Question 1: When may the reduce method of a certain Reducer be invoked for the first time?

• As soon as a Mapper has emitted at least one record
• As soon as at least one Mapper has finished processing records
• It depends on the InputFormat used for the job
• Not until all the Mappers have finished processing records (Correct answer)

Correct answer: Not until all the Mappers have finished processing records

Before beginning the reduce process, the MapReduce engine makes sure that all of the Mappers have finished their execution.

Question 2: How can a client access a file on HDFS?

• The client asks NameNode where the block is located (s). The NameNode gives the client the block location(s) back. Data is immediately read by the client from the DataNode (s)
• The client simultaneously requests every DataNode. The client receives a response from the DataNode with the requested data. Data is immediately read by the client from the DataNode.
• For the block location, the Client contacts the NameNode (s). The NameNode contacts the DataNode that contains the desired data block. Data is exchanged from the DataNode to the NameNode to the Client from the NameNode to the Client.
• For the block location, the client contacts the NameNode (s). The NameNode then requests block locations from the DataNodes. The NameNode leads the client to the DataNode, holding the requested data block when the DataNodes react to it (s). Data is then read directly from the DataNode by the client. (Correct answer)

Correct answer: For the block location, the client contacts the NameNode (s). The NameNode then requests block locations from the DataNodes. The NameNode leads the client to the DataNode, holding the requested data block when the DataNodes react to it (s). Data is then read directly from the DataNode by the client.

For the block location, the client contacts the NameNode (s). The NameNode then requests block locations from the DataNodes. The NameNode leads the client to the DataNode, holding the requested data block when the DataNodes react to it (s). The data is then immediately read by the client from the DataNode.

Question 3: You are creating a combiner that receives input in text keys and IntWritable values and outputs text keys and IntWritable values. Which interface ought to be implemented by your class?

• Reducer <Text, IntWritable, Text, IntWritable>
• Combiner <Text, IntWritable, Text, IntWritable>
• Reducer <Text, Text, IntWritable, IntWritable>
• Combiner <Text, Text, IntWritable, IntWritable>

Reducer <Text, IntWritable, Text, IntWritable> is the correct syntax to implement the class.

Question 4: Which tool enables you to use any executable script as the Mapper or Reducer to generate and run MapReduce jobs?

• Oozie
• Flume
• Hadoop Streaming (Correct answer)
• Sqoop

Correct answer: Hadoop Streaming

MapReduce tasks may be created and executed using any executable script as the Mapper or Reducer by using Hadoop streaming.

Question 5: During a typical sort and shuffle phase of MapReduce, how are keys and data presented and delivered to Reducers?

• Keys are presented to a Reducer in sorted order; values for a given key are not sorted (Correct answer)
• Keys are presented to a Reducer in sorted order; values for a given key are sorted in ascending orde
• Keys are presented to a Reducer in random order; values for a given key are sorted in ascending order
• Keys are presented to a Reducer in random order; values for a given key are not sorted

Correct answer: Keys are presented to a Reducer in sorted order; values for a given key are not sorted

Values for a particular key are not sorted, although keys are delivered to reducers in sorted order.

Question 6: Which best reflects the sequence in which data is supplied to a Reducer's reduce function, assuming default settings?

• Neither keys nor values are in any predictable order
• The keys given to a Reducer aren't in a predictable order, but the values associated with those keys always are
• The keys given to a Reducer are in sorted order, but the values associated with each key are in no predictable order (Correct answer)
• Both the keys and values passed to a Reducer always appear in sorted order

Correct answer: The keys given to a Reducer are in sorted order, but the values associated with each key are in no predictable order

Although the values attached to each key are delivered to a Reducer in sorted order, there is no consistency in the order of the values.

Question 7: Which Linux command enables the display of a file or directory indication?

• man ls.
• ls.
• ls -a.
• ls -l. (Correct answer)

Correct answer: ls -l.

Linux users can display a file or directory indication by using the ls -l command.