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Hadoop Developer Interview Questions & Answers Which You Should Not Miss!

With more than 30,000 open Hadoop developer jobs, experts must make acquainted themselves with the each and every component of the Hadoop ecosystem to make sure that they have a profound know how of what Hadoop is so that they can form an effectual method to a given big data problem. Hadoop Training Course is the latest course that professionals who want to get into the Hadoop career, are yearning for

Big Data Hadoop Training Course is designed to prepare you for your next project in the world of Big Data. Hadoop is the industry leader among Big Data Technologies and it is a principal skill for every expert in this field. Spark is also gaining connotation with emphasis on real-time processing. As a big data professional these are mandatory skills.

1. What are real-time industry purposes of Hadoop?
Hadoop, familiar as Apache Hadoop, is a free software platform for scalable and distributed computing of big volumes of data. It provides quick, high performance and gainful analysis of structured and unstructured data generated on digital platforms and within the activity. It is used in roughly all departments and sectors today.

2. How is Hadoop diverse from other parallel computing systems?
Hadoop is a distributed file system, which lets you accumulate and handle the enormous amount of data on a cloud of machines, handling data redundancy. The main benefit is that since data is saved in several nodes, it is superior to process it in distributed mode.

3. Which modes Hadoop can be run in?
Hadoop can run in three modes:
a. Standalone Mode: . This mode is chiefly used for debugging purpose, and it does not support the use of HDFS.
b. Pseudo-Distributed Mode (Single Node Cluster):In this case, you need configuration for all the three files described above.
c. Fully-Distributed Mode (Multiple Cluster Node): This is the production stage of where data is utilized and dispersed across several nodes on a Hadoop cluster.

4. Explain the major distinction between HDFS block and InputSplit.
In simple terms, the block is the physical symbol of data while split is the logical representation of data present in the block. Split acts as a mediator between block and mapper

5. What is distributed cache and what are its advantages?
Distributed Cache, in Hadoop, is a service by MapReduce framework to cache files when needed.

6. Explain the disparity between NameNode, Checkpoint NameNode, and BackupNode.
NameNode is the core of HDFS that handles the metadata – the information of what file maps to what block locations and what blocks are saved on what datanode.

Checkpoint NameNode has the similar directory structure as NameNode and creates checkpoints for a namespace at regular periods by downloading the fsimage and edits the file and margining them within the local directory.

Backup Node offers similar functionality as Checkpoint, implementing harmonization with NameNode. It maintains an up-to-date in-memory copy of file system namespace and doesn’t necessitate getting hold of changes after regular phases.

7. What are the most frequent Input layouts in Hadoop?
There are three most regular key in formats in Hadoop:
• Text Input layout: Default input format in Hadoop.
• Key Value Input design: used for plain text files where the files are split into lines
• Sequence File Input Format: used for reading files in succession

8. Classify DataNode and how does NameNode tackle DataNode failures?
DataNode stores data in HDFS; it is a node where actual data exists in the file system. If the namenode does not obtain a message from datanode. The NameNode manages the duplication of data blocks from one DataNode to other

9. What are the chief approaches of a Reducer?
The three chief approaches of a Reducer are:
1. setup(): this approach is used for configuring different parameters like input data size, distributed cache.
2. reduce(): spirit of the reducer always called once per key with the connected reduced task
public void reduce(Key, Value, context)
3. cleanup(): this procedure is called to clean temporary files, only once at the conclusion of the task
public void cleanup (context)

10.What is SequenceFile in Hadoop?
Broadly used in MapReduce I/O formats, SequenceFile is a flat file containing binary key/value pairs.

11.What is Job Tracker role in Hadoop?
Job Tracker’s main purpose is resource administration, tracking resource availability and task life cycle management.

12.What is the utilization of RecordReader in Hadoop?
Since Hadoop splits data into different blocks, RecordReader is utilized to read the slit data into the single record.

13. What is Speculative Execution in Hadoop?
Hadoop tries to detect when the task runs slower than predictable and then launches other corresponding tasks as a backup. This backup mechanism in Hadoop is Speculative Execution.

14.What happens if you try to run a Hadoop job with an output directory that is already present?
It will throw an exemption saying that the output file directory previously subsists. To run the MapReduce job, you need to make sure that the output directory does not exist before in the HDFS.

15.How to debug Hadoop code?
Primary, make sure the list of MapReduce jobs at hand running. Next, we need to see that there are no incomplete jobs running; if yes, you need to decide the location of RM logs and then run.

16.How to organize duplication Factor in HDFS?
hdfs-site.xml is used to construct HDFS. Changing the dfs.duplication property in hdfs-site.xml will change the default duplication for all files placed in HDFS.

17.How to compress mapper output but not the reducer output?
To attain this compression, you should set:
conf.set(“”, true)
conf.set(“MapReduce.output.fileoutputformat.compress”, false)

18.What is the disparity between Map Side join and Reduce Side Join?
Map side Join at map side is performed data reaches the map. You need a stern structure for defining map side join.

19. How can you transport data from Hive to HDFS?
By writing the query: hive> insert overwrite directory ‘/’ select * from emp;
You can write down your query for the data you want to importation from Hive to HDFS. The output you be given will be saved in part files in the specified HDFS path.

20. Which firms use Hadoop, any idea?
Yahoo search engine utilizes Hadoop, Facebook – Developed Hive for analysis, Amazon, Adobe, Netflix eBay, Spotify, Twitter, Adobe.

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Hadoop Developer Interview Questions & Answers Which You Should Not Miss!


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