24 Hadoop Interview Questions & Answers for MapReduce developers | FromDev

24 Hadoop Interview Questions & Answers for MapReduce developers | FromDev

A good understanding of Hadoop Architecture is required to leverage the power of Hadoop. Below are few important practical questions which can be asked to a Senior Experienced Hadoop Developer in an interview. I learned the answers to them during my CCHD (Cloudera Certified Haddop Developer) certification. I hope you will find them useful. This list primarily includes questions related to Hadoop Architecture, MapReduce, Hadoop API and Hadoop Distributed File System (HDFS).

Hadoop is the most popular platform for big data analysis. The Hadoop ecosystem is huge and involves many supporting frameworks and tools to effectively run and manage it. This article focuses on the core of Hadoop concepts and its technique to handle enormous data.

Below list of hadoop interview questions and answers that may prove useful for beginners and experts alike. These are common set of questions that you may face at big data job interview or a hadoop certification exam (like CCHD).

What is a JobTracker in Hadoop? How many instances of JobTracker run on a Hadoop Cluster?

JobTracker is the daemon service for submitting and tracking MapReduce jobs in Hadoop. There is only One Job Tracker process run on any hadoop cluster. Job Tracker runs on its own JVM process. In a typical production cluster its run on a separate machine. Each slave node is configured with job tracker node location. The JobTracker is single point of failure for the Hadoop MapReduce service. If it goes down, all running jobs are halted. JobTracker in Hadoop performs following actions(from Hadoop Wiki:)

• Client applications submit jobs to the Job tracker.
• The JobTracker talks to the NameNode to determine the location of the data
• The JobTracker locates TaskTracker nodes with available slots at or near the data
• The JobTracker submits the work to the chosen TaskTracker nodes.
• The TaskTracker nodes are monitored. If they do not submit heartbeat signals often enough, they are deemed to have failed and the work is scheduled on a different TaskTracker.
  
• A TaskTracker will notify the JobTracker when a task fails. The JobTracker decides what to do then: it may resubmit the job elsewhere, it may mark that specific record as something to avoid, and it may may even blacklist the TaskTracker as unreliable.
  
• When the work is completed, the JobTracker updates its status.

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