(Big Data Hadoop Administrator) Flashcards

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

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.

How can a client access a file on HDFS?

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.

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

Answer: Hadoop Streaming

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

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

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.

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

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.

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

Answer: ls -l.

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