Describe the Nature and Use of MapReduce and Apache Hadoop DATA-SCIENCE-FOUNDATIONS Practice Questions (Page 5)

Questions 21–25

1. 21application · easy

   A data scientist writes a MapReduce job to compute the average rating per movie from a large dataset. The mapper emits (movie_id, rating). The reducer receives an iterable of ratings for each movie. What must the reducer do to produce the correct average?

   • ASum the ratings and divide by the number of ratings.
   • BEmit the maximum rating.
   • CEmit the count of ratings.
   • DEmit the first rating as the average.
   Reveal Solution Discussion Select an answer first
2. 22foundation · easy

   In Hadoop's master-slave architecture, which component is responsible for executing tasks on a slave node?

   • ADataNode
   • BNodeManager
   • CNameNode
   • DResourceManager
   Reveal Solution Discussion Select an answer first
4. 23application · medium

   A MapReduce job processes a 1 GB input file. The cluster has 4 nodes. The job runs with 4 mappers and 1 reducer. The output is written to HDFS. Which statement about the data flow is correct?

   • AEach mapper writes its own output file to HDFS.
   • BThe single reducer processes the entire input file directly.
   • CThe reducer runs on the same node as the NameNode.
   • DEach mapper processes a different split of the input, and all intermediate data is sent to the single reducer.
   Reveal Solution Discussion Select an answer first
5. 24application · medium

   A marketing team needs to analyze years of clickstream data stored in HDFS. They run a MapReduce job every night to compute daily unique visitors per campaign. The job takes several hours. Which characteristic of Hadoop makes this batch processing approach suitable?

   • AParallel processing of large datasets across many nodes.
   • BReal-time stream processing.
   • CIn-memory caching of all data.
   • DLow-latency interactive queries.
   Reveal Solution Discussion Select an answer first
6. 25application · easy

   A MapReduce job is designed to find the maximum temperature recorded by each weather station. The mapper emits (station_id, temperature). The reducer receives an iterable of temperatures for each station. What should the reducer output?

   • AThe average temperature.
   • BThe count of temperatures.
   • CThe sum of all temperatures.
   • DThe maximum temperature in the iterable.
   Reveal Solution Discussion Select an answer first