Hadoop Interview Question Part II

1) What is Hadoop Streaming?

Hadoop streaming is a utility which allows you to create and run map/reduce job. It is a generic API that allows programs written in any languages to be used as Hadoop mapper

2) What is a combiner in Hadoop?

A Combiner is a mini-reduce process which operates only on data generated by a Mapper. When Mapper emits the data, combiner receives it as input and sends the output to reducer.

3) Is it possible to provide multiple inputs to Hadoop?

Yes, It is possible. The input format class provides methods to insert multiple directories as input to a Hadoop job.

4) What is the relation between job and task in Hadoop?

In Hadoop, A job is divided into multiple small parts known as task.

5) What is distributed cache in Hadoop?

Distributed cache is a facility provided by MapReduce Framework. It is provided to cache files (text, archives etc.) at the time of execution of the job. The Framework copies the necessary files to the slave node before the execution of any task at that node.

6) How JobTracker assign tasks to the TaskTracker?

The TaskTracker periodically sends heartbeat messages to the JobTracker to assure that it is alive. This messages also inform the JobTracker about the number of available slots. This return message updates JobTracker to know about where to schedule task.

7) Is it necessary to write jobs for Hadoop in Java language?

No, There are many ways to deal with non-java codes. Hadoop Streaming allows any shell command to be used as a map or reduce function.

8)What commands are used to see all jobs running in the Hadoop cluster and kill a job in LINUX?

Hadoop job - list

Hadoop job - kill jobID

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