Exam CCD-410 topic 1 question 32 discussion

Actual exam question from Cloudera's CCD-410

Question #: 32
Topic #: 1

[All CCD-410 Questions]

Which process describes the lifecycle of a Mapper?

A. The JobTracker calls the TaskTracker's configure () method, then its map () method and finally its close () method.
B. The TaskTracker spawns a new Mapper to process all records in a single input split.
C. The TaskTracker spawns a new Mapper to process each key-value pair.
D. The JobTracker spawns a new Mapper to process all records in a single file.

Show Suggested Answer

Suggested Answer: C 🗳️
For each map instance that runs, the TaskTracker creates a new instance of your mapper.
Note:
* The Mapper is responsible for processing Key/Value pairs obtained from the InputFormat. The mapper may perform a number of Extraction and Transformation functions on the Key/Value pair before ultimately outputting none, one or many Key/Value pairs of the same, or different Key/Value type.
* With the new Hadoop API, mappers extend the org.apache.hadoop.mapreduce.Mapper class. This class defines an 'Identity' map function by default - every input Key/Value pair obtained from the InputFormat is written out.
Examining the run() method, we can see the lifecycle of the mapper:
/**
* Expert users can override this method for more complete control over the
* execution of the Mapper.
* @param context
* @throws IOException
*/
public void run(Context context) throws IOException, InterruptedException { setup(context); while (context.nextKeyValue()) { map(context.getCurrentKey(), context.getCurrentValue(), context);
}
cleanup(context);
}
setup(Context) - Perform any setup for the mapper. The default implementation is a no-op method. map(Key, Value, Context) - Perform a map operation in the given Key / Value pair. The default implementation calls Context.write(Key, Value) cleanup(Context) - Perform any cleanup for the mapper. The default implementation is a no-op method.
Reference: Hadoop/MapReduce/Mapper

by johikepe at April 5, 2025, 1:51 p.m.

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