the data into memory in the configure method of the mapper.

Answer : C

Question 4

In a MapReduce job, the reducer receives all values associated with same key. Which statement best describes the ordering of these values?

AThe values are in sorted order.

BThe values are arbitrarily ordered, and the ordering may vary from run to run of the same MapReduce job.

CThe values are arbitrary ordered, but multiple runs of the same MapReduce job will always have the same ordering.

DSince the values come from mapper outputs, the reducers will receive contiguous sections of sorted values.

Answer : B

Note:

* Input to theReduceris the sorted output of the mappers.

* The framework calls the application's Reduce function once for each unique key in the sorted order.

* Example:

For the given sample input the first map emits:

< Hello, 1>

< World, 1>

< Bye, 1>

< World, 1>

The second map emits:

< Hello, 1>

< Hadoop, 1>

< Goodbye, 1>

< Hadoop, 1>

Question 5

Which HDFS command displays the contents of the file x in the user's HDFS home directory?

Ahadoop fs -Is x

Bhdfs fs -get x

Chadoop fs -cat x

Dhadoop fs -cp x

Answer : C

Free Practice Questions for Hortonworks HDPCD Exam

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