Top 50 Apache Hadoop Interview Questions

Apache Hadoop is an essential part of Big Data systems. For a career in Data Science, Data Analytics and Data Warehousing, good knowledge of Hadoop is required.
This book contains basic to expert level Hadoop interview questions that an interviewer asks. Each question is accompanied with an answer so that you can prepare for job interview in short time.
We have compiled this list after attending dozens of technical interviews in top-notch companies like- Google, Facebook, Netflix, Amazon etc.
Often, these questions and concepts are used in our daily programming work. But these are most helpful when an Interviewer is trying to test your deep knowledge of Hadoop.
The difficulty rating on these Questions varies from a Fresher level software programmer to a Senior software programmer.
Once you go through them in the first pass, mark the questions that you could not answer by yourself. Then, in second pass go through only the difficult questions.
After going through this book 2-3 times, you will be well prepared to face a technical interview on Hadoop for an experienced programmer.

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Some of the questions are:

  • What are the four Vs of Big Data?
  • What is the difference between Structured and Unstructured Big Data?
  • What are the main components of a Hadoop Application?
  • What is the core concept behind Apache Hadoop framework?
  • What is Hadoop Streaming?
  • What is the difference between NameNode, Backup Node and Checkpoint NameNode in HDFS?
  • What is the optimum hardware configuration to run Apache Hadoop?
  • What do you know about Block and Block scanner in HDFS?
  • What are the default port numbers on which Name Node, Job Tracker and Task Tracker run in Hadoop?
  • How will you disable a Block Scanner on HDFS DataNode?
  • How will you get the distance between two nodes in Apache Hadoop?
  • Why do we use commodity hardware in Hadoop?
  • How does inter cluster data copying works in Hadoop?
  • How can we update a file at an arbitrary location in HDFS?
  • What is Replication factor in HDFS, and how can we set it?
  • What is the difference between NAS and DAS in Hadoop cluster?
  • What are the two messages that NameNode receives from DataNode in Hadoop?
  • How does indexing work in Hadoop?
  • What data is stored in a HDFS NameNode?
  • What would happen if NameNode crashes in a HDFS cluster?
  • What are the main functions of Secondary NameNode?
  • What happens if HDFS file is set with replication factor of 1 and DataNode crashes?
  • What is the meaning of Rack Awareness in Hadoop?
  • If we set Replication factor 3 for a file, does it mean any computation will also take place 3 times?
  • How will you check if a file exists in HDFS?
  • Why do we use fsck command in HDFS?
  • What will happen when NameNode is down and a user submits a new job?
  • What are the core methods of a Reducer in Hadoop?
  • What are the primary phases of a Reducer in Hadoop?
  • What is the use of Context object in Hadoop?
  • How does partitioning work in Hadoop?
  • What is a Combiner in Hadoop?
  • What is the default replication factor in HDFS?
  • How much storage is allocated by HDFS for storing a file of 25 MB size?
  • Why does HDFS store data in Block structure?
  • How will you create a custom Partitioner in a Hadoop job?
  • What are the differences between RDBMS and HBase data model?
  • What is a Checkpoint node in HDFS?
  • What is a Backup Node in HDFS?
  • What is the meaning of term Data Locality in Hadoop?
  • What is the difference between Data science, Big Data and Hadoop?
  • What is a Balancer in HDFS?
  • What are the important points a NameNode considers before selecting the DataNode for placing a data block?
  • What is Safemode in HDFS?
  • How will you replace HDFS data volume before shutting down a DataNode?
  • What are the important configuration files in Hadoop?
  • How will you monitor memory used in a Hadoop cluster?
  • Why do we need Serialization in Hadoop map reduce methods?
  • What is the use of Distributed Cache in Hadoop?
  • How will you synchronize the changes made to a file in Distributed Cache in Hadoop?

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